Abstracts from All Scientist's Meeting

Acker, S.A., M.E. Harmon, T.A. Spies and A. McKee.  SPATIAL PATTERNS
 OF MORTALITY IN AN Abies Procera-Pseudostuga menziesii
 STAND. Department of Forest Science, Oregon State Univ., Corvallis,
 OR. 97331-7501, and Pacific Northwest Research Station, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  Spatial patterns may help
 explain causes and effects of tree mortality.  We studied a 1 ha
 old-growth stand in the western Cascade Mountains, OR, from 1977 to
 1988.  Basal area was mostly Abies procera; most stems were
 A. amabilis.  These two species dominated mortality.  Dying
 A. amabilis were mostly small and often suppressed or damaged by
 falling limbs or trees.  Dying A. procera ranged in size and were
 often attacked by pathogens.  These facts suggested a positive
 spatial association of dying A. amabilis and canopy trees, and
 aggregation of dying A. procera.  Using contingency table analysis,
 dying A. amabilis and canopy trees were weakly associated within 2 m
 quadrats.  From variance:mean ratios, both dying and all A. procera
 were aggregated within 20 m quadrats.  A. procera death may help form
 gaps; it is unclear whether aggregation is associated with mortality.
 Adams, Phyllis C.; Leslie A. Viereck. EFFECTS OF SNOW BREAKAGE ON
 SUCCESSIONAL PROCESSES IN INTERIOR ALASKA. University of Alaska
 Fairbanks and USDA Forest Service, Institute of Northern Forestry,
 Fairbanks, AK. 99775. BNZ.  Natural disturbances alter the structure
 and dynamics of boreal forest ecosystems.  Record snowfall in
 interior Alaska during the winter of 1990-1991 caused extensive tree
 breakage, resulting in major reductions in standing biomass.  The
 positions of all individual trees were recorded at 18 50 x 60 m Long
 Term Ecological Research (LTER) plots at the Bonanza Creek
 Experimental Forest.  The condition of each tree, including death and
 height at breakage from heavy snow load was recorded.  Second-order
 spatial statistics were used to examine spatial and mortality
 patterns within the study area.  The greatest loss of biomass due to
 snow occurred in mature white spruce stands.  Continuing monitoring
 will assess the effects of these events on the understory vegetation
 and canopy species composition.  Adams, Phyllis C.; Leslie
 A. Viereck; JoBea Way; Cynthia L. Williams. MONITORING LONG-TERM
 FOREST SUCCESSION WITH SYNTHETIC APERTURE RADAR IN THE TAIGA OF
 INTERIOR ALASKA. University of Alaska Fairbanks, USDA Forest Service,
 Institute of Northern Forestry, Fairbanks, AK 99775, and Jet
 Propulsion Laboratory, Pasadena CA. 91109. BNZ Synthetic aperture
 radar(SAR) has potential for monitoring successional dynamics by
 providing information about biophysical properties of vegetation,
 including biomass, canopy moisture content, canopy geometry, and
 phenology.  At Bonanza Creek Experimental Forest near Fairbanks,
 Alaska, images from aircraft missions in March 1988 and May 1991 have
 clearly demonstrated ability to monitor environmental conditions such
 as snow cover, frozen and thawed ground and vegetation, river ice,
 and flooding with SAR.  We have conducted extensive monitoring of
 structural characteristics and environmental parameters of
 successional stands along the Tanana River as ground truth for ERS-1
 spaceborne and NASA AIRSAR aircraft missions.  Stand density,
 biomass, species composition, and spatial and temporal patterns have
 been analyzed, and will be examined for relationships to radar
 backscatter signatures.  This work contributes to the development and
 calibration of mechanistic ecosystem models which attempt to predict
 ecosystem response to changes.

Aguiar, Martin R. William K. Lauenroth and Debra P. Coffin. INTENSITY
 AND IMPORTANCE OF INTER- AND INTRASPECIFIC COMPETITION BETWEEN C4
 GRASSES. Colorado State University, Fort Collins, CO 80523, USA CPR
 We conducted a field experiment to compare inter- and intraspecific
 competition between two codominant grasses Bouteloua gracilis and
 Buchloe dactyloides. Plants of similar size of both species were
 grown surrounded by either six conspecific plants or six plants of
 the other species. In half of the plants metal tubes were used to
 restrict belowground competition; isolated plants were used to
 investigate conditions of no competition. Biomass accumulation and
 reproductive output were reduced under conditions of inter- and
 intraspecific competition (compared to growing in tubes) for both
 species. But intensity and importance of inter- and intraspecific
 competition were different for both species. Our results suggest that
 competitive interactions explain the relative dominance of these two
 warm season short grasses.  Allison, Taber D., Michael Binford, David
 R. Foster. POST-SETTLEMENT CHANGES IN VEGETATION AND LAND-WATER
 INTERACTIONS IN CENTRAL NEW ENGLAND. Harvard University, Cambridge,
 MA 02138 and Harvard Forest, Petersham, MA 01366.  HFR We address two
 aspects of the impact of European settlement on the New England
 landscape: 1) the magnitude of change from pre-settlement conditions
 resulting from contrasting land-use practices and 2) the extent to
 which the reforested landscape has returned to original conditions in
 terms of forest composition and lake trophic status.  Our study area
 comprises lakes in northern Massachusetts from the Connecticut River
 Valley to the Atlantic Coast.  Sediment cores have been removed from
 several small lake basins and analyzed for physical, biological, and
 chemical characteristics.  Peak settlement activity, as indicated
 from pollen percentages, is associated with sharply increasing bulk
 density values, decreased loss-on-ignition, and increased relative
 inputs of phosphorus.  Principal Components Analysis indicates
 distinct differences between pre- and post-settlement pollen
 assemblages.  Changes in axis scores by sample age indicate that
 post-settlement vegetation is not converging on pre-settlement
 composition, but is becoming increasingly different.  Alternatively,
 regional differences in pre-settlement forest composition have become
 less distinct following forest clearing and subsequent reforestation.

Anderson, Virginia, Iris Anderson and Paul Brooks.  USE OF A
 15N2O-ISOTOPE DILUTION TECHNIQUE FOR THE MEASUREMENT OF LINKED
 NITRIFICATION-DENITRIFICATION IN WETLAND ECOSYSTEMS.  School of
 Marine Science, Virginia Institute of Marine Science, College of
 William and Mary, Gloucester Point, VA 23062 and Department of Soil
 Science, University of California, Berkeley, Berkeley, CA 94720.
 Surface sediments in saltmarsh ecosystems typically contain low
 concentrations of nitrate; therefore, most of the denitrification
 that occurs is dependent upon substrate supplied by
 nitrification. Since acetylene blocks nitrification, use of the
 acetylene blockage technique to measure linked
 nitrification-denitrification is questionable.  We will describe a
 15N2O-isotope dilution technique which we are currently testing for
 the measurement of denitrification in saltmarsh sediments.
 Denitrification rates measured using acetylene block were slightly
 higher than those measured using 15N2O isotope dilution in anaerobic
 slurries of saltmarsh sediments amended with 1 mM nitrate.
 Application of 15N2O-isotope dilution to measurement of in situ
 denitrification in saltmarsh sediments requires application of a
 first-order kinetic model.  Baron, Jill, Dennis S. Ojima, Elisabeth
 A. Holland, and William J. Parton. SOURCES AND SINKS OF N SPECIES IN
 HIGH ELEVATION ROCKY MOUNTAIN ECOSYSTEMS. Natural Resource Ecology
 Laboratory, Colorado State University, Fort Collins CO 80523,
 National Park Service Water Resources Division, and National Center
 for Atmospheric Research, Boulder CO 80307. CPR and NWT.  We are
 exploring processes that affect nitrogen cycling in the Loch Vale
 Watershed by combining biogeochemical data from the past 9 years with
 the CENTURY ecosystem process model. With current N deposition, soil
 carbon content decreased at a rate of 2.6 g C m-2 with time; N
 leaching from the forest floor was steady over time at an annual rate
 of 0.1 g N m-2. This corresponds to measured leaching rates and low N
 accrual due to the maturity of the forest and the severe climate at
 3100 m. Forest response under greater N deposition was an initial
 retention of soil carbon, followed by similar rates of loss of C as
 above. Nitrogen loss was greatly accelerated, and N yield
 approximated deposition at the end of 100 years. Further model
 experiments are planned with lower N deposition rates corresponding
 to pre-urban emissions in an attempt to define the inflection point
 at which terrestrial processes were no longer N- limited. Output from
 both the tundra and forest models will be aerially weighted to
 develop a watershed-scale picture of nitrogen dynamics.

Benning, T.L.* and T.R. Seastedt.  PATTERNS AND CONTROLS OF ROOT
 DYNAMICS IN TALLGRASS PRAIRIE.  Department of Environmental,
 Organismic and Population Biology and Institute of Arctic and Alpine
 Research, University of Colorado Boulder, CO 80309-0450 * Present
 address: Department of Biological Sciences, Stanford University Palo
 Alto, CA 94305. NWT.  Root cores and root windows were used to study
 the influence of fire, mowing and nitrogen availability on root
 lengths, biomass, and nitrogen content in tallgrass prairie near
 Manhattan, Kansas.  Four years of 10 g/m2/yr of nitrogen additions
 increased belowground plant mass by about 15%, from 1255 g/m2 to 1450
 g/m2 (p<.001). Living roots and rhizomes in nitrogen addition plots
 increased in nitrogen concentration by an average of 77%; dead roots
 and rhizomes increased in nitrogen concentration by an average of
 38%. Dead roots and rhizomes were capable of immobilizing 3 to 3.5
 g.m-2 of nitrogen; live roots and rhizomes increased from 1.5 to 5
 g.m-2 of nitrogen, depending upon treatment.  Plots on annually
 burned prairie were able to sequester substantially more nitrogen
 than plots from unburned sites; however, the nitrogen immobilization
 potential of microbes on dead roots and rhizomes appeared equal
 across treatments. Patterns of root appearance and disappearance were
 highly variable from one year to the next and were only marginally
 controlled by precipitation.  Annual new root growth was positively
 correlated with peak foliage biomass (r = 0.75, n=8, p =0.03), while
 average root length was marginally negatively correlated with peak
 foliage biomass (r=-0.65, n=8, p=.08). Average root lengths exhibited
 less year-to-year variation than average annual peak foliage biomass
 for the four year study. Root window observations indicated that
 mowing initially decreased then increased the turnover rates of
 roots; root cores indicated that live root mass in the top 20 cm of
 soil was increased by four years of annual mowing.  Benson, Barbara
 and Thomas Frost.  DETECTION OF EFFECTS OF EXPERIMENTAL ACIDIFICATION
 ON ZOOPLANKTON COMMUNITY STRUCTURE.  University of Wisconsin-Madison,
 Madison, WI 573706. NTL.  Little Rock Lake in northern Wisconsin has
 been the site of a whole-lake acidification experiment.  The effects
 of acidification on the zooplankton community were initially assessed
 by examining the response of individual species.  Here we employ
 ordination methods to expand the assessment to community level
 analysis.  The lake was divided into a reference basin and a
 treatment basin which was systematically acidified from pH 6.1 to 4.7
 in two year stages over the period 1985-1990.  Principal components
 analysis was performed on zooplankton biomass data from both the
 reference and treatment basins.  The trajectory of the zooplankton
 community in the treatment basin diverged from that of the reference
 basin community following acidification.  The degree of this
 divergence increased with the intensity of the acidification.
 Comparison with two LTER lakes in the region using principal
 components analysis showed the trajectory for the treatment basin was
 originally similar to the LTER reference lake with a pH near 6.0.
 With acidification, the treatment-basin trajectory approached that of
 the second LTER reference lake, an acid bog lake. Thus, experimental
 acidification produces a zooplankton community similar to naturally
 acid systems within the region.

Blair, John, Jack Shaw, and Charles Rice. SPATIAL AND TEMPORAL
 PATTERN'S OF SOIL N AVAILABILITY AND PLANT UPTAKE ALONG TOPOEDAPHIC
 GRADIENTS IN TALLGRASS PRAIRIE. Kansas State University, Manhattan,
 KS 66506.KNZ.  Pronounced landscape-level variation exists at Konza
 Prairie with respect to topographic position and edaphic factors,
 which can significantly affect seasonal and long-term soil-plant
 nutrient relationships. Previous studies at Konza have demonstrated
 that topoedaphic position influences plant ecophysiological responses
 and net primary production. However data on soil N dynamics along
 these topoedaphic gradients are lacking. In 1993 we initiated a study
 of soil N dynamics in relation to patterns of plant N uptake along
 topoedaphic gradients across watersheds being intensively studied as
 part of the Konza LTER program.  Sampling inn the first year was
 directed at quantifying (1) patterns of soil N availability at
 upland, lowland and mid-slope sites on watersheds with different fire
 frequencies (annual burn and 20 year burn regimes) and (2) net
 primary production, including seasonal patterns of N accumulation and
 plant N use efficiency at these sites. We also measured potentially
 mineralizable N pools at the beginning of the summer and microbial
 biomass N on selected sample dates. Results to date indicate a strong
 early season relationship between topographic position and soil
 inorganic N on the annually burned watershed only, with highest
 concentrations occurring at lowland sites. Differences in inorganic N
 between upland and lowland sites were attenuated by early summer. The
 relationship of soil N pools to plant uptake during the growing
 season will be presented.

Blum, Linda and Robert Christian. BELOWGROUND MARSH GRASS PRODUCTION
 AND DECAY ALONG A TIDAL/ELEVATIONAL GRADIENT. Univ. Virginia,
 Charlottesville, VA 22903 and East Carolina Univ., Greenville, NC
 27858. VCR.  Organic matter accumulation in marsh sediments is
 dependent on the balance between production and decay of belowground
 materials which in turn are dependent on the plant species and the
 sediment properties. We used a litter bag technique to compare root
 and rhizome decay of Spartina alterniflora and Juncus roemerianus
 along a transect including a creekside (intermediate height-form
 S. alterniflora), a mid-marsh (short height-form S. alterniflora),
 and a high-marsh (J. roemerianus) location.  Root and rhizome
 production was estimated from measures of root growth into the litter
 bags at each location. Sediment chemical properties at these marsh
 locations were different: mid-marsh pore water salinities, sulfide
 concentrations, and ammonium concentrations were consistently greater
 than those of the creekside and high marsh locations, while the
 creekside location had consistently greater pore water concentrations
 of phosphate. Little difference in weight loss was observed between
 the mid-marsh and highmarsh locations (69% and 71% ash-free
 dry-weight remaining after 1 yr. respectively), but weight loss at
 the creekside location may be more rapid (59% AFDW remaining after 1
 yr.) than at the 2 interior locations. Decay constants (mean k for
 all locations = -0.00178 d-1 and -0.00118 d-1; J. roemerianus and
 S. alterniflora. respectively) were calculated using an exponential
 model for both types of plant material and were significantly
 different (Student's t = 3.13, p = 0.001395, a = 0.05). The greater k
 for J. roemerianus is consistent with the difference in the starting
 C/N ratios for the 2 plant materials (37:1 and 47:1; J. roemerianus
 and S. alterniflora, respectively) . Measures of root production were
 highly variable, especially for the creekside and high marsh
 locations where the total amount of live roots in the litter bags did
 not exceed 0.05 AFDW. Root growth was much greater and less variable
 at the mid-marsh location (0.10 - 0.13 g AFDW per bag) than near the
 creek or in the high marsh. For all locations, live roots were found
 in the litter bags within 120 days (early June) after burial in the
 marsh. These data support the hypothesis that the type of plant and
 its ability to produce roots are responsible for differences in
 biogenic accretion in salt marsh sediments.

Boose, Emery R., David R. Foster, and Marcheterre Fluet.  MODELING
 LANDSCAPE-LEVEL HURRICANE DISTURBANCE IN PUERTO RICO AND NEW ENGLAND.
 Harvard Forest, Harvard University, Petersham, MA 01366.  HFR.
 Hurricanes represent an important natural disturbance process in
 tropical and temperate forests in many coastal areas of the world.
 The complex patterns of damage created in forests by hurricane winds
 result from the interaction of meteorological, physiographic, and
 biotic factors on a range of spatial scales. We have developed the
 following approach to study landscape to regional level impacts on
 forests: (1) A simple meteorological model reconstructs wind
 conditions at specific sites and regional gradients in wind speed and
 direction during a hurricane. (2) A simple topographic exposure model
 estimates landscape-level exposure to the strongest winds. (3) Actual
 forest damage is assessed through remote sensing, archival records,
 and field measurements.  We are using this approach to study
 long-term hurricane disturbance regimes at two LTER sites: Luquillo
 and Harvard Forest.  Work to date has focused on Hurricane Hugo
 (1989) and the 1938 New England Hurricane.  For both storms patterns
 of damage on a regional scale were found to agree with the predicted
 distribution of peak wind gust velocities.  On a landscape scale
 there was good agreement between patterns of forest damage and
 predicted exposure to the strongest winds.  At the Harvard Forest the
 average orientation of windthrown trees was close to the predicted
 peak wind direction, while at Luquillo there was reasonable
 agreement, with some apparent modification of wind direction by the
 mountainous terrain.

Boring, L.R., E.R. Blood, S.W. Golladay, L.K. Kirkman, W.K. Michener,
 R.J. Mitchell, and B.J. Palik.  ICHAUWAY AND THE JONES ECOLOGICAL
 RESEARCH CENTER - NEW PROGRAMS AND ECOSYSTEMS OF THE S.E. COASTAL
 PLAIN.  Jones Ecological Research Center, Rt. 2, Box 2324, Newton GA
 31770.  This new center and the Ichauway site are dedicated to the
 development of research, education and conservation programs that
 couple ecological disciplines with the management of natural
 resources, especially of forest, wetland and riverine ecosystems.
 Core funding is provided by the Robert W. Woodruff Foundation.  The
 staff are conducting both short and long-term research using
 reference and disturbed landscapes.  Initial research projects
 include fire ecology of longleaf pine forests and species, forest
 nitrogen cycling processes, patch disturbances and mortality in
 longleaf forests, forest fragmentation effects upon native and
 invasive species, vegetation and hydrologic dynamics of non-alluvial
 wetlands, coarse woody debris in forest and riverine systems, surface
 and groundwater linkages, and biogeochemical studies of stream and
 river systems.  Initial studies will direct future long-term research
 objectives as well as those addressing management of forest, wetland
 and riverine ecosystems.  Ichauway is a 11,300 ha reserve located in
 the SE coastal plain of SW GA.  It includes 4,800 ha of longleaf
 pine/wiregrass, 800 ha of wetlands and 42 km of rivers.  It will be
 managed as a biosphere reserve model for numerous research, education
 and conservation objectives.

Bowden, William B.; Jacques C. Finlay, Patricia E. Maloney; and John
 S. Terninko.  CONTROLS ON THE DISTRIBUTION AND PRODUCTION OF
 BRYOPHYTES IN CONTROL AND LONG-TERM, P-FERTILIZED REACHES OF AN
 ARCTIC TUNDRA RIVER (ALASKA).  Department of Natural Resources,
 University of New Hampshire, Durham, NH, 03824.  ARC.  Each year
 since 1983, H3PO4 has been added continuously during the ice-free
 season to a P-limited tundra stream (Kuparuk River, North Slope,
 Alaska).  In 1990, seven years after the fertilization began, we
 noted extensive coverage by bryophytes within the fertilized reach of
 the river, where very few had been noted previously.  Surveys of
 macroalgal and bryophyte cover in 1991, 1992, and 1993 showed that
 the moss Schistidium (Grimmia) agassizii was distributed similarly in
 both control and fertilized reaches of the river.  In contrast, two
 species of Hygrohypnum (H. alpestre [Hedw.] Loeske and H. ochraceum
 [Turn.] Loeske) were found primarily in the fertilized reach, within
 riffles, where peak areal biomass approached 800 g dry matter/m2.  A
 fourth bryophyte species (Fontinalis neomexicana) was also
 distributed primarily in the fertilized reach, also in riffles, but
 was less abundant than the Hygrohypnum species.  These species were
 essentially absent from fertilized pools.  Clumps of Hygrohypnum
 spp. lost weight over 30 d in control riffle environments but
 accumulated 181+44% of their initial mass in fertilized riffles.
 F. neomexicana accumulated 38+39 and 98+47% of initial biomass in
 unfertilized and fertilized riffles.  Epiphytic and detrital mass
 accumulation on artificial mosses (unbraided hemp rope) averaged
 about 4 to 4.5 times greater in slow-flowing pool environments than
 in fast-flowing riffle environments.  These data suggest that both
 Hygrohypnum spp. and F. neomexicana are capable of growth throughout
 the river, but are limited first by nutrients (P) and are smothered
 by epiphytic growth in fertilized pools.  Analysis of total N and P
 in the tissues of the Hygrohypnum spp. and estimates of average
 coverage (~15%) and biomass (~150 g dry weight/m2) over an 8k
 fertilized reach, suggest that these species alone may remove 2/3 of
 the P added in the fertilizer experiment.  As a group, the bryophyte
 community in this stream is now likely to be the dominant sink for P
 in the fertilized reach. Furthermore, the mosses appear to have
 profound effects on the stream community structure and function,
 aspects of which are currently under investigation.

Bowman, William D., Theresa A. Theodose, James C. Schardt, and Richard
 Conant. CONSTRAINTS OF NUTRIENT AVAILABILITY ON PRIMARY PRODUCTION IN
 TWO ALPINE TUNDRA COMMUNITIES. Environmental, Population, and
 Organismic Biology, Campus Box 334, and Institute of Arctic and
 Alpine Research, Campus Box 450, University of Colorado, Boulder CO
 80309. NWT.  A nutrient amendment experiment (N, P, and N+P) was
 conducted for two growing seasons in two alpine tundra communities,
 dry and wet meadows,to determine if primary production is limited by
 nutrient availability, and whether physiological and developmental
 constraints act to limit the responses of plants from a nutrient poor
 community more than plants from a more nutrient rich
 community. Photosynthetic, nutrient uptake, and growth responses of
 the dominants in the two communities showed little difference in the
 relative capacity of these plants to respond to the nutrient
 additions. Aboveground production responses of the communities
 indicated N was limiting to production in the dry meadow community
 while N and P co-limited production in the wet meadow
 community. There was a greater production response to the N and N+P
 amendments in the dry meadow relative to the wet meadow, despite
 equivalent functional responses of the dominant species of both
 communities. The greater production response in the dry meadow was in
 part related to changes in community structure, with an increase in
 the proportion of graminoid and forb biomass, and a decrease in the
 proportion of community biomass made up by the dominant sedge
 Kobresia myosuroides. Species richness increased significantly in
 response to the N+P treatment in the dry meadow. Graminoids increased
 significantly in biomass in the wet meadow N and N+P plots, while
 forb biomass decreased significantly, suggesting a competitive
 interaction for light. Thus the difference in community response to
 nutrient amendments was not the result of functional changes at the
 leaf level of the dominant species, but rather was related to changes
 in community structure in the dry meadow, and to a shift from a
 nutrient to a light limitation of production in the wet meadow.
 Bowser, Carl J.  LAKE-GROUNDWATER INTERACTION STUDIES BASED ON
 ISOTOPIC AND MAJOR ION CHEMICAL TECHNIQUES, Univ Wisconsin, Madison,
 WI 53706. NTL Mass fluxes of water and associated solutes to and from
 lakes at NTL is significant.  Quantification of these fluxes is
 critical for understanding the variance of chemical and
 biogeochemical parameters in lakes, for understanding the role of
 lakes in carbon dioxide budgets of the lake-land system, and
 estimates of the influence of landscape position on lake chemistry
 and dynamics.  Stable isotopes of hydrogen and oxygen provide a means
 to estimate groundwater fluxes to lakes.  Results from the NTL site
 for 20 lakes indicates groundwater provides up to 26 percent of the
 total water to lakes (Range 2-26 %, mean 11.3 %).  Solute loading by
 groundwater (mass flux times concentration) ranges from 50% to nearly
 100 % of the total lake load, reflective of the "leverage" that
 groundwaters exert on the chemistry of lakes compared to other
 possible water inputs (e.g. runoff, precipitation).  Combined mass
 balance equations for isotopes and solutes provides a means to
 estimate the average groundwater composition of waters entering the
 lakes. Both calcium and magnesium exhibit conservative behavior in
 lakes.  Uptake by diatoms is the main loss mechanism for silica, and
 the isotope/solute budgets allow estimation of total lake silica
 loading and therefore estimates of the ratio between internally
 cycled and externally loaded silica.  Potassium loading to lakes
 exceeds the amount estimated from groundwater fluxes, and is
 interpreted as due to leaf litterfall from the forest canopy
 surrounding the lakes.  These studies allow estimates of carbon
 loading to lakes (alkalinity, aqueous CO2, and dissolved organic
 carbon) via groundwater and leaf litterfall.  The results integrate
 with lake P-CO2 studies (Kratz and Bowser) to provide insights into
 the relative roles of lake and terrestrial carbon fixation Briggs,
 John M. and Alan K. Knapp.  LONG TERM PATTERNS OF ABOVEGROUND
 PRODUCTION IN TALLGRASS PRAIRIE: ROLE OF SOIL MOISTURE. Kansas State
 University, Manhattan, KS 66506. KNZ Aboveground biomass production
 at the Konza Prairie Research Natural Area has varied from 645 g/m2
 to 202 g/m2 over the past 19 years. In years with adequate rainfall
 (i.e., 80% of mean growing season precipitation), spring fire
 increased aboveground production relative to unburned sites (17 year
 mean of burned sites = 482 g/m2 (SE=24); unburned sites = 386 g/m2
 (SE=24)). However, contrary to most other grasslands, no single
 meteorological variable (total precipitation, growing season
 precipitation, pan water evaporation, etc.) explains this variance in
 biomass. We have found that dormant season (October to March) soil
 moisture may be critical for determining biomass on annually burned
 sites. On unburned sites, biomass is less sensitive to variation in
 soil moisture and it appears that forbs respond differently to soil
 moisture than do grasses. These results can be partially explained by
 recognizing the nonequilibrium nature of resource availability in
 this system.  Brokaw, N., B. L. Haines, D. J. Lodge,
 L. R. Walker. SEEDING ECOLOGY AFTER A HURRICANE IN A PUERTO RICAN
 FOREST. Manomet Bird Observatory, Manomet, MA 02345, Univ. of
 Georgia, Athens, GA 30602, Forest Products Laboratory, Rio Piedras,
 PR 00928-2500, Univ. of Nevada, Las Vegas, NV 89154-4004. LUQ.  After
 a hurricane in a Puerto Rican forest we studied seedling dynamics and
 environmental factors for 2.5 yr.  For all species combined, seedling
 numbers were positively correlated with cover of leaf litter,
 disturbance, and canopy openness.  Total seedling densities increased
 over the period, then declined.  Pioneers seedling densities
 increased rapidly soon after the hurricane, then steeply declined,
 while some shade tolerant dominants increased gradually over the
 period.  But some species showed no definite pattern and every
 species reacted individualistically. Disturbance has both immediate
 effects on seedling numbers of some species, e.g., by enhancing seed
 germination, and delayed effects, e.g., by enhancing seed production.
 Brooks, Paul D., Mark W. Williams, and Steven K. Schmidt. PRELIMINARY
 INFORMATION ON WINTER/SPRING NITROGEN CYCLING IN THE COLORADO
 ALPINE. Environmental, Population, and Organismic Biology, Campus Box
 334, Department of Geography, Campus Box 260, and the Institute of
 Arctic and Alpine Research, Campus Box 450, University of Colorado,
 Boulder CO 80309. NWT.  Inputs, outputs, and fluxes of nitrogen were
 followed from October 1992 through June 1993 at Niwot Ridge in the
 Colorado Front Range. Concentrations of soil inorganic nitrogen, snow
 inorganic nitrogen, and microbial biomass nitrogen were measured
 monthly from January to March, biweekly through April, and weekly
 until the first of June. Temporal variability in nitrogen inputs from
 precipitation to tundra soils were estimated from ion exchange resins
 harvested in mid winter and at the end of the snow covered
 season. Nitrogen outputs from the system through leaching were
 estimated using ion exchange resins at a depth of 10 cm. Gaseous
 losses as N2O were measured at two sites on the tundra and one just
 below treeline. Soil inorganic nitrogen concentrations were highest
 in January when tundra soils were completely frozen. Concentrations
 decreased rapidly as soils under the snowpack warmed above -5 degrees
 C. As snow depth decreased in the spring, concentrations again
 increased presumably due to freeze/thaw cycles. Significant
 concentrations of CO2 under the snowpack, suggesting microbial
 activity, were first observed in early March. Nitrous oxide
 production under snow was first observed in April, corresponding to
 soil temperatures above -3 degrees C. These data suggest that the
 insulating effect of snow cover during the long alpine winter may
 allow soil microbial activity during this season to significantly
 affect the N cycle in these systems.

Caine, Nel, John C. Iott, and Brian P. Menounos. SPATIAL PATTERNS OF
 SUMMER PRECIPITATION IN AN ALPINE ENVIRONMENT. Department of
 Geography, Campus Box 260, and Institute of Arctic and Alpine
 Research, Campus Box 450, University of Colorado, Boulder CO
 80309. NWT.  In 1992 and 1993, summer precipitation was being
 measured by a network of 35 storage raingauges in a 550 m grid over
 the Green Lakes Valley. In the summer months of 1992, precipitation
 totalled about 250 mm in the basin and showed little spatial pattern
 and no elevational effects. When totals for June, July, and August
 are treated separately, weak spatial patterns reflecting north-south
 contrasts rather than elevational influences are
 evident. Predictably, individual storms yielding more than 8 mm of
 precipitation are more variable in space. Correlations of storm
 totals with elevation are usually significant but inconsistent in
 sign. Semivariograms of storm depths suggest a range of 2.5 to 3.0 km
 and are improved when the drift due to elevation is removed from the
 original data. This suggests that areal mean precipitation amounts in
 summer may be empirically estimated by a model equivalent to that
 defined by Chua and Bras (1982) for winter storms in the San Juan
 Mountains.  Caldwell, Bruce A., Robert P. Griffiths, John E. Baham,
 Michael A. Castellano and Kermit Cromack, Jr.  ENZYME ACTIVITIES IN
 ECTOMYCORRHIZAL MAT COMMUNITIES.  Departments of Forest Science and
 Crops and Soil Science, Oregon State Univ. and USDA Forest Service,
 Corvallis, OR 97331.  AND.  'Direct cycling' from detritus by
 ectomycorrhizal fungi may be a significant path of nitrogen and
 phosphorus to host trees.  Distinct ectomycorrhizal rhizomorph and
 hyphal mats have been found in the forest floor and upper mineral
 soils of conifer and mixed hardwood forests at the H.J. Andrews
 Experimental Forest, Bonanza Creek Experimental Forest and Coweeta
 Hydrological Laboratory.  Depending on the fungal species, levels of
 phosphatase, peroxidase, proteinase, (beta)-1-3 glucanase, cellulase
 and/or xylanase were significantly higher in the ectomycorrhizal mat
 than in adjacent soil or litter without obvious mat development.
 Where pure cultures of the causal fungi could be isolated, we have
 confirmed production of the enzyme(s) responsible for the hydrolytic
 activities observed in the mats.  Cammack, Shannon E., and Bruce
 Haines.  SEEDLING RECRUITMENT AND GROWTH ON HURRICANE-DISTURBED
 PLOTS: THE ROLE OF LIGHT, WATER, AND NUTRIENTS University of Georgia,
 Athens, GA 30602-7271. LUQ.  Seedling growth of 64 species was
 examined in 60 plots on a 9 ha grid in a Dacryodes excelsa
 (Tabonuco)-dominated rain forest damaged by Hurricane Hugo in
 1989. The relationship between height growth and environmental
 parameters was evaluated. Parameters included 1) light, estimated as
 canopy openness with hemispherical photography, 2) nutrients,
 estimated as NH4 standing stocks and mineralization rates determined
 from in situ incubations and 2 N KCL extractions, and 3) soil water
 content, estimated by time domain reflectometry. R-square values and
 stepwise regressions were calculated for plant growth and
 environmental variables for all species combined and for 13
 individual species. R-square values ranged from 0.0005 to 0.46. While
 significant regressions were found for each of the environmental
 variables, species differed in their requirements for light,
 nutrients, and water.  Cavigelli, Michel A. and G. Philip
 Robertson. THE FUNCTIONAL SIGNIFICANCE OF DENITRIFIER POPULATION
 DIVERSITY TO NITROUS OXIDE PRODUCTION IN TERRESTRIAL
 ECOSYSTEMS. Center for Microbial Ecology, W.K. Kellogg Biological
 Station and Department of Crop and Soil Sciences, Michigan State
 University, Hickory Corners MI 49060. KBS.  Controls on in situ N2O
 production by denitrifying microorganisms are very poorly understood
 in most ecosystems, and the global N2O budget is far from
 balanced. Environmental factors that affect N2O fluxes are
 well-studied, but are poor predictors of measured rates, which
 exhibit high and unexplained temporal and spatial variability. An
 untested contributor to systematic variation in N2O production is
 denitrifier population diversity. Pure culture studies show that
 disparate denitrifier populations can express significantly different
 rates of N2O production when grown under identical conditions and at
 low (0.5-2.5%) O2 concentrations. We have initiated a project to test
 whether denitrifier population diversity is important to rates of N2O
 production in soils at the Kellogg Biological Station and the Central
 Plains Experimental Range LTER sites. We will sample soils that
 differ widely in long-term C stores, NO3- availability, pH, and
 water-filled pore space -- factors that affect N2O flux rates and
 should select for disparate denitrifying populations. We have
 designed a soil slurry incubation technique to characterize the
 potential N2O production of whole soil denitrifier communities that
 should also allow us to distinguish among soils that have
 functionally distinct denitrifying communities. We will also isolate
 denitrifiers and reintroduce them to sterilized soils in order to
 evaluate each population's contributions to overall rates of N2O
 production.

Christian, Robert, Mark Brinson and Linda Blum.  BELOWGROUND DYNAMICS
 IN A SALT MARSH AS DETERMINED BY DIFFERENT METHODS.  East Carolina
 Univ., Greenville, NC 27858 and Univ. Virginia, Charlottesville, VA
 22903. VCR.  In higher elevations of salt marshes, accretion is
 largely biogenic.  It results from production of belowground organic
 matter in excess of its decomposition.  We evaluated belowground
 organic matter dynamics at the VCR/LTER site by two methods.  In the
 first, plots were clipped of aboveground plant biomass; roots and
 rhizomes were pruned around the peripheries; and the plots were
 enclosed to restrict belowground lateral growth into them.  With
 continued attention, new primary production was largely prevented
 within the plots for a period of 2 y.  For the second method we
 inserted litter bags of roots and rhizomes into the soil within the
 root zone and followed the loss of organic matter.  Whereas little to
 no discernible decomposition was found for the clipped, pruned and
 enclosed plots during 2 y; biomass in litter bags decreased by 30 to
 50% over 1 y.  Much of the loss in the litter bags occurred during
 the first 120 d. The difference between results from the two studies
 can be reconciled if the vast majority of belowground organic matter
 is old, nonliving and recalcitrant and/or if the removal of new
 production restricts the decomposition of the organic matter present.

Cisneros, Rigel O. THE DETECTION OF CRYPTIC INVASIONS AND LOCAL
 EXTINCTIONS OF FISHES USING LONG-TERM DATASETS. Center for Limnology,
 University of Wisconsin-Madison, Madison, WI 53706. NTL.  Cryptic
 invasions and extinctions are dynamic biological processes that
 determine local range expansions and contractions of fish species
 found in a lake district. The occurrence of these processes is
 usually unnoticed and poorly studied. This work proposed and tested
 the use of four criteria found in four kinds of information available
 in long-term fish datasets. Presence-absence, abundance, size range
 and dispersion were the criteria used as trend indicators for
 invasion or extinction. Presence-absence information (criterion 1)
 was transformed into plots that evaluate persistence after appearance
 for invasion and persistence until disappearance for
 extinction. Abundance (crtn. 2), size range (crtn. 3) and dispersion
 (crtn. 4) were correlated against time to identify positive trends in
 case of invasion or negative trends in case of extinction. A simple
 score system was applied to categorize trends with different
 probability of significance.  Cryptic invasion evidence was found for
 the bluegill in Crystal Lake and burbot in Big Muskellunge
 Lake. Local extinction evidence was obtained for Iowa darter in Big
 Muskellunge Lake and blacknose shiner in Trout Lake.  An exotic
 invader, the rainbow smelt, was obtained for Iowa darter in Big
 Muskellunge Lake.  Lack of consistency in strong evidence across all
 criteria seems to be a pattern typical of cryptic invasions. Strong
 evidence from extinction trends in criteria 2 to 4 suggested a number
 of potential future extinctions. The low frequency of cryptic
 invasions and local extinctions were independent of lake area and
 corresponded to a previously reported percentage of species turnover
 in the lakes studied.  Clein, Joy S. and Joshua P. Schimel.
 MINERALIZATION AND NITRIFICATION DURING THE TRANSITION FROM ALDER TO
 POPLAR IN THE ALASKAN TAIGA. University of Alaska Fairbanks,
 Fairbanks AK 99775. BNZ Primary succession on the Tanana river
 floodplains progresses from alder, with an open nitrogen cycle and
 rapid nitrification, to poplar, with a closed cycle and little
 nitrification. To determine the mechanism(s) controlling this shift,
 we transplanted soils between alder and poplar sites with controls
 held in their home site. Mineralization rates and nitrification
 potential were measured before placement in the field, after 1 month
 and over the following growing season. The nitrification potential of
 the transplanted alder soil was lower than its control, while that of
 the transplanted poplar soil was higher than its control. This
 pattern parallels the pattern of NO3- concentrations in the
 field. Lab incubations show similar respiration rates, but the ratio
 of C to N mineralized in poplar was much greater than in alder (40
 vs. 20) suggesting that microbes in the poplar soil were
 N-limited. Our results suggest that the decrease in nitrification as
 poplar becomes dominant is due to changes in C and N availability
 rather than any specific chemical effects.

Cleveland, Cory C., Elisabeth A. Holland, and Jason
 C. Neff. TEMPERATURE REGULATION OF SOIL RESPIRATION IN AN ALPINE
 TUNDRA ECOSYSTEM. Atmospheric Chemistry Division, National Center for
 Atmospheric Research, Boulder CO 80307 and Environmental, Population
 and Organismic Biology, Campus Box 0334, University of Colorado,
 Boulder CO 80309-0334. NWT Climate is an important force regulating
 microbial activity and decomposition in soils. Significant increases
 in temperature, like those which are predicted in many global warming
 scenarios, will increase CO2 release (respiration) from
 soils. Because a large proportion of terrestrial carbon is stored in
 arctic and alpine soils, it is important to understand how
 temperature influences soil respiration fluxes from these soils. The
 purpose of this study was to measure the effect of temperature on
 soil respiration in an alpine tundra ecosystem. We collected surface
 soil samples from a range of plant communities at Niwot Ridge
 including wet meadow, moist meadow, dry meadow, and fellfield
 communities. Soil moistures were amended to field capacity and soils
 were incubated at 5, 10, 15, 25 and 35 degrees C. CO2 evolution
 resulting from soil respiration was measured on day 1, and days 3 and
 6 of the incubation. At all sites, CO2 production increased to a
 maximum at 35 degrees C. For all soils averaged, rates of respiration
 tended to be highest on day one, with a gradual decline over
 time. Calculated Q10 values were higher than Q10s for tropical and
 temperature ecosystems.

Collins, Harold P., Michael J. Klug, Helen J. Garchow and Janene
 Bohan. CHANGES IN THE STRUCTURE AND FUNCTION OF SOIL MICROBIAL
 COMMUNITIES ASSOCIATED WITH THE INTENSITY AND FREQUENCY OF
 DISTURBANCE.  W.K. Kellogg Biological Station, Michigan State Univ.,
 Hickory Corners, MI 49060 Soil disturbances resulting from
 agricultural practices are known to affect the size of microbial
 populations and their activities.  The intensity and frequency of
 disturbance may also determine the structure and function of the
 active soil community.  Soil can be described by a wide variety of
 physical, chemical, and biological characteristics.  Although
 individual analyses are easily done, few attempts have been made to
 link soil microbial community structure to function.  Long-term
 cropping and native successional treatments, located on the LTER at
 the W.K. Kellogg Biological Station, offers a unique opportunity to
 study changes in soil microbial communities resulting from shifts in
 management.  Soil biogeochemical characteristics of a corn-soybean,
 tilled native succession, and never-tilled native succession were
 compared to the C oxidation profiles of whole soil microbial
 communities using the micro-titer plate system of BIOLOG,
 INC. (Hayward, CA).  Multivariate analyses were used to evaluate the
 relationship between microbial community structure and function
 within and among each treatment.  In addition, fatty acid methyl
 ester profiles were determined.  These profiles were used to identify
 differences in soil microbial community structure.

Conn, Christine E. and Frank P. Day. FINE ROOT DECOMPOSITION ON
 BARRIER ISLANDS (THE VCR-LTER SITE). Old Dominion University,
 Norfolk, VA, 23529. VCR.  The interaction between landform age,
 topographic position and environmental regime was used to study
 environmental controls on belowground decomposition rates at the
 VCR-LTER. A transect was selected that passed through a
 chronosequence of 4 dune and swale associations, aged from 6 to 120
 years old. At each site, litter bags containing Spartina patens roots
 were buried. Hydrology, soil redox potential, soil temperature, soil
 pH and soil water salinity were monitored. Notable differences in
 hydrology and soil redox potential were evident between dune and
 swale sites. Mean water table position dropped from younger to older
 sites and was higher in swales (4.8 cm aboveground to 14.7 cm
 belowground) than in dunes (91.2 cm to 116.5 cm belowground). Mean
 soil redox potentials exhibited no differences between dunes (423 to
 573 mV) and were lower in swales (-35 to 239 mV). Older swales had
 higher soil redox potentials. Decomposition of Spartina patens roots
 was greater in dunes (40.8- 57-5 % mass remaining) than in swales
 (74.2-86.3 % mass remaining). Multiple regression analysis
 demonstrated hydrology and soil redox potential were strongly
 correlated with belowground decomposition rates. Nutrient analysis of
 decayed roots indicated that while organic matter accumulated in
 swale sites, more nitrogen and phosphorus were lost, presumably due
 to leaching processes. Hydrologic factors strongly influence
 belowground decay and nutrient dynamics.

Coull, Bruce C. FIELD AND LABORATORY EXPERIMENTS GENERATED BY LONG
 TERM BENTHIC INVERTEBRATE DATA. Univ of South Carolina, Columbia SC
 29208. NIN.  Long-term biological data sets are typically collected,
 analyzed for their periodicities, correlated with some suspected
 forcing function(s), published and forgotten.  Rarely are they used
 to generate testable hypotheses and subsequently, test these
 hypotheses experimentally.  Nineteen years of monthly or fortnightly
 data on meiofaunal abundance and community structure from a mud and a
 sand site in North Inlet (SC) indicate very different seasonal
 patterns, and thus controlling mechanisms, at the two sites.  We have
 conducted many experiments the results of which suggest the mud site
 fauna is biologically controlled but the sand site fauna is more
 physically controlled.  Juvenile fish predation plays an important
 role in regulating the mud assemblage; the fish are unimportant
 regulators in the sand.  In the field the dominant mud copepod (the
 dominant prey of the fish) only reaches 26% of its maximum potential
 adult productivity; model predictions suggest this is due to low
 naupliar survival, most likely due to fish predation.  The
 experiments and the model would not have even been thought of without
 the long-term data sets.  Long-term data sets need to be more fully
 utilized to generate testable hypotheses.

Crawford, Edward R., David W. Martin, Donald R. Young and Frank
 P. Day. GAP DYNAMICS FOR BARRIER ISLAND SHRUB THICKETS (Myrica
 cerifera). Virginia Commonwealth University and Old Dominion
 University. VCR.  Shrub thickets frequently represent an intermediate
 seral stage in the development of maritime forests on barrier
 islands. The purpose of this study was to quantify natural thicket
 gaps to better elucidate barrier island successional processes. The
 study focused on Hog Island, a primary field site of the Virginia
 Coast Reserve, where island accretion patterns have produced a
 chronosequence of soils and Myrica cerifera shrub thickets. Gaps were
 most frequent in the oldest thickets (> 40 years) at the bay side
 edge of the island, with only a few gaps formed in the most
 productive thickets (15-30 years) in the island interior. The sizes
 and causes of gap formation were variable. Although most gaps were
 formed due to shrub senescence and competition with vines, disease
 and weather related disturbances also influenced gap development. An
 analysis of both the soil seed bank and the existing seedlings in the
 thicket understory revealed greater density and diversity in the
 oldest thickets as compared to the productive, mid-island
 thickets. Myrica cerifera may respond (i.e. recover) most quickly to
 gaps that form in the mid-island thickets. In contrast, shrub
 response in older thickets may be limited by competition from vines
 and by rapid seedling establishment from the well developed seed
 bank. Gap formation in barrier island shrub thickets may accelerate
 succession towards a maritime forest.

Crocker, M. Tad, Clifford N. Dahm, and Manuel C. Molles, Jr. PHYSICAL
 AND CHEMICAL PROPERTIES OF AN EPHEMERAL FLOOD IN NEW MEXICO.
 Department of Biology, University of New Mexico, Albuquerque, New
 Mexico, 87131.  SEV.  Water represents both an agent of physical
 disturbance and a critical resource within ephemeral streams in
 semi-arid regions. Riparian plants are removed during periodic floods
 and dense stands of recruits quickly colonize newly disturbed
 streambed surfaces.  Water directly controls ecological processes
 and, as a solvent, indirectly controls the availability of
 nutrients. The ephemeral nature of these brief floods severely limits
 the opportunity to observe and quantify flood and water
 properties. On July 17, 1991, researchers were trapped within the
 Sevilleta LTER Sierra Ladrones Study Basins (SLSB) by an intense
 thunderstorm (32mm/75min).  The most extensive flooding during four
 years of observations ensued.  Remote video imaging systems recorded
 flooding at two sites within the SLSB and these videos will be
 presented.  Storm intensity and flood hydrographs were estimated form
 these video data.  Stream velocity was measured at the leading edge
 of the flood (the bore) and during near peak discharge.  Grab samples
 of stream water were taken for analyses from one location prior to
 the bore (local flow), the bore, 5 min after peak flow, and at very
 low flow.  These samples were divided into four size classes.  Basin
 response time was 5 min at the upstream site (11 ha) and 20 min at
 the downstream site (76 ha).  The bore progressed at 1.2 m/s and
 stream velocity was 2.3 m/s 4 min. after peak discharge.  Water
 properties are summarized in the accompanying presentation.

Currie, William, John Aber, William McDowell and Richard Boone. THE
 ROLES OF DOC AND DON IN FOREST ECOSYSTEM RESPONSE TO CHRONIC NITROGEN
 ADDITIONS.  Complex Systems, Morse Hall, University of New Hampshire,
 Durham, NH 03824.  HFR.  An integrated study of ecosystem response to
 chronic nitrogen additions began in 1988 at Harvard Forest with N
 amendments to two forest stands. One of the driving questions behind
 many of the studies under way in the Chronic N experiment plots is to
 discover the mechanisms responsible for the observed high levels of N
 retention.  Study of dissolved organics (specifically DOC and DON)
 comprises one set of studies providing insight into such
 mechanisms. The movement of dissolved organics from the forest floor
 to mineral soil amounts to approximately 5% to 24% of leaf litter C
 flux and 15% to 37% of leaf litter N flux in the few temperate
 forests studied. Additionally, dissolved organics exert some control
 on decomposition, humification and C and N turnover by acting as
 substrates for microbial activity and as reactive intermediates for
 abiotic processes.  Our projects at Harvard Forest include the
 collection of throughfall and forest-floor leachate for calculation
 of dissolved organic C and N concentrations and fluxes under control
 and N-addition treatments in two forest stands.  The results will be
 used to improve or parameterize models that address N retention, C
 and N turnover in forest soils.

Dail, d. Bryan and John W. Fitzgerald.  FORMATION OF ORGANIC S,
 S-ADSORPTION AND ACCUMULATION OF ORGANIC S IN FOREST SOILS AND
 BENTHIC SEDIMENTS AT COWEETA HYDROLOGIC LABORATORY.  Dept. of
 Microbiology, University of Georgia, Athens, GA. 30602 CWT Sulfur
 additions to a riparian system may come from deciduous senescence and
 acidic precipitation.  Additions of 35S labelled sodium sulfate to
 mimic acid precipitation were used to quantify microbial
 transformations in A-horizon soils and benthic sediments.  The fate
 of anthropogenic S additions, in particular, the potential to form
 organic-S, mobilization (mineralization) of recently formed
 organic-S, and the adsorptive potential of soils and sediments were
 measured.  Adsorption of S ranged from 3.63(0.39) to 4.83(0.48) nmol
 S/g dwt in 48 hrs.  The lowest adsorptive capacities in the riparian
 zone were observed in the benthic sediments.  Organic-S formation
 ranged from 0.5(.02) to 5.5(.13) nmol S/g dwt 48hrs-1.  Mobilization
 of recently formed organic-S ranged from 82 to 93%, with an
 accumulation to the system of 0.2055 to 0.2791 nmol S/g dwt 48hrs-1.
 Positive values for accumulation of organic-S were observed for all
 sites and all sampling dates, with the highest rates of formation of
 organic-S seen in the stream wet perimeter.

Davinroy, Thomas C.  COULOIR EROSION RATES AND ACTIVITY, COLORADO
 FRONT RANGE.  Department of Geography, Campus Box 260, University of
 Colorado, Boulder, CO 80309 NWT.  Rock movement through alpine
 couloirs has been measured repeatedly over a full year to determine
 the rates of erosion and associate them with meteorological, fluvial,
 and kinetic geomorphologic processes.  Downslope movement is analyzed
 according to particle size, particle shape, initial position, slope,
 and fluvial regime.  Contributions of climatic variation, quantity
 and intensity of precipitation are also assessed.  Avalanche paths
 and debris are examined for geomorphic activity, and rockfall onto
 snow is tracked for size and deposition pattern.  Rock temperature is
 sampled twice hourly to monitor freeze-thaw cycling and sediment
 traps collect bulk rockfall.  Consequent accumulation on sub-couloir
 talus cones has also been studied for rate, mechanism of transport,
 and depositional pattern.  Reoccupation of antecedent talus motion
 studies has extended observation to a 25-yr. study period.  This
 period includes dynamic climatic variation, including a
 100-yr. precipitation event.  Correlation with long-term climate data
 from D-1 and Niwot Saddle meteorological stations permits inferences
 to be drawn on the influence of climate on geomorphic activity.
 Lichenometric analysis of couloir-wall ages reveals periods of
 increased incision in periods following Holocene glacial retreats.

Day, Frank P. PLANT RESPONSE TO NITROGEN FERTILIZATION ACROSS A
 VIRGINIA COAST RESERVE DUNE CHRONOSEQUENCE. Old Dominion University,
 Norfolk VA 23529. VCR.  Experimental and control plots (1 m2) were
 established on three different age dunes (24, 36, and 120 yr old) on
 Hog Island, part of the Virginia Coast Reserve LTER site. Nitrogen
 (15 g m2 yr1) was added to the treatment plots in the form of
 urea. At the end of the 1991 growing season, plant biomass was
 harvested from the plots and weighed. Biomass decreased from young to
 old dune (174 g m2 to 108 g m2 in controls), but root/shoot ratios
 increased in the controls (0.35 to 0.50)). Biomass increased in
 response to fertilization on all three sites; however, the response
 was muted on the oldest dune (54% g m2 to 338 g m2 from young to
 old). Root/shoot ratios decreased in response to fertilization, but
 were the same across sites (0.21). The damping of the response to N
 additions from younger to older dunes may reflect the higher natural
 levels of N in the older dune soils or other limiting factors such as
 soil moisture.  Dodds, Walter, John Blair, Geoff Henebry, Rosemary
 Ramundo, Tim Seastedt1, and Cathy Tate2.  NITROGEN TRANSPORT FROM
 TALLGRASS PRAIRIE BY STREAMS. Kansas State University, Manhattan, KS
 66506; Current Address 1University of Colorado Boulder CO 80309, 2WRD
 United States Geological Survey, Denver CO 80225. KNZ.  Discharge and
 nitrogen content of water flowing from four watersheds on Konza
 Prairie Research Natural Area was monitored from 1986-1992.  The
 watersheds were on different burn frequencies. Streams were
 characterized by highly variable flow: data include a 100 year flood
 and a drought period that dried all channels for approximately 1
 year. Nitrogen yield per unit area increased as the surface area of
 the watershed increased. This is probably because groundwater losses
 were greatest in the smaller watersheds, although it is difficult to
 directly quantify the groundwater losses from this system. Nitrogen
 yield per unit area was also greater with more annual
 precipitation. Loss of nitrogen from streams made up a small portion
 (0.1 - 6.0 % ) of nitrogen coming in from precipitation. Neither
 recent burning nor introduction of bison in the watersheds had
 statistically significant effects on nitrogen content of the
 water. Increased precipitation was significantly correlated (P <
 0.03) to higher concentrations of nitrate. Good water quality is
 typical of these streams with ammonium always below 0. 1 ?M, nitrate
 ranging from below 0.1?M to 28 ?M and total N from 1.5 - 51 ?M.

Doran, Kathleen.  A LABORATORY INVESTIGATION OF THE RESPONSE OF WHITE
 SPRUCE (Picea glauca) TO LIGHT AND NITROGEN CHANGES. Institute of
 Arctic Biology, University of Alaska, Fairbanks, Alaska.  Taiga
 floodplain white spruce were grown from seeds in a 3x2, light and
 nitrogen factorial experiment to investigate growth and succession in
 floodplain environments.  Photosynthetic responses to a range of
 light intensities were used to construct light response curves to
 determine quantum yields and saturation light intensities for each
 treatment.  Plant height and above and below ground biomass were used
 as measures of growth rate and root/shoot ratios.  The experimental
 results indicated that there were no significant differences in
 photosynthetic rates between treatments.  However, there were
 significant differences in root/shoot ratios between treatments.
 Root/shoot ratios within the medium and high light treatments
 increased with low nitrogen fertilizer levels, while the low light
 treatment did not show a difference between high and low nitrogen
 levels. Future research will involve measuring the above and below
 ground tissue nitrogen concentrations.  Photosynthetic and biomass
 data will be collected from additional plants at 2 month intervals to
 investigate possible difference as the plants mature.

Dueser, R.D. and John Porter. EFFECTS OF AREA AND HABITAT COMPLEXITY
 ON INSULAR SMALL MAMMAL DIVERSITY ON THE VIRGINIA BARRIER
 ISLANDS. Department of Fisheries and Wildlife, Utah State University,
 Logan, UT 84322, and Department of Environmental Sciences, University
 of Virginia, Charlottesville, VA 22903 There is continuing debate
 about the relative effects of island area and habitat complexity on
 insular faunal richness.  Island area and habitat complexity tend to
 be positively correlated with most measures of faunal richness.
 Experimental studies of the independent effects of these variables
 usually are impractical, unethical or both.  Few correlational
 studies incorporate a sufficient number of islands and sufficient
 information on habitat complexity to allow a rigorous test.  We
 report a correlational study which allows such a test.  The
 biogeography of seven small mammal species on the Virginia barrier
 islands (N=23) has been studied since 1975.  These islands range from
 23 to 7,029 ha in area.  The number of species found on an island
 (0-7) varies directly with island area, maximum elevation, vegetation
 height, number of plant associations and number of woody plant
 association, and varies inversely with distance from mainland.
 Partial correlation analyses, controlling for island area, indicate
 that two measures of habitat complexity (i,.e., number of woody plant
 associations and total number of plant associations) are particularly
 useful predictors of insular species richness. Habitat complexity
 thus carries information independent of island area.  The patterns of
 occurrence of the species on the islands suggest that the
 distributions of some species are constrained by the relative lack of
 suitable habitat, while other sources are limited primarily by
 isolating barriers such as open water.  Three apparent extinctions of
 island populations observed since 1975 appear to be unrelated to the
 availability to suitable habitat.  Edwards, D. and
 S. Hutchinson. IDENTIFYING RARE EVENTS IN NORTH INLET ECOLOGICAL DATA
 SETS USING SHEWHART CONTROL CHARTS.  Department of Statistics, U. of
 South Carolina, Columbia SC and Coastal Carolina College, Conway SC.
 NIN.  Events and disturbances have been widely used to explain
 variability in ecological data; these explanations, however, were
 highly subjective.  Events tend to be over-reported in short-term
 studies and under-reported in long-term studies.  Shewhart control
 charts, a quantitative technique for identifying unusual events in
 industrial processes, were used here to identify four classes of
 "events" in biological, physical, chemical, and meteorological data
 collected at North Inlet Estuary, SC.  Both intensity and duration of
 events are included in the classification.  Measurements were
 collected at various temporal scales, ranging from hourly weather
 observations, daily water samples, biweekly fauna samples, to monthly
 primary production estimates.  Prior to control charting, LOWESS
 smoothing was used to remove long-term trends and seasonal patterns
 in both the mean and standard deviation of each series.  Following
 event identification, the data were merged to examine relationships
 between physical events and the occurrence of chemical and biological
 events.  Relating these events, in data collected at different
 temporal scales, is a complex problem.  Limitations also emerge
 because ecosystems cannot be shutdown and "reset", as in the
 manufacturing environment.  The value of this technique is that
 intensity and duration of events are quantified and the rate of false
 events are quantified.

Elder, Bradley, O. J. Reichman, David Hartnett, Nancy Huntly*, Richard
 Inouye*, William Rogers, Tony Wasley*, and Eric Burr*. THE INFLUENCE
 OF ANIMAL-GENERATED DISTURBANCES ON MULTI-SCALE PATTERNS OF RESOURCES
 AND VEGETATION.  Div. of Biology, Kansas State Univ., Manhattan, KS
 and (*) Dept. of Biological Sciences, Idaho State Univ., Pocatello,
 ID. CDR, KNZ.  While the effects of disturbances on plant communities
 have been investigated for some time, the impact of the spatial and
 temporal patterns of disturbances have only recently received similar
 attention from ecologists.  In order to investigate the effect of
 specific patterns of disturbance on plant communities we have
 initiated a study of the influence of pocket gopher burrows and
 mounds on overlying vegetation. Previous studies have shown that
 pocket gopher burrows occur in highly uniform patterns of spacing
 even though individual burrows are convoluted.  Mounds, conversely,
 are significantly clustered in their distribution.  Furthermore, both
 burrows and mounds produce a spatially explicit pattern of influence
 on the plant community adjacent to the disturbances.  This pattern is
 consistent with a competition induced wave of biomass and is
 initiated by a significant reduction in plant biomass directly over
 the disturbance.  This, in turn, increases the availability of
 resources to plants adjacent to the disturbances.  This wave of
 biomass is continued out to at least 50 cm from the disturbances in a
 pattern that appears to be related to alternating levels of
 resources.  Our investigation centers on a study of the biomass wave
 pattern in relation to burrow and mound spacing at two LTER sites
 that differ significantly in soil nutrients (Konza Prairie and Cedar
 Creek).  We will employ both naturally occurring burrows and mounds,
 and simulated disturbances, and measure their influence on plant
 biomass and diversity at scales from 10 cm to 128 m.  We anticipate
 that specific patterns of influence will emerge at different scales,
 and that these will differ between the two sites.  Elias, Scott A.,
 and Susan K. Short. BIOTIC RESPONSE TO CHANGING ALPINE ENVIRONMENTS
 DURING THE HOLOCENE. Institute of Arctic and Alpine Research, Campus
 Box 450, University of Colorado, Boulder CO 80309-0450. NWT.  As part
 of our research on biotic response to changing alpine environments,
 researchers in the paleoecology group of the Niwot LTER project have
 studied a transect of ten Holocene-age sites in the Colorado Front
 Range. Pollen, fossil insects, and plant macrofossils have been
 investigated. At the end of the last glaciation, the alpine tundra
 zone extended 500 m downslope from its modern limit. Early Holocene
 treeline reached its modern elevation by about 9,500 yr BP. During
 the Holocene, the study region has experienced a series of climatic
 fluctuations, with fossil data indicative of warmer than present
 conditions between 9500 and 7000 yr BP, and colder than present
 conditions between 4500 and 3000 yr BP and again in the last 1000
 years. The insect response has essentially been in phase with
 vegetational changes.  Engman, J.A. DISTRIBUTION OF THE GENUS
 HETEROCOPE (COPEPODA, CALANOIDA): ECOLOGICAL IMPLICATIONS FROM
 BIOGEOGRAPHIC, PHYLOGENETIC AND GIS ANALYSIS. Univ. Cincinnati,
 Dept. Biol. Sciences, Cincinnati, OH 45221. ARC.  At the arctic
 tundra LTER, species composition of zooplankton communities varies
 significantly and predictably, based on a series of simple biotic and
 abiotic factors. The presence of the large copepod Heterocope
 septentrionalis has a deterministic effect on the cladoceran
 community on which it preys.  H.septentrionalis is found in
 significant numbers only when visually feeding predators are reduced
 or absent, as a result of top-down control by piscivores, or as a
 result of fish exclusion by ice formation in shallower bodies of
 water. At a larger scale, factors influencing distribution of
 zooplankton species are being examined in a study of biogeography of
 the six species of the genus Heterocope. This research includes
 reconstruction of the phylogenetic relationships of Heterocope
 species, characterization of the global distribution of these
 species, and a GIS-based analysis of current and historic factors
 which may explain distribution.  Phylogeny of species of Heterocope
 is being examined based on cladistic analysis of morphological
 characters and molecular genetic (mtDNA sequence) data; this provides
 a pattern of species relationships within the genus, and may give
 estimates for ages of individual speciation events.  Distribution of
 the individual species has been characterized based on our field
 collections, and a thorough literature search. Using United Nations
 global climate databases as estimators of overall environmental
 conditions, GIS applications are allowing comparison of Heterocope
 occurrence with factors that may be responsible for determining
 limits of individual species distribution.  At a global scale,
 determination of distribution appears primarily historic, reflecting
 speciation patterns within the genus.  At intermediate scales, both
 ecological and historic (primarily glacial event) factors can explain
 much of Heterocope distribution.  At regional and local scales,
 occurrence of populations can be correlated with environmental
 variables including temperature, elevation and vegetation type.
 Ehrman, Terry and Jack Webster. TRANSPORT DYNAMICS OF FINE
 PARTICULATE ORGANIC MATTER. Biology Dept, Virginia Polytechnic
 Institute and State University, Blacksburg, VA 24061. CWT.  Pollen
 and glass beads were used as trackable surrogates for natural fine
 particulate organic matter. Transport dynamics of these particles in
 several streams were best described by a negative exponential model,
 from which average travel distances for pollen and glass beads could
 be calculated. Distances traveled generally lengthened with
 increasing stream flow. Average travel distances for pollen and glass
 beads during the highest flow (96 L/sec) were 185 m and 114 m,
 respectively. During the lowest flow (4 L/sec), these particles only
 traveled 11 m and 2 m, respectively. Pollen, less dense than glass
 beads, usually traveled further than the beads.  In order to account
 for the variability in retention of these particles, several stream
 characteristics, such as discharge, velocity, substrate type, amount
 of large woody debris, gradient, depth, and temperature, were
 measured but not, as yet, analyzed statistically.  Epstein, H. E.1,
 Lauenroth, W. K.1, Burke, I. C.2 and D. P.  Coffin1 ANALYSES OF THE
 ABUNDANCE OF DOMINANT GRASS SPECIES ALONG TWO REGIONAL TRANSECTS IN
 THE CENTRAL GRASSLANDS OF THE UNITED STATES.  1Dept. of Range Science
 and 2Dept. of Forest Science Colorado State University Fort Collins,
 CO 80523.  CPR.  We conducted research to quantify large-scale
 relationships between grass species abundances and their
 environmental controls.  We analyzed the production of several
 dominant grasses along two transects in the central Grassland Region
 of the United States.  To perform the analyses, we constructed a
 plant species database for the central Grasslands.  The database
 utilizes ARC/INFO, a geographic information system, to combine Soil
 Conservation Service (SCS) range site descriptions with spatial data
 from the SCS State Soil Geographic (STATSGO) database.  The outcome
 is a spatial database of the abundances of individual plant species.
 Analyses were performed on latitude (surrogate for mean annual
 temperature) versus biomass for four dominant grass species in the
 plains region extending from southern Colorado to northern Montana.
 The abundances of Bouteloua gracilis and Buchle dactyloides, both C4
 species, decreased with increasing latitude, whereas the
 relationships between latitude and biomass for Agropyron smithii and
 Stipa comata, both C3 species, were less clear.  Analyses were also
 performed on longitude (surrogate from mean annual precipitation)
 versus biomass for four dominant C4 grass species in the plains
 region extending from the shortgrass steppe in eastern Colorado to
 the tallgrass prairie in eastern Kansas.  The abundances of Bouteloua
 gracilis and Buchle dactyloides decreased, whereas the abundances of
 Andropogon gerardii and Schizachyrium scoparium increased, from west
 to east.  These results provide insight into the quantitative
 relationships between individual species production and climate at a
 regional scale.  Fay, Phil, David C. Hartnett, Laura E. Fischer, Bill
 Adamsen. TALLGRASS PRAIRIE GALL INSECT POPULATION TRENDS AFTER FIRE.
 Division of Biology, Kansas State University, Manhattan, KS
 66506-4901. KNZ.  Gall insects are a common but understudied
 component of the tallgrass prairie fauna, and are excellent subjects
 for long-term population studies because they leave a semi- permanent
 record of their presence.  We have begun yearly sampling to determine
 how galler populations respond to spring fires. Gall insect densities
 are censured on Solidago canadensis (tall goldenrod), Vernonia
 baldwinii (Baldwin ironweed), and Ceanothus herbaceous (New Jersey
 tea) at the end of the growing season on sites at Konza Prairie
 varying in the number of years since the site was last burned. Sites
 have been censured for the last 4 years, covering the range from 1 to
 14 years since fire.  Densities of gallers on all three plant species
 increased with year since fire. On goldenrod, there appeared to be
 resistant clones where gall populations increase more slowly and
 susceptible clones where populations increased more rapidly. There
 are several possible mechanisms controlling these patterns: 1) direct
 fire mortality followed by immigration and recolonization of burned
 sites, 2) indirect effects of fire on galled survivorship and
 performance through changes in plant quality, 3) effects of fire on
 host plant population density.

Fischer, Janet M. and Thomas M. Frost. LINKING DEMOGRAPHY AND
 POPULATION DYNAMICS OF THE PHANTOM MIDGE (Chaoborus): EXPERIMENTAL
 AND MODELING APPROACHES. Center for Limnology, University of
 Wisconsin, Madison, WI, 53706.  Like many organisms that undergo
 dramatic changes in size and form as they develop, Chaoborus are
 subject to a variety of constraints during their life cycle.  We used
 a combination of experimental and modeling approaches to investigate
 the population consequences of changes in the relative strengths of
 these constraints for Chaoborus punctipennis.  Abundance of Chaoborus
 has increased approximately two-fold with the acidification of the
 treatment basin of Little Rock Lake, WI.  Results of cohort analysis
 indicate that the observed population increase is driven by increased
 early instar survivorship.  We used field data from Little Rock Lake
 to construct a stage-based projection model for Chaoborus.  Model
 simulations demonstrate that changes in survival and development
 rates can dramatically alter seasonal population dynamics.  These
 changes in Chaoborus seasonal dynamics may have important
 implications for the zooplankton community due to shifts in the
 strength of interaction between Chaoborus and their zooplankton prey.

Fischer, Laura, Barbara Hetrick, David Hartnett, and Arthur
 Schwab. MYCORRHIZAL- MEDIATED INTERPLANT PHOSPHORUS TRANSFER AMONG
 TALLGRASS PRAIRIE SPECIES. Kansas State University, Manhattan, KS
 66506. KNZ.  We investigated the potential for phosphorus transfer
 through VA-mycorrhizal hyphal bridges among several plant species in
 tallgrass prairie. We applied 32P-labelled phosphate to the leaves of
 "donor" Andropogon gerardii plants, harvested randomly selected
 "receivers" of nine species within a 50-cm radius of the donor, and
 determined the amount of label transferred by liquid scintillation
 counting.  The amount of label received differed significantly among
 species and was significantly correlated with the distance from the
 donor. The biomass of the receiver relative to that of the donor did
 not significantly affect phosphorus transfer. In a following study,
 we harvested receiver plants of three species 10, 17, and 24 days
 after labelling donor Andropogon plants. At two of the harvests,
 receiver species and distance from the donor had a significant effect
 on the amount of 32P received. Again, there was no main effect of
 relative biomass of donor and receiver plants. These studies
 demonstrate nonrandom transfer of phosphorus among neighboring
 individuals of several plant species in tallgrass prairie. Subsequent
 studies will evaluate the relationship between patterns of interplant
 nutrient transfer and plant competitive interactions.

Fisk, Melany C., and Steven K. Schmidt. MICROBIAL RESPONSE TO
 INCREASED SOIL MOISTURE IN COLORADO ALPINE TUNDRA
 SOILS. Environmental, Population, and Organismic Biology, Campus Box
 334, University of Colorado, Boulder CO 80309-0334. NWT.  The
 response of microbial community composition and nitrogen
 mineralization to increased soil moisture was investigated in lab
 incubations and field manipulations of alpine tundra soil. Microbial
 respiration, net nitrogen mineralization, and total and active
 bacterial numbers were higher in soils incubated at 85% than at 30%
 gravimetric soil moisture, while fungal hyphal lengths showed no
 difference between soil moisture levels. In incubated, watered
 treatments higher bacterial numbers corresponded to lower net N
 mineralization per unit C mineralized, suggesting that higher N
 immobilization occurred as a result of stimulated bacterial activity
 and growth. Similarly in field experiments microbial biomass N was
 high in watered compared to unwatered soils, whereas net N
 mineralization did not increase in response to watering. While fungal
 biomass showed little response to higher soil moisture, short-term
 bacterial immobilization of N appears to be an important component of
 N dynamics, especially in response to wetting and drying cycles in
 alpine tundra soil.

Foster, Bryan L., and Katherine L Gross. STUDIES OF TREE ESTABLISHMENT
 IN ABANDONED AGRICULTURAL FIELDS AT THE W. K. KELLOGG BIOLOGICAL
 STATION LTER. Michigan State University, W. K. Kellogg Biological
 Station, Hickory Corners MI. 49060.  An understanding of the factors
 regulating the invasion, establishment and persistence of woody plant
 species is critical to understanding old field succession. Our
 studies to date suggest that the mode of seed dispersal, mammalian
 post-dispersal seed predators, browsing by deer, and the direct and
 indirect effects of early successional dominant species are important
 determinants of the spatial and temporal patterns of tree
 establishment in old fields. We have utilized these initial studies
 to develop a set of hypotheses concerning the mechanisms by which the
 above factors can control woody plant establishment during old field
 succession. Future research will focus on experiments designed to
 test these hypotheses.  Freckman, Diana W. and Ross
 A. Virginia. NEMATODES AND SOIL PROPERTIES IN THE DRY VALLEYS OF
 ANTARCTICA. Colorado State Univ., Fort Collins, CO 80523 and
 Antarctic Dry Valley LTER and Dartmouth College, Hanover, NH 03755
 and Jornada LTER.  JRN The Antarctic Dry Valleys are one of the most
 extreme soil environments on earth. We are studying factors
 controlling soil biota distribution and function near the limits for
 life.  We studied the distribution and community structure of
 nematodes in relation to soil properties that affect their
 distribution in other desert systems (i.e., moisture, soil chemical
 and physical properties) in eight ice-free Antarctic Dry Valleys.
 Nematodes were widely distributed and occurred in > 65% of Dry Valley
 soils.  Nematode abundance reached 4200/kg dry soil and was not
 significantly correlated with soil moisture or most other physical
 and chemical properties.  However, soils lacking nematodes had
 greater salinity.  We found 7 nematode species with bacterivores
 comprising 66-100% of the nematode community (Scottnema lindsayae,
 Plectus spp.) and omnivore/predators (Eudorylaimus spp.) the rest.
 S. lindsayae dominated all samples.  Nematode distribution in the Dry
 Valleys is more patchy than in hot desert soils, but, where nematodes
 occur, densities can be comparable to those of hot desert soils. A
 one year field experiment showed that increasing temperature,
 moisture and carbon together increased nematode numbers, whereas
 these treatments alone had negative effects. Laboratory studies of
 the life cycle of S. lindsayae at 10C and 15C indicated the higher
 temperature decreased fecundity and development to adults.  These
 field and lab results suggest that elevated soil temperatures may
 negatively affect nematode reproduction.  Gage, Stuart H., Manuel
 Colunga and Peggy Ostrom. FLOW OF INSECTS THROUGH A
 LANDSCAPE. Michigan State University, E. Lansing, MI 48824. KBS
 Insects play an important role in native and human managed ecosystems
 as herbivores, as detritivores, as predators and as food for birds
 and mammals. Studies focus on insects at the landscape level because
 of their multi-dimensional role and because insects utilize multiple
 habitats as they traverse the landscape in search for overwinter
 sites, oviposition sites and places to find food.  Insects selected
 to study dispersal include a complex of general predators (ladybird
 beetles and lacewings) as well as selected herbivores (rootworms,
 leafhoppers). The primary focus has been to measure and quantify
 dispersing adults of these organisms as they traverse the landscape
 in search of resources. Since 1989, weekly measurements of 15 species
 of adult insects have been made using a standardized sampling method
 in several hundred sites representing different habitat types
 associated with agroecosystems. In addition to long term regular
 sampling in different habitats, measurements of isotopic signatures
 of plants and insects are made to characterize trophic relations
 between plants, herbivores and predators. Stable isotopesignatures of
 nitrogen and carbon from plants and insects are used to characterize
 dispersal of predatory and plant feeding insects.  Seasonal patterns
 of response by dispersing insects to different habitats have been
 documented including predicting temporal occurrence within
 habitats. Regulation of pest populations by predatory ladybird
 beetles has been observed and documented. Association between
 resident and dispersing predators is being quantified. Vegetation,
 both natural and human managed plantings have been mapped within
 landscape at KBS and work is underway to use satellite imagery to
 characterize landscape complexity. A temporal and spatial simulation
 model is being developed to characterize the flow of insects through
 landscapes of varying complexities. From this analysis we will
 determine landscape characteristics which will enable manipulation of
 insect populations including enhancement of diversity of insect
 species which are beneficial to agriculture.

Garman, S.L., A.J. Hansen and D.L. Urban.  ALTERNATIVE SILVICULTURAL
 PRESCRIPTIONS & BIODIVERSITY IN THE PACIFIC NORTHWEST: A SIMULATION
 APPROACH.  Dept. of Forest Science, Oregon State Univ., Corvallis, OR
 97331-7501, and Colorado State Univ., Ft. Collins, CO.  AND.  We are
 developing a computer simulation approach to evaluate trade-offs
 between timber production and animal-habitat diversity under
 alternative stand-level management prescriptions in western
 Oregon. Our approach uses an existing forest succession model, ZELIG,
 which we have modified to better simulate custom-designed
 silvicultural prescriptions and to evaluate suitability of modeled
 stands as animal habitat using empirically-derived statistical models
 of animal-habitat associations.  Description of our modeling
 approach, model verification, and a demonstration of a trade-off
 analysis are presented.  Gillham, Marla L., and Phillip Sollins.
 MULTIVARIATE CLASSIFICATION, AND NUTRIENT STATUS, OF MONTANE RIPARIAN
 SOILS.  Dept. of Forest Science, Oregon State Univ., Corvallis, OR
 97331-7501.  AND Third-order riparian ecosystems of the western
 Cascades of Oregon develop on geomorphic surfaces of diverse origins
 and ages.  A variety of erosional and depositional processes have
 created an extremely heterogeneous set of geomorphic surfaces and
 corresponding soils. Objectives were to develop a system for
 classifying these soils with regard to factors that might control
 primary production, especially nitrogen availability.  Study sites
 were a 500-year old Douglas fir forest, and a mature red alder forest
 occupying a 35-year old clearcut.  At 30 locations at each site, soil
 was sampled at 0-15 cm and 15-30 cm depths, and the location
 classified as to geomorphic surface and plant community type.
 Principal components analysis and discriminant analysis grouped
 similar observations and identified substantial internal structure
 within the data.  Soils with higher levels of carbon and
 mineralizable nitrogen developed generally on older and/or aggrading
 geomorphic surfaces, suggesting a relationship between geomorphology
 and primary productivity.  Classification by geomorphic surface
 appeared to work better than traditional soil classification for
 characterizing these extremely complex and heterogeneous systems.

Gray, Andrew N., and Thomas A. Spies.  USE OF TIME DOMAIN
 REFLECTOMETRY (TDR) TO DETERMINE WATER CONTENT OF MINERAL AND ORGANIC
 SUBSTRATES IN CONIFEROUS FOREST CANOPY GAPS.  Oregon State Univ.,
 Corvallis, OR, 97331 and Forest Science Laboratory, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  The accuracy of Time Domain
 Reflectometry (TDR) for determining volumetric water content was
 evaluated for soils from four forest stands, decayed wood, and forest
 floor.  The TDR system operates by measuring the dielectric constant
 within waveguides defined by parallel steel probes, making it a
 rapid, non-destructive, and repeatable method.  Proven effective in
 agricultural soils, TDR has rarely been applied to heterogeneous,
 high organic content forest substrates.  Regressions developed from
 TDR measurement of gravimetric soil samples were accurate within .03
 cm3/cm3 volumetric water.  Some soil types required separate
 regressions.  Estimates of water content in organic substrates were
 less accurate than for soils.  The TDR technique was able to detect
 differences in soil moisture patterns within and among canopy gaps of
 different sizes.  Griffiths, R.P., J. E. Baham and B. A. Caldwell.
 SOIL SOLUTION CHEMISTRY OF ECTOMYCORRHIZAL MAT SOILS.  Departments of
 Forest Science and Crop and Soil Science, Oregon State Univ.,
 Corvallis, OR 97331-7501.  AND.  Ectomycorrhizal fungal mats are
 important features of Pacific Northwest coniferous forests and other
 forests throughout the world. Organic acids produced by these fungi
 play an important role in nutrient availability and mineral
 weathering within the soil ecosystem.  We have conducted a study in
 which chemical composition of soil solutions isolated from two
 ectomycorrhizal fungi mat soils were compared to those isolated from
 adjacent soils with no visible mat development.  The concentrations
 of dissolved constituents were greater, in all cases, for the mat
 soils.  The differences between mat and non-mat soil solutions were
 significant (p < 0.05) in all but three of the twenty-seven
 comparisons.  The concentrations of ions in soil solutions isolated
 from Gautieria monticola mats were usually greater than those found
 in Hysterangium setchellii mat soils.  The chemical constituents
 showing the largest differences between mat and non-mat soils for
 both mat types included: Al, Fe, Mg, Mn, PO4, SO4, Cl, Oxalate (Ox),
 and DOC.  The correlation between the elevated levels of Ox and DOC
 isolated from the G. monticola mat soil solutions with the
 concentrations of other ions suggests that oxalate plays an important
 role in weathering and bioavailability.

Griffiths, R.P., G.A. Bradshaw and B.A. Caldwell.  DISTRIBUTION OF
 ECTOMYCORRHIZAL MATS IN CONIFEROUS FOREST OF THE PACIFIC
 NORTHWEST. Department of Forest Science, Oregon State Univ.,
 Corvallis, OR 97331-7501, and Forest Science Laboratory, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  Ectomycorrhizal mat soils have
 been used as model systems for studying the role of mycorrhizae in
 forest ecosystems and have been shown to play several important roles
 in the normal function of forest soils. There is limited information
 on the factors influencing mat spatial and successional distribution.
 Surveys were conducted to determine the spatial distribution of mats
 relative to live and dead trees, rocks and understory vegetation.
 All features within 2 x 10 m grids were measured and the presence of
 two types of mats at the base of understory trees was documented.  We
 found that ectomycorrhizal mats were associated with 80-100% of
 Pacific yew trees and that the occurrence of mats was significantly
 higher in all understory tree plots relative to equal-sized control
 plots without trees.  Stand age influenced the percent area covered
 by Gautieria but not Hysterangium.  These observations suggest that
 understory trees may play a role in the distribution of
 ectomycorrhizal fungal mats and that different mats may play
 different roles along the successional trajectories of Douglas-fir
 forests.

Griffiths, R.P., J.L. Liles and B.A. Caldwell.  SOIL RESPIRATION IN A
 PACIFIC NORTHWEST CONIFEROUS FOREST.  Department of Forest Science,
 Oregon State Univ, Corvallis, OR 97331-7501.  AND.  A seasonal study
 of forest floor respiration is being conducted at the H. J. Andrews
 Experimental Forest.  The main objective of the study is to determine
 how seasonal shifts in temperature and moisture altered both field
 and laboratory respiration rates and to determine how respiration
 rates are related to dissolved organic carbon (DOC) concentrations.
 Field respiration rates show a significant positive correlation with
 soil temperatures but seasonal patterns observed thus far show that
 moisture extremes also have a profound effect on respiration rates.
 When moisture limited respiration by being either too high or too
 low, DOC concentrations increase as respiration rates decrease.
 Grubaugh, J.W., J.B. Wallace, L.S. Houston and A. Marcilio.  PATTERNS
 IN MACROINVERTEBRATE COMMUNITY STRUCTURE ALONG AN ELEVATION AND
 STREAM SIZE GRADIENT IN THE SOUTHEASTERN APPALACHIAN
 MOUNTAINS. Institute of Ecology, University of Georgia, Athens, GA
 30602. CWT.  We assessed longitudinal changes of the benthic
 macroinvertebrate community with respect to habitat availability,
 functional group contribution, and taxa distribution and richness
 with changing stream size.  We investigated macroinvertebrate
 distribution at 15 stations over a reach of 66 river-km, beginning in
 headwater streams of the Coweeta basin and into the Little Tennessee
 River in western North Carolina.  This continuous gradient
 encompasses 1st through 7th-order streams with catchment areas
 varying from <10 ha to >100,000 ha, an elevational change of ca. 600
 m, and varying thermal regimes ranging from 3,000 degree-days in the
 headwaters to ca. 6,000 degree-days in the Little Tennessee River. We
 sampled bedrock outcrops, cobble, and depositional areas at most
 stations, depending on availability.  There was extensive replacement
 of macroinvertebrate taxa along the gradient; however, within a given
 habitat type the proportion of functional group representation
 remained relatively consistent.  Shredder biomass was greatest in
 depositional and cobble habitats, scraper biomass on cobble and rock
 outcrops, collector-gatherers on rock outcrops and depositional
 areas, and filterers on rock outcrop and cobble.  Predators were more
 evenly distributed among the three habitats.  Percent contribution of
 all functional groups to total macroinvertebrate biomass was
 significantly correlated (p < 0.05) to stream size.  Shredders,
 collector-gatherers, and predators were highest in the smaller
 streams and declined as stream size increased.  Conversely,
 collector-filterer contribution was small in the headwater streams
 and highest in the large river reaches.  Scraper contribution to
 total biomass was highest at mid-gradient sites (catchment areas
 >1,000 and <10,000 ha) and declined with both increasing and
 decreasing stream size.  Results of this study emphasize the need to
 consider sampling scale and the importance of habitat availability
 when characterizing trends in macroinvertebrate community structure
 over a stream size gradient.

Haberman, Karen L., Robin M. Ross and Langdon B. Quetin.  GRAZING BY
 THE ANTARCTIC KRILL Euphasia superbe, ON Nitschia spp. AND
 Phaeocystis spp. MONOCULTURES.  Marine Science Institute, University
 of California, Santa Barbara, CA 93106.  PAL Antarctic krill are
 important first order consumers in the Southern Ocean food web, and
 in turn are the principle prey for higher order consumers, including
 several species of penguins, seals and whales. While the krill
 primarily feed upon phytoplankton, it is not known whether they
 ingest and assimilate different types of phytoplankton with similar
 rates and efficiencies.  Such knowledge is important if we wish to
 understand how the patterns of phytoplankton species composition
 affect the krill's food availability.  This study focuses on one type
 of phytoplankton, Phaeocystis spp., which periodically occurs in
 thick blooms and can dominate the standing crop at certain places and
 times. The question of its edibility and nutritional value has been
 the subject of several investigations.  During laboratory feeding
 experiments, ingestion rates were calculated based on the rate of
 disappearance of chlorophyll a from the experimental tubs. Krill
 ingested the diatom Nitschia and single-celled Phaeocystis at similar
 rates, but did not ingest Phaeocystis colonies.  The difference in
 ingestion rate between these two physiological states of Phaeocystis
 suggests that food quality may be an important variable when
 assessing what proportion of the phytoplankton standing stock is
 useful to the krill.

Haines, B., D. Coleman, R. Davis. SOIL BIOLOGY; MICROSCOPE AND CAMERA
 SYSTEM FOR OBSERVING SOIL ORGANISMS AND QUANTIFYING ROOT GROWTH
 DYNAMICS. University of Georgia, Athens, GA. 30602 The challenge of
 studying roots and root associated organisms along an elevational
 gradient on the steep and often rocky forested watersheds was
 addressed by constructing observation boxes of poly vinyl chloride.
 The boxes were 65cm long, 57cm wide, 71.6cm tall at one end and
 39.5cm tall at the other end.  A window of flat glass of 31cm long
 and 15cm height was counter-sunk into short (39cm high) end wall, 8cm
 below the top.  The interior of the box was fitted with a mount for a
 35mm camera and a separate mount to position a dissecting microscope.
 The box was covered with a PVC lid which overlapped the outside of
 the walls.  A gasket inside this lid excluded water vapor.  The
 system provided both white light and ultraviolet light for
 observation and photography.  A 12 volt rechargeable battery powered
 an invertor which supplied 120 volts to the lights.  A timer
 controlled the light for sequential photographs.  Haines, Bruce L.,
 Bonnie Mccaig and James Hamrick. SUSCEPTIBILITY OF Robinia
 pseudoacacia L.(BLACK LOCUST) TO ATTACK BY Megacyllene robiniae
 (LOCUST STEM BORER): ROLES OF GENOTYPE AND STAND AGE. University of
 Georgia, Athens GA 30602. CWT.  Increased mortality of Robinia
 pseudoacacia is associated with evidence of trunk girdling by the
 black locust stem borer Megacyllene robiniae (Forster) (Coleoptera,
 Cerambycidae). Robinia pseudoacacia is often clonal in the southern
 Appalachians, USA. The possible pre-disposition of some clones or age
 classes to girdling by Megacyllene was investigated at the Coweeta
 Hydrologic Laboratory, North Carolina. The incidence of Megacyllene
 emergence holes was evaluated on 1629 Robinia stems.  Stems were
 mapped and foliage analyzed for genotype via protein gel
 electrophoresis for 15 polymorphic loci. The average number of
 emergence holes per tree for the 5, 13, 30 and 40 year old stands
 were 0.41, 1.6, 3.0 and 0.4 respectively. There is no evidence for
 genotypic correlation. Other factors contributing to incidence of
 Megacyllene could be the abundance of its intermediate host Solidago
 near Robinia stands.  Hall, Robert O. Jr.  THE USE OF A STABLE
 ISOTOPE ADDITION TO TRACE MICROBIAL CARBON THROUGH A STREAM FOOD
 WEB. University of Georgia, Athens, GA 30602. CWT.  I examined the
 importance of dissolved organic carbon to a stream food web using a
 13C addition. 13C as sodium acetate was dripped into a headwater
 spring at Coweeta Hydrologic Laboratory for three weeks during the
 summer. The addition was calculated to raise the del value of DOC
 from approximately -26 per mil to approximately 100 per mil. Before
 and after addition samples of CPOM, FPOM, and 20 taxa of organisms
 were analyzed on a Europa Tracermass mass spectrometer. Before
 addition samples ranged from -36 per mil to - 22 per mil. There was
 much variability between and within taxa after the
 addition. Predators were less labelled than collectors, shredders,
 and scrapers. Organisms appeared to preferentially assimilate
 microbial carbon.  Stenonoma, a biofilm scraper, was the most highly
 labelled taxon (up to 128 per mil), even though biofilm del value was
 -16 per mil. Chironomids had a higher del value than FPOM.  Although
 both the adults and larvae of an elmid beetle, Optioservus, are
 scrapers, the adults were more labelled than the larvae, indicating
 greater dependence on microbial carbon.  This technique is useful to
 discriminate between particulate and dissolved sources of carbon
 where no differences in the natural abundance of 13C exist. Hence it
 appears to be a useful technique for resolving detrital food webs.

Halstead, S. J. , W. R. Reed, M.  Krisfalusi and
 G. P. Robertson. SPATIAL PATTERNS OF SOIL DENITRIFICATION POTENTIALS
 IN THREE TILLAGE SYSTEMS .  W. K. Kellogg Biological Station, Hickory
 Corners, MI 49060.  KBS.  Denitrification plays an important role in
 the loss of nitrogen fertilizer from agricultural systems.  We
 examined the effect of tillage and position within the crop row on
 the rates of nitrous oxide production at three times within the
 growing season.  Intact cores were taken pre- and post-plant and
 post-fertilization from mold-board plow, notill and ridge till
 systems.  Within each tillage type, cores were taken at 0, 20 and 40
 cm starting in the row and moving to the interrow.  Cores were
 incubated with acetylene and sampled at 3 h intervals for 12 h.
 Nitrous oxide production was greatest from moldboard plowed systems
 with decreased rates observed in the other tillages.  Within a
 tillage system, losses appear to be greatest within the crop row.
 Further work will attempt to correlate enzyme activity with nitrous
 oxide production rates in the field.  Hendricks, Joseph J. and John
 D. Aber.  THE EFFECTS OF NITROGEN AVAILABILITY ON FINE ROOT SUBSTRATE
 QUALITY.  Institute of Natural Resources, University of New
 Hampshire, Durham, NH 03824.  HFR.  The effect of nitrogen
 availability on fine root substrate quality was assessed using
 samples from the chronic nitrogen addition plots in the Harvard
 Forest LTER site.  Fine roots (generally < 1 mm in diameter) from the
 organic and mineral (0-10 cm) soil horizons of red pine and
 mixed-hardwood control (0 kg N ha-1 yr-1), low (50 kg N ha-1 yr-1),
 and high (150 kg N ha-1 yr-1) treatment plots were collected on
 monthly intervals during the 1991 growing season and analyzed for
 nitrogen and carbon fraction concentrations.  Nitrogen concentrations
 (range of 1.1 to 2.8%) differed significantly between treatments,
 horizons, and sample periods for both red pine and
 mixed-hardwoods. In contrast, carbon fractions (predominately lignin,
 range of 46 to 51%) did not differ significantly among classes.
 These results indicate that fine root substrate quality and potential
 decompositionrate are positively correlated with nitrogen
 availability.  Herrera, Jose, O.J. Reichman, and
 C. L. Kramer. COMMUNITY STRUCTURE OF FUNGI INHABITING RODENT DENS.
 Division of Biology, Kansas State University, Manhattan, KS, KBS.
 Relatively few studies have included analyses of the spatial and
 temporal patterns of fungal communities and the effect of ambient
 conditions on these patterns.  At Sevilleta we are investigating the
 abundance and diversity of fungi that inhabit food caches of two
 rodent species (white-throated woodrats and bannertailed kangaroo
 rats) and how these features vary over space (along a transect) and
 time (over two years).  Temperature and relative humidity are also
 being monitored and compared to the fungal patterns.  Samples are
 taken from 6 adjacent core dens and from individual dens along a
 transect of geometrically increasing distance from the core (up to
 3.2 km ).  Fungi are isolated, identified, and enumerated, and alpha
 and beta diversity indices are calculated.  Preliminary results
 indicate that more spores are produced in woodrat dens than in
 kangaroo rat dens.  Furthermore, there are no apparent differences in
 the abundances of spores between dens along their respective
 transects.  Spore abundances also are fairly uniform between sampling
 dates, except for an increase in spores in kangaroo dens in January.
 The community of fungi inhabiting the caches differs from that
 observed in samples from ambient air directly above the dens.
 Specifically, cache samples have an unexpected number of sterile
 (non-sporulating) fungi compared to overlying air samples. Analyses
 are being conducted on the relationship of fungal patterns to
 temperature and humidity in dens and the ambient air.  In the future,
 our investigation will center on an examination of the diversity
 patterns and how they are influenced by the rodents.  In addition, we
 will determine how fungal populations affect the storage and
 consummatory strategies of the rodents.  Hobbie, John E., et al. AN
 LTER PROGRAM FOR THE ALASKAN ARCTIC. The Ecosystem Center, Marine
 Biological Laboratory, Woods Hole, MA 02543. ARC The goal of the
 Arctic LTER program is to understand how tundra, streams and lakes
 function in the Arctic and predict how they respond to human-induced
 changes, including climate change.  Terrestrial Studies: Manipulation
 of temperature, light, and nutrients indicate that, over 9 years of
 treatment, direct effects of air temperature change on plants is
 slight.  Additions of nutrients elicit a large response in this
 strongly nutrient limited environment.  Respiratory rates of arctic
 soils are high compared to temperate soils and respiration rates are
 highest above a threshold temperature of 9xC. Lake Studies:
 Whole-system experiments on the mechanisms of nutrient cycling are
 underway in 2 area lakes.  Although the response time of one lake
 (N-1, currently being fertilized) has been twice as rapid as the
 second (N-2, fertilized 1985-1990), both lakes appear to be strongly
 limited by phosphorus.  Two large-bodied species of zooplankton
 border on extinction probably brought about by an increase in the
 population of zooplanktivorous arctic grayling as a result of
 increased human fishing of the lake trout, the grayling primary
 predator.  Stream Studies: Since 1983, the Kuparuk River has been
 fertilized with phosphorus and results indicate that the productivity
 of the river food chain, from algae to grayling, is closely tied to
 the supply of external nutrients.  A 15N-NH4 tracer addition to the
 Kuparuk River revealed a 900 meter spiraling distance and a retention
 of 15N in all parts of the food web for at least 1 year.  Land-Water
 Interactions: The pCO2 and CH4 in soil water, streams, and lakes is
 supersaturated; the excess CO2 and CH4 appears to originate during
 decomposition in the soils and moves toward the streams and lakes via
 groundwater flow.  Modeling: GEM simulated the present stocks and
 turnovers of C and N at the Arctic and Harvard Forest LTER sites.
 Simulations were run to examine the response over 50 years to
 doubling of atmospheric CO2, a 5xC temperature rise, and increased N
 deposition.  Although there are very different amounts of wood in
 each system and different distributions of C and N in the vegetation
 and soils, the simulations revealed qualitatively similar responses.
 There was very little response to increased CO2; both systems
 increased C in plants by 1.5 times due to the increased temperature
 and CO2.

Holland, Elisabeth A., C. Coxwell, D.S. Schimel, and D. Valentine. A
 MODEL OF METHANE PRODUCTION IN SOILS. National Center for Atmospheric
 Research, P.O. Box 3000, Boulder CO 80307 and Natural Resource
 Ecology Laboratory, Colorado State University, Fort Collins CO
 80523. NWT and CPR.  We have developed a simple model of methane
 production for flooded soils. Labile substrate supply is simulated as
 a proportion of the carbon decomposed and is controlled by
 temperature, moisture, and litter quality (lignin:N). The proportion
 of labile substrate converted to methane (rather than CO2) is
 controlled by redox, temperature, pH, substrate supply and
 quality. The model parameterizations are based on a series of
 laboratory experiments which examined the CH4 response to ethanol,
 litter, and root amendments, temperature and pH manipulations in
 anaerobic slurries. Preliminary comparisons demonstrate that the
 model is able to effectively simulate CH4 production for a range of
 environmental conditions and that methane production is sensitive to
 both the amount and quality of incoming carbon.  Homann, Peter, and
 Phillip Sollins.  MODELING SOIL C AND N DYNAMICS THROUGH THE SOLUBLE
 ORGANIC POOL.  Dept. of Forest Science, Oregon State Univ., Corvallis
 OR 97331-7501.  AND.  Soluble organics are important in
 redistributing C and associated elements in forest soil profiles.
 Some soluble organics also serve as readily available energy sources
 for microorganisms.  In a compartment model developed to simulate
 soil C and N dynamics in forest soils, soluble organics are
 represented by two pools which differ in their potentials to be taken
 up and mineralized by microorganisms.  Soluble organics enter the
 soil as components of plant detritus and in solutions such as
 throughfall and stemflow.  They are leached through the profile in
 soil solutions.  Soluble organics are transferred to solid-phase
 organic pools by sorption, precipitation and condensation reactions.
 They are produced by microbial activity, microbial death, and
 extracellular enzymatic processes operating on solid-phase
 pools. Depending on the specific pool, N may enhance or reduce the
 stability of organic C against enzymatic breakdown and microbial
 respiration. The model is designed to simulate the balance of soluble
 organics resulting from these soil processes over periods of one to
 ten years.

Homann, P.S., P. Sollins, H.N. Chappell, D. Lammers,
 A.G. Stangenberger, and M. Fiorella.  CONSTRAINTS ON REGIONAL
 ESTIMATES OF ORGANIC C CONTENTS OF FOREST SOILS.  Department of
 Forest Science, Oregon State Univ., Corvallis OR 97331-7501; Univ. of
 Washington, Seattle, WA; U.S. Forest Service, Corvallis, OR; and
 Univ. of California, Berkeley.  AND.  We compared two methods of
 estimating soil organic C over the western Oregon region.  The Oregon
 STATSGO soil map yielded an area-weighted average of 4.9 kg C/m2 for
 the 0-20 cm depth of mineral soil. The 393 soil pits averaged 6.1 kg
 C/m2 for the 0-20 cm depth and 13.2 for 0-100 cm.  For the soil-pit
 locations, there was good agreement between soil-pit and STATSGO
 averages, but STATSGO values were lower than soil-pit values in areas
 of low soil C and higher in areas of high soil C.  Major constraints
 in using this information for regional estimates of C storage in
 forest soils are: lack of O horizon data in STATSGO and limited O
 horizon data for soil pits; organic matter estimates limited to
 surface horizon in STATSGO; non-random distribution of soil pits
 across the region.  Horwath, William, Eldor Paul and Kurt Pregitzer.
 THE DYNAMICS OF CARBON, NITROGEN AND SOIL ORGANIC MATTER IN POPULUS
 PLANTATION USDA/ARS, Corvallis, OR 97331 and Michigan State
 University, East Lansing, MI 48824.  The lack of root turnover
 studies has led to an inadequate understanding of below-ground
 production and turnover in nutrient cycling processes and global C
 budgets.  The current study examined: (i) above-and below-ground C
 and N allocation patterns; (ii) the role of leaf litter and fine root
 turnover in soil organic matter maintenance; and (iii) the kinetics
 of C mineralization from recently incorporated soil C.  We labeled
 two-year-old hybrid poplars with 14C and 15N at different times in
 the growing season to encompass seasonal C and N allocation patterns.
 A controlled environment chamber was used for 14C uptake and 15N was
 injected into the stem.  The tree-soil and leaf litter decomposition
 plots were sampled for two years following labeling.  Estimates of
 root turnover were less than once per year based on 14C dilution and
 total tree reserves.  Despite low root turnover estimates, the amount
 of 14C stabilized in soil was similar from leaf and root turnover.
 The mean residence time of the recently stabilized 14C in soil from
 both leaf and root turnover was approximately 4 years.

Huberty, Lisa, Katherine Gross, and Karen Renner. RESOURCE COMPETITION
 AMONG CROPS AND WEEDS IN RESPONSE TO TILLAGE AND NUTRIENT
 MANAGEMENT. Michigan State University, East Lansing MI 48824 and
 Kellogg Biological Station, Hickory Corners MI 49060. KBS.  The
 pattern and frequency of disturbance are managed by plowing,
 planting, and harvesting in the conventional till (CT) and no-till
 (NT) treatments of the LTER in agriculture at Kellogg Biological
 Station, MI. The disturbance regime in CT produced an annual weed
 community with low species diversity. The lower disturbance rate in
 NT produced a biennial and perennial weed community with higher
 species diversity. These differences in life-history and species
 composition create plant communities with different growth forms and
 different seasonal patterns of primary production. The biennial and
 perennial NT weed community accumulated more biomass than the annual
 CT weed community early in the season. As a result, the seasonal
 dynamics of resource depletion differed between the two
 treatments. Light at the soil surface and soil nitrate concentrations
 were depleted to lower levels early in the growing season in the NT
 (biennial/perennial) plant community than in the CT (annual) plant
 community. However, by the end of the growing season, the annual weed
 community depleted light and soil nitrate to the same levels as the
 NT community. The early season dynamics of resource depletion were
 critical to explain the differences in how weeds regulated the
 primary production of the crop (soybean) measured at the end of the
 growing season. Nitrogen uptake patterns of the top three dominant
 weed species in the context of the whole community will be used to
 compare the resource use and productivity patterns of annual species
 and perennial species.  Huenneke, Laura and Esteban Muldavin.
 SPATIAL HETEROGENEITY OF ECOSYSTEM STRUCTURE AND FUNCTION: DESERT
 SHRUBLANDS AND GRASSLANDS OF THE JORNADA LTER SITE.  New Mexico State
 University, Las Cruces, NM 88003 and NM Natural Heritage Program,
 University of New Mexico, Albuquerque, NM 87131.  JRN.  We developed
 a method for estimating live aboveground biomass and net primary
 production on a per-unit-area basis, using simple measures of plant
 dimension in permanent quadrats.  This approach has been used to
 estimate biomass and production in 15 sites representing grass- and
 shrub-dominated ecosystems of the northern Chihuahuan desert.  Sites
 are sampled three times per year: in winter (February), late spring
 (May), and late summer (September/October).  Data from 1989 - 1992
 were used to evaluate the differences in biomass, productivity, and
 spatial variability in biomass and productivity among vegetation
 types.  There are no substantial differences in mean biomass or mean
 net primary production per m2.  However, shrub-dominated systems
 (including Larrea tridentata or creosote bush scrub, and Prosopis
 glandulosa or mesquite dunes) show significantly greater variation in
 aboveground biomass within a site than do grass- dominated systems
 (black grama or Bouteloua eriopoda stands, and grassy playas).  Net
 primary production shows less striking differences in heterogeneity
 among vegetation types, but production in black grama grasslands is
 very homogeneous spatially, while shrublands show tremendous
 heterogeneity for at least some seasons.  Our results indicate that
 conversion of black grama grasslands to Larrea- and
 Prosopis-dominated communities may not have altered average ecosystem
 properties, but it has certainly increased the spatial heterogeneity
 of both structure and function of these desert systems.

Hutches, Jr., J.J., E.F. Benfieid, and J.R. Webster. EFFECTS OF LEAF
 TYPE ON THE GROWTH OF A LEAF-EATING CADDISFLY, Pycnopsyche
 gentilis. Dept. of Biology, VPI&SU, Blacksburg, VA 24061. CWT.  A
 recent study examining long-term responses of stream-dwelling
 leaf-eating insects to clearcut logging found a caddisfly,
 Pycnopsyche gentilis, population was significantly more productive in
 streams draining an 11-year-old logged watershed as compared to a
 population in streams draining an undisturbed, reference
 watershed. However, there was 40% more leaf material, i.e., food
 available in undisturbed streams. We studied P. gentilis larval
 growth in the library using fast and slow-processing leaves (black
 birch and white oak, respectively) to determine whether leaf quality
 could explain the higher production. Birch leaves were significantly
 softer than oak leaves (p<0.05) and thus, were possibly better
 resources. However, P. gentilis growth rates were significantly
 higher on the oak leaf diet than the birch leaf diet
 (p<0.05). Assimilation and net growth efficiencies were not
 significantly different between diets (p>0.05) and could not explain
 the results. However, consumption rates indicate larvae were probably
 not fed ad libitum for the birch diet, possibly explaining higher
 larval growth rates on white oak leaves.

Irons, J.G., III1, R.J. Stout2, M.W. Oswood3, C.M. Pringle4 and
 J.P. Bryant3. LATITUDINAL GRADIENTS IN LEAF LITTER DECOMPOSITION IN
 STREAMS: EFFECTS OF LEAF CHEMISTRY AND TEMPERATURE.  1Inst. of
 Northern Forestry, Fairbanks, AK, 2Michigan St. Univ E. Lansing,
 MI. 3Univ. Alaska, Fairbanks, AK, 4Univ. Georgia, Athens, GA. BNZ.
 Autumnal leaf litter that falls into streams of forested regions
 constitutes a major source of energy for stream food webs. The
 processing of this litter has been studied for many years (especially
 in temperate forest streams), and two generalizations have come from
 this research: 1) nitrogen concentration is positively correlated
 with breakdown rate, and 2) water temperature is negatively
 correlated with breakdown rate. We examined these generalizations by
 estimating breakdown rates of litter of ten tree species with widely
 varying nutritional quality (condensed tannin and nitrogen
 concentrations) along the latitudinal gradient from the tropics to
 the subarctic. Study sites were chosen in Costa Rica, Michigan, and
 Alaska in reaches of similar stream size, depth, and velocity. Litter
 breakdown rates of ten tree species were analyzed both on a time
 basis (per day) and a temperature basis (per degree-day above OoC),
 and were compared among locations. We found that: 1) breakdown rates
 were positively correlated with litter nitrogen concentrations, but
 were more highly correlated (negatively) with condensed tannin
 concentrations, and 2) although breakdown rates (per day) were
 highest in Costa Rica, temperature-adjusted rates (per degree-day)
 were much higher in Alaska than in Costa Rica or Michigan. We propose
 a model of leaf litter breakdown in which microbial breakdown is
 negatively correlated with latitude (i.e. temperature) and
 invertebrate breakdown is positively correlated with latitude. In
 this model, we propose that the relative importance in litter
 breakdown shifts from microbes in the tropics to shredder
 invertebrates in the subarctic, and that temperature influences the
 microbial component more than the shredders. Furthermore, we suggest
 that secondary compounds, especially the wide- spread condensed
 tannins, co-determine, along with nitrogen concentration, leaf litter
 breakdown rates.  Johnson, N. C. SELECTION PRESSURES AND EFFECTIVITY
 OF VAM FUNGI. Department of Biology, University of New Mexico,
 Albuquerque, NM 87131. CDR.  Any factor that causes differential
 reproduction and survival of vesicular-arbuscular mycorrhizal (VAM)
 fungi is a selective force and can impact composition of VAM fungal
 communities.  Since VAM fungi depend upon plants for all of their
 carbon (C) requirements, factors that influence the availability of C
 in root exudates (like soil fertility and irradiance) are likely to
 be strong selection pressures on populations of VAM fungi.  VAM fungi
 are usually mutualists, but they can also be parasites.  Their effect
 on plants (effectivity) may be influenced by selection pressures.
 The same characteristics that make a VAM fungus successful when the C
 content of root exudates is reduced (e.g. due to fertilization or
 shading) may also reduce their mutualistic effects.  Namely,
 successful fungi may acquire C not allocated to root exudates, and
 thus, parasitically provision their own growth without contributing
 to plant fitness.  At Cedar Creek Natural History Area a series of
 field and greenhouse experiments were conducted to test the
 hypothesis that fertilizing soil selects for VAM fungi that are
 inferior mutualists.  Results showed that 1) fertilization changed
 the composition of VAM fungal communities and 2) VAM fungi from
 fertilized soils were less mutualistic than those from unfertilized
 soils.  A mechanism to account for these results will be presented
 from physiological, population and community perspectives.

Johnson, Stephen R. and Alan K. Knapp.  EFFECT OF FIRE ON GAS EXCHANGE
 AND GROWTH IN Spartina pectinata WETLANDS. Kansas State University,
 Manhattan,KS, 66506, USA. KNZ.  Photosynthetic and growth responses
 of Spartina pectinata were compared in annually burned and unburned
 wetlands in a northeastern Kansas tallgrass prairie.  Culm density
 was not affected by fire, however, inflorescence density and plant
 height at maturity were all significantly greater in annually burned
 wetlands.  Aboveground production in annually burned wetlands was
 1558 g/m2 vs. 607 g/m2 in unburned wetlands.  CO2 Uptake was also
 consistently higher in burned plants (38.2 mol m-2 s-1 vs. 28.6 mol
 m-2 s-1 in unburned plants) and there was a seasonal difference in
 maximum uptake rates between annually burned and unburned wetlands.
 These results indicate that Spartina pectinata may be a fire
 dependent species, with post-fire responses similar to the dominant
 grasses in tallgrass prairie, as well as other Spartina species.
 Jones, J.A., and G.E. Grant.  LONG TERM STORMFLOW RESPONSES TO
 CLEARCUTTING AND ROADS, WESTERN CASCADES, OREGON: I.  SMALL
 BASINS. Department of Geosciences, Oregon State Univ., Corvallis, OR
 97331 and Pacific Northwest Research Station, U.S. Forest Service,
 Corvallis, OR 97331.  AND.  This study examined a 33-year record of
 matched storm data from three 60 to 100 ha experimental basins in the
 Andrews LTER in western Oregon to determine the effect of
 clearcutting, with and without roads, on storm hydrographs.  One
 treated basin was 100% clearcut with no roads while the other had 6%
 of its area in roads for four years before it was 25% patch clearcut.
 The differences between treated and untreated basins were assessed by
 examining six hydrograph variables (storm begin date/time, peak
 date/time, time to peak, storm duration, peak discharge, and total
 storm volume) for about 320 matched storm hydrographs for each basin
 pair.  Clearcutting with no roads increased the peak discharge,
 volume, time to peak, and duration, advanced the begin time and
 delayed the peak time of storms.  Road construction with no
 clearcutting increased peak discharge, did not change volume,
 advanced time of peak and begin time, and increased time to peak and
 duration of storms.  Road construction with 25% clearcuts increased
 the peak discharge, volume, time to peak, and duration, advanced the
 begin time and did not change the peak time of storms.  The most
 pronounced effects were for small storms whose peak discharges and
 volumes increased 15 to 20% in the first five years after 100%
 clearcutting or 25% clearcutting with roads.  However, even 25 years
 after these treatments large storm peak discharges and storm volumes
 were still 5 to 10% higher than before treatment.  Roads alone
 increased peak discharges by 8% but did not affect storm
 volumes. Clearcutting and road construction appear to have additive
 effects on peak discharges but counteracting effects on peak timing.
 We hypothesize that clearcutting modifies the water balance to
 produce increases in both peak discharge and storm volume, whereas
 roads modify flow routing and thus increase peak discharges without
 affecting storm volumes.  Jones, J.A., and G.E. Grant.  LONG TERM
 STORMFLOW RESPONSES TO CLEARCUTTING AND ROADS, WESTERN CASCADES,
 OREGON: II.  LARGE BASINS. Department of Geosciences, Oregon State
 Univ., Corvallis, OR 97331 and Pacific Northwest Research Station,
 U.S. Forest Service, Corvallis, OR 97331.  AND.  This study examined
 the effect of cumulative clearcutting with roads on storm hydrographs
 in three pairs of adjacent basins ranging from 60 to 600 km2 in the
 western Cascade Range of Oregon.  For each basin pair, landuse
 history (clearcutting and road construction) over the period from
 1930 to 1990 was compiled on a geographic information system (GIS)
 and compared to 150 to 175 matched hydrographs from large storms with
 > 1.1 yr return intervals.  An additional 300 hydrographs from small
 storms were examined for the Lookout Creek/Blue River pair. One pair
 of basins (Lookout Creek, site of the Andrews LTER, and upper Blue
 River) had strongly contrasting cumulative harvest patterns, with
 cumulative harvests of nearly 25% by 1990 and differences in
 cumulative area cut ranging from 0 to 15% of basin area.  The other
 two basin pairs, the North Fork of the Willamette Middle Fork/Salmon
 Creek and the Breitenbush River/N. Santiam River, had more similar
 historical harvest patterns with cumulative harvests of 18 to 24% and
 differences in cumulative area cut from 0 to 4% of basin area.  For
 large storms in all three basin pairs, clearcutting with roads was
 associated with increased peak discharge in the basin with greater
 cumulative area cut over the preceding decade.  Peak discharges were
 significantly increased even when basins differed by as little as 1%
 (6 km2) in area cut.  Timing of peaks was not consistently related to
 between-basin differences in cumulative area cut.  These results are
 consistent with our analyses of small experimental basins in Lookout
 Creek, which suggested that clearcutting with roads would increase a
 basin's storm peak discharge but produce no net effect on storm peak
 timing.  However, small storm peak discharges in the Lookout
 Creek/Blue River pair had a less clear relationship to between-basin
 cumulative cutting, in contrast to the findings from the small
 experimental basins where small storms responded more than large
 storms.  We hypothesize that in large basins the effect of
 clearcutting with roads on peak discharges depends upon the relative
 rates of clearcutting and road construction, as well as channel
 routing processes which propagate stormflow from small to large
 basins.

Juday, Glenn Patrick.  AGE STRUCTURE AND GROWTH HISTORY OF A BOREAL
 WHITE SPRUCE FOREST.  Forest Sciences Dept. Univ. of Alaska
 Fairbanks, Fairbanks Alaska 99775-0080. BNZ A white spruce reference
 hectare that burned in the 1983 Rosie Creek Fire at BNZ was compared
 with an unburned hectare and a 102-tree sample of basal and breast
 height bole sections was analyzed for radial growth to produce a
 master chronology.  Over 90% of the white spruce bole sample trees
 belong to a cohort that originated in the mid 1780s, apparently
 following a fire.  The second cohort appears to have originated about
 8 years after the first, probably from the next abundant white spruce
 seed crop.  The master chronology exhibits three distinct sets of
 marker rings; (1) an 1878-79 trauma that decimated stand growth,
 probably as a result of a snow or ice loading event that stripped off
 branches; (2) a 1910-12 sequence of small, normal, and small rings
 respectively; and (3) a severe growth reduction in 1958-59 which
 followed an exceptionally warm and dry summer of 1957 in interior
 Alaska.  The radial growth and development of the stand was reshaped
 by the 1878-79 trauma, producing three subpopulations of trees here
 termed winners, normal, and losers.  In winner trees the ratio of
 cross-sectional bole area in 1883 compared to 1982 (each representing
 growth intervals of about a century) is greater than 2, in normal
 trees the ratio is between 1 and 2, and in loser trees the ratio is
 less than 1.  The original stand location of all 102 trees was
 analyzed and no systematic pattern was seen in the location of
 winners, losers, or normal trees.  No evidence of intermediate
 regeneration of white spruce was seen.  Thus the structure of this
 stand is largely explained by one initial stand replacement
 (regeneration) event, subsequent gradual stand growth
 differentiation, and a trauma in the middle of the life of the stand
 that improved the competitive performance of some trees and worsened
 the performance of others.  The radial growth record was compared
 with the longest instrument-based climate record in interior Alaska,
 University Experiment Station (UES) located 34 km east of the LTER.
 A comparison of UES warm season temperature with average stand radial
 growth at Bonanza Creek LTER shows an inverse relationship.  Contrary
 to expectations the stand as a whole grew best in the cooler years,
 suggesting that moisture limitations may be the operative controlling
 factor than temperature.  A comparison of UES annual precipitation
 with stand radial growth reveals a one to 4-year lagged response,
 again suggesting that soil moisture is a limiting factor.  White
 spruce are determinate growers and their current years growth
 primarily reflects the previous seasons carbon gain which is stored
 as winter reserves.  Kaufman, Donald W., Glennis A. Kaufman and Elmer
 J. Finck. TEMPORAL VARIATION IN POPULATIONS OF SMALL MAMMALS IN
 TALLGRASS PRAIRIE.  Kansas State Univ., Manhattan, KS 66506.  KNZ.
 Small mammals in ungrazed tallgrass prairie were studied from autumn
 1981 to spring 1991 on Konza Prairie to assess interspecific
 differences in both abundance and temporal patterns of abundance and
 to search for possible factors driving the temporal patterns.
 Estimates of abundance were from permanent live-trap lines set in
 sites whose periodicities of recurring fire ranged from annual to 20
 years.  In descending order of abundance, common species (8 of 14
 species of small mammals captured) were Peromyscus maniculatus,
 Reithrodontomys megalotis, Blarina hylophaga, Peromyscus leucopus,
 Microtus ochrogaster, Sigmodon hispidus, Spermophilus
 tridecemlineatus, and Synaptomys cooperi.  Temporal variation
 (standard deviation of log abundance) differed among species with
 that of the two Peromyscus species much less variable than that of
 the two microtine rodents.  Fluctuations exhibited by Microtus and
 Synaptomys appeared cyclic and were relatively synchronous with each
 other, but not other small mammals.  For other species, temporal
 patterns varied in timing and magnitude of high and low abundances.
 However, autumn abundances of individual species of cricetine rodents
 (Peromyscus, Reithrodontomys, and Sigmodon) were
 intercorrelated. Finally, abundance of species of small mammals did
 not consistently correlate with indices of temperature,
 precipitation, and productivity and, therefore, such factors
 individually do not appear to be simple driving factors behind
 temporal patterns of abundance of small, prairie mammals.  Kaufman,
 Glennis A., Donald W. Kaufman and Elmer J. Finck.  EFFECTS OF FIRE ON
 POPULATIONS AND COMMUNITIES OF SMALL MAMMALS IN TALLGRASS PRAIRIE.
 Kansas State Univ., Manhattan, KS 66506.  KNZ.  In autumn 1981, we
 initiated a long-term study of small mammals in burned and unburned
 tallgrass prairie on the Konza Prairie to understand fire as an
 influence on populations and communities of rodents and shrews.  Our
 analyses of responses of rodents and shrews to experimental spring
 fires in ungrazed prairie are based on data from autumn 1981 to
 spring 1991. Peromyscus maniculatus, Sigmodon hispidus, and
 Spermophilus tridecemlineatus were fire-positive, whereas Blarina
 hylophaga, Reithrodontomys megalotis, Microtus ochrogaster, and
 Synaptomys cooperi were fire-negative.  Assemblages of small mammals
 were greatly altered by fire with P. maniculatus increasing from 35%
 of the average assemblage in unburned prairie to 64% in burned
 prairie, R. megalotis decreasing from 25% to 8%, and B. hylophaga
 decreasing from 17% to 7%.  Further, the diversity and evenness of
 community structure decreased following fire.  In addition to this
 general fire effect, frequency of fire influenced diversity,
 richness, and evenness but not combined abundance of small mammals.
 For example, diversity, richness, and evenness were lower in burned
 sites that were burned annually than burned sites that were burned
 periodically.  Further, an effect of fire history was evident for
 small mammals in burned areas burned annually, burned areas burned
 every two years, and burned areas burned every four years.  In this
 case, diversity and richness decreased with time since the previous
 fire.

Kitajima, Kaoru and Tilman, G. David.  SPATIAL HETEROGENEITY AND
 SUCCESSIONAL CHANGE IN SOIL SEED BANK FLORA IN CENTRAL
 MINNESOTA. Department of Ecology, Evolution, and Behavior, University
 of Minnesota, St. Paul, MN 55108.  CDR.  We report the method and an
 early analysis of our investigation of seed bank in a chronosequence
 of old fields (23 fields ranging between 6 and 65 yr after
 abandonment) and three oak savanna sites (=climax community at Ceder
 Creek LTER).  Our central objective is to examine the correlations
 between soil seed bank flora and past and present vegetation under
 successional change that has been censured over 10 years.  We found
 high heterogeneities of species composition and abundance of seeds in
 the soil in both small and large spatial scales.  Although soil seed
 bank is considered to be important in understanding vegetation
 dynamics in response to disturbances, the labor intensiveness and
 lack of standard protocol obstacle community level studies.  We would
 like to call for an open discussion in search of a standardized
 method that can accommodate long term studies as well as intersite
 comparative studies of soil seed bank communities.  Knapp, A.K.,
 J.M. Briggs, J.M. Blair, W.K. Dodds, D.C. Hartnett, D.W. Kaufman and
 C.W. Rice.  LONG TERM ECOLOGICAL RESEARCH AT THE KONZA PRAIRIE
 RESEARCH NATURAL AREA. Kansas State University, Manhattan, KS
 66506. KNZ.  The long term ecological research program at the Konza
 Prairie Research Natural Area (KPRNA) was one of the initial programs
 established by NSF in 1981. The KPRNA is 3,487 ha of pristine
 (unplowed) tallgrass prairie representative of the native vegetation
 of the Flint Hills of NE Kansas and the western extent of the
 original distribution of this grassland. A fully replicated
 watershed-level experimental design has been established on KPRNA
 that focuses on fire frequency and grazing by large ungulates. The
 primary goal of the LTER program is to understand how grazing and
 fire frequency interact to influence biotic and ecosystem patterns
 and processes over the landscape mosaic, all of which are subjected
 to a highly variable (and possibly directional) climatic
 regime. Research to date has only begun to encompass the range of
 variability in the system, but these data have provided us with an
 appreciation for the nonequilibrium nature of tallgrass prairie. With
 this perspective, we have developed conceptual models that have
 predictive capabilities for a number of key system attributes.

Knoepp, Jennifer Donaldson, Swank, Wayne T.  LONG-TERM SOIL CHEMISTRY
 CHANGES IN AGGRADING FOREST SYSTEMS.  USDA Forest Service, Coweeta
 Hydrologic Laboratory, Otto, NC 28763.  Identification of processes
 regulating long-term soil chemistry changes requires monitoring
 cation leaching and biomass accretion.  We resampled the litter layer
 and upper two mineral soil horizons, A and AB/BA, in two aggrading
 southern Appalachian watersheds 20 years after an earlier sampling.
 Soils from mixed-hardwood Watershed 18 (HDWD), undisturbed since
 1927, exhibited a small but significant decrease in soil pH.
 Extractable base cation content declined substantially in both
 mineral horizons.  For example, Ca levels in the A horizon fell from
 236 kg/ha in 1970 to 80 kg/ha in 1990.  Proportionally, the decline
 was greatest for Mg, which dropped form 111 to 20 kg/ha.  White pine
 (Pinus strobus L.) plantation Watershed 17 (WP) was planted in 1956
 after clear-felling hardwoods and recutting sprouts for 15 successive
 years.  Soil pH and base cation concentrations declined in the A
 horizon since 1970.  Soil pH declined from 5.9 to 5.0 and Ca levels
 from 534 to 288 kg/ha.  Cation content did not change significantly
 in the AB/BA soil horizon.  Nutrient budgets were constructed using
 these soil and litter data plus existing biomass and stream chemistry
 data.  Decreases in soil base cations and soil pH are attributed to
 leaching and sequestration of nutrients in biomass.

Kratz, T.K. and Carl J. Bowser.  PATTERNS OF CO2 SATURATION IN SEVEN
 NORTHERN WISCONSIN LAKES. University of Wisconsin, Madison, WI
 53706. NTL We examined seasonal and annual patterns of CO2 saturation
 in seven lakes in the Northern Highland Lake District in northern
 Wisconsin. The lakes are the primary study lakes of the Northern
 Temperate Lakes Long-Term Ecological Research Project.  We calculated
 degree of CO2 saturation from data on in-situ pH, air-equilibrated
 pH, DIC, and total alkalinity taken at monthly intervals from 1987
 through 1991. Surface waters in the lakes were over-saturated except
 for summer months when surface waters were near equilibrium or
 slightly under-saturated. Annual ice-free season average CO2 for
 surface waters were above atmospheric equilibrium for each of the
 study lakes, indicating that on an annual basis the lakes are net
 sources of CO2 to the atmosphere. This excess carbon must originate
 in the terrestrial system and is transported into surface water most
 likely via hydrologic pathways, but also as dry particulate
 deposition. These results underscore the role surface waters play in
 landscape-level carbon dynamics..

Krievs, Lolita, Stuart Gage, Manuel Colunga and G. Philip Robertson
 ERROR AS A FUNCTION OF RECEIVER DISTANCE FOR DIFFERENTIALLY
 POST-PROCESSED GPS DATA W. K. Kellogg Biological Station, Michigan
 State University, MI KBS.  Global Positioning Systems (GPS) depend
 for their accuracy on a constellation of satellites orbiting at an
 altitude of approximately 10,000 miles.  GPS receivers translate
 radio signals emitted by these satellites into distance measures to
 determine receiver locations on earth.  Electrical interference in
 the atmosphere and geographic variation in landcover and elevation
 are two of many potential influences that can degrade the precision
 of single receiver data processing.  The degree of error caused by
 signal degradation can, however, be substantially reduced by GPS
 differential post-processing.  Differential post-processing is
 performed by comparing satellite signals simultaneously logged by a
 mobile and a base GPS receiver and then correcting the mobile unit's
 location by triangulation.  To be effective, the base unit must log
 signals from a known coordinate location.  Differential GPS (DGPS)
 assumes that the difference between receiver signal errors associated
 with upper atmospheric conditions is negligible in comparison to the
 difference in signal errors associated with the immediate
 environment.  The effectiveness of DGPS should also depend on the
 distance separating the mobile and base units, but the relationship
 between separation distance and error reduction is not well known for
 most landscapes.  We attempted to define this relationship by
 surveying locations of first order geodetic controls using a Trimble
 Basic GPS Receiver while simultaneously logging satellite signals
 with a Trimble Pathfinder Community Base Station at KBS.  Geodetic
 markers were chosen along a 300 mile gradient in southwest
 Michigan. Data were post-processed using Trimble Software.
 Preliminary results indicate that locational accuracy decreases
 significantly with distance from the base station; the extent to
 which this error can be predicted and minimized is discussed.
 Landis1, Douglas A. and Paul C. Marino2. EFFECT OF LANDSCAPE
 STRUCTURE ON PARASITOID DIVERSITY AND PARASITISM IN
 AGROECOSYSTEMS. 1Department of Entomology and Pesticide Research
 Center, State University, E. Lansing, MI. 48824. 2Department of
 Biological Sciences,PO Drawer GY, Mississippi State University,
 Starkville, MS 39762-5759. KBS.  The structural complexity of
 agroecosystems may have important effects on diversity of parasitoid
 communities and their impact on crop herbivores. We examined
 parasitism of Pseudaletia unipuncta (Haworth) (Lepidoptera:
 Noctuidae), a native, polyphagous herbivore with a diverse parasitoid
 community. The study area in south-central Michigan consisted of an
 agricultural matrix dominated by maize, soybean and wheat. Native
 habitats included woodlots (beech-sugar maple association), old
 fields, hedgerows and wetlands. The study area bridged a transition
 zone between structurally complex versus simple agricultural
 landscapes.  The structurally simple area was characterized by large
 agricultural fields (mean 12.4 ha), with few non-cultivated
 habitats. The complex area was characterized by small fields (mean
 3.4 ha) and abundant non-cultivated habitats. Within each area three
 maize fields were selected, each with a minimum of one edge bordered
 by a hedgerow. P. unipuncta larvae from a laboratory colony were
 released in each field on plants 5 m and 90 m from the hedgerow
 border. Larvae were subsequently recovered and reared to determine
 percent parasitism and parasitoid diversity. Seven parasitoid species
 were recovered, four from the structurally simple sites and five from
 the complex sites. No differences were detected in parasitism or
 species diversity between edge and interior sites. However, overall
 parasitism in the complex sites was more than three times higher than
 in the simple sites (18.2% versus 5.l% ). Differences were largely
 attributable to one species, Meterous communis (Hymenoptera:
 Braconidae) which was far more abundant in complex sites. Abundance
 and proximity of preferred habitats for alternate hosts of
 M. communis may account for the observed differences.  Lakshmi,
 Bharatha and Frank P. Day. NITROGEN AVAILABILITY AND N MINERALIZATION
 RATES ALONG A COMMUNITY CHRONOSEQUENCE ON HOG ISLAND, VIRGINIA COAST
 RESERVE. Department of Biological Sciences, Old Dominion University,
 Norfolk, VA 23529-0266. VCR.  Available soil nitrogen and
 N-mineralization rates along a dynamic nutrient-poor island are
 important in understanding the succession of coastal island
 systems. On a 6, 24, 36 and 120 year-old chronosequence on Hog
 Island, the nitrogen availability in the dunes increased with
 age. But in the associated swales the nitrogen concentrations were
 higher with the dominance of Myrica cerifera, a nitrogen fixing
 species. In general, the swales had higher soil nitrogen levels
 (0.016-0.052 g m2) than dunes (0.015-0.038 g m2) and the
 concentrations of ammonium-N were higher than the
 nitrate+nitrite-N. Application of urea to the dunes resulted in a
 10-13 fold increase in nitrogen with highest accumulation in the
 oldest dune. Net N-mineralization was highest in the younger dune
 (0.053 mg kg-1 day-1), and with fertilization this rate increased
 15-fold. Fertilization had only a minimal effect on mineralization in
 the oldest dune. These results indicated that the younger dunes were
 N limited and the limitation was minimized with age. Higher nitrogen
 levels in the older dunes might be due to an input of N-rich litter
 from the adjacent Myrica dominated swales.

Lascara, C.M., E.E. Hofmann, R.M. Ross, and L.B. Quetin. DISTRIBUTION
 OF ANTARCTIC KRILL WITHIN THE PALMER LTER STUDY REGION BASED ON
 BIOACOUSTICS. Center for Coastal Physical Oceanography,Old Dominion
 University, Norfolk, VA 23529 and Marine Science Institute,
 University of California, Santa Barbara, CA 93106.  PAL.  The Palmer
 LTER is using bioacoustics to quantitatively map the spatial and
 temporal distribution of Antarctic krill (Euphausia superba), which
 is one of the key species of the pelagic marine ecosystem.
 Acoustical measurements are coordinated with collection of a suite of
 multi-disciplinary data at stations within the large-scale peninsula
 grid. The objective is to interpret krill distribution patterns in
 relation to other habitat characteristics, in particular, the
 concentration and composition of food resources, ice history,
 large-scale flow regimes, and hydrography. Three cruises have been
 conducted off the west coast of the Antarctic Peninsula, austral
 spring 1991, austral summer and fall 1993.  Over 2000 swarms have
 been identified from 135 acoustic tows, totaling 260 linear
 km. Generally swarms were < 50 m in length, < 10 m in height,
 positioned in the upper 80 m of the water column with mean biomass
 values < 20 g m3. Several large dense aggregations were also observed
 extending 100s of m horizontally and up to 50 m vertically. In spring
 1991, mean krill biomass ranged from 0-95 g m2 and was highest in
 three areas: inside Dallman Bay, open waters within 20 km of the ice
 edge, and an offshore station located over Circumpolar Deep Water.
 In summer 1993, mean krill biomass ranged from 0-460 g m2 and
 exceeded 100 g m2 at many nearshore stations where the influence of
 ice melt on hydrographic structure and water column stability was
 evident.

Lauster, George H., James Hurley, Paul Garrison, Martin Schafer and
 David Armstrong. DEEP PRODUCTION IN LAKES: EFFECTS ON NUTRIENT
 TRANSPORT, TRACE METAL CYCLING AND PALEOLIMNOLOGY. Univ. Wisconsin,
 Water Chemistry Program, Madison WI 53706. NTL companion project.
 Recent research has shown that deep production of phytoplankton and
 phototrophic bacteria are common, and may play an important role in
 controlling the water quality and biological resources of lakes. In
 this study, we are evaluating the importance of deep planktonic
 production to overall lake production and water quality. Secondly, we
 are evaluating the effects of deep production on the trace metal
 transport by comparing selected trace metals both within lakes and
 among lakes of differing particle types and differing redox
 characteristics. Thirdly, we are examining the effects of deep
 production on phosphorus cycling. Finally, we are evaluating the
 influence of deep production in controlling the pigment record in
 sediments. The first phase of our study, begun in the autumn of 1992,
 is synoptic in an attempt to define sets of characteristics
 controlling deep production and the potential effects on nutrient
 transport and trace metal cycling. The results of our Fall 1992
 survey of nineteen Wisconsin lakes indicate the diversity of
 conditions under which deep production is present in north temperate
 lakes. This project supported in part by the United Geological
 Survey.

Lezberg, Ann L. and David R. Foster.  TREE SPROUTING AND SURVIVAL IN A
 TEMPERATE FOREST AFTER SIMULATED HURRICANES.  Harvard Forest, Harvard
 University, Petersham MA 01366.  HFR.  Hurricane damage was simulated
 by pulling down selected trees with a cable and winch in two Quercus
 borealis - Acer rubrum stands (0.8 ha, 0.3 ha) in Central New
 England. All damaged and residual trees were surveyed for extent of
 sprouting and leafout for two and three growing seasons to explore
 the role of vegetative growth and of survival to forest recovery, and
 the influence of individual tree characteristics on initial response
 to damage. Of previously live, damaged trees, over 42% still leafed
 out in the second growing season and over 50% sprouted from the base,
 stem, or branches. Sprouting frequency for damaged trees increased by
 the second year and declined in year three while crown leafout
 declined each year.  Bent stems sprouted more frequently than
 uprooted, snapped or leaning trees, but leaning trees leafed out more
 frequently than other damaged stems.  Acer rubrum was more likely to
 have sprouts at the base than other species. While a significant
 portion of the propensity for sprouting and leafing out was explained
 by differences in damage type and to a lesser degree by other tree
 characteristics, these parameters were linked in a complex way,
 suggesting that variation in initial tree response to wind damage is
 the result of a mosaic of inherent tree characteristics, damage type,
 and untested variables such as the local light regime.

Lovett, G.M., S.V. Ollinger, K.C. Weathers, and J.D. Aber. EVALUATING
 PATTERNS OF ATMOSPHERIC DEPOSITION AT LANDSCAPE AND REGIONAL SCALES.
 Institute of Ecosystem Studies, Box AB, Millbrook NY 12545, and
 Complex Systems Research Center, University of New Hampshire, Durham
 NH 03824. HBR and HFR.  Atmospheric deposition, including wet, dry
 and cloud water deposition, is usually measured at individual sites
 or in sparse monitoring networks which are assumed to be applicable
 to whole landscapes and regions.  However, high spatial variability
 in atmospheric deposition can be generated by the combined effects of
 topographic and vegetational features of the landscape and the air
 flow patterns within a region.  Using existing monitoring data for
 precipitation chemistry, air chemistry, and precipitation amount, we
 have estimated patterns of sulfur and nitrogen deposition across the
 northeastern region.  West-to-east gradients in wet deposition and
 south-to-north gradients in dry deposition are evident, as well as
 increases in wet deposition associated with orographic precipitation
 in the major mountain ranges.  Within one of those mountain ranges,
 the Catskills, we have used Pb in the forest floor as an indicator of
 finer-scale patterns of atmospheric deposition associated with
 elevation, slope aspect, vegetation type, and forest edges.  All of
 these factors influence deposition rates, with the highest rates
 found at high-elevation coniferous forest edges on west facing
 slopes.  These sites can receive as much as fivefold more deposition
 than an average low-elevation site.

Macko, Stephen A., Robert Tappe, Michael Engel. STABLE CARBON ISOTOPIC
 COMPOSITIONS OF INDIVIDUAL MOLECULAR COMPONENTS. Univ. Virginia,
 Charlottesville, VA 22903. VCR.  Stable isotope compositions of
 individual chemical constituents offers a unique and powerful
 approach toward the understanding of the history of an environment
 and origins of the materials which are preserved in the
 environment. The techniques can involve the analysis of dissolved
 materials, such as ammonium or nitrate, or the assessment of
 compounds that make up the organic matter in the study
 area. Dissolved nitrogenenous materials can be analyzed to indicate
 inputs of fertilizer nitrogen, animal wastes, or the extent of
 denitrification in a soil or groundwater. The latter characterization
 of compounds can be applied to determine the carbon isotopic
 compositions of amino acids, fatty acids, carbohydrates and
 hydrocarbons extracted from sediments, plants or animals. Inputs from
 bacterial processing of organic matter, as well as preservation of
 indigenous materials within a sediment can readily be distinguished
 with compound specific isotope analysis, and more importantly, can
 indicate new production of materials which have the same chemical
 composition as that which was in the environment
 originally. Dissolved inorganic nitrogen analysis necessitates the
 isolation of the nitrate, or ammonium, from the sample through
 extraction, and distillation. Compound specific analysis usually
 entails hydrolysis of the sample and often derivatization of the free
 component to a volatile material suitable for gas chromatographic
 analysis. This addition of carbon to the compound can be corrected
 for through back calculations involving knowledge of the
 stoichiometry of the carbon addition and the kinetic isotope effect
 of the bond formation in derivatization. Preliminary results from the
 above analyses have allowed for the assessment of contributions of
 fertilizer nitrate to groundwaters, and the quantification of
 bacterial inputs into the more refractory materials which are
 eventually preserved in a deposit. Potentially, compound specific
 isotope approaches could also be used in the same manner to follow
 the flow of essential biochemical components from primary production
 to higher level consumers.

Magill, Alison H. and John D. Aber.  EFFECTS OF CHRONIC NITROGEN
 ADDITIONS ON SOIL MINERALIZATION, NITRIFICATION RATES AND DISSOLVED
 ORGANIC CARBON AVAILABILITY.  Complex Systems Research Center,
 University of New Hampshire, Durham, NH 03824. HFR.  Chronic nitrogen
 addition plots are located at the Harvard Forest LTER site. Ammonium
 nitrate (NH4NO3) fertilizer additions have been ongoing in two stands
 (mixed hardwood and red pine) since 1988 at four different treatment
 levels on 8- 30x30 m plots: control, 50 Kg-N*ha-1*yr-1; 150*ha-1*yr-1
 and a nitrogen plus sulfur treatment (50*ha-1*yr-1 plus 75
 Kg-S*ha-1*yr-1) as Na2SO4. Several different ecosystem components are
 monitored for changes in carbon and nitrogen pools including soils
 (buried bags/KCl extracts), soil solution (lysimeters), green
 foliage, litterfall, tree growth and trace gas emissions. In 1992,
 only one set of buried bags was collected in mid-summer. Data from
 that 6-week period show the mineral soil as being the region of
 greatest mineralization which follows the same pattern as seen in
 1991. Nitrification appears to be an increasingly greater portion of
 total mineralization in the pine plots. In addition, nitrification
 rates are beginning to increase in the hardwood high treatment
 plot. A full set of buried bags is being collected for 1993.  The
 soil solution chemistry results for the pine plots show a range of
 3.2 mg NO3-N*L-1 to 18.6 mg NO3-N*L-1 over the growing season in the
 high treatment plot where the low and control plots had no soil
 solution greater than 0.38 mg NO3-N*L-1. This is similar to 1991
 data. However, ammonium is beginning to show up in the high pine
 lysimeters for the first time in 1992. The hardwood plots are also
 beginning to show some leaking of NO3; the low N plot lysimeters were
 6.4 mg NO3-N*L-1 for the July collection. However, lack of water in
 the high treatment plot during that same sampling period creates a
 lack of data for comparison. Green foliage and litterfall have also
 been collected each year; tree diameter data was collected in
 November 1992. A laboratory experiment has been conducted in order to
 help determine the mechanisms behind the decrease in soil organic
 horizon mineralization rates over the course of the fertilizer
 applications. One hypothesis for the decrease is the depletion of
 available carbon for microbial metabolism, i.e., DOC. Litterfall from
 7 species was collected, air-dried, and incubated in the lab for 15
 weeks. Three treatments (DI water (control) NO3 and NH4) were added
 to the samples weekly. The litter was leached with DI water 11 times
 and the leachate analyzed for NO3-N, NH4-N and DOC. Preliminary
 values for leachate DOC concentrations show NO3 treated litter to
 have the highest DOC and a wide variety between species.

Martin, Mary E and John D. Aber.  THE USE OF NEAR INFRARED REFLECTANCE
 TO MEASURE CANOPY CHEMISTRY AT HARVARD FOREST, PETERSHAM, MA. Complex
 Systems Research Center, University of New Hampshire, Durham, NH
 03824. HFR.  The concentrations of nitrogen, lignin, and cellulose in
 canopy foliage are related to important ecosystem parameters such as
 litter decomposition rate, nutrient availability, and plant
 productivity.  Previous laboratory work with both agricultural
 products and forest foliage has shown that relationships exist
 between reflectance at selected wavelengths in the near infrared
 (NIR) spectrum and nitrogen, lignin and cellulose concentrations. In
 this project we extend this work to both the fresh leaf and canopy
 scales using data from an NIRS model 6250 spectrophotometer (leaf
 scale) and the Airborne Visible Infrared Imaging Spectrometer
 (AVIRIS, canopy scale). AVIRIS image data were acquired over the
 Harvard Forest in Petersham, MA in September 1990,1991 and June 1992.
 This instrument measures visible and infrared radiance in 224 bands
 from 400-2500nm with a spectral resolution of 10nm.  Spatial
 resolution of AVIRIS data is 17-20m.  Twenty sites (50x50m) were
 sampled at Harvard Forest within 1 week of the 1992 overflight(15
 June).  These sites were chosen to represent a wide range of species
 composition (both broad-leaved and needle-leaved species).  Foliage
 samples collected from these sites were analyzed for nitrogen,
 cellulose, lignin, and water content. Canopy biomass for each site is
 determined by litterfall collection. Both field and image data has
 been collected on an additional 30 sites at Harvard Forest in 1993
 for validation purposes.  The collection of AVIRIS spectral data and
 field data at these sites will provide the information necessary to
 determine with what degree of accuracy canopy chemistry can be
 measured by airborne (and spaceborne) sensors.  One goal of this work
 is to use algorithms to map species and nitrogen concentration from
 the AVIRIS image data.  Such maps will be used to drive a model
 predicting forest ecosystem carbon balances(PnET) at Harvard Forest.
 Martinez-Turanzas Gustavo A1 and Walter G. Whitford2. EFFECTS OF
 WATER ON CREOSOTEBUSH GROWTH AND DECOMPOSITION PROCESS IN THE
 NORTHERN CHIHUAHUAN DESERT. 1Colorado State University, Ft. Collins,
 CO., 80523, USA.; 2USEPA Environmental Monitoring Systems Laboratory,
 Las Vegas, NV, 89193, USA. JRN.  This study evaluated effects of
 precipitation on creosotebush growth and decomposition process in a
 plant community dominated by creosotebush (Larrea tridentata (DC)
 Cov.] in the Jornada LTER site (northern Chihuahuan Desert). Three
 treatments were imposed during summer period from 1987 to 1992:
 1)control plots received only natural precipitation; 2) drought plots
 received no precipitation and 3) irrigated plots received natural
 precipitation and 25mm of supplemental water applied every 15 days
 from July to September. Effects of draught and irrigation on the
 creosotebush growth and decomposition of surface creosotebush leaf
 litter bags and buried roots of the herb, senna [Cassia bauhinioides
 (Gray)] were determined by measuring dry weight of branch tips and
 mass loss respectively.  Results showed that creosotebush exhibited a
 tolerance to disturbance. The supplemental water did not result in
 significantly more biomass on the irrigated creosotebushes. Surface
 leaf litter and buried root decomposition rates were not affected by
 water. The supplemental water did not stimulate higher rates of
 surface litter and buried root decomposition. In surface litter
 decomposition, initial rapid mass loss seems to be primarily due to
 abiotic processes followed by losses due to biological activity,
 which is also the major factor in buried root decomposition.

Mason, Owen K. and James E. Beg�ét. RECONSTRUCTION OF LATE HOLOCENE
 ALLUVIAL HISTORY: GEOMORPHIC CONSTRAINTS OVER ECOLOGICAL SUCCESSION
 ON THE TANANA RIVER, ALASKA.  Univ. of Alaska, Fairbanks, AK
 99775. BNZ.  A sequence of historic and prehistoric flood deposits of
 the Tanana River is preserved on the anastomosing channel islands
 southwest of Fairbanks in the Bonanza Creek Long Term Ecological
 Research (LTER) site.  A suite of > 20 radiometric dates,
 granoulmetric differences and microstratigraphic observations
 establish the lower limiting ages on the stability of the islands for
 the establishment of spruce (Picea spp.)  forest.  Channel shifts and
 island evolution are mapped using 14C ages and dendrochronological
 inferences and will be integrated into the LTER geographical
 information system (GIS).  Most islands are less than 700 yrs old:
 older deposits are found on terraces.  Several major
 lithostratigraphic units are observed: (1) thick cross-bedded,
 pedogenically unaltered alluvial silty sands deposits 3000-2000 BP,
 recording an interval of large floods: (2) thin silty beds and
 paleosols formed after 2000 yrs ago when large floods were uncommon:
 and (3) sand units recording large floods during the last several
 hundred years.  Flood frequencies changed in response to regional
 climate changes, with more frequent flooding during times of
 widespread alpine glaciation.

Mccaig, B. C., J. L. Hamrick, and B. L. Haines.. CLONAL STRUCTURE OF
 Robinia pseudoacacia (black locust) IN THE SOUTHERN
 APPALACHIANS.University of Georgia, Athens. GA 30602 Clonal
 structure, the genotypic patchiness within populations due to
 vegetative reproduction, was investigated in Robinia pseudoacacia
 (black locust) on four watersheds in the Southern Appalachians.
 Watershed ages were 5, 13, 30, and 40 years following clear cutting.
 A total of 1200 trees and juveniles were mapped.  Foliage samples
 were analyzed by protein gel electrophoresis for 15 polymorphic loci
 to identify clones.  Average heterozygosity of polymorphic loci was
 52.3% and their was an average of 4.27 alleles per polymorphic locus.
 The number of clones in a plot ranged from 24 to 52.  In the 30 year
 old stand, 2 clones accounted for 86.7% of the ramets.  Clonal
 structure does not appear to be correlated to age, but there were
 significant differences in structure between populations.  Number of
 genotypes, population structure before a disturbance, and the history
 of succeeding disturbance events could be additional factors
 influencing the clonal structure of this species.  McKnight, D.M. and
 E.D. Andrews.  HYDROLOGIC AND GEOCHEMICAL PROCESSES AT THE
 STREAM-LAKE INTERFACE IN A PERMANENTLY ICE-COVERED LAKE IN THE
 MCMURDO DRY VALLEYS, ANTARCTICA.  U.S. Geological Survey, 3215 Marine
 St., Boulder, CO 80303 For many ice-covered lakes in the McMurdo Dry
 Valleys lake levels have risen progressively over the past 20 years,
 as a result of increases in glacial meltwater streamflow.  These
 amictic lakes have stable water columns with mixing dominated by
 chemical diffusion. During the summer, a moat of openwater forms
 between the ice edge and the lake shore.  We conducted an experiment
 using LiCl as a hydrologic tracer to determine flowpaths and
 velocities of streamwater mixing with moat water and moat water
 mixing into the lake.  Results indicate that substantial hyporheic
 (substream) interactions occur in the stream and that wind-driven
 currents in the moat are important in advecting moat-water through
 and under the moat/ice-cover boundary.  These mixing processes will
 influence the biogeochemical response to raising lake levels.
 McSwiney, Claire P. and William H. McDowell. CONTROLS ON NITROUS
 OXIDE PRODUCTION IN THE LUQUILLO FOREST.  Department of Natural
 Resources, University of New Hampshire, Durham, NH 03824.  Tropical
 areas are considered major sources in the global nitrous oxide
 budget, but factors controlling nitrous oxide production are poorly
 described for non-agricultural tropical ecosystems.  Previous work in
 the Luquillo Forest has shown that gas production rates are high, and
 show strong spatial variation as a function of landscape position in
 some watersheds.  The objectives of the proposed study are to
 determine the processes that control nitrous oxide production in
 different biogeochemical environments in the Luquillo Forest, and to
 document the effects of rainfall on production rates.  Both field and
 laboratory experiments will be conducted.  Refined estimates of
 watershed-level nitrous oxide flux will be calculated by weighting
 plot-level fluxes by spatial (landscape) and temporal (rainfall)
 variation.  Micks, Pat and John D. Aber.  SOIL RESPIRATION RESPONSE
 TO CHRONIC NITROGEN APPLICATION IN TWO STANDS AT THE HARVARD FOREST.
 Complex Systems Research Center, University of New Hampshire, Durham,
 NH 03824. HFR.  Soil respiration was measured in nitrogen-treated
 soils in the Chronic Nitrogen Addition Experiment at the Harvard
 Forest in Petersham, MA. The objective was to monitor short-term soil
 microbial response to continued nitrogen applications in soils which
 have received nitrogen applications since 1988 in an ongoing
 experiment to determine forest ecosystem response to atmospheric
 nitrogen deposition. This respiration study was designed to test the
 hypothesis that microbial immobilization is responsible for the high
 nitrogen retention in the treated plot soils.  Soil CO2 efflux was
 monitored in situ by the soda lime technique in a red pine and a
 mixed hardwood stand throughout two consecutive monthly nitrogen
 application periods during July and August 1992.  In each stand,
 measurements were made in an untreated control plot, a high-N plot
 receiving 150 Kg N ha-1 yr-1 as NH4NO3, and a plot of previously
 untreated soil which received nitrogen application identical to the
 high-N plots during the two-month study period.  In mid-August a
 third nitrogen application was made to the previously untreated
 plots. Extractable nitrogen was monitored throughout August in these
 two plots. Short term soil microbial response to individual nitrogen
 applications was evaluated by comparing changes in soil CO2 afflux
 rates among the six plots and by disappearance of the applied
 nitrogen in the previously untreated soils. CO2 afflux data revealed
 no conclusive evidence of increased soil microbial activity resulting
 from single nitrogen applications, nor any differences due directly
 to long-term nitrogen treatments. However, soil extract data showed
 rapid disappearance of the applied nitrogen. Possible explanations
 are: 1) microbial immobilization occurred without measurable increase
 in respiration; and 2) nitrogen was immobilized by abiotic as well as
 microbial mechanisms.  Millikin, Catherine and Rich Bowden.  EFFECTS
 OF PIT AND MOUND DISTURBANCE ON CO2 EFFLUXES FOLLOWING A SIMULATED
 HURRICANE BLOWDOWN IN A TEMPERATE FOREST.  Univ. of California, Davis
 CA 95616 and Allegheny College, Meadville PA.  Extensive uprooting of
 trees by hurricanes can create areas of severe soil disturbance in
 temperate forests.  In particular, uprooted trees leave shaded pits
 and mounds of exposed roots and mineral soil.  To assess the
 contribution of pit and mound microhabitats to overall CO2 emissions
 for an experimental blowdown at the Harvard Forest LTER (MA), CO2
 fluxes during summer were measured using the soda lime technique on
 pit, mound, and control plots.  Mean flux values were 45.4, 80.1, and
 99.0 mg C/m2/hr for pit, mound and control plots, respectively.
 Although CO2 emissions from pits were lower than from mounds or
 controls, total contribution (5.3%) from pits and mounds to the
 overall flux rate at the site was not important.  Therefore,
 measurements taken from undisturbed soils are representative of
 effluxes over the entire disturbed site.  Moorhead, Daryl, and Robert
 Wharton. ALGAL MAT PRODUCTION IN AN ANTARCTIC LAKE: RESULTS OF A
 PRELIMINARY MODEL. Texas Tech Univ., Lubbock, TX 79409 and The Desert
 Research Inst., Reno, NV. MCM.  The perennially ice-covered lakes of
 Taylor Valley, South Victoria Land, Antarctica, have well-developed
 benthic algal communities.  Portions of this mat tear loose (liftoff)
 from the sediments and float to the surface, where they are frozen
 within the overlying ice.  This material is transferred through the
 ice by ablation and distributed by wind throughout the valley.  The
 extremely low productivities of terrestrial ecosystems in this region
 suggest that allochthonous inputs of algal mat may be an important
 source of the organic carbon found in soils.  A mathematical model
 was developed to examine the productivities of these algal mats,
 based on previous studies of Antarctic streams and lakes.  Gross
 primary production is driven by light intensity, utilizing the
 equation for a rectangular hyperbola, given the maximum observed
 photosynthetic rate and half-saturation coefficient.  For a
 subAntarctic Signy Island lake, simulated annual net production is
 equivalent to estimates based on field observations (4 g C per square
 meter), verifying reasonable model behavior.  The 1988-1989 light
 regime beneath the ice at Lake Hoare, Taylor Valley, yields gross
 primary productivities ranging from 155 to 3 g C per square meter at
 depths ranging from 0 to 10 m, respectively.  These rates are
 comparable to production estimates based on studies of other
 Antarctic lakes and are sufficient to supply quantities of mat
 materials that are lost by liftoff, ablation and wind action from
 Lake Hoare.

Morris, James T. ESTUARINE NUTRIENT DYNAMICS AT NORTH INLET: TIDAL
 HARMONICS, LONG TERM TRENDS, AND REGULATION BY EXCHANGE WITH
 INTERTIDAL MARSHES. Univ. South Carolina, Columbia, SC 29208. NIN.
 North Inlet is an oligotrophic estuary with minimal input of surface
 water.  There is considerable drainage of tidal water into intertidal
 marsh sediments, where microbial transformations of nutrients occur,
 and subsurface return to tidal creeks.  Where salt has been used as a
 conservative tracer to calculate the turnover of water in sediments,
 I estimate that 8-10 l m-2 d-1 of tidal water drains through marsh
 sites located at mean high tide.  These exchanges appear to dominate
 the nutrient chemistry of the estuary.  Nutrients and chlorophyll
 have been monitored daily at 3 stations within the estuary for 10+yr.
 The stations are located at the mouth (M), center (C), and
 most-landward margin (L) of the estuary. The majority of nutrients
 show statistically significant increases in concentration over time.
 Furthermore, ammonium, nitrate, and phosphate have increased most
 rapidly at L and least at M, which suggests a land and/or marsh
 source.  All nutrients display harmonics with periodicities
 corresponding to the principal lunar or M2 (12.42 hr), lunar monthly
 (27.6 d), and annual solar tides, but the M2 nutrient harmonics are
 not in phase with the tides, i.e., maximum nutrient concentrations
 occur at low tide.  With few exceptions, the amplitudes increase from
 the mouth landward.  N:P atom ratios are generally less than 15,
 which indicates nitrogen limitation of phytoplankton.  These
 observations are all consistent with the hypothesis that the
 intertidal marshes function as a net source of nutrients to the
 estuary and that hydrologic exchanges between creeks and intertidal
 sediments control the nutrient dynamics of the estuary.  Mullen,
 Renee B., and Steven K. Schmidt. DYNAMICS OF PHOSPHORUS AND NITROGEN
 UPTAKE AS RELATED TO DEVELOPMENT OF FUNGAL ENDOPHYTES IN RANUNCULUS
 ADONEUS. Environmental, Population, and Organismic Biology, Campus
 Box 334, University of Colorado, Boulder CO 80309-0334. NWT.
 Phosphorus and nitrogen levels, phenology of roots and shoots, and
 development of vesicular arbuscular mycorrhizal (VAM) fungi and other
 endophytes were monitored for two years in natural populations of the
 perennial alpine herb, Ranunculus adoneus. The purpose of this study
 was to understand how endophyte development relates to phosphorus and
 nitrogen uptake in R. adoneus. This was accomplished by
 quantification of structures of VAM fungi and other root endophytes
 during maximum nutrient accumulation. Arbuscules were only present
 for a few weeks during the growing season of R. adoneus and their
 presence corresponded with increased phosphorus accumulation in both
 the roots and shoots of R. adoneus. Nitrogen accumulation appeared to
 be related to relatively high levels of a dark septate fungus. In
 addition, phosphorus accumulation and peaks in mycorrhizal
 development occurred well after plant reproduction and most plant
 growth had occurred. The late season accumulation of phosphorus by
 mycorrhizal roots of R. adoneus could be stored for use during early
 season growth and flowering the following spring. In this way
 R. adoneus can flower before soils thaw and root or mycorrhizal
 nutrient uptake can occur.

Myster, Randall and Lawrence Walker. SUCCESSIONAL PATHWAY VARIATION
 WITHIN AND AMONG 16 PUERTO RICAN LANDSLIDES. University of Puerto
 Rico, San Juan PR and University of Nevada, Las Vegas, NV. LUQ.  We
 counted the number of tree stems in 3 x 5m permanent landslide plots,
 generated successional pathways in Principal Components Analysis
 (PCA) space and explored variation within and among landslides.  We
 found that PCA separated plots well, with nitrogen-fixing,
 non-vascular and other rare species represented in early succession.
 PCA defined plant groupings implicating mycorrhizae association
 strategy as important in regeneration.  Within slides, many plots
 stayed close to the origin and did not show much community
 development in the sampling time frame of three years, but a slide in
 the Espirtu Santo watershed had the most pathway variation, defining
 the dimensions of PCA space.  PCA axis I separated plots of differing
 microhabitats (edge and center), while PCA axis II separated plots
 from different transects.  However, evidence of successional rate
 decrease and convergence over time was minimal.  Among slides,
 landslides with the most variation and most distinct pathways were
 also among the largest and oldest.  The other landscape parameters of
 elevation, landuse, slope and aspect seem to affect landslide
 occurrence more than development after disturbance.  We conclude that
 compared to other rainforest disturbances, landslide pathways maybe
 longer with more local variation, have less convergence due to
 recurrent disturbance and a slower rate of recovery.

Neff, Jason C., William D. Bowman, and Elisabeth A. Holland. FLUXES OF
 NITROUS OXIDE AND METHANE FROM NITROGEN AMENDED SOILS IN THE COLORADO
 ALPINE. Environmental, Population, and Organismic Biology, Campus Box
 334, and Institute of Arctic and Alpine Research, Campus Box 450,
 University of Colorado, Boulder CO 80309 and Atmospheric Chemistry
 Division, National Center for Atmospheric Research, P. O. Box 3000,
 Boulder CO 80307. NWT.  Fluxes of nitrous oxide and methane between
 soils and the atmosphere strongly contribute to the global
 atmospheric balance of radioactively important trace gases. In
 addition, the exchange of nitrous oxide and methane between tundra
 soils and the atmosphere may represent an important step in the
 cycling of nitrogen and carbon through alpine ecosystems. The
 microbial processes governing nitrous oxide and methane fluxes are
 sensitive to the availability of nitrogen in soils. This sensitivity,
 however, has not been quantified in alpine tundra soils. We examine
 the influence of nitrogen additions on the fluxes of nitrous oxide
 and methane from wet and dry meadow communities on Niwot Ridge. Urea
 nitrogen was added to experimental plots in June of 1990 and July of
 1991. Using flux chambers installed in the tundra from June to August
 of 1992, we measured emissions from five nitrogen-amended plots and
 five control plots in each community. Our results indicate that the
 addition of nitrogen to the dry meadow community resulted in a 60%
 reduction in methane uptake (oxidation) and a 22 fold increase in
 nitrous oxide emissions. Nitrous oxide emissions in the wet meadow
 community increased by a factor of 45 while methane fluxes were not
 significantly changed.

Nolen, Barbara.  JORNADA LTER GIS AND REMOTE SENSING DATABASES. New
 Mexico State University. Las Cruces, New Mexico 88003. JRN.  This
 poster represents the basic GIS and remote sensing data layers for
 the Jornada LTER research site.  The research area map was designed
 to include the entire Jornada basin.  Hydrology was important in
 determining the extent of the mapping area. Data layers used for the
 research area map include roads, hydrology, ownership and research
 sites. The first three data layers were converted from MOSS files
 created at the Bureau of Land Management. The digital elevation model
 was composed of 22 USGS topographic quadrangles using the 1:24000
 dems. From this model slope, aspect and contour lines are
 composed. The Landsat TM scene is a combination of path/rows 33/36
 and 33/37 from Landsat 5 taken in August and September 1992.  North,
 Malcolm and Jerry Franklin ANALYZING CANOPY STRUCTURE IN CONIFEROUS
 FORESTS College of Forest Resources, AR-10, University of Washington,
 Seattle, WA 98195.  NET.  Complex canopy structure is a
 distinguishing characteristic of old growth and is believed to
 provide unique habitat for arboreal wildlife.  In this initial effort
 at quantifying canopy structure, we used two stand-level measures:
 the percent of available canopy space occupied by foliage, and the
 diversity of vertical layering of foliage.  We compared the
 heterogeneity of foliage layers in three distinct stand types:
 managed mature (70 year old trees originating from a clearcut and
 slash burn), natural mature (70 year old trees originating from a
 wind storm) and old growth.  The analysis tested whether tree
 diameter or ocular height estimates can provide good assessments of
 these two canopy structure measures.  Tree diameter was highly
 correlated with crown volume and therefore was used to calculate the
 percentage of canopy space occupied by foliage.  Tree diameter,
 however, was not correlated with foliage layering.  Ocular height
 estimates, when analyzed with the Berger- Parker diversity index,
 provided a more robust index of foliage layering within a stand.  Old
 growth compared to managed mature showed a higher percent of
 available canopy space occupied by foliage (p<0.05) and much greater
 diversity of foliage layering (p<0.001).  Natural mature stands were
 closer to old growth in both the percent of available canopy space
 occupied (scale adjusted for height) and vertical layering.  These
 exploratory results suggest stand origin is a stronger influence on
 canopy structure than stand age.  The measures used in this pilot
 study suggest one method for comparing canopy structure between
 forested LTER sites.  O'Lear, Heather A., and Timothy
 R. Seastedt. MICROARTHROPOD DENSITIES AND IMPACTS ON DECOMPOSITION
 ACROSS THE ALPINE LANDSCAPE. Institute of Arctic and Alpine Research,
 Campus Box 450, and Environmental, Population, and Organismic
 Biology, Campus Box 334, University of Colorado, Boulder CO
 80309. NWT.  Densities of microarthropods were measured in the top 5
 cm of litter and soil in xeric, mesic, and wet alpine tundra
 habitats. Previous studies have underestimated densities due, we
 believe, to inefficient extraction techniques. High-gradient
 extraction produced densities ranging from about 70,000 to 200,000
 individuals per m2; wetter habitats had higher
 densities. Microarthropod densities were higher in moist litter. This
 litter also had the highest decay rates. A basidiocarp fungus
 decomposition experiment was conducted in summer 1993, using
 naphthalene to exclude microarthropods from this detritus. Results of
 this experiment will be reported.  O'Reilly, Mary A., and Timothy
 R. Seastedt. PLANT CONTROLS ON SOIL MOISTURE IN ALPINE
 TUNDRA. Institute of Arctic and Alpine Research, Campus Box 450, and
 Environmental, Organismic, and Population Biology, Campus Box 334,
 University of Colorado, Boulder CO 80309. NWT.  The extent to which
 plants control surface (15 cm deep) soil moisture and the extent to
 which the organic matter fraction of the soil influences soil
 moisture characteristics was studied in alpine tundra. Plots with and
 without substantial vegetation cover and with and without fertilizer
 additions were monitored over the growing season for soil moisture
 using the non-destructive Time Domain Reflectometry (TDR)
 technique. Preliminary results indicated measurable plant and
 fertilizer effects on soil moisture. Results on measurements of the
 field capacity (maximum water capacity of soil held against gravity)
 of sites denuded over 10 years ago and adjacent vegetated plots will
 be reported. Also, field capacities of wet, mesic, and xeric tundra
 will be compared and related to estimates of soil organic matter
 content and soil texture.  Osgood, D., M.C.F.V. Santos,
 J.C. Zieman. COMPARISON OF PHYSICO-CHEMICAL SUBSTRATE PARAMETERS
 ALONG THE INTERTIDAL ZONE OF A STORM-DEPOSITED SAND FLAT AND
 UNDISTURBED MARSH. Department of Environmental Sciences, University
 of Virginia, Charlottesville, VA 22903. VCR.  A tropical storm in
 Oct. 1991 destroyed dune systems on portions of the Virginia barrier
 islands and laid the foundation for future marsh development. Two
 transects were established on the storm-deposited sand flat and a
 nearby, undisturbed marsh. Three stations were established at high
 marsh, short Spartina alterniflora, and tall Spartina zones on the
 marsh transects. Identical elevations were determined for the sand
 flat transects by surveying to USGS benchmarks. Porewater at each
 station was analyzed monthly for ammonium, phosphate, sulfide, iron,
 pH, EH, and salinity. A two month pilot study initiated in July, 1992
 was continued in May, 1993. The pilot study revealed porewater
 salinity comparable to or lower than flooding water (~32 ppt) at all
 stations in both transects. Hydrogen sulfide was greatest at the
 lowest (tall Spartina) stations of the marsh transects and was lower
 than three ?mol 1-1 at the sand flat transects. Higher ammonium
 concentration was evident at the lowest station of both sand flat
 transects compared to the marsh transects. Nutrient concentrations
 were equivalent at the two highest (high marsh and short Spartina)
 stations between all transects. The data from the sand flat suggest
 that conditions are favorable for plant growth, especially at the
 lowest station in the intertidal zone where tall Spartina is
 predicted to dominate. Results from the summer, 1993, further support
 these Panov, Vadim E.  LONG-TERM ECOLOGICAL RESEARCH IN ST.PETERSBURG
 REGION, RUSSIA Zoological Institute, Russian Academy of Sciences,
 199034 St.Petersburg, Russia The main ecological research activities
 in the St.Petersburg (Leningrad) region are connected with freshwater
 sites in Lake Ladoga - the Neva River - the Neva River Estuary Water
 System.  Regular studies were started in 1956 for Lake Ladoga, in
 1961 for Lake Krasnoye in the Lake Ladoga Basin and in 1981 for the
 Neva River Estuary. Some research at the sites began over 80 years
 ago.  Scientists from a number of institutions are engaged in studies
 of seasonal and annual changes in hydrophysical and hydrochemical
 characteristics, studies of primary and secondary productivity and
 cycles of nutrients.  Future sites for terrestrial and aquatic
 long-term research are proposed to be established in areas with
 practically undisturbed nature.  One of these sites is planned for
 the north part of the Karelian Isthmus in a zone characterized by a
 high concentration of lakes.  The main topics of research will
 include studies of interactions between aquatic ecosystem structure
 and processes, top-down and bottom-up controls, and nutrient cycles
 and bottom-water interface transport processes.  Paruelo, J.M.(*) and
 W.K. Lauenroth. FUNCTIONAL CHARACTERISTICS OF NORTH AMERICAN
 SHRUBLANDS AND GRASSLANDS AT A REGIONAL SCALE. Dept. Range Science
 and CPR LTER site - Colorado State University Fort Collins, CO
 80523. (*) Permanent addresses: IFEVA - Depto. Ecolog!a - Facultad de
 Agronomia. Universidad de Buenos Aires. Av.San Mart!n 4453, (1417)
 Buenos Aires - Argentina.  We are interested in understanding how the
 functional characteristics of North American grasslands and
 shrublands differ at a regional scale.  We described the ecosystem
 function from the seasonal curve of the Normalized Difference
 Vegetation Index (NDVI), derived from the Large Area Coverage (LAC)
 data of AVHRR/NOAA satellites provided by the LTER Network
 Office. Study sites,ranging from grama-tobosa shrub steppe to
 bluestem prairie vegetation types, corresponded to areas of low
 cultural impact (National Parks, National Grasslands, Experimental
 Stations, etc.) and included four LTER sites: Konza, CPR, Sevilleta
 and Jornada. We selected several sites for each vegetation type in
 order to have replications. We processed the NDVI images using an
 ERDAS 7.5 system. Each study site was characterized as a 21 element
 vector, where each element corresponded to a date. A Principal
 Component Analysis was performed over the 46 sites x 21 dates
 matrix. The first principal component, that explained 47% of the
 total variance, was closely related to the annual integrated
 NDVI. The second axis, that accounted for 30% of the variance, was
 associated with the difference between average NDVI during the
 coldest and warmest months of the year. Our analysis suggests that at
 a regional scale grassland and shrubland functional characteristics
 differ in two main directions. The first one is related with Annual
 Net Primary Production value, and the second one with the seasonality
 of the production.

Paul, Eldor, Alvin and Harris, David.  MICROBIAL GROWTH RATES IN
 SOIL. Michigan State University. East Lansing, MI 48824. KBS.
 Knowledge of the growth rates of microorganisms is fundamental to an
 understanding of the mineralization - immobilization of nutrients and
 C cycling These processes largely control ecosystem functioning,
 agricultural soil productivity and soil inputs to the atmosphere,
 determining global change.  Estimates of the average growth rate of
 the soil microbiota can be made from C turnover if values for
 specific maintenance coefficient (m) and growth yield coefficient (Y)
 are known or assumed.  These two parameters are difficult to measure
 in soil and are frequently combined as an overall efficiency term.
 Since maintenance is independent of growth its inclusion in a yield
 efficiency parameter makes it impossible to estimate growth rate from
 C turnover data. 3H thymidine uptake into DNA is a powerful and exact
 means of directly measuring replication rates in bacteria providing
 the limiting requirements and underlying assumptions are taken into
 account.  The combined estimation of DNA synthesis and specific
 respiration rates of soil biomass allows the limits for microbial
 growth rates in soil to be defined and offers a method for the
 estimation of maintenance and yield coefficients in soil.  We used
 this combined approach to measure specific growth rates in soils from
 three treatments of the LTER site at the Kellogg Biological Station,
 conventional corn-soybean rotation, native grassland and a reversion
 to native, taken out of cultivation in 1988.  Thymidine incorporation
 showed generation times of 80 to 115 days at 25 C with the reversion
 treatment being the most active.  Specific respiration rates ranked
 the treatments in the same order.  The specific maintenance
 coefficient was estimated as 0.0005 h-1 and the growth yield
 coefficient as 0.14.  At the specific growth rates defined by
 thymidine uptake and at Q10 of 2, microbial productivity was
 calculated as 29 g C m-2 y-1 for the corn soybean treatment, 74 g C
 m-2 y-1 for the reversion treatment and 83 g C m-2 y-1 for the
 grassland.  Paul, Eldor, Tom Willson, Dave Harris and Ernesto Franco.
 SOIL MICROBIAL DYNAMICS AND CARBON MINERALIZATION KINETICS. Michigan
 State Univ. 48824. KBS.  The agronomic, grassland, and old-field
 reversion plots established at the Kellogg Biological Station
 (KBS-LTER) in 1988 provide a valuable opportunity for studying the
 effects of management on soil microbial populations and carbon
 transformations.  Over the last five years, we have documented total
 microbial C and N (CFIM), bacterial and fungal bio-volumes,
 extractable DNA, arginine deamination activity, and long term
 mineralization kinetics for each of eight management treatments as
 they diverge toward their respective equalibria.  The 6 intensively
 managed treatments (four corn based field-crop rotations, an alfalfa
 monoculture, and a Populus plantation) have tended to support lower
 levels of microbial C than either the old-field successional
 treatment or the 100 year grassland.  Short term C mineralization
 (microbial respiration) and arginine deamination rates have each been
 closely correlated with total microbial biomass across these
 treatments.  Direct microscopy suggests a fungal C : Bacterial C
 ratio of apx. 3:1 in all treatments.  On the other hand, over 90% of
 the extractable microbial DNA is associated with the bacterial rather
 than the fungal fraction.  This suggests that most hyphae contain
 little or no DNA.  Long term (200d) mineralization curves provide an
 excellent fit for the model Cm = C1(1-ek1t) + C2(1-ek2t) + C3(0)
 where Cm is the carbon mineralized over time t and C1, C2, and C3 are
 partitions of the total organic carbon such that C3 = C1 + C2 = 1/2
 CTotal .  While the CTotal is roughly identical for the old-field and
 agronomic plots (9500*g g-1soil), the Cm of the reversion plots is
 nearly twice as high as the Cm of the conventional corn and soybeans
 rotation and only fractionally lower than the Cm of the grassland.
 As a result the old-field reversion plots exceed all other treatments
 with respect to their mineralization rate constants (k1 and k2) and
 mineralization per unit microbial C.  Paustian, Keith.  THE THEORY OF
 ORGANIC MATTER DECOMPOSITION: LESSONS FROM STEADY-STATE ANALYSIS OF
 THE CENTURY AND ROTHAMSTED MODELS. Colorado State Univ., Ft. Collins,
 CO 80523. KBS Simple analytical models in ecology are routinely
 evaluated as to their steady-state properties, but this kind of
 analysis is less often conducted in the case of more complex
 ecosystem simulation models.  However, by using simplifying
 assumptions regarding stochastic driving variables, simple analytical
 steady-state solutions of multi-compartment organic matter models can
 be obtained which help elucidate several fundamental properties of
 the models.  Steady-state analytical solutions were derived for the
 CENTURY and ROTHAMSTED models, both of which have been used
 extensively in site-level and global change-related analyses of soil
 carbon.  The analyses reveal close similarities between the models
 including the linear relationship between C input rates and soil C
 levels and the influence of litter quality on soil C amounts and
 composition.  The analysis shows that predicted SOM composition
 (i.e. pool fractions) is independent of C input rates and climatic
 conditions but dependent on soil texture, litter quality and soil
 management.  The steady-state solutions provide a useful tool for
 estimating initial conditions for the simulation models and to
 analyze land use and climate change effects on potential soil C
 levels.

Paustian, Keith and Peter H. Stahl. LITTER DECOMPOSITION AND LITTER
 DECOMPOSER ACTIVITY IN THE KBS-LTER PLOTS. Colorado State Univ.,
 Ft. Collins, CO 80523 and USDA National Soil Tilth Lab, Ames, IA
 50011. KBS.  Mesh bags containing corn (Zea mays), soybean (Glycine
 max), poplar (Populus spp.), alfalfa (Medicago sativa), quackgrass
 (Agropyron repens) and chickweed (Cerastinum vulgatum) litter were
 sampled following 4, 5, 7 and 11 months incubation in no till and
 conventional till corn-soybean rotations, poplar and alfalfa
 monocultures and native successional vegetation, on the KBS-LTER
 site.  Mass losses rates of above-ground incubated litter were
 primarily controlled by litter composition rather than edaphic or
 microclimate differences between systems.  In no-till vs tilled
 plots, mean decomposition rates were the same after 5 months (just
 prior to litter burial in tilled plots) but remaining mass in no-till
 litter averaged twice that in conventional till plots after 11
 months.  Fungi accounted for 60-80%, and bacteria 20-40%, of
 metabolic activity as determined by substrate-induced
 respiration/selective inhibition on corn and soybean leaves and
 stems. There were no significant differences in decomposer dominance
 (based on relative respiratory activity) between litter type or
 litter location. The initial 5 month surface incubation in both
 systems may have allowed fungal dominance to be established and
 maintained through the first year of decomposition.

Perkins, Reed.  SCALING ANALYSIS OF PEAK FLOWS FROM SEMI-NESTED BASINS
 IN THE WESTERN CASCADES OF OREGON.  Department of Forest Science,
 Oregon State University, Corvallis, OR 97331.  AND.  This study
 examined the scaling properties of matched peak flow data for 400
 storms over the period 1955 to 1990 from 10 semi-nested basins
 ranging from 10 to 10,000 ha in the Andrews LTER in the Western
 Cascades of Oregon.  Empirical data showed simple scaling, implying
 that average flow frequency distributions have statistically similar
 shapes at each spatial scale.  Simulations showed that the shape of
 the scaling curve is sensitive to changes in the shape of the average
 flow frequency distribution with scale, but the scaling curve shape
 is not sensitive to variability among flow frequency distributions at
 any single spatial scale, the number of basins at any single scale,
 nor the omission of the largest storms.  This analysis suggests that
 scaling analysis may provide useful insights about averaged flow
 outing behavior from nested gauging stations, but does not reflect
 the relative variability of flows at any single spatial scale as
 previously suggested.  These results imply that scaling analyses
 using data from non-nested basins will not be able to discriminate
 the effects of flow routing behavior from climate variability effects
 on hydrologic peak flows.  We hypothesize that flow frequency
 distributions of nested basins reflect the relative importance of
 hillslope and channel processes as well as the propagation of
 clearcutting and road-related disturbances downstream.  We will test
 this hypothesis using distributed parameter modelling for the Andrews
 LTER basin and its sub-basins.

Pfeiffer, Kent, and David Hartnett. BISON SELECTIVITY AND GRAZING
 RESPONSES OF Schizachyrium Scoparium AND Andropogon Gerardii IN
 BURNED AND UNBURNED TALLGRASS PRAIRIE. Kansas State University,
 Manhattan, KS 66506. KNZ.  Two closely related grasses with
 contrasting growth form, S. scoparium and A. gerardii were studied on
 tallgrass prairie to determine how fire influences their relative use
 by bison and their responses to grazing. On unburned prairie, bison
 grazed the bunchgrass S. scoparium far less frequently than the
 rhizomatous A. gerardii, but the two species were grazed at equal
 frequencies on burned sites. Burning removes the persistent standing
 dead tillers of S. scoparium which serve as physical deterrent to
 grazing. Grazing shifted the size structure of S. scoparium
 populations toward a higher frequency of small individuals, and plant
 size (basal area/ strongly influenced its probability of being
 grazed.  On burned prairie, plants of intermediate size classes were
 the least abundant but were grazed most frequently. In the absence of
 grazing, mean plant size and densities of S. scoparium were increased
 by burning. Thus, burning favors S. Scoparium under ungrazed
 conditions but is detrimental to it under grazed conditions.  The
 results indicate that plant growth form, population size structure,
 and fire interact to influence bison grazing patterns on these
 dominant grasses and their responses to grazers on tallgrass prairie.

Phinn, Stuart , Janet Franklin, Allen Hope, Douglas Stow and Laura
 Huenneke. BIOMASS DISTRIBUTIONS OF A SEMI-ARID DESERT FROM AIRBORNE
 DIGITAL VIDEO IMAGING, FIELD SAMPLING AND SPATIAL STATISTICAL
 METHODS. Department of Geography, San Diego State University, San
 Diego, CA 92182-0381. Department of Biology, New Mexico State
 University, Las Cruces, NM, 88003. JRN.  Biomass distributions mapped
 from airborne multispectral video image data and field samples were
 compared for 70m x 70m sample sites from five vegetation types within
 the Jornada LTER, New Mexico. Normalized Difference Vegetation Index
 (NDVI) images were calculated at 0.5, 1.0, 2.0 and 4.0m pixel
 resolutions by averaging. Contoured NDVI images were compared to
 contour plots derived from field sampling of biomass at 10m
 intervals, interpolated by Kriging. Their similarity indicates that
 field sampling adequately represented the spatial distribution of
 biomass in the grassland plots and some of the shrubland plots with
 more continuous cover. However, image variograms show that a higher
 sampling intensity (5.0m or less) would capture the fine scale
 pattern of the heterogeneous biomass distribution in degraded shrub
 sites given the average diameter (5 - 7.5m) of the shrubs.  Poister,
 David, David E.Armstrong, and James P. Hurley. A SIX YEAR RECORD OF
 NUTRIENT ELEMENT SEDIMENTATION AND RECYCLING IN THREE NORTH TEMPERATE
 LAKES. North Temperate Lakes Site. Water Chemistry Program, WI
 53706.University of Wisconsin, 660 North Park Street, Madison,
 WI. NTL.  Sedimentation of C, N, and P from the water column was
 assessed during the ice-free season in three northern Wisconsin lakes
 from 1986-1991.  Seasonal trend in mass sedimentation different in
 each lake but consistent from year to year within a lake.  High rates
 of nutrient sedimentation were associated with spring and fall blooms
 of large siliceous algae.  Nutrient recycling, calculated as the
 difference between uptake during photosynthesis and loss to
 sedimentation, showed seasonal trends that were related to
 sedimentation.  Recycling was the most important source of nutrients
 to primary producers, accounting for 85-90% of phosphorus demand
 during the summer stratified period.  Porter, John H. and James
 T. Callahan. ECOLOGICAL ASSESSMENT USING REMOTELY-SENSED DATA: A
 COMPARISON OF IMAGE SOURCES.  University of Virginia,
 Charlottesville, VA 22903, USA and National Science Foundation,
 Washington, DC 20550. VCR.  We compared thematic maps, derived from
 different contemporaneous image sources using a standardized
 methodology, to assess how our perceptions of ecological landscapes
 are affected by the source of the image data. Specifically, we
 examined similarity in areal estimates, patchiness, and spatial
 coincidence of cover classes for a scanned aerial photograph and SPOT
 and Thematic Mapper satellite imagers. Images were rectified to two
 common resolutions (5 and 30 m), classified using the ISODATA
 clustering technique and recoded into cover classes. Most cover
 classes had similar areas across image sources. Changing the grain
 size of the images to 30 m had virtually no effect on the areal
 estimates. The number and character of the patches derived from the 5
 m images varied widely between image sources. However, patchiness in
 the 30 m resolution images was similar to that observed in the 5 m
 images. Spatial coincidence was highest between the SPOT and TM
 derived classifications, with an overall agreement of 75%.  Agreement
 among the both satellite images and the photo was poorer, with an
 overall agreement of only 50%.

Porter, John H. and James T. Callahan. EMERGING TRENDS IN SHARING OF
 ECOLOGICAL DATA.  LTER, University of Virginia, Charlottesville, VA
 22903, USA and National Science Foundation, Washington, DC
 20550. VCR.  Success of shared data bases depends of two primary
 qualities: (1) contributions of data to the data bases, and (2) uses
 of the data bases. There is a fundamental dilemma embedded in data
 base creation and management. At least on a perceptual level, the
 benefits derived from a data base are greater for the user of the
 data than for the contributor of the data.  Ultimately, however, the
 utility of a data base depends upon the quality of the data provided
 and the accessibility of the data to users. We examine the means by
 which LTER sites have provided for the creation, management and
 utilization of large, multi-source data bases. Also, based on a
 review of recent literature we examine the speed of consumption (the
 time between data generation and publication of results) of
 ecological data.  Reagan, Douglas and Robert Waide. PROPERTIES AND
 ORGANIZATION OF THE FOOD WEB OF A PUERTO RICAN RAIN
 FOREST. Terrestrial Ecology Division, University of Puerto Rico, Rio
 Piedras, Puerto Rico 00936. LUQ.  Multiple investigators coordinated
 efforts to define the major feeding relationships among all animal
 species inhabiting the Luguillo Experimental Forest near El Verde,
 Puerto Rico. These studies have provided a comprehensive
 understanding of the properties and organization of the forest
 community food web and included the analysis of a food web matrix
 consisting of 156 "kinds of organisms" (2,056 known species). The
 food web is characterized by low faunal richness, an absence of large
 herbivores and carnivores, and a superabundance of frogs and
 lizards. Cross predation and food loops involving large invertebrates
 and small vertebrates are distinctive features of the food
 web. Results also indicate the community food web is divided into
 day, and night compartments.  Rice, Charles W., Clarence L. Turner,
 Tracy L. Benning, and Timothy R. Seastedt.  FIRE FREQUENCY AND
 FERTILIZATION EFFECTS ON PLANT PRODUCTION AND N UPTAKE, MICROBIAL
 BIOMASS, AND SOIL N AVAILABILITY IN TALLGRASS PRAIRIE.  Kansas State
 University, Manhattan, KS 66506.  In tallgrass prairie, fire
 frequency can affect net primary production and microbial activity.
 The objective of this study was to examine the relationships between
 fire frequency, net primary production and microbial biomass.  A
 wildfire in 1991 on Konza Prairie Research Natural Area made it
 possible to estimate primary production on six watersheds last burned
 1 to 2, 4 to 5, and 10 to 11 years.  Experimental treatments designed
 to magnify the effects of fire frequency were established on these
 watersheds and included a control; added N (1.5 g/m2); and added C
 (250 g/m2).  Plant biomass and N concentration, soil inorganic N, and
 microbial biomass were measured during 1991 and 1992.  Potential
 differences in aboveground biomass attributable to fertilization or
 fire frequency were minimized by severe water stress in 1991.  Forb
 biomass responded to fire frequency with higher biomass on
 infrequently burned(4-5 y) than frequently burned watersheds.  Grass
 biomass responded to N fertilization but not fire frequency.  Plants
 quickly assimilated added N with the greatest response on frequently
 burned watersheds. Higher levels of soil inorganic N remained after
 two growing seasons with added N.  The effects of fertilization and
 fire on microbial biomass C were inconsistent while added N increased
 microbial biomass N.

Riddervold, Leif Bjorn, Tanya Furman, and Ted Hegnauer. ISLANDS OF
 FRESH WATER IN A SALT MARSH. University of Virginia, Charlottesville
 VA, 22903. VCR.  On Parramore Island (Virginia Coastal Reserve) are
 several hundred land forms known as the Parramore Pimples.  The
 pimples are typically round (<5 - 200 m diameter), elevated features
 (0.5 - 2.5 m above surrounding topography) distributed randomly
 within salt marshes throughout the island. Pimples with a diameter of
 at least 30 m have developed a fresh water lens (recharged by
 precipitation) which supports an island of terrestrial vegetation
 within a salt marsh community.  Several grass species predominate on
 the flat, sandy plain of the pimple interior, while trees and shrubs
 form a ring around the edge of the feature where the fresh water lens
 is closest to the surface. Surrounding the pimples, various marsh
 grasses define concentric rings that reflect the salinity and
 topographic gradients outward from the feature. The focus of this
 study is to determine the extent of the fresh water lens, and to
 monitor the lens following overwash events.  As the south end of
 Parramore Island is eroding quickly, several of the pimples are
 subject to frequent overwash by salt water during winter storms. Many
 of the trees and shrubs display signs of stress, including mortality
 from the saline intrusions. Normal zonation of the salt marsh
 vegetation around the pimples will be studied in order to understand
 the physical conditions responsible for supporting each zone. Several
 nests of three wells each have been installed on three pimples with
 common morphological characteristics. Two of the pimples are
 regularly subject to overwash events and their vegetation shows signs
 of stress. The third pimple is not overwashed frequently, and the
 vegetation appears healthy. Salinity profiles were determined with 5
 m depth for each pimple. Preliminary results indicate that the
 thickness of the fresh water lens varies with the elevation of the
 feature, but does not exceed 2 m. Below the fresh water, the salinity
 increases downward at a constant rate of roughly 10 ppt/m (a result
 of diffusion and mixing due to tidal oscillations), to a maximum of
 30-31 ppt (equivalent to salinities of water in surrounding marsh)
 near the center of each feature. The wells were installed during a
 relatively dry period, and therefore it is unknown whether the lens
 will expand substantially during the winter months when
 evapotranspiration is at a minimum.

Ritchie, M. E. and David Tilman*. CASCADING EFFECTS OF BIRDS ON
 DIVERSITY OF GRASSHOPPERS AND PLANTS.  Utah State University, Logan
 UT 84322-5210, *University of Minnesota, St. Paul MN 55105. CDR..
 The effects of predators on the diversity of their prey are
 well-documented, but few studies have addressed whether predators can
 influence diversity across two lower trophic levels. With a four-year
 experiment, we addressed this question in unfertilized and fertilized
 sections of an old field at Cedar Creek Natural History Area in
 Minnesota. Specifically, we excluded birds (predators) from 9x9 m
 plots and measured responses of the biomass and species diversity of
 grasshoppers (herbivores) and plants. In general, birds increased
 grasshopper biomass and diversity, had no effect on plant biomass,
 but decreased plant diversity. These effects were similar in both
 unfertilized and fertilized plots for 1989-1991. In 1992 on
 unfertilized plots, however, birds decreased grasshopper biomass and
 increased plant diversity. For all years and plots combined, plant
 diversity was negatively associated with grasshopper
 biomass. Overall, bird predation affected grasshopper biomass and
 diversity, and increased grasshopper biomass decreased plant
 diversity. These results suggest that coupled trophic linkages can
 lead to cascading effects of predators on diversity across two or
 more lower trophic levels.

Roberts, Christine, Julia A. Jones and David Perry.  SPATIAL PATTERNS
 OF SOIL MOISTURE, NITROGEN MINERALIZATION, VA MYCORRHIZAL INFECTION,
 AND SOIL ORGANISMS IN A Juniperus occidentalis - Artemesia tridentata
 PERENNIAL GRASS COMMUNITY IN CENTRAL OREGON.  Departments of Forest
 Science and Geosciences, Oregon State University, Corvallis, OR,
 97331.  AND.  This study examined whether juniper invasion was
 associated with a change in spatial patterns of soil moisture, pH,
 nitrogen mineralization, VA mycorrhizal infection and soil organisms
 in sagebrush-grassland with and without invading junipers on the
 Island, an undisturbed area of central Oregon.  Fifty-two surface
 samples were collected in each of ten 50-m radius plots using a
 nested randomized grid design to test for spatial variation at <1m,
 1-5m, and 5-50 m scales.  Four plots were sampled in December of
 1991, two in sage-grassland and two under juniper/sage/grass.  Six
 plots were sampled in May of 1992, three each under sage/grass and
 juniper/sage/grass. Species composition of soil organisms differed
 between vegetation types and by season but biomass and functional
 groups did not.  The coefficient of variation for most properties was
 higher in plots with juniper than without.  In plots sampled in
 winter, semivariograms and correlograms showed greater short range
 variation and smaller patches for moisture and N mineralization in
 plots without juniper, and higher long-range variation and large
 patches in plots with juniper. However, soil arthropods showed the
 reverse pattern, while VA mycorrhizal infection had no spatial
 pattern.  In plots sampled in summer, spatial patterns varied
 considerably within each vegetation type depending on plot location
 under juniper canopies, but sage/grass plots generally showed greater
 short-range variation and smaller patch size whereas
 juniper/sage/grass plots had small and large patch sizes. Fractal
 dimensions for moisture and N mineralization were higher in plots
 with juniper, suggesting that juniper invasion increased long-range
 variation.  These results suggest that competition between and within
 species may produce patterns in soil resources that in turn affect
 soil ecological processes, further modifying observed soil spatial
 patterns.  Rossow, Loni. HERBIVORE EFFECTS ON Salix/Populus
 ECTOMYCORRHIZAE AND ENDOMYCORRHIZAE IN THE BONANZA CREEK FLOODPLAIN
 EXPERIMENTAL TAIGA FOREST SITES, ALASKA. Univ. of Alaska, Fairbanks,
 AK 99775. BNZ.  Mycorrhizae, a mutualistic symbiosis between plants
 and fungi, may be one of the most important and least understood
 biological associations regulating community and ecosystem
 functioning. Both animal and fungus depend on mycorrhizal plants for
 carbon. Therefore, any herbivory reduces the carbon available for the
 fungus. Herbivory has been found to suppress mycorrhizae by removing
 photosynthetic tissue which in turn reduces the photosynthate
 available for maintaining the fungus-plant mutualism. In the Alaskan
 taiga, selective mammals browse on plants in the Salicaceae family
 (Salix spp. and Populus spp.). My project involves quantification of
 both ecto- and endomycorrhizae on willow and poplar roots to study
 this effect of herbivory using the paired plots inside and outside of
 exclosures replicated along the Tanana River. Since I have recently
 started this graduate project, I have no results at present. My
 methods include taking soil cores, processing soil cores, and
 quantifying subsamples of willow/poplar roots for ecto- and
 endomycorrhizae.

Sanderson, B. L. and Thomas Frost. DINOFLAGELLATE RESPONSE TO
 MANIPULATION OF ZOOPLANKTON AND NUTRIENT CONCENTRATIONS IN TWO
 WISCONSIN LTER LAKES. Center for Limnology, University of Wisconsin,
 Madison, WI, 53706, USA. NTL.  Dinoflagellates are an integral part
 of many marine and freshwater phytoplankton communities, yet few
 investigators have evaluated the comparative importance of growth and
 loss processes in their population dynamics. We investigated
 dinoflagellate population dynamics in two Wisconsin bog lakes at the
 North Temperate Lakes Long-Term Ecological Research Site. The bogs
 have a number of common chemical features but distinctly different
 dinoflagellate populations. We tested the alternative hypotheses that
 growth processes driven by nutrient limitation or loss processes
 driven by zooplankton grazing control the populations in the bog
 lakes. Nutrient concentrations (N&P) and zooplankton density were
 manipulated in two, 12-day enclosure experiments conducted
 simultaneously in each lake. Results show no evidence of zooplankton
 grazing on dinoflagellates, suggesting that large cell size renders
 them resistant to grazing. Dinoflagellate populations in treatments
 receiving nutrients did not exhibit increased growth and in one
 experiment exhibited significantly lower densities that non-nutrient
 treatments. Pigment analysis using HPLC suggests that other algae
 were better competitors for nutrients and may negatively influence
 dinoflagellate population.  Our study highlights the importance of
 understanding algal community dynamics in order to elucidate the
 mechanisms for changes in dinoflagellate populations.

Sankovskii, Alexei and Yuri Puzachenko. SPECIES ORDINATION AS A TOOL
 FOR INTERSITE COMPARISON. Institute of Ecology, University of
 Georgia, Athens GA, 30602-2202 and Lab. of General Ecology, Moscow,
 Russia. CWT.  The objective of the current study was to compare the
 structure of a tree layer in the Southern Appalachian (Coweeta
 Hyd. Lab., USA) and Western Caucasus (Caucasus Biosphere Reserve,
 Russia) forest communities.  The comparative analysis was based on
 the following assumptions: - every species ensemble is controlled by
 the various environmental factors which can be intercorrelated, - the
 combined reaction of species to the specific set of factors creates
 an "ecological space" dimensions of which are independent; each
 dimension of this space corresponds to the combination of
 environmental factors or reflects some biotic processes such as
 competition or succession. - each species occupies a certain portion
 of ecological space - its ecological niche; ecological niche is not
 predefined a priori but is forming during the development of species
 ensemble in ecological and evolutionary time.  The structure of
 ecological space of the selected forest communities was analyzed
 using the non-metric multidimensional scaling. The results of
 analysis suggested that the tree layers in the Western Caucasus and
 Southern Appalachian forest communities are regulated by the
 different number of independent factors - 3 in the Caucasus and 4 in
 the Appalachians. Dominant tree species in both sites have the
 similar relative size of the ecological niches (based on the
 frequency of occurrence) and comparable degree of the niche overlap.

Santos, M�árcio CFV and Joseph C. Zieman. THE ROLE OF SUBSURFACE
 HYDROLOGY IN UPPER MID-LITTORAL HYPERSALINITY DEVELOPMENT. Department
 of Environmental Sciences. University of Virginia, Charlottesville,
 VA, 22903. VCR.  Porewater hypersalinity is one of the main natural
 stressors in upper mid-littorals exposed to dry or seasonally dry
 climates. It is well established that climate determines the
 potential for hypersalinity development at the regional level, while,
 at the micro-scale spatial level, salinity build-up is usually
 associated with the occurrence of upland freshwater seepage (surface
 and subsurface). Unfortunately, most of the knowledge about upper
 mid-littoral hypersalinity comes from conceptual models that lack a
 quantitative basis and field testing. In order to measure the
 relative importance of upland seepage on hypersalinity prevention at
 the VCR-LTER, twenty-three transects were established at the upper
 mid-littoral zone of sites with different sediment composition and
 upland hydrology. The transects were instrumented with piezometer and
 pressure lysimeter nests. At each transect we measured topographic
 slope, porewater salinity and upland subsurface flow. Preliminary
 data analysis revealed that hypersalinity developed only on slopes
 smaller than 0.5 degrees, suggesting the decrease in upper
 mid-littoral subsurface drainage as a potential mechanism. Upland
 seepage flow prevented salinity build-up in only one transect, and in
 the form of surface flow. We conclude that the development of upper
 mid-littoral hypersalinity, at the micro-scale spatial level, is
 governed by topographic slope, with associated changes in subsurface
 drainage as the possible mechanism. Upland seepage is restricted to
 the role of shaping the porewater salinity regime, which is
 determined by the topographic slope setting.  Schmidt, Steven K.,
 Lesley K. Smith, Melany C. Fisk, Charles H. Jaeger, Paul D. Brooks,
 Gregory M. Colores, Ann E. West, Elisabeth A. Holland, and William
 D. Bowman. TEMPORAL AND SPATIAL VARIATION IN N2O AND CH4 FLUXES
 ACROSS AN ALPINE LANDSCAPE. Environmental, Population, and Organismic
 Biology. Campus Box 334, and Institute of Arctic and Alpine Research,
 Campus Box 450, University of Colorado, Boulder CO 80309. NWT.
 Fluxes of N2O and CH4 were measured in three alpine tundra plant
 communities (3 sites per community) on Niwot Ridge. Measurements were
 taken weekly to bi-weekly from before snowmelt to well after plant
 senescence in 1992 and 1993. In addition, soil moisture, temperature
 and inorganic N levels were measured at each site on all sampling
 dates. Nitrogen mineralization, nitrification, microbial biomass
 nitrogen and plant assimilation of N were also measured periodically
 throughout the growing season at each site. N2O production was
 highest in May and June in wet and moist meadow sites and tapered off
 to almost zero for July, August and September. In dry meadow
 communities, N2O production showed a peak early in the season but
 also showed peaks of production in response to late season rainfall
 events. Moist and dry meadow sites were sinks for CH4 for all but the
 earliest sampling dates in May of 1993. Wet meadow sites were always
 a source of CH4. Overall, soil moisture was the most important
 environmental variable controlling N2O and CH4 fluxes from alpine
 tundra sites in 1992. Because moist and dry meadows are the dominant
 community types in the Colorado alpine, it appears that alpine tundra
 acts as a net source of N2O and a net sink for CH4.

Scott V. Ollinger, John D. Aber, C. Anthony Federer(*) and Jenn
 M.Ellis.  PnET-GIS: MODELING FOREST PRODUCTIVITY AND WATER BUDGETS
 ACROSS THE NORTHEASTERN U.S.  Complex Systems Research Center,
 University of New Hampshire, Durham, NH 03824 and (*) Northeastern
 Forest Experiment Station. U.S.D.A. Forest Service, Durham, NH
 03824. HFR and HBR.  Environmental perturbations such as climate
 change and atmospheric deposition can affect ecosystems at regional
 to global scales.  In order to predict their effects across real
 landscapes, site-level information must be scaled up to the levels at
 which these disturbances act.  Linking ecosystem models to geographic
 information systems allows us to accomplish this by combining the
 complexity of ecosystem processes with the spatial heterogeneity of
 driving environmental variables.  The current research involves
 linking PnET, a monthly time step model of forest carbon and water
 balances, to a GIS of the northeastern U.S. (New York and New
 England).  PnET is based on the following relationships: 1) maximum
 photosynthetic rate is a function of foliar N concentration, and 2)
 stomatal conductance is a function of actual photosynthetic rate.
 These relationships are combined with equations for photosynthetic
 response to light attenuation through the canopy, along with soil
 moisture stress and vapor pressure deficit, to predict monthly leaf
 area and carbon and water balances.  PnET has been validated against
 field data from 10 temperate and boreal forest ecosystems. PnET-GIS
 is run at 30 arc second resolution, corresponding to the elevation
 and land use maps of the northeast region.  For each grid cell,
 vegetation and soil parameters are read from existing data planes,
 and climate drivers are calculated as functions of latitude,
 longitude, elevation, and slope position.  Model predictions of net
 primary production, wood production, and water yield are output
 directly into map form.  By adding climate change scenarios to model
 runs, we use PnET-GIS to examine potential effects of climate change
 on the carbon and water balances of forest ecosystems across the
 region.  Seastedt, Timothy R., and Marilyn D. Walker. CONTROLS OF
 DECOMPOSITION IN ALPINE TUNDRA.  Institute of Arctic and Alpine
 Research, Campus Box 450, and Environmental, Population, and
 Organismic Biology, Campus Box 334, University of Colorado, Boulder
 CO 80309. NWT.  Litterbag studies were used to evaluate the
 importance of landscape position and substrate quality on
 decomposition processes. Sites of intermediate snowdepth exhibit the
 highest decomposition rates for surface litter during both the first
 and second years of decay. Such sites are neither strongly
 temperature limited (snowfield sites) or moisture limited (e.g.,
 sites blown free of ca. 80% of annual precipitation). Initial
 nitrogen content of litter was positively correlated with decay rates
 for the first year of decomposition; initial lignin content was
 inversely correlated with decay rates. Substrates with similar
 lignin:nitrogen ratios appeared to decay more rapidly in soil than on
 the surface. Wood decay, however, was similar for surface and soil
 samples.  Shelley E. Arnott. TEMPORAL VARIATION IN THE DETECTION OF
 ZOOPLANKTON SPECIES. Center for Limnology, University of
 Wisconsin-Madison, Madison, Wisconsin 53706. NTL.  Zooplankton
 species richness and abundance vary within and among seasons and
 among years. Understanding patterns of variability is of importance
 for questions of biodiversity because samples taken at a single point
 in time are frequently used in estimates of richness and diversity. A
 7 year survey of zooplankton from Little Rock Lake, North Temperate
 Lakes Long-Term Ecological Research Site was used to calculate yearly
 species diversity, richness, extinction and immigration rates and
 rates of species turnover. Patterns of species abundance and
 persistence throughout the season were compared among years to
 determine the stability of zooplankton communities and the influence
 of environmental conditions such as weather patterns. Temporal
 variation in community structure and the low probability of detecting
 rare species resulted in an underestimation of species richness by 15
 - 50 % for single samples taken at any one time during the summer. A
 sampling regime that maximizes diversity, but minimizes cost (effort)
 will be presented.

Sievering, Herman1, Lori Marquez1, Timothy Bardsley2 and Christine
 Seibold2.  ATMOSPHERIC LOADING OF NITROGEN TO ALPINE TUNDRA AT THE
 NIWOT LTER. 1 Center for Environmental Sciences, CB 136, PO Box
 173364, and 2 Institute of Arctic and Alpine Research, CB 450,
 University of Colorado, Boulder, CO.  Atmospheric gaseous nitric acid
 (HNO3) as well as particulate matter nitrate (NO3-) and ammonium
 (NH4+) concentrations have been determined for the Niwot Ridge LTER
 Saddle site on an approximately biweekly basis during the winter of
 1992-93 and on a weekly to twice-weekly basis since April 1993.
 These N species are the dominant contributors to atmospheric N
 deposition (dry and wet loading) at the Niwot LTER alpine
 tundra. Results include: -very low minimum detectable NH4+ air
 concentration measurement capability; -sufficient ambient air
 concentration data obtained to assess atmospheric N deposition during
 1993 spring snowmelt conditions and during summer peak N species
 (especially HNO3) concentration periods; -hypothesis, based on a
 comparison of average summer 1993 HNO3, NO3-, and NH4+
 concentrations, that the atmosphere over the Niwot alpine tundra is
 ammonia gas (NH3) limited; -dry deposition of N species is,
 approximately, of the same magnitude as wet deposition at the Niwot
 alpine tundra, despite the fact that wet deposition of NO3- is higher
 here than at any other location in the Colorado Rockies; -dry
 deposition of N species may be greater or less than wet deposition
 depending upon whether NH3 is emitted from or deposited to the Niwot
 alpine tundra during May-September. Conclusions: The growing season N
 dry deposition at the Niwot alpine tundra, >1 mg N m-2 d-1, plus N
 wet deposition of 1 mg N m-2 d-1 may be compared with biological N
 fixation of <0.2 mg N m-2 d-1, <0.03 mg N m- 2 d-1 by lighting
 fixation and, perhaps most interesting, N mineralization of 8-12 mg N
 m-2 d-1. It appears that new available N, about 20% as much as
 recycled N mineralization, is delivered to the Niwot alpine tundra
 yearly by way of atmospheric dry and wet deposition.  Sinton, Diana.
 RECONSTRUCTING DISTURBANCE PATTERNS FROM WINDTHROW AND FIRE IN THE
 BULL RUN WATERSHED, MT. HOOD NATIONAL FOREST, OREGON, USA.
 Department of Geosciences, Oregon State Univ., Corvallis, OR 97331.
 AND.  (Faculty advisors: J. Agee, J.A. Jones, T. Spies, F.J. Swanson;
 Andrews LTER contacts: J.A. Jones, T. Spies, F.J. Swanson). AND.
 This study examined windthrow and its historical relationship with
 fire and forest cutting in the Bull Run watershed, a 500 km2 forested
 basin which is the principal municipal water supply for the City of
 Portland, Oregon.  Although windthrow occurred in the Bull Run prior
 to 1958 when timber harvesting began, edges created by clearcutting
 and fires may have increased the incidence of windthrow and altered
 its natural spatial and temporal distribution.  The overall study
 involves (1) examining how mapped disturbance patterns are related to
 topography, vegetation, soils, exposure to wind, edges created by
 natural openings in the forest cover, road and stream networks, and
 clearcut patches based on (2) mapping and dating of pre- and
 post-harvest fire patches (J. Agee and F. Krusemark of the University
 of Washington), and (3) mapping and dating pre- and post-harvest
 windthrow patterns (D. Sinton, J.A. Jones, and F.J. Swanson).  The
 first phase was an examination of landscape-scale effects on
 windthrow disturbance produced by a large storm in December of 1983.
 Windthrow was mapped from historical aerial photography and maps and
 tabular data were created from a geographic information system
 (GIS). Northeast-facing slopes and ridgetops, and stands downwind of
 a clearcut edge, had the highest rates of windthrow.  A significantly
 higher number of windthrow patches were associated with clearcut
 edges than natural edges.  Moreover, several of the windthrow patches
 from the 1983 storm were associated with clearcut edges which had
 been created by salvaging timber from previous windstorms, suggesting
 a pattern of disturbance propagation across the landscape.  Continued
 work will include spatial modeling based on random (no spatial
 pattern) and landscape-controlled conceptual models of disturbance
 spread to assess the relative importance of landforms and human
 actions on the spatial and temporal propagation of disturbance in
 this forested basin.  Smucker, Alvin, Kurt Pregitzer and Liisa
 Pietola. ALFALFA AND POPLAR ROOT DYNAMICS IN LTER EXPERIMENTS AT
 KELLOGG BIOLOGICAL STATION. Michigan State University East Lansing,
 Michigan. KBS.  Root development, distribution and turnover rates of
 alfalfa and poplar fields were evaluated by the minirhizotron (MR)
 and microvideo camera methods during a four-year study on a
 stratified loam soil. Clear plastic MR tubes were installed at 45
 degrees at planting. Video recordings were taken to depths of 110 cm
 at 1 - 3 week intervals during the most dynamic growth periods or
 following each cutting of the alfalfa fields. Root images were
 quantified into numbers of total, new and senescent roots. Root
 growth and death rates of alfalfa were highly dynamic during their
 first three years. Roots of both species accumulated at the soil
 horizon interfaces between the Ap, B, and Bt horizons of the soil
 profile. Nonuniform development and death of roots, in these horizon
 interface regions, suggest possible accumulations of nutrients and
 water at soil horizon interfaces. Root development and distribution
 were modified more by the seasons and ages of the alfalfa than by
 defoliation. Storage carbon in the taproots appeared to be
 remobilized and transported to the fibrous branched roots following
 each cutting of the alfalfa. Poplar roots were most dynamic during
 the first 3 to 4 months following the spring planting. During
 subsequent years, root growth was most active in the early spring and
 late autumn. Evaluations of alfalfa root dynamics became less
 effective as the depth of active root growth increased to depths
 greater than the MR tubes. This problem could be resolved by
 installing longer MR tubes or by installing horizontal MR tubes at
 depths greater than 110 cm.  Spaulding, S.A., D.M. McKnight and
 R.L. Smith. PHYTOPLANKTON POPULATION DYNAMICS IN PERENNIALLY
 ICE-COVERED LAKE FRYXELL, ANTARCTICA.  U.S. Geological Survey, 3215
 Marine St., Boulder CO. 80303 Phytoplankton were collected over 5
 austral summers to examine seasonal and annual fluctuation in species
 composition and biomass in Lake Fryxell, a perennially ice-covered
 lake in southern Victoria Land, Antarctica.  The lake is amictic and
 has perennial and dramatic gradients of salinity, dissolved oxygen,
 and nutrients. Algal species diversity was low (58 total taxa and
 between 18 and 26 taxa within a given year), confirming the results
 of previous short term studies.  The phytoplankton consisted
 primarily of cryptophyte and chlorophyte flagellates and filamentous
 cyanobacteria.  Each year one dominant species contributed over 70%
 of total biovolume; Chroomonas lacustris was dominant in one year
 while Cryptomonas spp. dominated in the following 4 years.  Several
 species of filamentous cyanobacteria were abundant in the plankton;
 only one species had previously been reported, and it was not
 abundant.  Some common taxa were strongly vertically stratified
 (Oscillatoria limnetica, Phormidium anqustissimum, Pyramimonas spp.,
 Oscillatoria spp.), while others showed no distinct vertical
 stratification (Chlamydomonas subcaudata, Cryptomonas spp.).
 Phytoplankton stratification reflects gradients of nutrients and
 light, and water column stability.

Stammerjohn, Sharon.  VARIABILITY IN SEA ICE AREAL COVERAGE ALONG THE
 WESTERN ANTARCTIC PENINSULA.  Computer Systems Laboratory - Girvetz
 1140, Center for Remote Sensing and Environmental Optics (UCSB),
 Santa Barbara, CA 93106. PAL.  The Antarctic Marine Ecosystem Long
 Term Ecological Research (LTER) project proposes that interannual and
 annual variability in sea ice extent may be the major physical
 determinant in spatial and temporal changes in Antarctic marine
 biota.  Research presented here focuses on the annual and interannual
 variability in sea ice areal coverage in the LTER study area along
 the Western Antarctic Peninsula and compares the variability to other
 regions in the Antarctic.  A 12.5 year time series (from 10/78 to
 3/91) of surface ice concentrations was obtained from passive
 microwave temperature brightnesses recorded by NASA's Scanning
 Multi-channel Microwave Radiometer (SMMR) and DMSP's Special Sensor
 Microwave/Imager (SSM/I) using the NASA algorithm.  Ice areal
 coverage was calculated from the percent surface ice
 concentrations. The time series of ice areal coverage shows that the
 interannual variability in the LTER study area is distinct from other
 regions in the Southern Ocean.  This is confirmed by cross spectral
 analysis.  The mean annual cycle also shows that the timing of
 maximum/minimum ice area, as well as the period of ice advance and
 retreat, are different for each region, in particular for the LTER
 study area.  Lastly, this historical ice record quantifies the
 magnitude of a low and high ice year for the LTER study area,
 facilitating better characterization of ice coverage during current
 LTER research. A future objective of this LTER project is to model
 the links between ecosystem processes in the LTER study area and the
 interannual and annual variability of sea ice.  The historical sea
 ice record presented here will aid in such modelling efforts.
 Stevenson, Mark J.and Frank P. Day. FINE ROOT PRODUCTION ALONG A
 CHRONOSEQUENCE OF BARRIER ISLAND COMMUNITIES. Old Dominion
 University, Norfolk Va, 23529. VCR.  Fine root production was
 quantified by an ingrowth core method along a chronosequence of dune
 communities on Hog Island, a Virginia Coast Reserve LTER site. The
 dune communities are dominated by Ammophila breviligulata, Spartina
 patens, and Aristida tuberculosa. Production estimates for fine roots
 ( < 2 mm) were estimated using biomass ingrowth into root-free soil
 volumes for one growing season. Fine root production was greater in
 N-fertilized plots than unfertilized plots. The most substantial
 level of fine root production for unfertilized plots occurred in the
 upper 0-10 cm depth in R120. The unfertilized plots showed no real
 differences in production between communities at 10-20 cm, 20-30 cm
 and 30-40 cm depths. R24 and R36 produced similar the root production
 measurements in their N-fertilized plots. There was no substantial
 increase in total phosphorus concentrations in any of the dune
 communities. There was an increase in total nitrogen concentrations
 in fine roots from all dune communities in N-fertilized plots.

Stottlemyer, Robert, Charles A. Troendle and Raymond
 Herrmann. COMPARISON OF A DECADE OF CHEMICAL INPUT/OUTPUT BUDGETS IN
 FIRST ORDER WATERSHEDS: FRASER EXPERIMENTAL FOREST, COLORADO, CALUMET
 AND WALLACE LAKE WATERSHEDS, MICHIGAN.  National Park Service and
 National Forest Service, Rocky Mountain Forest and Range Experiment
 Station, Ft. Collins, CO 80526.  Streamwater samples have been
 collected for 10-12 y from watersheds in the Fraser Experimental
 Forest, Colorado, and the Calumet and Wallace Lake watersheds,
 Michigan, to compare surface water chemistry and watershed budgets at
 ecotonal sites receiving moderate (Michigan) and low (Colorado)
 inputs of anthropic atmospheric inputs. Precipitation inputs are
 dominated by snow.  No site retains 5042-inputs.  Midwinter thaws
 often result in streamwater NH4 ion "pulses".  During spring melt,
 streamwater No3 pulses are common, but >88% of NO and >95% of NH4 is
 retained in the watersheds.  Streamwater H pulses are not common.
 Watersheds with an elevation change >100 m show a significant
 increase in snowpack ion load as a result of higher input and better
 retention.  Over-winter N mineralization in soils coupled with late
 spring snowpack release account for the streamwater mineral N pulses.
 The increase in N inputs with elevation, good retention in the
 snowpack, late spring release in snowmelt, and strong ecosystem
 incorporation suggest probable effects on site biodiversity.

Su, Haiping, and Geoffrey M. Henebry. LANDSCAPE TRAJECTORIES USING
 AVHRR DATA. Division of Biology, Kansas State University, Manhattan
 KS 66506-4901. KNZ.  We demonstrate a novel decomposition of
 satellite images into spatial dependence, spatial heterogeneity, and
 spectral intensity.  This procedure defines a 3-space within which to
 plot trajectories, i.e. time series of vectors derived from multidate
 imagery.  Trajectories of different landscapes can thus be
 visualized, quantified, and compared.  We derive landscape
 trajectories of grazed grasslands in the Kansas Flint Hills from the
 biweekly composites of AVHRR NDVI data available from EROS Data
 Center for 1988, 1990, 1991, and 1992.  The trajectories capture 1)
 the seasonality of reflectance associated with canopy development and
 senescence, 2) patterns of spatial structure associated with
 available soil moisture, and 3) interseasonal variations due to
 climatic forcings.  Landscape trajectories constitute an important
 analytical concept for global and synoptic ecology.  Su, Haiping,
 Alan K. Knapp, John M. Briggs. EFFECTS OF FIRE AND TOPOGRAPHY ON SOIL
 MOISTURE MEASURED BY TIME DOMAIN REFLECTOMETRY. Kansas State
 University, Manhattan, KS 66506. KNZ.  Soil moisture is one of the
 important factors governing the growth and development of a tallgrass
 prairie canopy. Fire and topography can affect the distribution of
 soil moisture across a watershed or landscape. On the Konza Prairie
 Research Nature Area (KPRNA), near Manhattan, Kansas, we used a Time
 Domain Reflectometry (TDR) system to monitor soil moisture on an
 annually burned and a long-term unburned watershed during the early
 Spring and Summer months (March to September). For each watershed,
 eleven sites were selected along a transect that spanned
 upland-lowland-upland topographic positions. TDR soil moisture was
 measured for each transect at 15 and 30 cm depths (where
 possible). Measurements were made weekly or biweekly depending on
 weather conditions. Preliminary results from this year's measurements
 have shown a strong topographic redistribution of soil moisture from
 upland to lowlands at 15 cm depth. Relatively high soil moisture also
 was measured at the unburned transect relative to the annually burned
 transect. The results indicate that redistribution of soil moisture
 can be an important factor influencing landscape patterns in
 aboveground production. Long term measurement of soil moisture are
 planned to more clearly understand the importance of soil moisture
 redistribution as affected by fire and topography.

Theodose, Theresa A., and William D. Bowman. THE EFFECTS OF NEIGHBOR
 AND NITROGEN AVAILABILITY ON BIOMASS AND NITROGEN ACCUMULATION AND
 ALLOCATION IN TWO ALPINE GRAMINOIDS, Deschampsia caespitosa AND
 Kobresia myosuroides. Environmental, Population, and Organismic
 Biology, Campus Box 334, and Institute of Arctic and Alpine Research,
 Campus Box 450, University of Colorado, Boulder CO 80309. NWT.  Two
 dominant alpine tundra graminoids, Kobresia myosuroides from a low
 resource environment and Deschampsia caespitosa from a more resource
 rich environment were subjected to high and low N treatments in the
 absence and presence of inter- and intraspecific neighbors to
 investigate how each species responds to N and if that response is
 influenced by neighbors. Deschampsia accumulated significantly more
 biomass and N than Kobresia, regardless of N or neighbor
 treatment. Deschampsia responded significantly to N availability with
 increases in root and shoot biomass and nitrogen concentration and
 decreases in biomass and N root: shoot ratios in the high N
 treatment. Neighbor had no effect on Deschampsia biomass
 accumulation, but presence of a neighbor resulted in increased
 biomass and N allocated to shoots relative to roots. Kobresia biomass
 accumulation and N and biomass allocation did not respond
 significantly to N availability, but root nitrogen concentration
 increased in the high N treatment. When grown with Deschampsia,
 Kobresia increased N and biomass allocation to shoots relative to
 roots. Under high N, this response to Deschampsia resulted in
 increased tillering, biomass per tiller, total shoot biomass and
 possibly total plant biomass in Kobresia. Thus Deschampsia, a
 dominant of resource rich moist meadows accumulated more biomass and
 N and was more plastic in its response to N availability than
 Kobresia. Although Kobresia, a dominant of resource poor dry meadows
 had the more conservative growth response, allocation patterns
 shifted so that growth was not inhibited by the presence of
 Deschampsia, even under high N conditions.  Tirrell. Rebecca and
 Linda Blum.  RHIZOSPHERE ENHANCEMENT OF BELOWGROUND DECAY IN A
 Spartina alterniflora MARSH. Univ. Virginia, Charlottesville VA
 22903. VCR.  The potential for live roots of Spartina alterniflora to
 enhance below round decomposition was investigated over an 18 month
 period on the Eastern Shore of Virginia. Three clipped (no live
 roots) and 3 vegetated (live roots) plots were established in both
 the creekbank and interior sections of Phillips Creek marsh in May
 1991. One month later, litter bags containing dead Spartina roots and
 rhizomes were buried in the marsh sediments.  Every 2 months a litter
 bag was removed from each treatment plot and examined for decay and
 root in-growth. Samples for bacterial abundance and acetate
 mineralization were collected from each plot. Only 20% of the
 starting litter-bag root material was lost after 18 months of decay
 regardless of location in the marsh or the presence of vegetation.
 Little root production was observed even in the vegetated plots.
 Noticeably greater numbers of bacteria were evident in the vegetated
 plots of both creekbank and interior marsh locations. Greater acetate
 mineralization rates were measured in creekbank than in interior
 sediments regardless of the presence or absence of live
 roots. Acetate mineralization was greatest in the spring and Summer,
 and was minimal during fall and winter. A rhizosphere effect was
 demonstrated: bacterial cells were more abundant in the vegetated
 plots than in the clipped treatments. These weight loss data are not
 inconsistent with the hypothesis that decay is enhanced by the
 presence of live roots since few live roots grew into the litter bags
 throughout the study. However, the effect of live roots on decay and
 microbial activity is not clear.  Torgerson, Christian, and Mike
 Lemaster.  SPATIAL HETEROGENEITY OF SOIL INVERTEBRATES AND EDAPHIC
 PROPERTIES IN AN OLD-GROWTH FOREST PLOT IN THE ANDREWS LTER, WESTERN
 OREGON.  Research Experiences for Undergraduates, Andrews LTER, 1992
 and 1993.  (Faculty advisors and Andrews LTER contacts: J.A. Jones,
 A. Moldenke, D. Perry). AND.  This study examined how spatial
 patterns of living, dead, and downed trees in old-growth forest
 canopies are related to spatial patterns of soil arthropods,
 nematodes, O-horizon depth, soil pH, soil moisture content, and soil
 temperature in an old-growth forest plot in the Andrews LTER.
 Fifty-two surface samples were collected in each of six 50-m radius
 plots using a nested randomized grid design to test for spatial
 variation at <1m, 1-5m, and 5-50 m scales.  Two plots were sampled in
 the hot dry summer of 1992, one centered under a living old-growth
 Douglas fir (Pseudotsuga menziesii) in a cluster of remnant Douglas
 firs that survived a fire about 70 years ago, the other centered on a
 stump of a tree killed in that fire.  Four plots were sampled in the
 cold wet summer of 1993: one replicated the 1992 plot centered under
 the remnant Douglas fir, a second was centered on an isolated remnant
 Douglas fir, a third was centered on a Douglas fir snag estimated to
 have died 20 years ago, and a fourth was centered on a young (<30
 year old) Douglas fir.  Data were subjected to standard parametric
 statistical analysis and spatial analysis using semivariograms and
 correlograms.  Means and standard deviations of soil properties and
 organism counts were similar between plots within each year but
 differed by year, with much higher moisture contents and lower
 temperatures in summer 1993.  Spatial analysis revealed more
 pronounced short-range variation and smaller patches in plots lacking
 remnant trees, whereas plots containing remnant trees had greater
 long range variation and larger patches.  We hypothesize that
 litterfall, root crowns, and downed trees in remnant Douglas fir
 stands gradually produce a spatial pattern of large patches which
 becomes more pronounced as the trees age, and that this long-range
 pattern is lost within a few years of old-growth tree removal or
 death.  Tremmel, David C., James F. Reynolds, Ross A. Virginia, and
 Amrita G. De Soyza. MEASUREMENTS OF ROOT GROWTH AND WATER USE OF
 CREOSOTE BUSH AND MESQUITE IN THE CHIHUAHUAN DESERT.  Duke
 University, Durham, NC, 27708, Dartmouth College, Hanover, NH, 03755,
 and New Mexico State University, Las Cruces, NM, 88003.  JRN.  We are
 measuring in situ root growth and sap flow of creosote bush (Larrea
 tridentata) and mesquite (Prosopis glandulosa) plants at the Jornada
 LTER site near Las Cruces, NM, in order to obtain a better
 understanding of the coordination between above- and below-ground
 function in these species.  Root counts are made in 10 cm segments
 from three 1.2 m long minirhizotron tubes inserted around eight
 replicate plants of each species in both a summer rainfall exclusion
 treatment and control plots.  Our results show that creosote bush and
 mesquite differ in rooting density and patterns of root growth, and
 that plants denied summer rainfall maintain and produce fewer roots
 than control plants over the same time interval.  The magnitudes of
 the differences between species, and the effects of the rainout
 treatment, vary with depth in the soil profile and time of year.  We
 are measuring the diurnal course of water movement through stems of
 these species (a proxy for transpiration rate) using a heat-balance
 sap flow measurement system.  Sap flow rates in four plants of each
 species, along with several micrometeorological parameters, have been
 monitored continuously from the end of the spring dry season to the
 middle of the summer rainy season.  Preliminary results indicate that
 mesquite responds more markedly and rapidly than does the more
 xerophytic creosote bush to both changes in cloud cover throughout
 the course of a day and to rainfall events.

Turner, Clarence L., Alan K. Knapp and Timothy R. Seastedt. MECHANISMS
 OF PERSISTENCE OF LONG-LIVED PERENNIAL FORBS IN TALLGRASS PRAIRIE: A
 COMPARISON OF PHYSIOLOGICAL RESPONSES AND LONG-TERM DATA SETS ON
 PRODUCTION.  Kansas State University, Manhattan KS 66506 and
 University of Colorado, Boulder CO 80309.  KNZ.  Relatively little is
 known about the mechanisms by which long-lived forbs (non-woody,
 perennial herbs), maintain themselves in the face of competition from
 the dominant grasses in tallgrass prairie.  We investigated the roles
 of light and nitrogen limitation, as affected by burning and
 topographic position, on gas exchange responses in big bluestem (a C4
 grass) and 5 co-occurring forbs at Konza Prairie Research Natural
 Area in 1992 and 1993.  Unusually high rainfall amounts in both years
 reduced the potential for higher water stress typical of uplands
 (vs. lowlands) and burned (vs. unburned) areas in this system.  In
 1992, photosynthetic rates of forbs were 10-50% lower than big
 bluestem, were higher on burned areas than on unburned areas, but
 were not affected by topographic position.  In 1993, photosynthetic
 rates of forbs were higher following nitrogen additions.
 Photosynthetic rates of forbs peak at light levels equivalent to
 approximately half full sunlight.  Forbs appear to maximize their
 leaf area within the surrounding grass canopy at that light level,
 which is determined primarily by factors controlling production of
 the dominant grasses.  Analysis of long-term data on biomass
 production suggests that NPP of grasses is reduced to a greater
 degree than that of forbs in low light (unburned) conditions
 (reducing the competitive advantage of grasses), resulting in greater
 relative forb production.  This agrees with observations of greater
 forb abundance in unburned prairie and suggests that competition for
 light is a significant factor controlling year-to-year variation in
 forb production, distribution and abundance.  Turner, P.A.,
 E.F. Benfield, and J.R. Webster. PATTERNS OF MACROINVERTEBRATE DRIFT
 ALONG AN ELEVATIONAL AND STREAM SIZE GRADIENT IN A SOUTHERN
 APPALACHIAN STREAM. Dept. of Biology, VPI&SU, Blacksburg, VA
 24061. CWT.  The downstream movement of macroinvertebrates in drift
 has been shown to be important in stream ecosystems in terms of
 colonization and distribution, as well as being a vital energy link
 between upstream and downstream reaches. Drift was collected from
 each off our 100m reaches along an elevational and stream size
 gradient in a southern Appalachian stream in order to investigate the
 role of drift along the gradient. Preliminary results, based on 24h
 drift densities, suggest no elevational trends, except that highest
 drift densities occur at the highest, first order site (WS27).  A
 distinct diel periodicity was found for the lower three sites. These
 results may actually be an artifact of incomplete analysis because
 organisms have not yet been identified.  Uliassi, Daniel D.,
 R. W. Ruess, and K.M. Klingensmith. SUCCESSIONAL PATTERNS OF NITROGEN
 FIXATION AND DENITRIFICATION IN A TAIGA FLOODPLAIN FOREST. University
 of Alaska, Fairbanks Alaska, 99775 USA. BNZ.  Nitrogen fixation by
 Alnus tenuifolia is the major contributor to the nitrogen budget of
 taiga floodplain forests in interior Alaska.  Acetylene reduction and
 acetylene inhibition assays were used to measure root nodule nitrogen
 fixation rates and rhizosphere denitrification rates of A. tenuifolia
 within successional forests along the Tanana River floodplain.  Rates
 were measured in dense alder, alder/balsam poplar, balsam poplar, and
 white spruce stages during early, mid, and late growing season.
 Fixation rates were highest in the dense alder (38.41 �± 13.43 ?Mole
 C2H4 g Nodule DWT -1 hr -1), declined with increasing abundance of
 balsam poplar, and increased in white spruce stands. Significant
 intraseasonal variation in fixation rates were found, with peak
 fixation occurring during mid-summer (48.46 �± 11.48 ?Mole C2H4 g
 Nodule DWT -1 hr -1). Rhizosphere denitrification losses were highest
 in September (81.47 �± 16.43 ?g N g DWT Root -1 hr-1) and lowest in
 August (0.32 �± 0.16 ?g N g DWT Root -1 hr-1). Taken together, our
 estimates of nitrogen fixation inputs (68.9 g N m-2 yr-1) and
 denitrification losses (24.9 g N m-2 yr-1) for early successional
 stands yield a net ecosystem nitrogen input of 44.0 g N m-2
 yr-1. Given the potential uncertainties associated with these
 estimates, this value is similar to the ranges of values (15.6 to
 36.2 g N m-2 yr-1; Van Cleve et al. 1971;1993) estimated from
 nitrogen mass accumulation, and emphasizes the dynamic nature of
 nitrogen cycling processes in this ecosystem.

Wagener, Stephen M.1, J.M. Anderson2, Mark W. Oswood1, and Joshua P
 Schimel1. RIVER AND SOIL CONTINUA: PARALLELS IN CARBON AND NUTRIENT
 PROCESSING . 1lnstitute of Arctic Biology, University of Alaska
 Fairbanks, Fairbanks, AK 99775; 2Rothamsted Experimental Station,
 Harpenden, Herts AL5 2JQ, Great Britain. BNZ.  Both soil and stream
 ecosystems receive inputs from leaf litter and living primary
 producers. Despite this functional similarity, soil and stream
 ecologists have dissimilar views of trophic processes. Soil
 ecologists usually see decomposition as a process that mineralizes
 carbon from plant residues and provides nutrients for plant uptake,
 with invertebrates playing little role in carbon dynamics. In
 contrast, aquatic ecologists view litter decomposition in a forest
 stream as a series of transformations mediated by specialized
 invertebrates. Soil ecologists often underestimate the role of
 invertebrates in litter processing because they are mostly concerned
 with CO2 flux, little of which is directly a result of invertebrate
 respiration. In contrast, the stream ecologist's measure of carbon
 loss includes not only CO2 lost to the atmosphere, but leachates and
 fine particulates lost downstream as well. Stream ecologists
 underestimate the importance of microbes because much of the carbon
 is transported downstream to be eventually respired by microbes. Both
 a forest soil profile and a stream can each be divided into three
 analogous regions: an upper region where carbon is predominantly from
 leaf litter, a middle region where a significant proportion of carbon
 is derived from living primary producers in the form of roots (in
 soil) or macrophytes and algae (in running water), and a lower region
 dependent on fine particulate or dissolved carbon from higher in the
 soil profile or upstream. The differences in perspective of the soil
 and stream ecologists is likely due to the very different spatial and
 temperal scales in soils and streams. Soil process takes place over
 very small distances (cm), over long time periods (years), in the
 dark. In contrast, decomposition in a stream occurs over much longer
 distances (hundreds of km), over shorter time periods (months), and
 in daylight. What the stream ecologist fails to see is the entire
 river (analogous to a soil core) as an ecosystem. Despite great
 differences in the perceived importance of invertebrates in
 decomposition processes between streams and soils, invertebrates play
 very similar roles in carbon mineralization.

Wagener, Stephen M.1, J.M. Anderson2, and Joshua P
 Schimel1. BIOLOGICAL CHARACTERISTICS OF BIRCH LITTER
 COHORTS. 1lnstitute of Arctic Biology, University of Alaska
 Fairbanks, Fairbanks, AK 99775, 2Rothamsted Experimental Station,
 Harpenden, Herts AL5 2JQ, Great Britain. BNZ.  In the forest floor of
 Alaskan taiga, annual layers of Equisetum (horsetail) litter are a
 naturally occurring marker of birch litter cohorts. Equisetum litter,
 because of its texture and the presence of silica, leaves a
 long-lasting residue that provides a sharp contrast with birch
 litter. Due to the absence of macroinvertebrates, there is little
 bioturbation and litter cohorts generally maintain their location
 relative to surrounding litter. We collected box core samples of the
 forest floor in early September 1992. Forest floor material was
 separated into the following strata: Stratum 1, the 1991 year class;
 Stratum 2, the 1990 year class; Stratum 3, the 1989 year class;
 Stratum 4, the fermentation layer, 1988 year class and older; and
 Stratum 5, the upper white-colored zone of the fibrous root layer
 which made up the rest of the forest floor. Short-term respiration
 potential decreased with depth, as generally did the nitrogen content
 of the litter. Immobilization of nitrogen exceed mineralization in
 Strata 1 and 2, but net mineralization of nitrogen occurred in Strata
 3-5, with mineralization increasing with depth.  Some invertebrate
 taxa (such as Oribatida: Liodidae and Collembola: Entomobryidae) were
 found associated with upper strata, some taxa (such as Diptera larvae
 and Collembola: Onychiuridae) were found in deeper strata, and some
 (Oribatida: Nothridae) were evenly dispersed in all strata.

Walker, Donald A., William B. Krantz, Brad E. Lewis, Erik T. Price,
Ronald D.Tabler, Marilyn D. Walker, and Carol A. Wessman. MULTI-SCALE
STUDIES OF SNOW-VEGETATION INTERACTIONS IN THE ALPINE ZONE. Institute
of Arctic and Alpine Research, Campus Box 450, Environmental,
Population, and Organismic Biology, Campus Box 334, Chemical
Engineering, Campus Box 424, and Cooperative Institute for Research in
Environmental Sciences, Campus Box 216, University of Colorado,
Boulder CO 80309 and Tabler Associates, 7505 Estate Drive, Longmont
CO. NWT. The Niwot Long-Term Ecological Research (LTER) has begun a
snow-fence experiment to examine the consequences of altered snowpack
regimes in alpine ecosystems. This poster describes the principal
questions that are being addressed, the design of the experiment, an
update on the status of the fence construction and experimental plot
layout, and the results of the first winter's snow-depth and
ground-temperature observations. Snow depths are reported for a 350 x
500-m grid surrounding the experimental site and for more intensive
measurements in the 60 x 125-m snow-fence experiment study area. The
period November 1992 to April 1993 had 183% of average snowfall at
D-1, and April was the wettest month on record, so patterns of snow
distribution reported here may be representative of conditions that
could be expected with increased snow fall.  Walker, (Skip) D.A.,
William B. Krantz, Brad E. Lewis, Erik T. Price, Marilyn D. Walker,
and Carol A. Wessman. MULTI-SCALE STUDIES OF SNOW-VEGETATION
INTERACTIONS IN THE COLORADO ALPINE ZONE. Niwot LTER Project,
University of Colorado, Boulder, CO, 80309 NWT Alpine ecosystems are
thought to be particularly sensitive to climate change, and research
at the Niwot Long-Term Ecological Research (LTER) site in the Indian
Peaks of the Colorado Front Range is focusing on the consequences of
changed temperature and precipitation regimes.  We are particularly
interested in the effects of altered snowpack because of the known
importance of snow to the distribution of alpine plant and animal
communities.  The distribution of snow patches and windblown areas,
duration of the snow-free period, and position of melt water drainages
strongly affect the patterns of alpine plant communities.  Two of the
goals of the Niwot LTER project are to understand (1) how current
snowpack distributions affect patterns of vegetation and primary
production from species to regional scales, and (2) how will altered
snowpack regimes change the existing ecosystems.  We focus on making
fine- and intermediate-scale databases that provide linkages between
species-level studies and remotely sensed information in order to
develop a broad understanding of environmental and edaphic controls on
vegetation patterns.  A standardized method makes our approach useful
for multiscale and intersite comparisons.  At the plot level, the
abundance of key taxa in a Braun-Blanquet classification are closely
correlated with snow distribution.  At the landscape level, over 78
percent of the mapped areas are covered by communities typical of
snowbeds or windblown sites, an indication of the importance of wind
and snow cover to the vegetation of this alpine site.  Finally, at the
regional level, analysis of SPOT satellite data reveal strong negative
correspondence between elevation and the Normalized Difference
Vegetation Index (NDVI, an index of green biomass) on all slope-aspect
combinations except for west-facing slopes east of the Continental
Divide, where strong westerly winds control vegetation production at
all elevations.  The relationship may have general applicability for
studying the response of patterns of alpine production to climate
change.  The NDVI-elevation relationships developed for the Front
Range, Colorado will be examined in other mountain ranges including
the Big Horn Mountains, WY, San Juan Mountains, CO, Sierras, CA, and
Brooks Range, Alaska.  We predict that the position of the regression
line should shift in predictable ways in response to different
temperature, precipitation, and wind regimes. The influence of altered
snowpack is of particular concern in the alpine because over half of
the annual precipitation falls as snow, which is unequally distributed
on the landscape due to winds.  We have established a snow-fence
experiment that will examine the effects of altered snow regimes on
arctic tundra across several levels of ecosystem organization.  We are
building a large snow fences designed to impact a series of alpine
soils and plant communities.  We monitored snow-depths,
ground-temperatures, and soil and vegetation conditions prior to
erecting the fence in summer 1993.  Experimental design of the
experiment and results of the winter monitoring program will be
presented at the conference.

Walker, Lawrence R. FOREST REGENERATION UNDER UPROOTED TREES IN A
 PUERTO RICAN RAIN FOREST. Univ. Nevada, Las Vegas, NV 89154. LUQ.
 Forest regeneration was examined in soil pits created by uprooting of
 27 trees in Puerto Rico during Hurricane Hugo and compared to
 regeneration in the adjacent, undisturbed forest understory.  Soil N
 and P were lower in the disturbed mineral soils of the pits than in
 undisturbed forest soils. No differences in N and P levels were found
 between forest soils from under two N-fixing trees (Inga laurina and
 Ormosia krugii) and a species not known to fix N (Casearia arborea),
 but N levels were lower in the soil pits under Ormosia than under
 Casearia.  Sapling species richness and density of saplings 10-100 cm
 tall were greater in the forest plots than in the soil pits but did
 not differ between tree species.  Recruitment of Cecropia
 schreberiana saplings into the canopy (>5 m tall) 45 mo after the
 disturbance was entirely from the soil pits (80.5%) or root mounds
 (19.5%); no recruitment occurred in the forest plots during the same
 time interval.  Larger soil pits had more tree recruitment than
 smaller pits.  The exposed mineral soil from uprooted trees provided
 a microhabitat that favored recruitment of certain colonizing species
 despite low levels of soil nutrients.

Waller, Deborah. RESPONSE OF Reticulitermes virginicus (ISOPTERA,
 RHINOTERMITIDAE) REPRODUCTIVES TO ENVIRONMENTAL ACIDITY AND
 TEMPERATURE. Department of Biological Sciences, Old Dominion
 University, Norfolk, VA 23529 USA.  VCR.  Subterranean termites are
 important detritivores in forest ecosystems.  As part of an
 investigation of the effects of environmental factors on rates of
 dinitrogen fixation by termite hindgut bacterial symbionts, I
 confined alate reproductive males and females in containers (two
 pairs of alates in each of 96 units) saturated with solutions of
 sulfuric acid adjusted to pH 2 or pH 6.  Previous experiments had
 indicated that Reticulitermes prefers to eat filter paper treated
 with acid solutions of pH 2 over untreated paper.  Units were
 assigned to incubators at 24oC or 28oC.  After one month, there were
 no survivors in the 48 units held at 28oC.  At 24oC, one pH 2 unit
 contained living termites, and twelve (50%) of the pH 6 units held
 viable reproductives.  These results indicate that termite
 reproductive success is sensitive to environmental acidity and
 temperature.  A July survey of logs infested with termite foragers
 revealed a mean wood pH of 3.9 + 0.5 SD (n = 30) and a mean gallery
 temperature of 29.5 + 1.3oC (n = 30).

Way, J. B., L. Viereck, P. Adams, K. McDonald, E. Rignot,
 R. Zimmermann and C. Williams. MONITORING SEASONAL STATE IN THE
 BONANZA CREEK EXPERIMENTAL FOREST AND THE TOOLIK LAKE LTER SITES AS
 OBSERVED WITH IMAGING RADARS. Jet Propulsion Laboratory, Pasadena, CA
 91109 and Institute of Northern Forestry, Fairbanks, AK, 99701.  In
 1988, NASA's Jet Propulsion Laboratory and the Institute of Northern
 Forestry began a long-term joint project studying seasonal change in
 the floodplain forests of the Bonanza Creek Experimental Forest LTER
 site as observed by imaging radar. The project includes the analysis
 of both airborne multifrequency polarmetric radar acquired with
 NASA's AIRSAR, and spaceborne multitemporal radar acquired with the
 European Remote Sensing Satellite (ERS-1). The goal of the study is
 to determine the diurnal (water potential), seasonal (freeze/thaw,
 leaf on/off and flooding), and long term (biomass and forest type)
 properties of the floodplain forests which can be derived from radar
 data. Airborne data have been collected in the winter, spring and
 summer months. Freeze/thaw, flooding, leaf on and diurnal water
 potential changes have been captured in this data set. ERS-1 data
 have been collected on 3-7 day intervals since July 1991 and will
 continue indefinitely with the follow-on launches of ERS-2 and ASAR
 (an advanced version of ERS-1). Freeze/thaw transitions have been
 observed in this data set. Meteorological data from the LTER stations
 have been used to interpret the radar backscatter signatures using
 microwave models. One algorithm for freeze/thaw state has been
 applied to regional ERS-1 transects across Alaska; these transects
 intersect both the Bonanza Creek and the Toolik Lake LTER sites. The
 transects show freezing with time, latitude and elevation. Multi-year
 transects are currently being developed to improve our understanding
 of the effects of changes in growing season length on the annual
 carbon flux in Alaskan boreal forests.  Weber, Everett P. and Frank
 P. Day. MINIRHIZOTRON USE AT THE VCR-LTER SITE: FINE ROOT DENSITY ,
 GROWTH , AND PHENOLOGY ON BARRIER ISLANDS . Old Dominion University,
 Norfolk, VA 23529. VCR.  Little work has been done on the phenology
 of root growth and senescence largely due to methodological
 difficulties. The application of minirhizotron technology has enabled
 tracking of individual roots through an entire growing season. As a
 result, direct measures of turnover, root growth, and senescence are
 possible. Small plots on a 36 year old dune on Hog Island, a barrier
 island in the Virginia Coast Reserve Long Term Ecological Research
 Site, were fertilized with nitrogen. Minirhizotron tubes were
 installed in each fertilized and control plot. Each tube was sampled
 monthly for nine months, March through November. Preliminary results
 showed an increase in root density from March to April with
 fertilized plots showing a higher root density than unfertilized
 plots for both March (256% greater) and April (140% greater).  Only
 4% of the roots samples in April were present in the March
 sampling. The minirhizotron method allows a high resolution
 perspective of the belowground environment and direct monitoring of
 phenomena which previously were obtainable only through indirect
 measures.

Webster, Katherine, Carl Bowser, Tim Kratz, and John Magnuson.
 CHEMICAL SIGNALS RELATED TO CLIMATE IN LAKES SITUATED ACROSS A
 LANDSCAPE DEFINED BY GROUNDWATER - SURFACE WATER INTERACTIONS.
 Center for Limnology, University of Wisconsin, Madison, WI 53706.
 NTL.  An important feature of the NTL LTER lakes is their
 distribution along a gradient structured by the strength of their
 interaction with the local groundwater system.  Because groundwater
 discharge to these lakes is a primary source of several major ions,
 we expect that climatic fluctuations operating within the temporal
 scale of a given lake's water residence time, can alter ion
 concentrations.  Furthermore, we predict that the magnitude of
 signals in major ion chemistry driven by climatic fluctuations will
 be related to landscape position.  The hydrologic budgets of lakes
 higher in the landscape are increasingly dominated by precipitation
 relative to groundwater.  Thus, they should be more responsive to
 altered groundwater flow patterns caused by shifts in climatic
 variables.  A severe drought period (1987-89) which occurred midway
 through the data record available for the NTL lake set (1981-92),
 provides us with an opportunity to examine this prediction.  Previous
 work,Acker, S.A., M.E. Harmon, T.A. Spies and A. McKee.  SPATIAL
 PATTERNS OF MORTALITY IN AN Abies Procera-Pseudostuga menziesii
 STAND. Department of Forest Science, Oregon State Univ., Corvallis,
 OR. 97331-7501, and Pacific Northwest Research Station, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  Spatial patterns may help
 explain causes and effects of tree mortality.  We studied a 1 ha
 old-growth stand in the western Cascade Mountains, OR, from 1977 to
 1988.  Basal area was mostly Abies procera; most stems were
 A. amabilis.  These two species dominated mortality.  Dying
 A. amabilis were mostly small and often suppressed or damaged by
 falling limbs or trees.  Dying A. procera ranged in size and were
 often attacked by pathogens.  These facts suggested a positive
 spatial association of dying A. amabilis and canopy trees, and
 aggregation of dying A. procera.  Using contingency table analysis,
 dying A. amabilis and canopy trees were weakly associated within 2 m
 quadrats.  From variance:mean ratios, both dying and all A. procera
 were aggregated within 20 m quadrats.  A. procera death may help form
 gaps; it is unclear whether aggregation is associated with mortality.
 Adams, Phyllis C.; Leslie A. Viereck. EFFECTS OF SNOW BREAKAGE ON
 SUCCESSIONAL PROCESSES IN INTERIOR ALASKA. University of Alaska
 Fairbanks and USDA Forest Service, Institute of Northern Forestry,
 Fairbanks, AK. 99775. BNZ.  Natural disturbances alter the structure
 and dynamics of boreal forest ecosystems.  Record snowfall in
 interior Alaska during the winter of 1990-1991 caused extensive tree
 breakage, resulting in major reductions in standing biomass.  The
 positions of all individual trees were recorded at 18 50 x 60 m Long
 Term Ecological Research (LTER) plots at the Bonanza Creek
 Experimental Forest.  The condition of each tree, including death and
 height at breakage from heavy snow load was recorded.  Second-order
 spatial statistics were used to examine spatial and mortality
 patterns within the study area.  The greatest loss of biomass due to
 snow occurred in mature white spruce stands.  Continuing monitoring
 will assess the effects of these events on the understory vegetation
 and canopy species composition.  Adams, Phyllis C.; Leslie
 A. Viereck; JoBea Way; Cynthia L. Williams. MONITORING LONG-TERM
 FOREST SUCCESSION WITH SYNTHETIC APERTURE RADAR IN THE TAIGA OF
 INTERIOR ALASKA. University of Alaska Fairbanks, USDA Forest Service,
 Institute of Northern Forestry, Fairbanks, AK 99775, and Jet
 Propulsion Laboratory, Pasadena CA. 91109. BNZ Synthetic aperture
 radar(SAR) has potential for monitoring successional dynamics by
 providing information about biophysical properties of vegetation,
 including biomass, canopy moisture content, canopy geometry, and
 phenology.  At Bonanza Creek Experimental Forest near Fairbanks,
 Alaska, images from aircraft missions in March 1988 and May 1991 have
 clearly demonstrated ability to monitor environmental conditions such
 as snow cover, frozen and thawed ground and vegetation, river ice,
 and flooding with SAR.  We have conducted extensive monitoring of
 structural characteristics and environmental parameters of
 successional stands along the Tanana River as ground truth for ERS-1
 spaceborne and NASA AIRSAR aircraft missions.  Stand density,
 biomass, species composition, and spatial and temporal patterns have
 been analyzed, and will be examined for relationships to radar
 backscatter signatures.  This work contributes to the development and
 calibration of mechanistic ecosystem models which attempt to predict
 ecosystem response to changes.

Aguiar, Martin R. William K. Lauenroth and Debra P. Coffin. INTENSITY
 AND IMPORTANCE OF INTER- AND INTRASPECIFIC COMPETITION BETWEEN C4
 GRASSES. Colorado State University, Fort Collins, CO 80523, USA CPR
 We conducted a field experiment to compare inter- and intraspecific
 competition between two codominant grasses Bouteloua gracilis and
 Buchloe dactyloides. Plants of similar size of both species were
 grown surrounded by either six conspecific plants or six plants of
 the other species. In half of the plants metal tubes were used to
 restrict belowground competition; isolated plants were used to
 investigate conditions of no competition. Biomass accumulation and
 reproductive output were reduced under conditions of inter- and
 intraspecific competition (compared to growing in tubes) for both
 species. But intensity and importance of inter- and intraspecific
 competition were different for both species. Our results suggest that
 competitive interactions explain the relative dominance of these two
 warm season short grasses.  Allison, Taber D., Michael Binford, David
 R. Foster. POST-SETTLEMENT CHANGES IN VEGETATION AND LAND-WATER
 INTERACTIONS IN CENTRAL NEW ENGLAND. Harvard University, Cambridge,
 MA 02138 and Harvard Forest, Petersham, MA 01366.  HFR We address two
 aspects of the impact of European settlement on the New England
 landscape: 1) the magnitude of change from pre-settlement conditions
 resulting from contrasting land-use practices and 2) the extent to
 which the reforested landscape has returned to original conditions in
 terms of forest composition and lake trophic status.  Our study area
 comprises lakes in northern Massachusetts from the Connecticut River
 Valley to the Atlantic Coast.  Sediment cores have been removed from
 several small lake basins and analyzed for physical, biological, and
 chemical characteristics.  Peak settlement activity, as indicated
 from pollen percentages, is associated with sharply increasing bulk
 density values, decreased loss-on-ignition, and increased relative
 inputs of phosphorus.  Principal Components Analysis indicates
 distinct differences between pre- and post-settlement pollen
 assemblages.  Changes in axis scores by sample age indicate that
 post-settlement vegetation is not converging on pre-settlement
 composition, but is becoming increasingly different.  Alternatively,
 regional differences in pre-settlement forest composition have become
 less distinct following forest clearing and subsequent reforestation.

Anderson, Virginia, Iris Anderson and Paul Brooks.  USE OF A
 15N2O-ISOTOPE DILUTION TECHNIQUE FOR THE MEASUREMENT OF LINKED
 NITRIFICATION-DENITRIFICATION IN WETLAND ECOSYSTEMS.  School of
 Marine Science, Virginia Institute of Marine Science, College of
 William and Mary, Gloucester Point, VA 23062 and Department of Soil
 Science, University of California, Berkeley, Berkeley, CA 94720.
 Surface sediments in saltmarsh ecosystems typically contain low
 concentrations of nitrate; therefore, most of the denitrification
 that occurs is dependent upon substrate supplied by
 nitrification. Since acetylene blocks nitrification, use of the
 acetylene blockage technique to measure linked
 nitrification-denitrification is questionable.  We will describe a
 15N2O-isotope dilution technique which we are currently testing for
 the measurement of denitrification in saltmarsh sediments.
 Denitrification rates measured using acetylene block were slightly
 higher than those measured using 15N2O isotope dilution in anaerobic
 slurries of saltmarsh sediments amended with 1 mM nitrate.
 Application of 15N2O-isotope dilution to measurement of in situ
 denitrification in saltmarsh sediments requires application of a
 first-order kinetic model.  Baron, Jill, Dennis S. Ojima, Elisabeth
 A. Holland, and William J. Parton. SOURCES AND SINKS OF N SPECIES IN
 HIGH ELEVATION ROCKY MOUNTAIN ECOSYSTEMS. Natural Resource Ecology
 Laboratory, Colorado State University, Fort Collins CO 80523,
 National Park Service Water Resources Division, and National Center
 for Atmospheric Research, Boulder CO 80307. CPR and NWT.  We are
 exploring processes that affect nitrogen cycling in the Loch Vale
 Watershed by combining biogeochemical data from the past 9 years with
 the CENTURY ecosystem process model. With current N deposition, soil
 carbon content decreased at a rate of 2.6 g C m-2 with time; N
 leaching from the forest floor was steady over time at an annual rate
 of 0.1 g N m-2. This corresponds to measured leaching rates and low N
 accrual due to the maturity of the forest and the severe climate at
 3100 m. Forest response under greater N deposition was an initial
 retention of soil carbon, followed by similar rates of loss of C as
 above. Nitrogen loss was greatly accelerated, and N yield
 approximated deposition at the end of 100 years. Further model
 experiments are planned with lower N deposition rates corresponding
 to pre-urban emissions in an attempt to define the inflection point
 at which terrestrial processes were no longer N- limited. Output from
 both the tundra and forest models will be aerially weighted to
 develop a watershed-scale picture of nitrogen dynamics.

Benning, T.L.* and T.R. Seastedt.  PATTERNS AND CONTROLS OF ROOT
 DYNAMICS IN TALLGRASS PRAIRIE.  Department of Environmental,
 Organismic and Population Biology and Institute of Arctic and Alpine
 Research, University of Colorado Boulder, CO 80309-0450 * Present
 address: Department of Biological Sciences, Stanford University Palo
 Alto, CA 94305. NWT.  Root cores and root windows were used to study
 the influence of fire, mowing and nitrogen availability on root
 lengths, biomass, and nitrogen content in tallgrass prairie near
 Manhattan, Kansas.  Four years of 10 g/m2/yr of nitrogen additions
 increased belowground plant mass by about 15%, from 1255 g/m2 to 1450
 g/m2 (p<.001). Living roots and rhizomes in nitrogen addition plots
 increased in nitrogen concentration by an average of 77%; dead roots
 and rhizomes increased in nitrogen concentration by an average of
 38%. Dead roots and rhizomes were capable of immobilizing 3 to 3.5
 g.m-2 of nitrogen; live roots and rhizomes increased from 1.5 to 5
 g.m-2 of nitrogen, depending upon treatment.  Plots on annually
 burned prairie were able to sequester substantially more nitrogen
 than plots from unburned sites; however, the nitrogen immobilization
 potential of microbes on dead roots and rhizomes appeared equal
 across treatments. Patterns of root appearance and disappearance were
 highly variable from one year to the next and were only marginally
 controlled by precipitation.  Annual new root growth was positively
 correlated with peak foliage biomass (r = 0.75, n=8, p =0.03), while
 average root length was marginally negatively correlated with peak
 foliage biomass (r=-0.65, n=8, p=.08). Average root lengths exhibited
 less year-to-year variation than average annual peak foliage biomass
 for the four year study. Root window observations indicated that
 mowing initially decreased then increased the turnover rates of
 roots; root cores indicated that live root mass in the top 20 cm of
 soil was increased by four years of annual mowing.  Benson, Barbara
 and Thomas Frost.  DETECTION OF EFFECTS OF EXPERIMENTAL ACIDIFICATION
 ON ZOOPLANKTON COMMUNITY STRUCTURE.  University of Wisconsin-Madison,
 Madison, WI 573706. NTL.  Little Rock Lake in northern Wisconsin has
 been the site of a whole-lake acidification experiment.  The effects
 of acidification on the zooplankton community were initially assessed
 by examining the response of individual species.  Here we employ
 ordination methods to expand the assessment to community level
 analysis.  The lake was divided into a reference basin and a
 treatment basin which was systematically acidified from pH 6.1 to 4.7
 in two year stages over the period 1985-1990.  Principal components
 analysis was performed on zooplankton biomass data from both the
 reference and treatment basins.  The trajectory of the zooplankton
 community in the treatment basin diverged from that of the reference
 basin community following acidification.  The degree of this
 divergence increased with the intensity of the acidification.
 Comparison with two LTER lakes in the region using principal
 components analysis showed the trajectory for the treatment basin was
 originally similar to the LTER reference lake with a pH near 6.0.
 With acidification, the treatment-basin trajectory approached that of
 the second LTER reference lake, an acid bog lake. Thus, experimental
 acidification produces a zooplankton community similar to naturally
 acid systems within the region.

Blair, John, Jack Shaw, and Charles Rice. SPATIAL AND TEMPORAL
 PATTERN'S OF SOIL N AVAILABILITY AND PLANT UPTAKE ALONG TOPOEDAPHIC
 GRADIENTS IN TALLGRASS PRAIRIE. Kansas State University, Manhattan,
 KS 66506.KNZ.  Pronounced landscape-level variation exists at Konza
 Prairie with respect to topographic position and edaphic factors,
 which can significantly affect seasonal and long-term soil-plant
 nutrient relationships. Previous studies at Konza have demonstrated
 that topoedaphic position influences plant ecophysiological responses
 and net primary production. However data on soil N dynamics along
 these topoedaphic gradients are lacking. In 1993 we initiated a study
 of soil N dynamics in relation to patterns of plant N uptake along
 topoedaphic gradients across watersheds being intensively studied as
 part of the Konza LTER program.  Sampling inn the first year was
 directed at quantifying (1) patterns of soil N availability at
 upland, lowland and mid-slope sites on watersheds with different fire
 frequencies (annual burn and 20 year burn regimes) and (2) net
 primary production, including seasonal patterns of N accumulation and
 plant N use efficiency at these sites. We also measured potentially
 mineralizable N pools at the beginning of the summer and microbial
 biomass N on selected sample dates. Results to date indicate a strong
 early season relationship between topographic position and soil
 inorganic N on the annually burned watershed only, with highest
 concentrations occurring at lowland sites. Differences in inorganic N
 between upland and lowland sites were attenuated by early summer. The
 relationship of soil N pools to plant uptake during the growing
 season will be presented.

Blum, Linda and Robert Christian. BELOWGROUND MARSH GRASS PRODUCTION
 AND DECAY ALONG A TIDAL/ELEVATIONAL GRADIENT. Univ. Virginia,
 Charlottesville, VA 22903 and East Carolina Univ., Greenville, NC
 27858. VCR.  Organic matter accumulation in marsh sediments is
 dependent on the balance between production and decay of belowground
 materials which in turn are dependent on the plant species and the
 sediment properties. We used a litter bag technique to compare root
 and rhizome decay of Spartina alterniflora and Juncus roemerianus
 along a transect including a creekside (intermediate height-form
 S. alterniflora), a mid-marsh (short height-form S. alterniflora),
 and a high-marsh (J. roemerianus) location.  Root and rhizome
 production was estimated from measures of root growth into the litter
 bags at each location. Sediment chemical properties at these marsh
 locations were different: mid-marsh pore water salinities, sulfide
 concentrations, and ammonium concentrations were consistently greater
 than those of the creekside and high marsh locations, while the
 creekside location had consistently greater pore water concentrations
 of phosphate. Little difference in weight loss was observed between
 the mid-marsh and highmarsh locations (69% and 71% ash-free
 dry-weight remaining after 1 yr. respectively), but weight loss at
 the creekside location may be more rapid (59% AFDW remaining after 1
 yr.) than at the 2 interior locations. Decay constants (mean k for
 all locations = -0.00178 d-1 and -0.00118 d-1; J. roemerianus and
 S. alterniflora. respectively) were calculated using an exponential
 model for both types of plant material and were significantly
 different (Student's t = 3.13, p = 0.001395, a = 0.05). The greater k
 for J. roemerianus is consistent with the difference in the starting
 C/N ratios for the 2 plant materials (37:1 and 47:1; J. roemerianus
 and S. alterniflora, respectively) . Measures of root production were
 highly variable, especially for the creekside and high marsh
 locations where the total amount of live roots in the litter bags did
 not exceed 0.05 AFDW. Root growth was much greater and less variable
 at the mid-marsh location (0.10 - 0.13 g AFDW per bag) than near the
 creek or in the high marsh. For all locations, live roots were found
 in the litter bags within 120 days (early June) after burial in the
 marsh. These data support the hypothesis that the type of plant and
 its ability to produce roots are responsible for differences in
 biogenic accretion in salt marsh sediments.

Boose, Emery R., David R. Foster, and Marcheterre Fluet.  MODELING
 LANDSCAPE-LEVEL HURRICANE DISTURBANCE IN PUERTO RICO AND NEW ENGLAND.
 Harvard Forest, Harvard University, Petersham, MA 01366.  HFR.
 Hurricanes represent an important natural disturbance process in
 tropical and temperate forests in many coastal areas of the world.
 The complex patterns of damage created in forests by hurricane winds
 result from the interaction of meteorological, physiographic, and
 biotic factors on a range of spatial scales. We have developed the
 following approach to study landscape to regional level impacts on
 forests: (1) A simple meteorological model reconstructs wind
 conditions at specific sites and regional gradients in wind speed and
 direction during a hurricane. (2) A simple topographic exposure model
 estimates landscape-level exposure to the strongest winds. (3) Actual
 forest damage is assessed through remote sensing, archival records,
 and field measurements.  We are using this approach to study
 long-term hurricane disturbance regimes at two LTER sites: Luquillo
 and Harvard Forest.  Work to date has focused on Hurricane Hugo
 (1989) and the 1938 New England Hurricane.  For both storms patterns
 of damage on a regional scale were found to agree with the predicted
 distribution of peak wind gust velocities.  On a landscape scale
 there was good agreement between patterns of forest damage and
 predicted exposure to the strongest winds.  At the Harvard Forest the
 average orientation of windthrown trees was close to the predicted
 peak wind direction, while at Luquillo there was reasonable
 agreement, with some apparent modification of wind direction by the
 mountainous terrain.

Boring, L.R., E.R. Blood, S.W. Golladay, L.K. Kirkman, W.K. Michener,
 R.J. Mitchell, and B.J. Palik.  ICHAUWAY AND THE JONES ECOLOGICAL
 RESEARCH CENTER - NEW PROGRAMS AND ECOSYSTEMS OF THE S.E. COASTAL
 PLAIN.  Jones Ecological Research Center, Rt. 2, Box 2324, Newton GA
 31770.  This new center and the Ichauway site are dedicated to the
 development of research, education and conservation programs that
 couple ecological disciplines with the management of natural
 resources, especially of forest, wetland and riverine ecosystems.
 Core funding is provided by the Robert W. Woodruff Foundation.  The
 staff are conducting both short and long-term research using
 reference and disturbed landscapes.  Initial research projects
 include fire ecology of longleaf pine forests and species, forest
 nitrogen cycling processes, patch disturbances and mortality in
 longleaf forests, forest fragmentation effects upon native and
 invasive species, vegetation and hydrologic dynamics of non-alluvial
 wetlands, coarse woody debris in forest and riverine systems, surface
 and groundwater linkages, and biogeochemical studies of stream and
 river systems.  Initial studies will direct future long-term research
 objectives as well as those addressing management of forest, wetland
 and riverine ecosystems.  Ichauway is a 11,300 ha reserve located in
 the SE coastal plain of SW GA.  It includes 4,800 ha of longleaf
 pine/wiregrass, 800 ha of wetlands and 42 km of rivers.  It will be
 managed as a biosphere reserve model for numerous research, education
 and conservation objectives.

Bowden, William B.; Jacques C. Finlay, Patricia E. Maloney; and John
 S. Terninko.  CONTROLS ON THE DISTRIBUTION AND PRODUCTION OF
 BRYOPHYTES IN CONTROL AND LONG-TERM, P-FERTILIZED REACHES OF AN
 ARCTIC TUNDRA RIVER (ALASKA).  Department of Natural Resources,
 University of New Hampshire, Durham, NH, 03824.  ARC.  Each year
 since 1983, H3PO4 has been added continuously during the ice-free
 season to a P-limited tundra stream (Kuparuk River, North Slope,
 Alaska).  In 1990, seven years after the fertilization began, we
 noted extensive coverage by bryophytes within the fertilized reach of
 the river, where very few had been noted previously.  Surveys of
 macroalgal and bryophyte cover in 1991, 1992, and 1993 showed that
 the moss Schistidium (Grimmia) agassizii was distributed similarly in
 both control and fertilized reaches of the river.  In contrast, two
 species of Hygrohypnum (H. alpestre [Hedw.] Loeske and H. ochraceum
 [Turn.] Loeske) were found primarily in the fertilized reach, within
 riffles, where peak areal biomass approached 800 g dry matter/m2.  A
 fourth bryophyte species (Fontinalis neomexicana) was also
 distributed primarily in the fertilized reach, also in riffles, but
 was less abundant than the Hygrohypnum species.  These species were
 essentially absent from fertilized pools.  Clumps of Hygrohypnum
 spp. lost weight over 30 d in control riffle environments but
 accumulated 181+44% of their initial mass in fertilized riffles.
 F. neomexicana accumulated 38+39 and 98+47% of initial biomass in
 unfertilized and fertilized riffles.  Epiphytic and detrital mass
 accumulation on artificial mosses (unbraided hemp rope) averaged
 about 4 to 4.5 times greater in slow-flowing pool environments than
 in fast-flowing riffle environments.  These data suggest that both
 Hygrohypnum spp. and F. neomexicana are capable of growth throughout
 the river, but are limited first by nutrients (P) and are smothered
 by epiphytic growth in fertilized pools.  Analysis of total N and P
 in the tissues of the Hygrohypnum spp. and estimates of average
 coverage (~15%) and biomass (~150 g dry weight/m2) over an 8k
 fertilized reach, suggest that these species alone may remove 2/3 of
 the P added in the fertilizer experiment.  As a group, the bryophyte
 community in this stream is now likely to be the dominant sink for P
 in the fertilized reach. Furthermore, the mosses appear to have
 profound effects on the stream community structure and function,
 aspects of which are currently under investigation.

Bowman, William D., Theresa A. Theodose, James C. Schardt, and Richard
 Conant. CONSTRAINTS OF NUTRIENT AVAILABILITY ON PRIMARY PRODUCTION IN
 TWO ALPINE TUNDRA COMMUNITIES. Environmental, Population, and
 Organismic Biology, Campus Box 334, and Institute of Arctic and
 Alpine Research, Campus Box 450, University of Colorado, Boulder CO
 80309. NWT.  A nutrient amendment experiment (N, P, and N+P) was
 conducted for two growing seasons in two alpine tundra communities,
 dry and wet meadows,to determine if primary production is limited by
 nutrient availability, and whether physiological and developmental
 constraints act to limit the responses of plants from a nutrient poor
 community more than plants from a more nutrient rich
 community. Photosynthetic, nutrient uptake, and growth responses of
 the dominants in the two communities showed little difference in the
 relative capacity of these plants to respond to the nutrient
 additions. Aboveground production responses of the communities
 indicated N was limiting to production in the dry meadow community
 while N and P co-limited production in the wet meadow
 community. There was a greater production response to the N and N+P
 amendments in the dry meadow relative to the wet meadow, despite
 equivalent functional responses of the dominant species of both
 communities. The greater production response in the dry meadow was in
 part related to changes in community structure, with an increase in
 the proportion of graminoid and forb biomass, and a decrease in the
 proportion of community biomass made up by the dominant sedge
 Kobresia myosuroides. Species richness increased significantly in
 response to the N+P treatment in the dry meadow. Graminoids increased
 significantly in biomass in the wet meadow N and N+P plots, while
 forb biomass decreased significantly, suggesting a competitive
 interaction for light. Thus the difference in community response to
 nutrient amendments was not the result of functional changes at the
 leaf level of the dominant species, but rather was related to changes
 in community structure in the dry meadow, and to a shift from a
 nutrient to a light limitation of production in the wet meadow.
 Bowser, Carl J.  LAKE-GROUNDWATER INTERACTION STUDIES BASED ON
 ISOTOPIC AND MAJOR ION CHEMICAL TECHNIQUES, Univ Wisconsin, Madison,
 WI 53706. NTL Mass fluxes of water and associated solutes to and from
 lakes at NTL is significant.  Quantification of these fluxes is
 critical for understanding the variance of chemical and
 biogeochemical parameters in lakes, for understanding the role of
 lakes in carbon dioxide budgets of the lake-land system, and
 estimates of the influence of landscape position on lake chemistry
 and dynamics.  Stable isotopes of hydrogen and oxygen provide a means
 to estimate groundwater fluxes to lakes.  Results from the NTL site
 for 20 lakes indicates groundwater provides up to 26 percent of the
 total water to lakes (Range 2-26 %, mean 11.3 %).  Solute loading by
 groundwater (mass flux times concentration) ranges from 50% to nearly
 100 % of the total lake load, reflective of the "leverage" that
 groundwaters exert on the chemistry of lakes compared to other
 possible water inputs (e.g. runoff, precipitation).  Combined mass
 balance equations for isotopes and solutes provides a means to
 estimate the average groundwater composition of waters entering the
 lakes. Both calcium and magnesium exhibit conservative behavior in
 lakes.  Uptake by diatoms is the main loss mechanism for silica, and
 the isotope/solute budgets allow estimation of total lake silica
 loading and therefore estimates of the ratio between internally
 cycled and externally loaded silica.  Potassium loading to lakes
 exceeds the amount estimated from groundwater fluxes, and is
 interpreted as due to leaf litterfall from the forest canopy
 surrounding the lakes.  These studies allow estimates of carbon
 loading to lakes (alkalinity, aqueous CO2, and dissolved organic
 carbon) via groundwater and leaf litterfall.  The results integrate
 with lake P-CO2 studies (Kratz and Bowser) to provide insights into
 the relative roles of lake and terrestrial carbon fixation Briggs,
 John M. and Alan K. Knapp.  LONG TERM PATTERNS OF ABOVEGROUND
 PRODUCTION IN TALLGRASS PRAIRIE: ROLE OF SOIL MOISTURE. Kansas State
 University, Manhattan, KS 66506. KNZ Aboveground biomass production
 at the Konza Prairie Research Natural Area has varied from 645 g/m2
 to 202 g/m2 over the past 19 years. In years with adequate rainfall
 (i.e., 80% of mean growing season precipitation), spring fire
 increased aboveground production relative to unburned sites (17 year
 mean of burned sites = 482 g/m2 (SE=24); unburned sites = 386 g/m2
 (SE=24)). However, contrary to most other grasslands, no single
 meteorological variable (total precipitation, growing season
 precipitation, pan water evaporation, etc.) explains this variance in
 biomass. We have found that dormant season (October to March) soil
 moisture may be critical for determining biomass on annually burned
 sites. On unburned sites, biomass is less sensitive to variation in
 soil moisture and it appears that forbs respond differently to soil
 moisture than do grasses. These results can be partially explained by
 recognizing the nonequilibrium nature of resource availability in
 this system.  Brokaw, N., B. L. Haines, D. J. Lodge,
 L. R. Walker. SEEDING ECOLOGY AFTER A HURRICANE IN A PUERTO RICAN
 FOREST. Manomet Bird Observatory, Manomet, MA 02345, Univ. of
 Georgia, Athens, GA 30602, Forest Products Laboratory, Rio Piedras,
 PR 00928-2500, Univ. of Nevada, Las Vegas, NV 89154-4004. LUQ.  After
 a hurricane in a Puerto Rican forest we studied seedling dynamics and
 environmental factors for 2.5 yr.  For all species combined, seedling
 numbers were positively correlated with cover of leaf litter,
 disturbance, and canopy openness.  Total seedling densities increased
 over the period, then declined.  Pioneers seedling densities
 increased rapidly soon after the hurricane, then steeply declined,
 while some shade tolerant dominants increased gradually over the
 period.  But some species showed no definite pattern and every
 species reacted individualistically. Disturbance has both immediate
 effects on seedling numbers of some species, e.g., by enhancing seed
 germination, and delayed effects, e.g., by enhancing seed production.
 Brooks, Paul D., Mark W. Williams, and Steven K. Schmidt. PRELIMINARY
 INFORMATION ON WINTER/SPRING NITROGEN CYCLING IN THE COLORADO
 ALPINE. Environmental, Population, and Organismic Biology, Campus Box
 334, Department of Geography, Campus Box 260, and the Institute of
 Arctic and Alpine Research, Campus Box 450, University of Colorado,
 Boulder CO 80309. NWT.  Inputs, outputs, and fluxes of nitrogen were
 followed from October 1992 through June 1993 at Niwot Ridge in the
 Colorado Front Range. Concentrations of soil inorganic nitrogen, snow
 inorganic nitrogen, and microbial biomass nitrogen were measured
 monthly from January to March, biweekly through April, and weekly
 until the first of June. Temporal variability in nitrogen inputs from
 precipitation to tundra soils were estimated from ion exchange resins
 harvested in mid winter and at the end of the snow covered
 season. Nitrogen outputs from the system through leaching were
 estimated using ion exchange resins at a depth of 10 cm. Gaseous
 losses as N2O were measured at two sites on the tundra and one just
 below treeline. Soil inorganic nitrogen concentrations were highest
 in January when tundra soils were completely frozen. Concentrations
 decreased rapidly as soils under the snowpack warmed above -5 degrees
 C. As snow depth decreased in the spring, concentrations again
 increased presumably due to freeze/thaw cycles. Significant
 concentrations of CO2 under the snowpack, suggesting microbial
 activity, were first observed in early March. Nitrous oxide
 production under snow was first observed in April, corresponding to
 soil temperatures above -3 degrees C. These data suggest that the
 insulating effect of snow cover during the long alpine winter may
 allow soil microbial activity during this season to significantly
 affect the N cycle in these systems.

Caine, Nel, John C. Iott, and Brian P. Menounos. SPATIAL PATTERNS OF
 SUMMER PRECIPITATION IN AN ALPINE ENVIRONMENT. Department of
 Geography, Campus Box 260, and Institute of Arctic and Alpine
 Research, Campus Box 450, University of Colorado, Boulder CO
 80309. NWT.  In 1992 and 1993, summer precipitation was being
 measured by a network of 35 storage raingauges in a 550 m grid over
 the Green Lakes Valley. In the summer months of 1992, precipitation
 totalled about 250 mm in the basin and showed little spatial pattern
 and no elevational effects. When totals for June, July, and August
 are treated separately, weak spatial patterns reflecting north-south
 contrasts rather than elevational influences are
 evident. Predictably, individual storms yielding more than 8 mm of
 precipitation are more variable in space. Correlations of storm
 totals with elevation are usually significant but inconsistent in
 sign. Semivariograms of storm depths suggest a range of 2.5 to 3.0 km
 and are improved when the drift due to elevation is removed from the
 original data. This suggests that areal mean precipitation amounts in
 summer may be empirically estimated by a model equivalent to that
 defined by Chua and Bras (1982) for winter storms in the San Juan
 Mountains.  Caldwell, Bruce A., Robert P. Griffiths, John E. Baham,
 Michael A. Castellano and Kermit Cromack, Jr.  ENZYME ACTIVITIES IN
 ECTOMYCORRHIZAL MAT COMMUNITIES.  Departments of Forest Science and
 Crops and Soil Science, Oregon State Univ. and USDA Forest Service,
 Corvallis, OR 97331.  AND.  'Direct cycling' from detritus by
 ectomycorrhizal fungi may be a significant path of nitrogen and
 phosphorus to host trees.  Distinct ectomycorrhizal rhizomorph and
 hyphal mats have been found in the forest floor and upper mineral
 soils of conifer and mixed hardwood forests at the H.J. Andrews
 Experimental Forest, Bonanza Creek Experimental Forest and Coweeta
 Hydrological Laboratory.  Depending on the fungal species, levels of
 phosphatase, peroxidase, proteinase, (beta)-1-3 glucanase, cellulase
 and/or xylanase were significantly higher in the ectomycorrhizal mat
 than in adjacent soil or litter without obvious mat development.
 Where pure cultures of the causal fungi could be isolated, we have
 confirmed production of the enzyme(s) responsible for the hydrolytic
 activities observed in the mats.  Cammack, Shannon E., and Bruce
 Haines.  SEEDLING RECRUITMENT AND GROWTH ON HURRICANE-DISTURBED
 PLOTS: THE ROLE OF LIGHT, WATER, AND NUTRIENTS University of Georgia,
 Athens, GA 30602-7271. LUQ.  Seedling growth of 64 species was
 examined in 60 plots on a 9 ha grid in a Dacryodes excelsa
 (Tabonuco)-dominated rain forest damaged by Hurricane Hugo in
 1989. The relationship between height growth and environmental
 parameters was evaluated. Parameters included 1) light, estimated as
 canopy openness with hemispherical photography, 2) nutrients,
 estimated as NH4 standing stocks and mineralization rates determined
 from in situ incubations and 2 N KCL extractions, and 3) soil water
 content, estimated by time domain reflectometry. R-square values and
 stepwise regressions were calculated for plant growth and
 environmental variables for all species combined and for 13
 individual species. R-square values ranged from 0.0005 to 0.46. While
 significant regressions were found for each of the environmental
 variables, species differed in their requirements for light,
 nutrients, and water.  Cavigelli, Michel A. and G. Philip
 Robertson. THE FUNCTIONAL SIGNIFICANCE OF DENITRIFIER POPULATION
 DIVERSITY TO NITROUS OXIDE PRODUCTION IN TERRESTRIAL
 ECOSYSTEMS. Center for Microbial Ecology, W.K. Kellogg Biological
 Station and Department of Crop and Soil Sciences, Michigan State
 University, Hickory Corners MI 49060. KBS.  Controls on in situ N2O
 production by denitrifying microorganisms are very poorly understood
 in most ecosystems, and the global N2O budget is far from
 balanced. Environmental factors that affect N2O fluxes are
 well-studied, but are poor predictors of measured rates, which
 exhibit high and unexplained temporal and spatial variability. An
 untested contributor to systematic variation in N2O production is
 denitrifier population diversity. Pure culture studies show that
 disparate denitrifier populations can express significantly different
 rates of N2O production when grown under identical conditions and at
 low (0.5-2.5%) O2 concentrations. We have initiated a project to test
 whether denitrifier population diversity is important to rates of N2O
 production in soils at the Kellogg Biological Station and the Central
 Plains Experimental Range LTER sites. We will sample soils that
 differ widely in long-term C stores, NO3- availability, pH, and
 water-filled pore space -- factors that affect N2O flux rates and
 should select for disparate denitrifying populations. We have
 designed a soil slurry incubation technique to characterize the
 potential N2O production of whole soil denitrifier communities that
 should also allow us to distinguish among soils that have
 functionally distinct denitrifying communities. We will also isolate
 denitrifiers and reintroduce them to sterilized soils in order to
 evaluate each population's contributions to overall rates of N2O
 production.

Christian, Robert, Mark Brinson and Linda Blum.  BELOWGROUND DYNAMICS
 IN A SALT MARSH AS DETERMINED BY DIFFERENT METHODS.  East Carolina
 Univ., Greenville, NC 27858 and Univ. Virginia, Charlottesville, VA
 22903. VCR.  In higher elevations of salt marshes, accretion is
 largely biogenic.  It results from production of belowground organic
 matter in excess of its decomposition.  We evaluated belowground
 organic matter dynamics at the VCR/LTER site by two methods.  In the
 first, plots were clipped of aboveground plant biomass; roots and
 rhizomes were pruned around the peripheries; and the plots were
 enclosed to restrict belowground lateral growth into them.  With
 continued attention, new primary production was largely prevented
 within the plots for a period of 2 y.  For the second method we
 inserted litter bags of roots and rhizomes into the soil within the
 root zone and followed the loss of organic matter.  Whereas little to
 no discernible decomposition was found for the clipped, pruned and
 enclosed plots during 2 y; biomass in litter bags decreased by 30 to
 50% over 1 y.  Much of the loss in the litter bags occurred during
 the first 120 d. The difference between results from the two studies
 can be reconciled if the vast majority of belowground organic matter
 is old, nonliving and recalcitrant and/or if the removal of new
 production restricts the decomposition of the organic matter present.

Cisneros, Rigel O. THE DETECTION OF CRYPTIC INVASIONS AND LOCAL
 EXTINCTIONS OF FISHES USING LONG-TERM DATASETS. Center for Limnology,
 University of Wisconsin-Madison, Madison, WI 53706. NTL.  Cryptic
 invasions and extinctions are dynamic biological processes that
 determine local range expansions and contractions of fish species
 found in a lake district. The occurrence of these processes is
 usually unnoticed and poorly studied. This work proposed and tested
 the use of four criteria found in four kinds of information available
 in long-term fish datasets. Presence-absence, abundance, size range
 and dispersion were the criteria used as trend indicators for
 invasion or extinction. Presence-absence information (criterion 1)
 was transformed into plots that evaluate persistence after appearance
 for invasion and persistence until disappearance for
 extinction. Abundance (crtn. 2), size range (crtn. 3) and dispersion
 (crtn. 4) were correlated against time to identify positive trends in
 case of invasion or negative trends in case of extinction. A simple
 score system was applied to categorize trends with different
 probability of significance.  Cryptic invasion evidence was found for
 the bluegill in Crystal Lake and burbot in Big Muskellunge
 Lake. Local extinction evidence was obtained for Iowa darter in Big
 Muskellunge Lake and blacknose shiner in Trout Lake.  An exotic
 invader, the rainbow smelt, was obtained for Iowa darter in Big
 Muskellunge Lake.  Lack of consistency in strong evidence across all
 criteria seems to be a pattern typical of cryptic invasions. Strong
 evidence from extinction trends in criteria 2 to 4 suggested a number
 of potential future extinctions. The low frequency of cryptic
 invasions and local extinctions were independent of lake area and
 corresponded to a previously reported percentage of species turnover
 in the lakes studied.  Clein, Joy S. and Joshua P. Schimel.
 MINERALIZATION AND NITRIFICATION DURING THE TRANSITION FROM ALDER TO
 POPLAR IN THE ALASKAN TAIGA. University of Alaska Fairbanks,
 Fairbanks AK 99775. BNZ Primary succession on the Tanana river
 floodplains progresses from alder, with an open nitrogen cycle and
 rapid nitrification, to poplar, with a closed cycle and little
 nitrification. To determine the mechanism(s) controlling this shift,
 we transplanted soils between alder and poplar sites with controls
 held in their home site. Mineralization rates and nitrification
 potential were measured before placement in the field, after 1 month
 and over the following growing season. The nitrification potential of
 the transplanted alder soil was lower than its control, while that of
 the transplanted poplar soil was higher than its control. This
 pattern parallels the pattern of NO3- concentrations in the
 field. Lab incubations show similar respiration rates, but the ratio
 of C to N mineralized in poplar was much greater than in alder (40
 vs. 20) suggesting that microbes in the poplar soil were
 N-limited. Our results suggest that the decrease in nitrification as
 poplar becomes dominant is due to changes in C and N availability
 rather than any specific chemical effects.

Cleveland, Cory C., Elisabeth A. Holland, and Jason
 C. Neff. TEMPERATURE REGULATION OF SOIL RESPIRATION IN AN ALPINE
 TUNDRA ECOSYSTEM. Atmospheric Chemistry Division, National Center for
 Atmospheric Research, Boulder CO 80307 and Environmental, Population
 and Organismic Biology, Campus Box 0334, University of Colorado,
 Boulder CO 80309-0334. NWT Climate is an important force regulating
 microbial activity and decomposition in soils. Significant increases
 in temperature, like those which are predicted in many global warming
 scenarios, will increase CO2 release (respiration) from
 soils. Because a large proportion of terrestrial carbon is stored in
 arctic and alpine soils, it is important to understand how
 temperature influences soil respiration fluxes from these soils. The
 purpose of this study was to measure the effect of temperature on
 soil respiration in an alpine tundra ecosystem. We collected surface
 soil samples from a range of plant communities at Niwot Ridge
 including wet meadow, moist meadow, dry meadow, and fellfield
 communities. Soil moistures were amended to field capacity and soils
 were incubated at 5, 10, 15, 25 and 35 degrees C. CO2 evolution
 resulting from soil respiration was measured on day 1, and days 3 and
 6 of the incubation. At all sites, CO2 production increased to a
 maximum at 35 degrees C. For all soils averaged, rates of respiration
 tended to be highest on day one, with a gradual decline over
 time. Calculated Q10 values were higher than Q10s for tropical and
 temperature ecosystems.

Collins, Harold P., Michael J. Klug, Helen J. Garchow and Janene
 Bohan. CHANGES IN THE STRUCTURE AND FUNCTION OF SOIL MICROBIAL
 COMMUNITIES ASSOCIATED WITH THE INTENSITY AND FREQUENCY OF
 DISTURBANCE.  W.K. Kellogg Biological Station, Michigan State Univ.,
 Hickory Corners, MI 49060 Soil disturbances resulting from
 agricultural practices are known to affect the size of microbial
 populations and their activities.  The intensity and frequency of
 disturbance may also determine the structure and function of the
 active soil community.  Soil can be described by a wide variety of
 physical, chemical, and biological characteristics.  Although
 individual analyses are easily done, few attempts have been made to
 link soil microbial community structure to function.  Long-term
 cropping and native successional treatments, located on the LTER at
 the W.K. Kellogg Biological Station, offers a unique opportunity to
 study changes in soil microbial communities resulting from shifts in
 management.  Soil biogeochemical characteristics of a corn-soybean,
 tilled native succession, and never-tilled native succession were
 compared to the C oxidation profiles of whole soil microbial
 communities using the micro-titer plate system of BIOLOG,
 INC. (Hayward, CA).  Multivariate analyses were used to evaluate the
 relationship between microbial community structure and function
 within and among each treatment.  In addition, fatty acid methyl
 ester profiles were determined.  These profiles were used to identify
 differences in soil microbial community structure.

Conn, Christine E. and Frank P. Day. FINE ROOT DECOMPOSITION ON
 BARRIER ISLANDS (THE VCR-LTER SITE). Old Dominion University,
 Norfolk, VA, 23529. VCR.  The interaction between landform age,
 topographic position and environmental regime was used to study
 environmental controls on belowground decomposition rates at the
 VCR-LTER. A transect was selected that passed through a
 chronosequence of 4 dune and swale associations, aged from 6 to 120
 years old. At each site, litter bags containing Spartina patens roots
 were buried. Hydrology, soil redox potential, soil temperature, soil
 pH and soil water salinity were monitored. Notable differences in
 hydrology and soil redox potential were evident between dune and
 swale sites. Mean water table position dropped from younger to older
 sites and was higher in swales (4.8 cm aboveground to 14.7 cm
 belowground) than in dunes (91.2 cm to 116.5 cm belowground). Mean
 soil redox potentials exhibited no differences between dunes (423 to
 573 mV) and were lower in swales (-35 to 239 mV). Older swales had
 higher soil redox potentials. Decomposition of Spartina patens roots
 was greater in dunes (40.8- 57-5 % mass remaining) than in swales
 (74.2-86.3 % mass remaining). Multiple regression analysis
 demonstrated hydrology and soil redox potential were strongly
 correlated with belowground decomposition rates. Nutrient analysis of
 decayed roots indicated that while organic matter accumulated in
 swale sites, more nitrogen and phosphorus were lost, presumably due
 to leaching processes. Hydrologic factors strongly influence
 belowground decay and nutrient dynamics.

Coull, Bruce C. FIELD AND LABORATORY EXPERIMENTS GENERATED BY LONG
 TERM BENTHIC INVERTEBRATE DATA. Univ of South Carolina, Columbia SC
 29208. NIN.  Long-term biological data sets are typically collected,
 analyzed for their periodicities, correlated with some suspected
 forcing function(s), published and forgotten.  Rarely are they used
 to generate testable hypotheses and subsequently, test these
 hypotheses experimentally.  Nineteen years of monthly or fortnightly
 data on meiofaunal abundance and community structure from a mud and a
 sand site in North Inlet (SC) indicate very different seasonal
 patterns, and thus controlling mechanisms, at the two sites.  We have
 conducted many experiments the results of which suggest the mud site
 fauna is biologically controlled but the sand site fauna is more
 physically controlled.  Juvenile fish predation plays an important
 role in regulating the mud assemblage; the fish are unimportant
 regulators in the sand.  In the field the dominant mud copepod (the
 dominant prey of the fish) only reaches 26% of its maximum potential
 adult productivity; model predictions suggest this is due to low
 naupliar survival, most likely due to fish predation.  The
 experiments and the model would not have even been thought of without
 the long-term data sets.  Long-term data sets need to be more fully
 utilized to generate testable hypotheses.

Crawford, Edward R., David W. Martin, Donald R. Young and Frank
 P. Day. GAP DYNAMICS FOR BARRIER ISLAND SHRUB THICKETS (Myrica
 cerifera). Virginia Commonwealth University and Old Dominion
 University. VCR.  Shrub thickets frequently represent an intermediate
 seral stage in the development of maritime forests on barrier
 islands. The purpose of this study was to quantify natural thicket
 gaps to better elucidate barrier island successional processes. The
 study focused on Hog Island, a primary field site of the Virginia
 Coast Reserve, where island accretion patterns have produced a
 chronosequence of soils and Myrica cerifera shrub thickets. Gaps were
 most frequent in the oldest thickets (> 40 years) at the bay side
 edge of the island, with only a few gaps formed in the most
 productive thickets (15-30 years) in the island interior. The sizes
 and causes of gap formation were variable. Although most gaps were
 formed due to shrub senescence and competition with vines, disease
 and weather related disturbances also influenced gap development. An
 analysis of both the soil seed bank and the existing seedlings in the
 thicket understory revealed greater density and diversity in the
 oldest thickets as compared to the productive, mid-island
 thickets. Myrica cerifera may respond (i.e. recover) most quickly to
 gaps that form in the mid-island thickets. In contrast, shrub
 response in older thickets may be limited by competition from vines
 and by rapid seedling establishment from the well developed seed
 bank. Gap formation in barrier island shrub thickets may accelerate
 succession towards a maritime forest.

Crocker, M. Tad, Clifford N. Dahm, and Manuel C. Molles, Jr. PHYSICAL
 AND CHEMICAL PROPERTIES OF AN EPHEMERAL FLOOD IN NEW MEXICO.
 Department of Biology, University of New Mexico, Albuquerque, New
 Mexico, 87131.  SEV.  Water represents both an agent of physical
 disturbance and a critical resource within ephemeral streams in
 semi-arid regions. Riparian plants are removed during periodic floods
 and dense stands of recruits quickly colonize newly disturbed
 streambed surfaces.  Water directly controls ecological processes
 and, as a solvent, indirectly controls the availability of
 nutrients. The ephemeral nature of these brief floods severely limits
 the opportunity to observe and quantify flood and water
 properties. On July 17, 1991, researchers were trapped within the
 Sevilleta LTER Sierra Ladrones Study Basins (SLSB) by an intense
 thunderstorm (32mm/75min).  The most extensive flooding during four
 years of observations ensued.  Remote video imaging systems recorded
 flooding at two sites within the SLSB and these videos will be
 presented.  Storm intensity and flood hydrographs were estimated form
 these video data.  Stream velocity was measured at the leading edge
 of the flood (the bore) and during near peak discharge.  Grab samples
 of stream water were taken for analyses from one location prior to
 the bore (local flow), the bore, 5 min after peak flow, and at very
 low flow.  These samples were divided into four size classes.  Basin
 response time was 5 min at the upstream site (11 ha) and 20 min at
 the downstream site (76 ha).  The bore progressed at 1.2 m/s and
 stream velocity was 2.3 m/s 4 min. after peak discharge.  Water
 properties are summarized in the accompanying presentation.

Currie, William, John Aber, William McDowell and Richard Boone. THE
 ROLES OF DOC AND DON IN FOREST ECOSYSTEM RESPONSE TO CHRONIC NITROGEN
 ADDITIONS.  Complex Systems, Morse Hall, University of New Hampshire,
 Durham, NH 03824.  HFR.  An integrated study of ecosystem response to
 chronic nitrogen additions began in 1988 at Harvard Forest with N
 amendments to two forest stands. One of the driving questions behind
 many of the studies under way in the Chronic N experiment plots is to
 discover the mechanisms responsible for the observed high levels of N
 retention.  Study of dissolved organics (specifically DOC and DON)
 comprises one set of studies providing insight into such
 mechanisms. The movement of dissolved organics from the forest floor
 to mineral soil amounts to approximately 5% to 24% of leaf litter C
 flux and 15% to 37% of leaf litter N flux in the few temperate
 forests studied. Additionally, dissolved organics exert some control
 on decomposition, humification and C and N turnover by acting as
 substrates for microbial activity and as reactive intermediates for
 abiotic processes.  Our projects at Harvard Forest include the
 collection of throughfall and forest-floor leachate for calculation
 of dissolved organic C and N concentrations and fluxes under control
 and N-addition treatments in two forest stands.  The results will be
 used to improve or parameterize models that address N retention, C
 and N turnover in forest soils.

Dail, d. Bryan and John W. Fitzgerald.  FORMATION OF ORGANIC S,
 S-ADSORPTION AND ACCUMULATION OF ORGANIC S IN FOREST SOILS AND
 BENTHIC SEDIMENTS AT COWEETA HYDROLOGIC LABORATORY.  Dept. of
 Microbiology, University of Georgia, Athens, GA. 30602 CWT Sulfur
 additions to a riparian system may come from deciduous senescence and
 acidic precipitation.  Additions of 35S labelled sodium sulfate to
 mimic acid precipitation were used to quantify microbial
 transformations in A-horizon soils and benthic sediments.  The fate
 of anthropogenic S additions, in particular, the potential to form
 organic-S, mobilization (mineralization) of recently formed
 organic-S, and the adsorptive potential of soils and sediments were
 measured.  Adsorption of S ranged from 3.63(0.39) to 4.83(0.48) nmol
 S/g dwt in 48 hrs.  The lowest adsorptive capacities in the riparian
 zone were observed in the benthic sediments.  Organic-S formation
 ranged from 0.5(.02) to 5.5(.13) nmol S/g dwt 48hrs-1.  Mobilization
 of recently formed organic-S ranged from 82 to 93%, with an
 accumulation to the system of 0.2055 to 0.2791 nmol S/g dwt 48hrs-1.
 Positive values for accumulation of organic-S were observed for all
 sites and all sampling dates, with the highest rates of formation of
 organic-S seen in the stream wet perimeter.

Davinroy, Thomas C.  COULOIR EROSION RATES AND ACTIVITY, COLORADO
 FRONT RANGE.  Department of Geography, Campus Box 260, University of
 Colorado, Boulder, CO 80309 NWT.  Rock movement through alpine
 couloirs has been measured repeatedly over a full year to determine
 the rates of erosion and associate them with meteorological, fluvial,
 and kinetic geomorphologic processes.  Downslope movement is analyzed
 according to particle size, particle shape, initial position, slope,
 and fluvial regime.  Contributions of climatic variation, quantity
 and intensity of precipitation are also assessed.  Avalanche paths
 and debris are examined for geomorphic activity, and rockfall onto
 snow is tracked for size and deposition pattern.  Rock temperature is
 sampled twice hourly to monitor freeze-thaw cycling and sediment
 traps collect bulk rockfall.  Consequent accumulation on sub-couloir
 talus cones has also been studied for rate, mechanism of transport,
 and depositional pattern.  Reoccupation of antecedent talus motion
 studies has extended observation to a 25-yr. study period.  This
 period includes dynamic climatic variation, including a
 100-yr. precipitation event.  Correlation with long-term climate data
 from D-1 and Niwot Saddle meteorological stations permits inferences
 to be drawn on the influence of climate on geomorphic activity.
 Lichenometric analysis of couloir-wall ages reveals periods of
 increased incision in periods following Holocene glacial retreats.

Day, Frank P. PLANT RESPONSE TO NITROGEN FERTILIZATION ACROSS A
 VIRGINIA COAST RESERVE DUNE CHRONOSEQUENCE. Old Dominion University,
 Norfolk VA 23529. VCR.  Experimental and control plots (1 m2) were
 established on three different age dunes (24, 36, and 120 yr old) on
 Hog Island, part of the Virginia Coast Reserve LTER site. Nitrogen
 (15 g m2 yr1) was added to the treatment plots in the form of
 urea. At the end of the 1991 growing season, plant biomass was
 harvested from the plots and weighed. Biomass decreased from young to
 old dune (174 g m2 to 108 g m2 in controls), but root/shoot ratios
 increased in the controls (0.35 to 0.50)). Biomass increased in
 response to fertilization on all three sites; however, the response
 was muted on the oldest dune (54% g m2 to 338 g m2 from young to
 old). Root/shoot ratios decreased in response to fertilization, but
 were the same across sites (0.21). The damping of the response to N
 additions from younger to older dunes may reflect the higher natural
 levels of N in the older dune soils or other limiting factors such as
 soil moisture.  Dodds, Walter, John Blair, Geoff Henebry, Rosemary
 Ramundo, Tim Seastedt1, and Cathy Tate2.  NITROGEN TRANSPORT FROM
 TALLGRASS PRAIRIE BY STREAMS. Kansas State University, Manhattan, KS
 66506; Current Address 1University of Colorado Boulder CO 80309, 2WRD
 United States Geological Survey, Denver CO 80225. KNZ.  Discharge and
 nitrogen content of water flowing from four watersheds on Konza
 Prairie Research Natural Area was monitored from 1986-1992.  The
 watersheds were on different burn frequencies. Streams were
 characterized by highly variable flow: data include a 100 year flood
 and a drought period that dried all channels for approximately 1
 year. Nitrogen yield per unit area increased as the surface area of
 the watershed increased. This is probably because groundwater losses
 were greatest in the smaller watersheds, although it is difficult to
 directly quantify the groundwater losses from this system. Nitrogen
 yield per unit area was also greater with more annual
 precipitation. Loss of nitrogen from streams made up a small portion
 (0.1 - 6.0 % ) of nitrogen coming in from precipitation. Neither
 recent burning nor introduction of bison in the watersheds had
 statistically significant effects on nitrogen content of the
 water. Increased precipitation was significantly correlated (P <
 0.03) to higher concentrations of nitrate. Good water quality is
 typical of these streams with ammonium always below 0. 1 ?M, nitrate
 ranging from below 0.1?M to 28 ?M and total N from 1.5 - 51 ?M.

Doran, Kathleen.  A LABORATORY INVESTIGATION OF THE RESPONSE OF WHITE
 SPRUCE (Picea glauca) TO LIGHT AND NITROGEN CHANGES. Institute of
 Arctic Biology, University of Alaska, Fairbanks, Alaska.  Taiga
 floodplain white spruce were grown from seeds in a 3x2, light and
 nitrogen factorial experiment to investigate growth and succession in
 floodplain environments.  Photosynthetic responses to a range of
 light intensities were used to construct light response curves to
 determine quantum yields and saturation light intensities for each
 treatment.  Plant height and above and below ground biomass were used
 as measures of growth rate and root/shoot ratios.  The experimental
 results indicated that there were no significant differences in
 photosynthetic rates between treatments.  However, there were
 significant differences in root/shoot ratios between treatments.
 Root/shoot ratios within the medium and high light treatments
 increased with low nitrogen fertilizer levels, while the low light
 treatment did not show a difference between high and low nitrogen
 levels. Future research will involve measuring the above and below
 ground tissue nitrogen concentrations.  Photosynthetic and biomass
 data will be collected from additional plants at 2 month intervals to
 investigate possible difference as the plants mature.

Dueser, R.D. and John Porter. EFFECTS OF AREA AND HABITAT COMPLEXITY
 ON INSULAR SMALL MAMMAL DIVERSITY ON THE VIRGINIA BARRIER
 ISLANDS. Department of Fisheries and Wildlife, Utah State University,
 Logan, UT 84322, and Department of Environmental Sciences, University
 of Virginia, Charlottesville, VA 22903 There is continuing debate
 about the relative effects of island area and habitat complexity on
 insular faunal richness.  Island area and habitat complexity tend to
 be positively correlated with most measures of faunal richness.
 Experimental studies of the independent effects of these variables
 usually are impractical, unethical or both.  Few correlational
 studies incorporate a sufficient number of islands and sufficient
 information on habitat complexity to allow a rigorous test.  We
 report a correlational study which allows such a test.  The
 biogeography of seven small mammal species on the Virginia barrier
 islands (N=23) has been studied since 1975.  These islands range from
 23 to 7,029 ha in area.  The number of species found on an island
 (0-7) varies directly with island area, maximum elevation, vegetation
 height, number of plant associations and number of woody plant
 association, and varies inversely with distance from mainland.
 Partial correlation analyses, controlling for island area, indicate
 that two measures of habitat complexity (i,.e., number of woody plant
 associations and total number of plant associations) are particularly
 useful predictors of insular species richness. Habitat complexity
 thus carries information independent of island area.  The patterns of
 occurrence of the species on the islands suggest that the
 distributions of some species are constrained by the relative lack of
 suitable habitat, while other sources are limited primarily by
 isolating barriers such as open water.  Three apparent extinctions of
 island populations observed since 1975 appear to be unrelated to the
 availability to suitable habitat.  Edwards, D. and
 S. Hutchinson. IDENTIFYING RARE EVENTS IN NORTH INLET ECOLOGICAL DATA
 SETS USING SHEWHART CONTROL CHARTS.  Department of Statistics, U. of
 South Carolina, Columbia SC and Coastal Carolina College, Conway SC.
 NIN.  Events and disturbances have been widely used to explain
 variability in ecological data; these explanations, however, were
 highly subjective.  Events tend to be over-reported in short-term
 studies and under-reported in long-term studies.  Shewhart control
 charts, a quantitative technique for identifying unusual events in
 industrial processes, were used here to identify four classes of
 "events" in biological, physical, chemical, and meteorological data
 collected at North Inlet Estuary, SC.  Both intensity and duration of
 events are included in the classification.  Measurements were
 collected at various temporal scales, ranging from hourly weather
 observations, daily water samples, biweekly fauna samples, to monthly
 primary production estimates.  Prior to control charting, LOWESS
 smoothing was used to remove long-term trends and seasonal patterns
 in both the mean and standard deviation of each series.  Following
 event identification, the data were merged to examine relationships
 between physical events and the occurrence of chemical and biological
 events.  Relating these events, in data collected at different
 temporal scales, is a complex problem.  Limitations also emerge
 because ecosystems cannot be shutdown and "reset", as in the
 manufacturing environment.  The value of this technique is that
 intensity and duration of events are quantified and the rate of false
 events are quantified.

Elder, Bradley, O. J. Reichman, David Hartnett, Nancy Huntly*, Richard
 Inouye*, William Rogers, Tony Wasley*, and Eric Burr*. THE INFLUENCE
 OF ANIMAL-GENERATED DISTURBANCES ON MULTI-SCALE PATTERNS OF RESOURCES
 AND VEGETATION.  Div. of Biology, Kansas State Univ., Manhattan, KS
 and (*) Dept. of Biological Sciences, Idaho State Univ., Pocatello,
 ID. CDR, KNZ.  While the effects of disturbances on plant communities
 have been investigated for some time, the impact of the spatial and
 temporal patterns of disturbances have only recently received similar
 attention from ecologists.  In order to investigate the effect of
 specific patterns of disturbance on plant communities we have
 initiated a study of the influence of pocket gopher burrows and
 mounds on overlying vegetation. Previous studies have shown that
 pocket gopher burrows occur in highly uniform patterns of spacing
 even though individual burrows are convoluted.  Mounds, conversely,
 are significantly clustered in their distribution.  Furthermore, both
 burrows and mounds produce a spatially explicit pattern of influence
 on the plant community adjacent to the disturbances.  This pattern is
 consistent with a competition induced wave of biomass and is
 initiated by a significant reduction in plant biomass directly over
 the disturbance.  This, in turn, increases the availability of
 resources to plants adjacent to the disturbances.  This wave of
 biomass is continued out to at least 50 cm from the disturbances in a
 pattern that appears to be related to alternating levels of
 resources.  Our investigation centers on a study of the biomass wave
 pattern in relation to burrow and mound spacing at two LTER sites
 that differ significantly in soil nutrients (Konza Prairie and Cedar
 Creek).  We will employ both naturally occurring burrows and mounds,
 and simulated disturbances, and measure their influence on plant
 biomass and diversity at scales from 10 cm to 128 m.  We anticipate
 that specific patterns of influence will emerge at different scales,
 and that these will differ between the two sites.  Elias, Scott A.,
 and Susan K. Short. BIOTIC RESPONSE TO CHANGING ALPINE ENVIRONMENTS
 DURING THE HOLOCENE. Institute of Arctic and Alpine Research, Campus
 Box 450, University of Colorado, Boulder CO 80309-0450. NWT.  As part
 of our research on biotic response to changing alpine environments,
 researchers in the paleoecology group of the Niwot LTER project have
 studied a transect of ten Holocene-age sites in the Colorado Front
 Range. Pollen, fossil insects, and plant macrofossils have been
 investigated. At the end of the last glaciation, the alpine tundra
 zone extended 500 m downslope from its modern limit. Early Holocene
 treeline reached its modern elevation by about 9,500 yr BP. During
 the Holocene, the study region has experienced a series of climatic
 fluctuations, with fossil data indicative of warmer than present
 conditions between 9500 and 7000 yr BP, and colder than present
 conditions between 4500 and 3000 yr BP and again in the last 1000
 years. The insect response has essentially been in phase with
 vegetational changes.  Engman, J.A. DISTRIBUTION OF THE GENUS
 HETEROCOPE (COPEPODA, CALANOIDA): ECOLOGICAL IMPLICATIONS FROM
 BIOGEOGRAPHIC, PHYLOGENETIC AND GIS ANALYSIS. Univ. Cincinnati,
 Dept. Biol. Sciences, Cincinnati, OH 45221. ARC.  At the arctic
 tundra LTER, species composition of zooplankton communities varies
 significantly and predictably, based on a series of simple biotic and
 abiotic factors. The presence of the large copepod Heterocope
 septentrionalis has a deterministic effect on the cladoceran
 community on which it preys.  H.septentrionalis is found in
 significant numbers only when visually feeding predators are reduced
 or absent, as a result of top-down control by piscivores, or as a
 result of fish exclusion by ice formation in shallower bodies of
 water. At a larger scale, factors influencing distribution of
 zooplankton species are being examined in a study of biogeography of
 the six species of the genus Heterocope. This research includes
 reconstruction of the phylogenetic relationships of Heterocope
 species, characterization of the global distribution of these
 species, and a GIS-based analysis of current and historic factors
 which may explain distribution.  Phylogeny of species of Heterocope
 is being examined based on cladistic analysis of morphological
 characters and molecular genetic (mtDNA sequence) data; this provides
 a pattern of species relationships within the genus, and may give
 estimates for ages of individual speciation events.  Distribution of
 the individual species has been characterized based on our field
 collections, and a thorough literature search. Using United Nations
 global climate databases as estimators of overall environmental
 conditions, GIS applications are allowing comparison of Heterocope
 occurrence with factors that may be responsible for determining
 limits of individual species distribution.  At a global scale,
 determination of distribution appears primarily historic, reflecting
 speciation patterns within the genus.  At intermediate scales, both
 ecological and historic (primarily glacial event) factors can explain
 much of Heterocope distribution.  At regional and local scales,
 occurrence of populations can be correlated with environmental
 variables including temperature, elevation and vegetation type.
 Ehrman, Terry and Jack Webster. TRANSPORT DYNAMICS OF FINE
 PARTICULATE ORGANIC MATTER. Biology Dept, Virginia Polytechnic
 Institute and State University, Blacksburg, VA 24061. CWT.  Pollen
 and glass beads were used as trackable surrogates for natural fine
 particulate organic matter. Transport dynamics of these particles in
 several streams were best described by a negative exponential model,
 from which average travel distances for pollen and glass beads could
 be calculated. Distances traveled generally lengthened with
 increasing stream flow. Average travel distances for pollen and glass
 beads during the highest flow (96 L/sec) were 185 m and 114 m,
 respectively. During the lowest flow (4 L/sec), these particles only
 traveled 11 m and 2 m, respectively. Pollen, less dense than glass
 beads, usually traveled further than the beads.  In order to account
 for the variability in retention of these particles, several stream
 characteristics, such as discharge, velocity, substrate type, amount
 of large woody debris, gradient, depth, and temperature, were
 measured but not, as yet, analyzed statistically.  Epstein, H. E.1,
 Lauenroth, W. K.1, Burke, I. C.2 and D. P.  Coffin1 ANALYSES OF THE
 ABUNDANCE OF DOMINANT GRASS SPECIES ALONG TWO REGIONAL TRANSECTS IN
 THE CENTRAL GRASSLANDS OF THE UNITED STATES.  1Dept. of Range Science
 and 2Dept. of Forest Science Colorado State University Fort Collins,
 CO 80523.  CPR.  We conducted research to quantify large-scale
 relationships between grass species abundances and their
 environmental controls.  We analyzed the production of several
 dominant grasses along two transects in the central Grassland Region
 of the United States.  To perform the analyses, we constructed a
 plant species database for the central Grasslands.  The database
 utilizes ARC/INFO, a geographic information system, to combine Soil
 Conservation Service (SCS) range site descriptions with spatial data
 from the SCS State Soil Geographic (STATSGO) database.  The outcome
 is a spatial database of the abundances of individual plant species.
 Analyses were performed on latitude (surrogate for mean annual
 temperature) versus biomass for four dominant grass species in the
 plains region extending from southern Colorado to northern Montana.
 The abundances of Bouteloua gracilis and Buchle dactyloides, both C4
 species, decreased with increasing latitude, whereas the
 relationships between latitude and biomass for Agropyron smithii and
 Stipa comata, both C3 species, were less clear.  Analyses were also
 performed on longitude (surrogate from mean annual precipitation)
 versus biomass for four dominant C4 grass species in the plains
 region extending from the shortgrass steppe in eastern Colorado to
 the tallgrass prairie in eastern Kansas.  The abundances of Bouteloua
 gracilis and Buchle dactyloides decreased, whereas the abundances of
 Andropogon gerardii and Schizachyrium scoparium increased, from west
 to east.  These results provide insight into the quantitative
 relationships between individual species production and climate at a
 regional scale.  Fay, Phil, David C. Hartnett, Laura E. Fischer, Bill
 Adamsen. TALLGRASS PRAIRIE GALL INSECT POPULATION TRENDS AFTER FIRE.
 Division of Biology, Kansas State University, Manhattan, KS
 66506-4901. KNZ.  Gall insects are a common but understudied
 component of the tallgrass prairie fauna, and are excellent subjects
 for long-term population studies because they leave a semi- permanent
 record of their presence.  We have begun yearly sampling to determine
 how galler populations respond to spring fires. Gall insect densities
 are censured on Solidago canadensis (tall goldenrod), Vernonia
 baldwinii (Baldwin ironweed), and Ceanothus herbaceous (New Jersey
 tea) at the end of the growing season on sites at Konza Prairie
 varying in the number of years since the site was last burned. Sites
 have been censured for the last 4 years, covering the range from 1 to
 14 years since fire.  Densities of gallers on all three plant species
 increased with year since fire. On goldenrod, there appeared to be
 resistant clones where gall populations increase more slowly and
 susceptible clones where populations increased more rapidly. There
 are several possible mechanisms controlling these patterns: 1) direct
 fire mortality followed by immigration and recolonization of burned
 sites, 2) indirect effects of fire on galled survivorship and
 performance through changes in plant quality, 3) effects of fire on
 host plant population density.

Fischer, Janet M. and Thomas M. Frost. LINKING DEMOGRAPHY AND
 POPULATION DYNAMICS OF THE PHANTOM MIDGE (Chaoborus): EXPERIMENTAL
 AND MODELING APPROACHES. Center for Limnology, University of
 Wisconsin, Madison, WI, 53706.  Like many organisms that undergo
 dramatic changes in size and form as they develop, Chaoborus are
 subject to a variety of constraints during their life cycle.  We used
 a combination of experimental and modeling approaches to investigate
 the population consequences of changes in the relative strengths of
 these constraints for Chaoborus punctipennis.  Abundance of Chaoborus
 has increased approximately two-fold with the acidification of the
 treatment basin of Little Rock Lake, WI.  Results of cohort analysis
 indicate that the observed population increase is driven by increased
 early instar survivorship.  We used field data from Little Rock Lake
 to construct a stage-based projection model for Chaoborus.  Model
 simulations demonstrate that changes in survival and development
 rates can dramatically alter seasonal population dynamics.  These
 changes in Chaoborus seasonal dynamics may have important
 implications for the zooplankton community due to shifts in the
 strength of interaction between Chaoborus and their zooplankton prey.

Fischer, Laura, Barbara Hetrick, David Hartnett, and Arthur
 Schwab. MYCORRHIZAL- MEDIATED INTERPLANT PHOSPHORUS TRANSFER AMONG
 TALLGRASS PRAIRIE SPECIES. Kansas State University, Manhattan, KS
 66506. KNZ.  We investigated the potential for phosphorus transfer
 through VA-mycorrhizal hyphal bridges among several plant species in
 tallgrass prairie. We applied 32P-labelled phosphate to the leaves of
 "donor" Andropogon gerardii plants, harvested randomly selected
 "receivers" of nine species within a 50-cm radius of the donor, and
 determined the amount of label transferred by liquid scintillation
 counting.  The amount of label received differed significantly among
 species and was significantly correlated with the distance from the
 donor. The biomass of the receiver relative to that of the donor did
 not significantly affect phosphorus transfer. In a following study,
 we harvested receiver plants of three species 10, 17, and 24 days
 after labelling donor Andropogon plants. At two of the harvests,
 receiver species and distance from the donor had a significant effect
 on the amount of 32P received. Again, there was no main effect of
 relative biomass of donor and receiver plants. These studies
 demonstrate nonrandom transfer of phosphorus among neighboring
 individuals of several plant species in tallgrass prairie. Subsequent
 studies will evaluate the relationship between patterns of interplant
 nutrient transfer and plant competitive interactions.

Fisk, Melany C., and Steven K. Schmidt. MICROBIAL RESPONSE TO
 INCREASED SOIL MOISTURE IN COLORADO ALPINE TUNDRA
 SOILS. Environmental, Population, and Organismic Biology, Campus Box
 334, University of Colorado, Boulder CO 80309-0334. NWT.  The
 response of microbial community composition and nitrogen
 mineralization to increased soil moisture was investigated in lab
 incubations and field manipulations of alpine tundra soil. Microbial
 respiration, net nitrogen mineralization, and total and active
 bacterial numbers were higher in soils incubated at 85% than at 30%
 gravimetric soil moisture, while fungal hyphal lengths showed no
 difference between soil moisture levels. In incubated, watered
 treatments higher bacterial numbers corresponded to lower net N
 mineralization per unit C mineralized, suggesting that higher N
 immobilization occurred as a result of stimulated bacterial activity
 and growth. Similarly in field experiments microbial biomass N was
 high in watered compared to unwatered soils, whereas net N
 mineralization did not increase in response to watering. While fungal
 biomass showed little response to higher soil moisture, short-term
 bacterial immobilization of N appears to be an important component of
 N dynamics, especially in response to wetting and drying cycles in
 alpine tundra soil.

Foster, Bryan L., and Katherine L Gross. STUDIES OF TREE ESTABLISHMENT
 IN ABANDONED AGRICULTURAL FIELDS AT THE W. K. KELLOGG BIOLOGICAL
 STATION LTER. Michigan State University, W. K. Kellogg Biological
 Station, Hickory Corners MI. 49060.  An understanding of the factors
 regulating the invasion, establishment and persistence of woody plant
 species is critical to understanding old field succession. Our
 studies to date suggest that the mode of seed dispersal, mammalian
 post-dispersal seed predators, browsing by deer, and the direct and
 indirect effects of early successional dominant species are important
 determinants of the spatial and temporal patterns of tree
 establishment in old fields. We have utilized these initial studies
 to develop a set of hypotheses concerning the mechanisms by which the
 above factors can control woody plant establishment during old field
 succession. Future research will focus on experiments designed to
 test these hypotheses.  Freckman, Diana W. and Ross
 A. Virginia. NEMATODES AND SOIL PROPERTIES IN THE DRY VALLEYS OF
 ANTARCTICA. Colorado State Univ., Fort Collins, CO 80523 and
 Antarctic Dry Valley LTER and Dartmouth College, Hanover, NH 03755
 and Jornada LTER.  JRN The Antarctic Dry Valleys are one of the most
 extreme soil environments on earth. We are studying factors
 controlling soil biota distribution and function near the limits for
 life.  We studied the distribution and community structure of
 nematodes in relation to soil properties that affect their
 distribution in other desert systems (i.e., moisture, soil chemical
 and physical properties) in eight ice-free Antarctic Dry Valleys.
 Nematodes were widely distributed and occurred in > 65% of Dry Valley
 soils.  Nematode abundance reached 4200/kg dry soil and was not
 significantly correlated with soil moisture or most other physical
 and chemical properties.  However, soils lacking nematodes had
 greater salinity.  We found 7 nematode species with bacterivores
 comprising 66-100% of the nematode community (Scottnema lindsayae,
 Plectus spp.) and omnivore/predators (Eudorylaimus spp.) the rest.
 S. lindsayae dominated all samples.  Nematode distribution in the Dry
 Valleys is more patchy than in hot desert soils, but, where nematodes
 occur, densities can be comparable to those of hot desert soils. A
 one year field experiment showed that increasing temperature,
 moisture and carbon together increased nematode numbers, whereas
 these treatments alone had negative effects. Laboratory studies of
 the life cycle of S. lindsayae at 10C and 15C indicated the higher
 temperature decreased fecundity and development to adults.  These
 field and lab results suggest that elevated soil temperatures may
 negatively affect nematode reproduction.  Gage, Stuart H., Manuel
 Colunga and Peggy Ostrom. FLOW OF INSECTS THROUGH A
 LANDSCAPE. Michigan State University, E. Lansing, MI 48824. KBS
 Insects play an important role in native and human managed ecosystems
 as herbivores, as detritivores, as predators and as food for birds
 and mammals. Studies focus on insects at the landscape level because
 of their multi-dimensional role and because insects utilize multiple
 habitats as they traverse the landscape in search for overwinter
 sites, oviposition sites and places to find food.  Insects selected
 to study dispersal include a complex of general predators (ladybird
 beetles and lacewings) as well as selected herbivores (rootworms,
 leafhoppers). The primary focus has been to measure and quantify
 dispersing adults of these organisms as they traverse the landscape
 in search of resources. Since 1989, weekly measurements of 15 species
 of adult insects have been made using a standardized sampling method
 in several hundred sites representing different habitat types
 associated with agroecosystems. In addition to long term regular
 sampling in different habitats, measurements of isotopic signatures
 of plants and insects are made to characterize trophic relations
 between plants, herbivores and predators. Stable isotopesignatures of
 nitrogen and carbon from plants and insects are used to characterize
 dispersal of predatory and plant feeding insects.  Seasonal patterns
 of response by dispersing insects to different habitats have been
 documented including predicting temporal occurrence within
 habitats. Regulation of pest populations by predatory ladybird
 beetles has been observed and documented. Association between
 resident and dispersing predators is being quantified. Vegetation,
 both natural and human managed plantings have been mapped within
 landscape at KBS and work is underway to use satellite imagery to
 characterize landscape complexity. A temporal and spatial simulation
 model is being developed to characterize the flow of insects through
 landscapes of varying complexities. From this analysis we will
 determine landscape characteristics which will enable manipulation of
 insect populations including enhancement of diversity of insect
 species which are beneficial to agriculture.

Garman, S.L., A.J. Hansen and D.L. Urban.  ALTERNATIVE SILVICULTURAL
 PRESCRIPTIONS & BIODIVERSITY IN THE PACIFIC NORTHWEST: A SIMULATION
 APPROACH.  Dept. of Forest Science, Oregon State Univ., Corvallis, OR
 97331-7501, and Colorado State Univ., Ft. Collins, CO.  AND.  We are
 developing a computer simulation approach to evaluate trade-offs
 between timber production and animal-habitat diversity under
 alternative stand-level management prescriptions in western
 Oregon. Our approach uses an existing forest succession model, ZELIG,
 which we have modified to better simulate custom-designed
 silvicultural prescriptions and to evaluate suitability of modeled
 stands as animal habitat using empirically-derived statistical models
 of animal-habitat associations.  Description of our modeling
 approach, model verification, and a demonstration of a trade-off
 analysis are presented.  Gillham, Marla L., and Phillip Sollins.
 MULTIVARIATE CLASSIFICATION, AND NUTRIENT STATUS, OF MONTANE RIPARIAN
 SOILS.  Dept. of Forest Science, Oregon State Univ., Corvallis, OR
 97331-7501.  AND Third-order riparian ecosystems of the western
 Cascades of Oregon develop on geomorphic surfaces of diverse origins
 and ages.  A variety of erosional and depositional processes have
 created an extremely heterogeneous set of geomorphic surfaces and
 corresponding soils. Objectives were to develop a system for
 classifying these soils with regard to factors that might control
 primary production, especially nitrogen availability.  Study sites
 were a 500-year old Douglas fir forest, and a mature red alder forest
 occupying a 35-year old clearcut.  At 30 locations at each site, soil
 was sampled at 0-15 cm and 15-30 cm depths, and the location
 classified as to geomorphic surface and plant community type.
 Principal components analysis and discriminant analysis grouped
 similar observations and identified substantial internal structure
 within the data.  Soils with higher levels of carbon and
 mineralizable nitrogen developed generally on older and/or aggrading
 geomorphic surfaces, suggesting a relationship between geomorphology
 and primary productivity.  Classification by geomorphic surface
 appeared to work better than traditional soil classification for
 characterizing these extremely complex and heterogeneous systems.

Gray, Andrew N., and Thomas A. Spies.  USE OF TIME DOMAIN
 REFLECTOMETRY (TDR) TO DETERMINE WATER CONTENT OF MINERAL AND ORGANIC
 SUBSTRATES IN CONIFEROUS FOREST CANOPY GAPS.  Oregon State Univ.,
 Corvallis, OR, 97331 and Forest Science Laboratory, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  The accuracy of Time Domain
 Reflectometry (TDR) for determining volumetric water content was
 evaluated for soils from four forest stands, decayed wood, and forest
 floor.  The TDR system operates by measuring the dielectric constant
 within waveguides defined by parallel steel probes, making it a
 rapid, non-destructive, and repeatable method.  Proven effective in
 agricultural soils, TDR has rarely been applied to heterogeneous,
 high organic content forest substrates.  Regressions developed from
 TDR measurement of gravimetric soil samples were accurate within .03
 cm3/cm3 volumetric water.  Some soil types required separate
 regressions.  Estimates of water content in organic substrates were
 less accurate than for soils.  The TDR technique was able to detect
 differences in soil moisture patterns within and among canopy gaps of
 different sizes.  Griffiths, R.P., J. E. Baham and B. A. Caldwell.
 SOIL SOLUTION CHEMISTRY OF ECTOMYCORRHIZAL MAT SOILS.  Departments of
 Forest Science and Crop and Soil Science, Oregon State Univ.,
 Corvallis, OR 97331-7501.  AND.  Ectomycorrhizal fungal mats are
 important features of Pacific Northwest coniferous forests and other
 forests throughout the world. Organic acids produced by these fungi
 play an important role in nutrient availability and mineral
 weathering within the soil ecosystem.  We have conducted a study in
 which chemical composition of soil solutions isolated from two
 ectomycorrhizal fungi mat soils were compared to those isolated from
 adjacent soils with no visible mat development.  The concentrations
 of dissolved constituents were greater, in all cases, for the mat
 soils.  The differences between mat and non-mat soil solutions were
 significant (p < 0.05) in all but three of the twenty-seven
 comparisons.  The concentrations of ions in soil solutions isolated
 from Gautieria monticola mats were usually greater than those found
 in Hysterangium setchellii mat soils.  The chemical constituents
 showing the largest differences between mat and non-mat soils for
 both mat types included: Al, Fe, Mg, Mn, PO4, SO4, Cl, Oxalate (Ox),
 and DOC.  The correlation between the elevated levels of Ox and DOC
 isolated from the G. monticola mat soil solutions with the
 concentrations of other ions suggests that oxalate plays an important
 role in weathering and bioavailability.

Griffiths, R.P., G.A. Bradshaw and B.A. Caldwell.  DISTRIBUTION OF
 ECTOMYCORRHIZAL MATS IN CONIFEROUS FOREST OF THE PACIFIC
 NORTHWEST. Department of Forest Science, Oregon State Univ.,
 Corvallis, OR 97331-7501, and Forest Science Laboratory, USDA Forest
 Service, Corvallis, OR, 97331.  AND.  Ectomycorrhizal mat soils have
 been used as model systems for studying the role of mycorrhizae in
 forest ecosystems and have been shown to play several important roles
 in the normal function of forest soils. There is limited information
 on the factors influencing mat spatial and successional distribution.
 Surveys were conducted to determine the spatial distribution of mats
 relative to live and dead trees, rocks and understory vegetation.
 All features within 2 x 10 m grids were measured and the presence of
 two types of mats at the base of understory trees was documented.  We
 found that ectomycorrhizal mats were associated with 80-100% of
 Pacific yew trees and that the occurrence of mats was significantly
 higher in all understory tree plots relative to equal-sized control
 plots without trees.  Stand age influenced the percent area covered
 by Gautieria but not Hysterangium.  These observations suggest that
 understory trees may play a role in the distribution of
 ectomycorrhizal fungal mats and that different mats may play
 different roles along the successional trajectories of Douglas-fir
 forests.

Griffiths, R.P., J.L. Liles and B.A. Caldwell.  SOIL RESPIRATION IN A
 PACIFIC NORTHWEST CONIFEROUS FOREST.  Department of Forest Science,
 Oregon State Univ, Corvallis, OR 97331-7501.  AND.  A seasonal study
 of forest floor respiration is being conducted at the H. J. Andrews
 Experimental Forest.  The main objective of the study is to determine
 how seasonal shifts in temperature and moisture altered both field
 and laboratory respiration rates and to determine how respiration
 rates are related to dissolved organic carbon (DOC) concentrations.
 Field respiration rates show a significant positive correlation with
 soil temperatures but seasonal patterns observed thus far show that
 moisture extremes also have a profound effect on respiration rates.
 When moisture limited respiration by being either too high or too
 low, DOC concentrations increase as respiration rates decrease.
 Grubaugh, J.W., J.B. Wallace, L.S. Houston and A. Marcilio.  PATTERNS
 IN MACROINVERTEBRATE COMMUNITY STRUCTURE ALONG AN ELEVATION AND
 STREAM SIZE GRADIENT IN THE SOUTHEASTERN APPALACHIAN
 MOUNTAINS. Institute of Ecology, University of Georgia, Athens, GA
 30602. CWT.  We assessed longitudinal changes of the benthic
 macroinvertebrate community with respect to habitat availability,
 functional group contribution, and taxa distribution and richness
 with changing stream size.  We investigated macroinvertebrate
 distribution at 15 stations over a reach of 66 river-km, beginning in
 headwater streams of the Coweeta basin and into the Little Tennessee
 River in western North Carolina.  This continuous gradient
 encompasses 1st through 7th-order streams with catchment areas
 varying from <10 ha to >100,000 ha, an elevational change of ca. 600
 m, and varying thermal regimes ranging from 3,000 degree-days in the
 headwaters to ca. 6,000 degree-days in the Little Tennessee River. We
 sampled bedrock outcrops, cobble, and depositional areas at most
 stations, depending on availability.  There was extensive replacement
 of macroinvertebrate taxa along the gradient; however, within a given
 habitat type the proportion of functional group representation
 remained relatively consistent.  Shredder biomass was greatest in
 depositional and cobble habitats, scraper biomass on cobble and rock
 outcrops, collector-gatherers on rock outcrops and depositional
 areas, and filterers on rock outcrop and cobble.  Predators were more
 evenly distributed among the three habitats.  Percent contribution of
 all functional groups to total macroinvertebrate biomass was
 significantly correlated (p < 0.05) to stream size.  Shredders,
 collector-gatherers, and predators were highest in the smaller
 streams and declined as stream size increased.  Conversely,
 collector-filterer contribution was small in the headwater streams
 and highest in the large river reaches.  Scraper contribution to
 total biomass was highest at mid-gradient sites (catchment areas
 >1,000 and <10,000 ha) and declined with both increasing and
 decreasing stream size.  Results of this study emphasize the need to
 consider sampling scale and the importance of habitat availability
 when characterizing trends in macroinvertebrate community structure
 over a stream size gradient.

Haberman, Karen L., Robin M. Ross and Langdon B. Quetin.  GRAZING BY
 THE ANTARCTIC KRILL Euphasia superbe, ON Nitschia spp. AND
 Phaeocystis spp. MONOCULTURES.  Marine Science Institute, University
 of California, Santa Barbara, CA 93106.  PAL Antarctic krill are
 important first order consumers in the Southern Ocean food web, and
 in turn are the principle prey for higher order consumers, including
 several species of penguins, seals and whales. While the krill
 primarily feed upon phytoplankton, it is not known whether they
 ingest and assimilate different types of phytoplankton with similar
 rates and efficiencies.  Such knowledge is important if we wish to
 understand how the patterns of phytoplankton species composition
 affect the krill's food availability.  This study focuses on one type
 of phytoplankton, Phaeocystis spp., which periodically occurs in
 thick blooms and can dominate the standing crop at certain places and
 times. The question of its edibility and nutritional value has been
 the subject of several investigations.  During laboratory feeding
 experiments, ingestion rates were calculated based on the rate of
 disappearance of chlorophyll a from the experimental tubs. Krill
 ingested the diatom Nitschia and single-celled Phaeocystis at similar
 rates, but did not ingest Phaeocystis colonies.  The difference in
 ingestion rate between these two physiological states of Phaeocystis
 suggests that food quality may be an important variable when
 assessing what proportion of the phytoplankton standing stock is
 useful to the krill.

Haines, B., D. Coleman, R. Davis. SOIL BIOLOGY; MICROSCOPE AND CAMERA
 SYSTEM FOR OBSERVING SOIL ORGANISMS AND QUANTIFYING ROOT GROWTH
 DYNAMICS. University of Georgia, Athens, GA. 30602 The challenge of
 studying roots and root associated organisms along an elevational
 gradient on the steep and often rocky forested watersheds was
 addressed by constructing observation boxes of poly vinyl chloride.
 The boxes were 65cm long, 57cm wide, 71.6cm tall at one end and
 39.5cm tall at the other end.  A window of flat glass of 31cm long
 and 15cm height was counter-sunk into short (39cm high) end wall, 8cm
 below the top.  The interior of the box was fitted with a mount for a
 35mm camera and a separate mount to position a dissecting microscope.
 The box was covered with a PVC lid which overlapped the outside of
 the walls.  A gasket inside this lid excluded water vapor.  The
 system provided both white light and ultraviolet light for
 observation and photography.  A 12 volt rechargeable battery powered
 an invertor which supplied 120 volts to the lights.  A timer
 controlled the light for sequential photographs.  Haines, Bruce L.,
 Bonnie Mccaig and James Hamrick. SUSCEPTIBILITY OF Robinia
 pseudoacacia L.(BLACK LOCUST) TO ATTACK BY Megacyllene robiniae
 (LOCUST STEM BORER): ROLES OF GENOTYPE AND STAND AGE. University of
 Georgia, Athens GA 30602. CWT.  Increased mortality of Robinia
 pseudoacacia is associated with evidence of trunk girdling by the
 black locust stem borer Megacyllene robiniae (Forster) (Coleoptera,
 Cerambycidae). Robinia pseudoacacia is often clonal in the southern
 Appalachians, USA. The possible pre-disposition of some clones or age
 classes to girdling by Megacyllene was investigated at the Coweeta
 Hydrologic Laboratory, North Carolina. The incidence of Megacyllene
 emergence holes was evaluated on 1629 Robinia stems.  Stems were
 mapped and foliage analyzed for genotype via protein gel
 electrophoresis for 15 polymorphic loci. The average number of
 emergence holes per tree for the 5, 13, 30 and 40 year old stands
 were 0.41, 1.6, 3.0 and 0.4 respectively. There is no evidence for
 genotypic correlation. Other factors contributing to incidence of
 Megacyllene could be the abundance of its intermediate host Solidago
 near Robinia stands.  Hall, Robert O. Jr.  THE USE OF A STABLE
 ISOTOPE ADDITION TO TRACE MICROBIAL CARBON THROUGH A STREAM FOOD
 WEB. University of Georgia, Athens, GA 30602. CWT.  I examined the
 importance of dissolved organic carbon to a stream food web using a
 13C addition. 13C as sodium acetate was dripped into a headwater
 spring at Coweeta Hydrologic Laboratory for three weeks during the
 summer. The addition was calculated to raise the del value of DOC
 from approximately -26 per mil to approximately 100 per mil. Before
 and after addition samples of CPOM, FPOM, and 20 taxa of organisms
 were analyzed on a Europa Tracermass mass spectrometer. Before
 addition samples ranged from -36 per mil to - 22 per mil. There was
 much variability between and within taxa after the
 addition. Predators were less labelled than collectors, shredders,
 and scrapers. Organisms appeared to preferentially assimilate
 microbial carbon.  Stenonoma, a biofilm scraper, was the most highly
 labelled taxon (up to 128 per mil), even though biofilm del value was
 -16 per mil. Chironomids had a higher del value than FPOM.  Although
 both the adults and larvae of an elmid beetle, Optioservus, are
 scrapers, the adults were more labelled than the larvae, indicating
 greater dependence on microbial carbon.  This technique is useful to
 discriminate between particulate and dissolved sources of carbon
 where no differences in the natural abundance of 13C exist. Hence it
 appears to be a useful technique for resolving detrital food webs.

Halstead, S. J. , W. R. Reed, M.  Krisfalusi and
 G. P. Robertson. SPATIAL PATTERNS OF SOIL DENITRIFICATION POTENTIALS
 IN THREE TILLAGE SYSTEMS .  W. K. Kellogg Biological Station, Hickory
 Corners, MI 49060.  KBS.  Denitrification plays an important role in
 the loss of nitrogen fertilizer from agricultural systems.  We
 examined the effect of tillage and position within the crop row on
 the rates of nitrous oxide production at three times within the
 growing season.  Intact cores were taken pre- and post-plant and
 post-fertilization from mold-board plow, notill and ridge till
 systems.  Within each tillage type, cores were taken at 0, 20 and 40
 cm starting in the row and moving to the interrow.  Cores were
 incubated with acetylene and sampled at 3 h intervals for 12 h.
 Nitrous oxide production was greatest from moldboard plowed systems
 with decreased rates observed in the other tillages.  Within a
 tillage system, losses appear to be greatest within the crop row.
 Further work will attempt to correlate enzyme activity with nitrous
 oxide production rates in the field.  Hendricks, Joseph J. and John
 D. Aber.  THE EFFECTS OF NITROGEN AVAILABILITY ON FINE ROOT SUBSTRATE
 QUALITY.  Institute of Natural Resources, University of New
 Hampshire, Durham, NH 03824.  HFR.  The effect of nitrogen
 availability on fine root substrate quality was assessed using
 samples from the chronic nitrogen addition plots in the Harvard
 Forest LTER site.  Fine roots (generally < 1 mm in diameter) from the
 organic and mineral (0-10 cm) soil horizons of red pine and
 mixed-hardwood control (0 kg N ha-1 yr-1), low (50 kg N ha-1 yr-1),
 and high (150 kg N ha-1 yr-1) treatment plots were collected on
 monthly intervals during the 1991 growing season and analyzed for
 nitrogen and carbon fraction concentrations.  Nitrogen concentrations
 (range of 1.1 to 2.8%) differed significantly between treatments,
 horizons, and sample periods for both red pine and
 mixed-hardwoods. In contrast, carbon fractions (predominately lignin,
 range of 46 to 51%) did not differ significantly among classes.
 These results indicate that fine root substrate quality and potential
 decompositionrate are positively correlated with nitrogen
 availability.  Herrera, Jose, O.J. Reichman, and
 C. L. Kramer. COMMUNITY STRUCTURE OF FUNGI INHABITING RODENT DENS.
 Division of Biology, Kansas State University, Manhattan, KS, KBS.
 Relatively few studies have included analyses of the spatial and
 temporal patterns of fungal communities and the effect of ambient
 conditions on these patterns.  At Sevilleta we are investigating the
 abundance and diversity of fungi that inhabit food caches of two
 rodent species (white-throated woodrats and bannertailed kangaroo
 rats) and how these features vary over space (along a transect) and
 time (over two years).  Temperature and relative humidity are also
 being monitored and compared to the fungal patterns.  Samples are
 taken from 6 adjacent core dens and from individual dens along a
 transect of geometrically increasing distance from the core (up to
 3.2 km ).  Fungi are isolated, identified, and enumerated, and alpha
 and beta diversity indices are calculated.  Preliminary results
 indicate that more spores are produced in woodrat dens than in
 kangaroo rat dens.  Furthermore, there are no apparent differences in
 the abundances of spores between dens along their respective
 transects.  Spore abundances also are fairly uniform between sampling
 dates, except for an increase in spores in kangaroo dens in January.
 The community of fungi inhabiting the caches differs from that
 observed in samples from ambient air directly above the dens.
 Specifically, cache samples have an unexpected number of sterile
 (non-sporulating) fungi compared to overlying air samples. Analyses
 are being conducted on the relationship of fungal patterns to
 temperature and humidity in dens and the ambient air.  In the future,
 our investigation will center on an examination of the diversity
 patterns and how they are influenced by the rodents.  In addition, we
 will determine how fungal populations affect the storage and
 consummatory strategies of the rodents.  Hobbie, John E., et al. AN
 LTER PROGRAM FOR THE ALASKAN ARCTIC. The Ecosystem Center, Marine
 Biological Laboratory, Woods Hole, MA 02543. ARC The goal of the
 Arctic LTER program is to understand how tundra, streams and lakes
 function in the Arctic and predict how they respond to human-induced
 changes, including climate change.  Terrestrial Studies: Manipulation
 of temperature, light, and nutrients indicate that, over 9 years of
 treatment, direct effects of air temperature change on plants is
 slight.  Additions of nutrients elicit a large response in this
 strongly nutrient limited environment.  Respiratory rates of arctic
 soils are high compared to temperate soils and respiration rates are
 highest above a threshold temperature of 9xC. Lake Studies:
 Whole-system experiments on the mechanisms of nutrient cycling are
 underway in 2 area lakes.  Although the response time of one lake
 (N-1, currently being fertilized) has been twice as rapid as the
 second (N-2, fertilized 1985-1990), both lakes appear to be strongly
 limited by phosphorus.  Two large-bodied species of zooplankton
 border on extinction probably brought about by an increase in the
 population of zooplanktivorous arctic grayling as a result of
 increased human fishing of the lake trout, the grayling primary
 predator.  Stream Studies: Since 1983, the Kuparuk River has been
 fertilized with phosphorus and results indicate that the productivity
 of the river food chain, from algae to grayling, is closely tied to
 the supply of external nutrients.  A 15N-NH4 tracer addition to the
 Kuparuk River revealed a 900 meter spiraling distance and a retention
 of 15N in all parts of the food web for at least 1 year.  Land-Water
 Interactions: The pCO2 and CH4 in soil water, streams, and lakes is
 supersaturated; the excess CO2 and CH4 appears to originate during
 decomposition in the soils and moves toward the streams and lakes via
 groundwater flow.  Modeling: GEM simulated the present stocks and
 turnovers of C and N at the Arctic and Harvard Forest LTER sites.
 Simulations were run to examine the response over 50 years to
 doubling of atmospheric CO2, a 5xC temperature rise, and increased N
 deposition.  Although there are very different amounts of wood in
 each system and different distributions of C and N in the vegetation
 and soils, the simulations revealed qualitatively similar responses.
 There was very little response to increased CO2; both systems
 increased C in plants by 1.5 times due to the increased temperature
 and CO2.

Holland, Elisabeth A., C. Coxwell, D.S. Schimel, and D. Valentine. A
 MODEL OF METHANE PRODUCTION IN SOILS. National Center for Atmospheric
 Research, P.O. Box 3000, Boulder CO 80307 and Natural Resource
 Ecology Laboratory, Colorado State University, Fort Collins CO
 80523. NWT and CPR.  We have developed a simple model of methane
 production for flooded soils. Labile substrate supply is simulated as
 a proportion of the carbon decomposed and is controlled by
 temperature, moisture, and litter quality (lignin:N). The proportion
 of labile substrate converted to methane (rather than CO2) is
 controlled by redox, temperature, pH, substrate supply and
 quality. The model parameterizations are based on a series of
 laboratory experiments which examined the CH4 response to ethanol,
 litter, and root amendments, temperature and pH manipulations in
 anaerobic slurries. Preliminary comparisons demonstrate that the
 model is able to effectively simulate CH4 production for a range of
 environmental conditions and that methane production is sensitive to
 both the amount and quality of incoming carbon.  Homann, Peter, and
 Phillip Sollins.  MODELING SOIL C AND N DYNAMICS THROUGH THE SOLUBLE
 ORGANIC POOL.  Dept. of Forest Science, Oregon State Univ., Corvallis
 OR 97331-7501.  AND.  Soluble organics are important in
 redistributing C and associated elements in forest soil profiles.
 Some soluble organics also serve as readily available energy sources
 for microorganisms.  In a compartment model developed to simulate
 soil C and N dynamics in forest soils, soluble organics are
 represented by two pools which differ in their potentials to be taken
 up and mineralized by microorganisms.  Soluble organics enter the
 soil as components of plant detritus and in solutions such as
 throughfall and stemflow.  They are leached through the profile in
 soil solutions.  Soluble organics are transferred to solid-phase
 organic pools by sorption, precipitation and condensation reactions.
 They are produced by microbial activity, microbial death, and
 extracellular enzymatic processes operating on solid-phase
 pools. Depending on the specific pool, N may enhance or reduce the
 stability of organic C against enzymatic breakdown and microbial
 respiration. The model is designed to simulate the balance of soluble
 organics resulting from these soil processes over periods of one to
 ten years.

Homann, P.S., P. Sollins, H.N. Chappell, D. Lammers,
 A.G. Stangenberger, and M. Fiorella.  CONSTRAINTS ON REGIONAL
 ESTIMATES OF ORGANIC C CONTENTS OF FOREST SOILS.  Department of
 Forest Science, Oregon State Univ., Corvallis OR 97331-7501; Univ. of
 Washington, Seattle, WA; U.S. Forest Service, Corvallis, OR; and
 Univ. of California, Berkeley.  AND.  We compared two methods of
 estimating soil organic C over the western Oregon region.  The Oregon
 STATSGO soil map yielded an area-weighted average of 4.9 kg C/m2 for
 the 0-20 cm depth of mineral soil. The 393 soil pits averaged 6.1 kg
 C/m2 for the 0-20 cm depth and 13.2 for 0-100 cm.  For the soil-pit
 locations, there was good agreement between soil-pit and STATSGO
 averages, but STATSGO values were lower than soil-pit values in areas
 of low soil C and higher in areas of high soil C.  Major constraints
 in using this information for regional estimates of C storage in
 forest soils are: lack of O horizon data in STATSGO and limited O
 horizon data for soil pits; organic matter estimates limited to
 surface horizon in STATSGO; non-random distribution of soil pits
 across the region.  Horwath, William, Eldor Paul and Kurt Pregitzer.
 THE DYNAMICS OF CARBON, NITROGEN AND SOIL ORGANIC MATTER IN POPULUS
 PLANTATION USDA/ARS, Corvallis, OR 97331 and Michigan State
 University, East Lansing, MI 48824.  The lack of root turnover
 studies has led to an inadequate understanding of below-ground
 production and turnover in nutrient cycling processes and global C
 budgets.  The current study examined: (i) above-and below-ground C
 and N allocation patterns; (ii) the role of leaf litter and fine root
 turnover in soil organic matter maintenance; and (iii) the kinetics
 of C mineralization from recently incorporated soil C.  We labeled
 two-year-old hybrid poplars with 14C and 15N at different times in
 the growing season to encompass seasonal C and N allocation patterns.
 A controlled environment chamber was used for 14C uptake and 15N was
 injected into the stem.  The tree-soil and leaf litter decomposition
 plots were sampled for two years following labeling.  Estimates of
 root turnover were less than once per year based on 14C dilution and
 total tree reserves.  Despite low root turnover estimates, the amount
 of 14C stabilized in soil was similar from leaf and root turnover.
 The mean residence time of the recently stabilized 14C in soil from
 both leaf and root turnover was approximately 4 years.

Huberty, Lisa, Katherine Gross, and Karen Renner. RESOURCE COMPETITION
 AMONG CROPS AND WEEDS IN RESPONSE TO TILLAGE AND NUTRIENT
 MANAGEMENT. Michigan State University, East Lansing MI 48824 and
 Kellogg Biological Station, Hickory Corners MI 49060. KBS.  The
 pattern and frequency of disturbance are managed by plowing,
 planting, and harvesting in the conventional till (CT) and no-till
 (NT) treatments of the LTER in agriculture at Kellogg Biological
 Station, MI. The disturbance regime in CT produced an annual weed
 community with low species diversity. The lower disturbance rate in
 NT produced a biennial and perennial weed community with higher
 species diversity. These differences in life-history and species
 composition create plant communities with different growth forms and
 different seasonal patterns of primary production. The biennial and
 perennial NT weed community accumulated more biomass than the annual
 CT weed community early in the season. As a result, the seasonal
 dynamics of resource depletion differed between the two
 treatments. Light at the soil surface and soil nitrate concentrations
 were depleted to lower levels early in the growing season in the NT
 (biennial/perennial) plant community than in the CT (annual) plant
 community. However, by the end of the growing season, the annual weed
 community depleted light and soil nitrate to the same levels as the
 NT community. The early season dynamics of resource depletion were
 critical to explain the differences in how weeds regulated the
 primary production of the crop (soybean) measured at the end of the
 growing season. Nitrogen uptake patterns of the top three dominant
 weed species in the context of the whole community will be used to
 compare the resource use and productivity patterns of annual species
 and perennial species.  Huenneke, Laura and Esteban Muldavin.
 SPATIAL HETEROGENEITY OF ECOSYSTEM STRUCTURE AND FUNCTION: DESERT
 SHRUBLANDS AND GRASSLANDS OF THE JORNADA LTER SITE.  New Mexico State
 University, Las Cruces, NM 88003 and NM Natural Heritage Program,
 University of New Mexico, Albuquerque, NM 87131.  JRN.  We developed
 a method for estimating live aboveground biomass and net primary
 production on a per-unit-area basis, using simple measures of plant
 dimension in permanent quadrats.  This approach has been used to
 estimate biomass and production in 15 sites representing grass- and
 shrub-dominated ecosystems of the northern Chihuahuan desert.  Sites
 are sampled three times per year: in winter (February), late spring
 (May), and late summer (September/October).  Data from 1989 - 1992
 were used to evaluate the differences in biomass, productivity, and
 spatial variability in biomass and productivity among vegetation
 types.  There are no substantial differences in mean biomass or mean
 net primary production per m2.  However, shrub-dominated systems
 (including Larrea tridentata or creosote bush scrub, and Prosopis
 glandulosa or mesquite dunes) show significantly greater variation in
 aboveground biomass within a site than do grass- dominated systems
 (black grama or Bouteloua eriopoda stands, and grassy playas).  Net
 primary production shows less striking differences in heterogeneity
 among vegetation types, but production in black grama grasslands is
 very homogeneous spatially, while shrublands show tremendous
 heterogeneity for at least some seasons.  Our results indicate that
 conversion of black grama grasslands to Larrea- and
 Prosopis-dominated communities may not have altered average ecosystem
 properties, but it has certainly increased the spatial heterogeneity
 of both structure and function of these desert systems.

Hutches, Jr., J.J., E.F. Benfieid, and J.R. Webster. EFFECTS OF LEAF
 TYPE ON THE GROWTH OF A LEAF-EATING CADDISFLY, Pycnopsyche
 gentilis. Dept. of Biology, VPI&SU, Blacksburg, VA 24061. CWT.  A
 recent study examining long-term responses of stream-dwelling
 leaf-eating insects to clearcut logging found a caddisfly,
 Pycnopsyche gentilis, population was significantly more productive in
 streams draining an 11-year-old logged watershed as compared to a
 population in streams draining an undisturbed, reference
 watershed. However, there was 40% more leaf material, i.e., food
 available in undisturbed streams. We studied P. gentilis larval
 growth in the library using fast and slow-processing leaves (black
 birch and white oak, respectively) to determine whether leaf quality
 could explain the higher production. Birch leaves were significantly
 softer than oak leaves (p<0.05) and thus, were possibly better
 resources. However, P. gentilis growth rates were significantly
 higher on the oak leaf diet than the birch leaf diet
 (p<0.05). Assimilation and net growth efficiencies were not
 significantly different between diets (p>0.05) and could not explain
 the results. However, consumption rates indicate larvae were probably
 not fed ad libitum for the birch diet, possibly explaining higher
 larval growth rates on white oak leaves.

Irons, J.G., III1, R.J. Stout2, M.W. Oswood3, C.M. Pringle4 and
 J.P. Bryant3. LATITUDINAL GRADIENTS IN LEAF LITTER DECOMPOSITION IN
 STREAMS: EFFECTS OF LEAF CHEMISTRY AND TEMPERATURE.  1Inst. of
 Northern Forestry, Fairbanks, AK, 2Michigan St. Univ E. Lansing,
 MI. 3Univ. Alaska, Fairbanks, AK, 4Univ. Georgia, Athens, GA. BNZ.
 Autumnal leaf litter that falls into streams of forested regions
 constitutes a major source of energy for stream food webs. The
 processing of this litter has been studied for many years (especially
 in temperate forest streams), and two generalizations have come from
 this research: 1) nitrogen concentration is positively correlated
 with breakdown rate, and 2) water temperature is negatively
 correlated with breakdown rate. We examined these generalizations by
 estimating breakdown rates of litter of ten tree species with widely
 varying nutritional quality (condensed tannin and nitrogen
 concentrations) along the latitudinal gradient from the tropics to
 the subarctic. Study sites were chosen in Costa Rica, Michigan, and
 Alaska in reaches of similar stream size, depth, and velocity. Litter
 breakdown rates of ten tree species were analyzed both on a time
 basis (per day) and a temperature basis (per degree-day above OoC),
 and were compared among locations. We found that: 1) breakdown rates
 were positively correlated with litter nitrogen concentrations, but
 were more highly correlated (negatively) with condensed tannin
 concentrations, and 2) although breakdown rates (per day) were
 highest in Costa Rica, temperature-adjusted rates (per degree-day)
 were much higher in Alaska than in Costa Rica or Michigan. We propose
 a model of leaf litter breakdown in which microbial breakdown is
 negatively correlated with latitude (i.e. temperature) and
 invertebrate breakdown is positively correlated with latitude. In
 this model, we propose that the relative importance in litter
 breakdown shifts from microbes in the tropics to shredder
 invertebrates in the subarctic, and that temperature influences the
 microbial component more than the shredders. Furthermore, we suggest
 that secondary compounds, especially the wide- spread condensed
 tannins, co-determine, along with nitrogen concentration, leaf litter
 breakdown rates.  Johnson, N. C. SELECTION PRESSURES AND EFFECTIVITY
 OF VAM FUNGI. Department of Biology, University of New Mexico,
 Albuquerque, NM 87131. CDR.  Any factor that causes differential
 reproduction and survival of vesicular-arbuscular mycorrhizal (VAM)
 fungi is a selective force and can impact composition of VAM fungal
 communities.  Since VAM fungi depend upon plants for all of their
 carbon (C) requirements, factors that influence the availability of C
 in root exudates (like soil fertility and irradiance) are likely to
 be strong selection pressures on populations of VAM fungi.  VAM fungi
 are usually mutualists, but they can also be parasites.  Their effect
 on plants (effectivity) may be influenced by selection pressures.
 The same characteristics that make a VAM fungus successful when the C
 content of root exudates is reduced (e.g. due to fertilization or
 shading) may also reduce their mutualistic effects.  Namely,
 successful fungi may acquire C not allocated to root exudates, and
 thus, parasitically provision their own growth without contributing
 to plant fitness.  At Cedar Creek Natural History Area a series of
 field and greenhouse experiments were conducted to test the
 hypothesis that fertilizing soil selects for VAM fungi that are
 inferior mutualists.  Results showed that 1) fertilization changed
 the composition of VAM fungal communities and 2) VAM fungi from
 fertilized soils were less mutualistic than those from unfertilized
 soils.  A mechanism to account for these results will be presented
 from physiological, population and community perspectives.

Johnson, Stephen R. and Alan K. Knapp.  EFFECT OF FIRE ON GAS EXCHANGE
 AND GROWTH IN Spartina pectinata WETLANDS. Kansas State University,
 Manhattan,KS, 66506, USA. KNZ.  Photosynthetic and growth responses
 of Spartina pectinata were compared in annually burned and unburned
 wetlands in a northeastern Kansas tallgrass prairie.  Culm density
 was not affected by fire, however, inflorescence density and plant
 height at maturity were all significantly greater in annually burned
 wetlands.  Aboveground production in annually burned wetlands was
 1558 g/m2 vs. 607 g/m2 in unburned wetlands.  CO2 Uptake was also
 consistently higher in burned plants (38.2 mol m-2 s-1 vs. 28.6 mol
 m-2 s-1 in unburned plants) and there was a seasonal difference in
 maximum uptake rates between annually burned and unburned wetlands.
 These results indicate that Spartina pectinata may be a fire
 dependent species, with post-fire responses similar to the dominant
 grasses in tallgrass prairie, as well as other Spartina species.
 Jones, J.A., and G.E. Grant.  LONG TERM STORMFLOW RESPONSES TO
 CLEARCUTTING AND ROADS, WESTERN CASCADES, OREGON: I.  SMALL
 BASINS. Department of Geosciences, Oregon State Univ., Corvallis, OR
 97331 and Pacific Northwest Research Station, U.S. Forest Service,
 Corvallis, OR 97331.  AND.  This study examined a 33-year record of
 matched storm data from three 60 to 100 ha experimental basins in the
 Andrews LTER in western Oregon to determine the effect of
 clearcutting, with and without roads, on storm hydrographs.  One
 treated basin was 100% clearcut with no roads while the other had 6%
 of its area in roads for four years before it was 25% patch clearcut.
 The differences between treated and untreated basins were assessed by
 examining six hydrograph variables (storm begin date/time, peak
 date/time, time to peak, storm duration, peak discharge, and total
 storm volume) for about 320 matched storm hydrographs for each basin
 pair.  Clearcutting with no roads increased the peak discharge,
 volume, time to peak, and duration, advanced the begin time and
 delayed the peak time of storms.  Road construction with no
 clearcutting increased peak discharge, did not change volume,
 advanced time of peak and begin time, and increased time to peak and
 duration of storms.  Road construction with 25% clearcuts increased
 the peak discharge, volume, time to peak, and duration, advanced the
 begin time and did not change the peak time of storms.  The most
 pronounced effects were for small storms whose peak discharges and
 volumes increased 15 to 20% in the first five years after 100%
 clearcutting or 25% clearcutting with roads.  However, even 25 years
 after these treatments large storm peak discharges and storm volumes
 were still 5 to 10% higher than before treatment.  Roads alone
 increased peak discharges by 8% but did not affect storm
 volumes. Clearcutting and road construction appear to have additive
 effects on peak discharges but counteracting effects on peak timing.
 We hypothesize that clearcutting modifies the water balance to
 produce increases in both peak discharge and storm volume, whereas
 roads modify flow routing and thus increase peak discharges without
 affecting storm volumes.  Jones, J.A., and G.E. Grant.  LONG TERM
 STORMFLOW RESPONSES TO CLEARCUTTING AND ROADS, WESTERN CASCADES,
 OREGON: II.  LARGE BASINS. Department of Geosciences, Oregon State
 Univ., Corvallis, OR 97331 and Pacific Northwest Research Station,
 U.S. Forest Service, Corvallis, OR 97331.  AND.  This study examined
 the effect of cumulative clearcutting with roads on storm hydrographs
 in three pairs of adjacent basins ranging from 60 to 600 km2 in the
 western Cascade Range of Oregon.  For each basin pair, landuse
 history (clearcutting and road construction) over the period from
 1930 to 1990 was compiled on a geographic information system (GIS)
 and compared to 150 to 175 matched hydrographs from large storms with
 > 1.1 yr return intervals.  An additional 300 hydrographs from small
 storms were examined for the Lookout Creek/Blue River pair. One pair
 of basins (Lookout Creek, site of the Andrews LTER, and upper Blue
 River) had strongly contrasting cumulative harvest patterns, with
 cumulative harvests of nearly 25% by 1990 and differences in
 cumulative area cut ranging from 0 to 15% of basin area.  The other
 two basin pairs, the North Fork of the Willamette Middle Fork/Salmon
 Creek and the Breitenbush River/N. Santiam River, had more similar
 historical harvest patterns with cumulative harvests of 18 to 24% and
 differences in cumulative area cut from 0 to 4% of basin area.  For
 large storms in all three basin pairs, clearcutting with roads was
 associated with increased peak discharge in the basin with greater
 cumulative area cut over the preceding decade.  Peak discharges were
 significantly increased even when basins differed by as little as 1%
 (6 km2) in area cut.  Timing of peaks was not consistently related to
 between-basin differences in cumulative area cut.  These results are
 consistent with our analyses of small experimental basins in Lookout
 Creek, which suggested that clearcutting with roads would increase a
 basin's storm peak discharge but produce no net effect on storm peak
 timing.  However, small storm peak discharges in the Lookout
 Creek/Blue River pair had a less clear relationship to between-basin
 cumulative cutting, in contrast to the findings from the small
 experimental basins where small storms responded more than large
 storms.  We hypothesize that in large basins the effect of
 clearcutting with roads on peak discharges depends upon the relative
 rates of clearcutting and road construction, as well as channel
 routing processes which propagate stormflow from small to large
 basins.

Juday, Glenn Patrick.  AGE STRUCTURE AND GROWTH HISTORY OF A BOREAL
 WHITE SPRUCE FOREST.  Forest Sciences Dept. Univ. of Alaska
 Fairbanks, Fairbanks Alaska 99775-0080. BNZ A white spruce reference
 hectare that burned in the 1983 Rosie Creek Fire at BNZ was compared
 with an unburned hectare and a 102-tree sample of basal and breast
 height bole sections was analyzed for radial growth to produce a
 master chronology.  Over 90% of the white spruce bole sample trees
 belong to a cohort that originated in the mid 1780s, apparently
 following a fire.  The second cohort appears to have originated about
 8 years after the first, probably from the next abundant white spruce
 seed crop.  The master chronology exhibits three distinct sets of
 marker rings; (1) an 1878-79 trauma that decimated stand growth,
 probably as a result of a snow or ice loading event that stripped off
 branches; (2) a 1910-12 sequence of small, normal, and small rings
 respectively; and (3) a severe growth reduction in 1958-59 which
 followed an exceptionally warm and dry summer of 1957 in interior
 Alaska.  The radial growth and development of the stand was reshaped
 by the 1878-79 trauma, producing three subpopulations of trees here
 termed winners, normal, and losers.  In winner trees the ratio of
 cross-sectional bole area in 1883 compared to 1982 (each representing
 growth intervals of about a century) is greater than 2, in normal
 trees the ratio is between 1 and 2, and in loser trees the ratio is
 less than 1.  The original stand location of all 102 trees was
 analyzed and no systematic pattern was seen in the location of
 winners, losers, or normal trees.  No evidence of intermediate
 regeneration of white spruce was seen.  Thus the structure of this
 stand is largely explained by one initial stand replacement
 (regeneration) event, subsequent gradual stand growth
 differentiation, and a trauma in the middle of the life of the stand
 that improved the competitive performance of some trees and worsened
 the performance of others.  The radial growth record was compared
 with the longest instrument-based climate record in interior Alaska,
 University Experiment Station (UES) located 34 km east of the LTER.
 A comparison of UES warm season temperature with average stand radial
 growth at Bonanza Creek LTER shows an inverse relationship.  Contrary
 to expectations the stand as a whole grew best in the cooler years,
 suggesting that moisture limitations may be the operative controlling
 factor than temperature.  A comparison of UES annual precipitation
 with stand radial growth reveals a one to 4-year lagged response,
 again suggesting that soil moisture is a limiting factor.  White
 spruce are determinate growers and their current years growth
 primarily reflects the previous seasons carbon gain which is stored
 as winter reserves.  Kaufman, Donald W., Glennis A. Kaufman and Elmer
 J. Finck. TEMPORAL VARIATION IN POPULATIONS OF SMALL MAMMALS IN
 TALLGRASS PRAIRIE.  Kansas State Univ., Manhattan, KS 66506.  KNZ.
 Small mammals in ungrazed tallgrass prairie were studied from autumn
 1981 to spring 1991 on Konza Prairie to assess interspecific
 differences in both abundance and temporal patterns of abundance and
 to search for possible factors driving the temporal patterns.
 Estimates of abundance were from permanent live-trap lines set in
 sites whose periodicities of recurring fire ranged from annual to 20
 years.  In descending order of abundance, common species (8 of 14
 species of small mammals captured) were Peromyscus maniculatus,
 Reithrodontomys megalotis, Blarina hylophaga, Peromyscus leucopus,
 Microtus ochrogaster, Sigmodon hispidus, Spermophilus
 tridecemlineatus, and Synaptomys cooperi.  Temporal variation
 (standard deviation of log abundance) differed among species with
 that of the two Peromyscus species much less variable than that of
 the two microtine rodents.  Fluctuations exhibited by Microtus and
 Synaptomys appeared cyclic and were relatively synchronous with each
 other, but not other small mammals.  For other species, temporal
 patterns varied in timing and magnitude of high and low abundances.
 However, autumn abundances of individual species of cricetine rodents
 (Peromyscus, Reithrodontomys, and Sigmodon) were
 intercorrelated. Finally, abundance of species of small mammals did
 not consistently correlate with indices of temperature,
 precipitation, and productivity and, therefore, such factors
 individually do not appear to be simple driving factors behind
 temporal patterns of abundance of small, prairie mammals.  Kaufman,
 Glennis A., Donald W. Kaufman and Elmer J. Finck.  EFFECTS OF FIRE ON
 POPULATIONS AND COMMUNITIES OF SMALL MAMMALS IN TALLGRASS PRAIRIE.
 Kansas State Univ., Manhattan, KS 66506.  KNZ.  In autumn 1981, we
 initiated a long-term study of small mammals in burned and unburned
 tallgrass prairie on the Konza Prairie to understand fire as an
 influence on populations and communities of rodents and shrews.  Our
 analyses of responses of rodents and shrews to experimental spring
 fires in ungrazed prairie are based on data from autumn 1981 to
 spring 1991. Peromyscus maniculatus, Sigmodon hispidus, and
 Spermophilus tridecemlineatus were fire-positive, whereas Blarina
 hylophaga, Reithrodontomys megalotis, Microtus ochrogaster, and
 Synaptomys cooperi were fire-negative.  Assemblages of small mammals
 were greatly altered by fire with P. maniculatus increasing from 35%
 of the average assemblage in unburned prairie to 64% in burned
 prairie, R. megalotis decreasing from 25% to 8%, and B. hylophaga
 decreasing from 17% to 7%.  Further, the diversity and evenness of
 community structure decreased following fire.  In addition to this
 general fire effect, frequency of fire influenced diversity,
 richness, and evenness but not combined abundance of small mammals.
 For example, diversity, richness, and evenness were lower in burned
 sites that were burned annually than burned sites that were burned
 periodically.  Further, an effect of fire history was evident for
 small mammals in burned areas burned annually, burned areas burned
 every two years, and burned areas burned every four years.  In this
 case, diversity and richness decreased with time since the previous
 fire.

Kitajima, Kaoru and Tilman, G. David.  SPATIAL HETEROGENEITY AND
 SUCCESSIONAL CHANGE IN SOIL SEED BANK FLORA IN CENTRAL
 MINNESOTA. Department of Ecology, Evolution, and Behavior, University
 of Minnesota, St. Paul, MN 55108.  CDR.  We report the method and an
 early analysis of our investigation of seed bank in a chronosequence
 of old fields (23 fields ranging between 6 and 65 yr after
 abandonment) and three oak savanna sites (=climax community at Ceder
 Creek LTER).  Our central objective is to examine the correlations
 between soil seed bank flora and past and present vegetation under
 successional change that has been censured over 10 years.  We found
 high heterogeneities of species composition and abundance of seeds in
 the soil in both small and large spatial scales.  Although soil seed
 bank is considered to be important in understanding vegetation
 dynamics in response to disturbances, the labor intensiveness and
 lack of standard protocol obstacle community level studies.  We would
 like to call for an open discussion in search of a standardized
 method that can accommodate long term studies as well as intersite
 comparative studies of soil seed bank communities.  Knapp, A.K.,
 J.M. Briggs, J.M. Blair, W.K. Dodds, D.C. Hartnett, D.W. Kaufman and
 C.W. Rice.  LONG TERM ECOLOGICAL RESEARCH AT THE KONZA PRAIRIE
 RESEARCH NATURAL AREA. Kansas State University, Manhattan, KS
 66506. KNZ.  The long term ecological research program at the Konza
 Prairie Research Natural Area (KPRNA) was one of the initial programs
 established by NSF in 1981. The KPRNA is 3,487 ha of pristine
 (unplowed) tallgrass prairie representative of the native vegetation
 of the Flint Hills of NE Kansas and the western extent of the
 original distribution of this grassland. A fully replicated
 watershed-level experimental design has been established on KPRNA
 that focuses on fire frequency and grazing by large ungulates. The
 primary goal of the LTER program is to understand how grazing and
 fire frequency interact to influence biotic and ecosystem patterns
 and processes over the landscape mosaic, all of which are subjected
 to a highly variable (and possibly directional) climatic
 regime. Research to date has only begun to encompass the range of
 variability in the system, but these data have provided us with an
 appreciation for the nonequilibrium nature of tallgrass prairie. With
 this perspective, we have developed conceptual models that have
 predictive capabilities for a number of key system attributes.

Knoepp, Jennifer Donaldson, Swank, Wayne T.  LONG-TERM SOIL CHEMISTRY
 CHANGES IN AGGRADING FOREST SYSTEMS.  USDA Forest Service, Coweeta
 Hydrologic Laboratory, Otto, NC 28763.  Identification of processes
 regulating long-term soil chemistry changes requires monitoring
 cation leaching and biomass accretion.  We resampled the litter layer
 and upper two mineral soil horizons, A and AB/BA, in two aggrading
 southern Appalachian watersheds 20 years after an earlier sampling.
 Soils from mixed-hardwood Watershed 18 (HDWD), undisturbed since
 1927, exhibited a small but significant decrease in soil pH.
 Extractable base cation content declined substantially in both
 mineral horizons.  For example, Ca levels in the A horizon fell from
 236 kg/ha in 1970 to 80 kg/ha in 1990.  Proportionally, the decline
 was greatest for Mg, which dropped form 111 to 20 kg/ha.  White pine
 (Pinus strobus L.) plantation Watershed 17 (WP) was planted in 1956
 after clear-felling hardwoods and recutting sprouts for 15 successive
 years.  Soil pH and base cation concentrations declined in the A
 horizon since 1970.  Soil pH declined from 5.9 to 5.0 and Ca levels
 from 534 to 288 kg/ha.  Cation content did not change significantly
 in the AB/BA soil horizon.  Nutrient budgets were constructed using
 these soil and litter data plus existing biomass and stream chemistry
 data.  Decreases in soil base cations and soil pH are attributed to
 leaching and sequestration of nutrients in biomass.

Kratz, T.K. and Carl J. Bowser.  PATTERNS OF CO2 SATURATION IN SEVEN
 NORTHERN WISCONSIN LAKES. University of Wisconsin, Madison, WI
 53706. NTL We examined seasonal and annual patterns of CO2 saturation
 in seven lakes in the Northern Highland Lake District in northern
 Wisconsin. The lakes are the primary study lakes of the Northern
 Temperate Lakes Long-Term Ecological Research Project.  We calculated
 degree of CO2 saturation from data on in-situ pH, air-equilibrated
 pH, DIC, and total alkalinity taken at monthly intervals from 1987
 through 1991. Surface waters in the lakes were over-saturated except
 for summer months when surface waters were near equilibrium or
 slightly under-saturated. Annual ice-free season average CO2 for
 surface waters were above atmospheric equilibrium for each of the
 study lakes, indicating that on an annual basis the lakes are net
 sources of CO2 to the atmosphere. This excess carbon must originate
 in the terrestrial system and is transported into surface water most
 likely via hydrologic pathways, but also as dry particulate
 deposition. These results underscore the role surface waters play in
 landscape-level carbon dynamics..

Krievs, Lolita, Stuart Gage, Manuel Colunga and G. Philip Robertson
 ERROR AS A FUNCTION OF RECEIVER DISTANCE FOR DIFFERENTIALLY
 POST-PROCESSED GPS DATA W. K. Kellogg Biological Station, Michigan
 State University, MI KBS.  Global Positioning Systems (GPS) depend
 for their accuracy on a constellation of satellites orbiting at an
 altitude of approximately 10,000 miles.  GPS receivers translate
 radio signals emitted by these satellites into distance measures to
 determine receiver locations on earth.  Electrical interference in
 the atmosphere and geographic variation in landcover and elevation
 are two of many potential influences that can degrade the precision
 of single receiver data processing.  The degree of error caused by
 signal degradation can, however, be substantially reduced by GPS
 differential post-processing.  Differential post-processing is
 performed by comparing satellite signals simultaneously logged by a
 mobile and a base GPS receiver and then correcting the mobile unit's
 location by triangulation.  To be effective, the base unit must log
 signals from a known coordinate location.  Differential GPS (DGPS)
 assumes that the difference between receiver signal errors associated
 with upper atmospheric conditions is negligible in comparison to the
 difference in signal errors associated with the immediate
 environment.  The effectiveness of DGPS should also depend on the
 distance separating the mobile and base units, but the relationship
 between separation distance and error reduction is not well known for
 most landscapes.  We attempted to define this relationship by
 surveying locations of first order geodetic controls using a Trimble
 Basic GPS Receiver while simultaneously logging satellite signals
 with a Trimble Pathfinder Community Base Station at KBS.  Geodetic
 markers were chosen along a 300 mile gradient in southwest
 Michigan. Data were post-processed using Trimble Software.
 Preliminary results indicate that locational accuracy decreases
 significantly with distance from the base station; the extent to
 which this error can be predicted and minimized is discussed.
 Landis1, Douglas A. and Paul C. Marino2. EFFECT OF LANDSCAPE
 STRUCTURE ON PARASITOID DIVERSITY AND PARASITISM IN
 AGROECOSYSTEMS. 1Department of Entomology and Pesticide Research
 Center, State University, E. Lansing, MI. 48824. 2Department of
 Biological Sciences,PO Drawer GY, Mississippi State University,
 Starkville, MS 39762-5759. KBS.  The structural complexity of
 agroecosystems may have important effects on diversity of parasitoid
 communities and their impact on crop herbivores. We examined
 parasitism of Pseudaletia unipuncta (Haworth) (Lepidoptera:
 Noctuidae), a native, polyphagous herbivore with a diverse parasitoid
 community. The study area in south-central Michigan consisted of an
 agricultural matrix dominated by maize, soybean and wheat. Native
 habitats included woodlots (beech-sugar maple association), old
 fields, hedgerows and wetlands. The study area bridged a transition
 zone between structurally complex versus simple agricultural
 landscapes.  The structurally simple area was characterized by large
 agricultural fields (mean 12.4 ha), with few non-cultivated
 habitats. The complex area was characterized by small fields (mean
 3.4 ha) and abundant non-cultivated habitats. Within each area three
 maize fields were selected, each with a minimum of one edge bordered
 by a hedgerow. P. unipuncta larvae from a laboratory colony were
 released in each field on plants 5 m and 90 m from the hedgerow
 border. Larvae were subsequently recovered and reared to determine
 percent parasitism and parasitoid diversity. Seven parasitoid species
 were recovered, four from the structurally simple sites and five from
 the complex sites. No differences were detected in parasitism or
 species diversity between edge and interior sites. However, overall
 parasitism in the complex sites was more than three times higher than
 in the simple sites (18.2% versus 5.l% ). Differences were largely
 attributable to one species, Meterous communis (Hymenoptera:
 Braconidae) which was far more abundant in complex sites. Abundance
 and proximity of preferred habitats for alternate hosts of
 M. communis may account for the observed differences.  Lakshmi,
 Bharatha and Frank P. Day. NITROGEN AVAILABILITY AND N MINERALIZATION
 RATES ALONG A COMMUNITY CHRONOSEQUENCE ON HOG ISLAND, VIRGINIA COAST
 RESERVE. Department of Biological Sciences, Old Dominion University,
 Norfolk, VA 23529-0266. VCR.  Available soil nitrogen and
 N-mineralization rates along a dynamic nutrient-poor island are
 important in understanding the succession of coastal island
 systems. On a 6, 24, 36 and 120 year-old chronosequence on Hog
 Island, the nitrogen availability in the dunes increased with
 age. But in the associated swales the nitrogen concentrations were
 higher with the dominance of Myrica cerifera, a nitrogen fixing
 species. In general, the swales had higher soil nitrogen levels
 (0.016-0.052 g m2) than dunes (0.015-0.038 g m2) and the
 concentrations of ammonium-N were higher than the
 nitrate+nitrite-N. Application of urea to the dunes resulted in a
 10-13 fold increase in nitrogen with highest accumulation in the
 oldest dune. Net N-mineralization was highest in the younger dune
 (0.053 mg kg-1 day-1), and with fertilization this rate increased
 15-fold. Fertilization had only a minimal effect on mineralization in
 the oldest dune. These results indicated that the younger dunes were
 N limited and the limitation was minimized with age. Higher nitrogen
 levels in the older dunes might be due to an input of N-rich litter
 from the adjacent Myrica dominated swales.

Lascara, C.M., E.E. Hofmann, R.M. Ross, and L.B. Quetin. DISTRIBUTION
 OF ANTARCTIC KRILL WITHIN THE PALMER LTER STUDY REGION BASED ON
 BIOACOUSTICS. Center for Coastal Physical Oceanography,Old Dominion
 University, Norfolk, VA 23529 and Marine Science Institute,
 University of California, Santa Barbara, CA 93106.  PAL.  The Palmer
 LTER is using bioacoustics to quantitatively map the spatial and
 temporal distribution of Antarctic krill (Euphausia superba), which
 is one of the key species of the pelagic marine ecosystem.
 Acoustical measurements are coordinated with collection of a suite of
 multi-disciplinary data at stations within the large-scale peninsula
 grid. The objective is to interpret krill distribution patterns in
 relation to other habitat characteristics, in particular, the
 concentration and composition of food resources, ice history,
 large-scale flow regimes, and hydrography. Three cruises have been
 conducted off the west coast of the Antarctic Peninsula, austral
 spring 1991, austral summer and fall 1993.  Over 2000 swarms have
 been identified from 135 acoustic tows, totaling 260 linear
 km. Generally swarms were < 50 m in length, < 10 m in height,
 positioned in the upper 80 m of the water column with mean biomass
 values < 20 g m3. Several large dense aggregations were also observed
 extending 100s of m horizontally and up to 50 m vertically. In spring
 1991, mean krill biomass ranged from 0-95 g m2 and was highest in
 three areas: inside Dallman Bay, open waters within 20 km of the ice
 edge, and an offshore station located over Circumpolar Deep Water.
 In summer 1993, mean krill biomass ranged from 0-460 g m2 and
 exceeded 100 g m2 at many nearshore stations where the influence of
 ice melt on hydrographic structure and water column stability was
 evident.

Lauster, George H., James Hurley, Paul Garrison, Martin Schafer and
 David Armstrong. DEEP PRODUCTION IN LAKES: EFFECTS ON NUTRIENT
 TRANSPORT, TRACE METAL CYCLING AND PALEOLIMNOLOGY. Univ. Wisconsin,
 Water Chemistry Program, Madison WI 53706. NTL companion project.
 Recent research has shown that deep production of phytoplankton and
 phototrophic bacteria are common, and may play an important role in
 controlling the water quality and biological resources of lakes. In
 this study, we are evaluating the importance of deep planktonic
 production to overall lake production and water quality. Secondly, we
 are evaluating the effects of deep production on the trace metal
 transport by comparing selected trace metals both within lakes and
 among lakes of differing particle types and differing redox
 characteristics. Thirdly, we are examining the effects of deep
 production on phosphorus cycling. Finally, we are evaluating the
 influence of deep production in controlling the pigment record in
 sediments. The first phase of our study, begun in the autumn of 1992,
 is synoptic in an attempt to define sets of characteristics
 controlling deep production and the potential effects on nutrient
 transport and trace metal cycling. The results of our Fall 1992
 survey of nineteen Wisconsin lakes indicate the diversity of
 conditions under which deep production is present in north temperate
 lakes. This project supported in part by the United Geological
 Survey.

Lezberg, Ann L. and David R. Foster.  TREE SPROUTING AND SURVIVAL IN A
 TEMPERATE FOREST AFTER SIMULATED HURRICANES.  Harvard Forest, Harvard
 University, Petersham MA 01366.  HFR.  Hurricane damage was simulated
 by pulling down selected trees with a cable and winch in two Quercus
 borealis - Acer rubrum stands (0.8 ha, 0.3 ha) in Central New
 England. All damaged and residual trees were surveyed for extent of
 sprouting and leafout for two and three growing seasons to explore
 the role of vegetative growth and of survival to forest recovery, and
 the influence of individual tree characteristics on initial response
 to damage. Of previously live, damaged trees, over 42% still leafed
 out in the second growing season and over 50% sprouted from the base,
 stem, or branches. Sprouting frequency for damaged trees increased by
 the second year and declined in year three while crown leafout
 declined each year.  Bent stems sprouted more frequently than
 uprooted, snapped or leaning trees, but leaning trees leafed out more
 frequently than other damaged stems.  Acer rubrum was more likely to
 have sprouts at the base than other species. While a significant
 portion of the propensity for sprouting and leafing out was explained
 by differences in damage type and to a lesser degree by other tree
 characteristics, these parameters were linked in a complex way,
 suggesting that variation in initial tree response to wind damage is
 the result of a mosaic of inherent tree characteristics, damage type,
 and untested variables such as the local light regime.

Lovett, G.M., S.V. Ollinger, K.C. Weathers, and J.D. Aber. EVALUATING
 PATTERNS OF ATMOSPHERIC DEPOSITION AT LANDSCAPE AND REGIONAL SCALES.
 Institute of Ecosystem Studies, Box AB, Millbrook NY 12545, and
 Complex Systems Research Center, University of New Hampshire, Durham
 NH 03824. HBR and HFR.  Atmospheric deposition, including wet, dry
 and cloud water deposition, is usually measured at individual sites
 or in sparse monitoring networks which are assumed to be applicable
 to whole landscapes and regions.  However, high spatial variability
 in atmospheric deposition can be generated by the combined effects of
 topographic and vegetational features of the landscape and the air
 flow patterns within a region.  Using existing monitoring data for
 precipitation chemistry, air chemistry, and precipitation amount, we
 have estimated patterns of sulfur and nitrogen deposition across the
 northeastern region.  West-to-east gradients in wet deposition and
 south-to-north gradients in dry deposition are evident, as well as
 increases in wet deposition associated with orographic precipitation
 in the major mountain ranges.  Within one of those mountain ranges,
 the Catskills, we have used Pb in the forest floor as an indicator of
 finer-scale patterns of atmospheric deposition associated with
 elevation, slope aspect, vegetation type, and forest edges.  All of
 these factors influence deposition rates, with the highest rates
 found at high-elevation coniferous forest edges on west facing
 slopes.  These sites can receive as much as fivefold more deposition
 than an average low-elevation site.

Macko, Stephen A., Robert Tappe, Michael Engel. STABLE CARBON ISOTOPIC
 COMPOSITIONS OF INDIVIDUAL MOLECULAR COMPONENTS. Univ. Virginia,
 Charlottesville, VA 22903. VCR.  Stable isotope compositions of
 individual chemical constituents offers a unique and powerful
 approach toward the understanding of the history of an environment
 and origins of the materials which are preserved in the
 environment. The techniques can involve the analysis of dissolved
 materials, such as ammonium or nitrate, or the assessment of
 compounds that make up the organic matter in the study
 area. Dissolved nitrogenenous materials can be analyzed to indicate
 inputs of fertilizer nitrogen, animal wastes, or the extent of
 denitrification in a soil or groundwater. The latter characterization
 of compounds can be applied to determine the carbon isotopic
 compositions of amino acids, fatty acids, carbohydrates and
 hydrocarbons extracted from sediments, plants or animals. Inputs from
 bacterial processing of organic matter, as well as preservation of
 indigenous materials within a sediment can readily be distinguished
 with compound specific isotope analysis, and more importantly, can
 indicate new production of materials which have the same chemical
 composition as that which was in the environment
 originally. Dissolved inorganic nitrogen analysis necessitates the
 isolation of the nitrate, or ammonium, from the sample through
 extraction, and distillation. Compound specific analysis usually
 entails hydrolysis of the sample and often derivatization of the free
 component to a volatile material suitable for gas chromatographic
 analysis. This addition of carbon to the compound can be corrected
 for through back calculations involving knowledge of the
 stoichiometry of the carbon addition and the kinetic isotope effect
 of the bond formation in derivatization. Preliminary results from the
 above analyses have allowed for the assessment of contributions of
 fertilizer nitrate to groundwaters, and the quantification of
 bacterial inputs into the more refractory materials which are
 eventually preserved in a deposit. Potentially, compound specific
 isotope approaches could also be used in the same manner to follow
 the flow of essential biochemical components from primary production
 to higher level consumers.

Magill, Alison H. and John D. Aber.  EFFECTS OF CHRONIC NITROGEN
 ADDITIONS ON SOIL MINERALIZATION, NITRIFICATION RATES AND DISSOLVED
 ORGANIC CARBON AVAILABILITY.  Complex Systems Research Center,
 University of New Hampshire, Durham, NH 03824. HFR.  Chronic nitrogen
 addition plots are located at the Harvard Forest LTER site. Ammonium
 nitrate (NH4NO3) fertilizer additions have been ongoing in two stands
 (mixed hardwood and red pine) since 1988 at four different treatment
 levels on 8- 30x30 m plots: control, 50 Kg-N*ha-1*yr-1; 150*ha-1*yr-1
 and a nitrogen plus sulfur treatment (50*ha-1*yr-1 plus 75
 Kg-S*ha-1*yr-1) as Na2SO4. Several different ecosystem components are
 monitored for changes in carbon and nitrogen pools including soils
 (buried bags/KCl extracts), soil solution (lysimeters), green
 foliage, litterfall, tree growth and trace gas emissions. In 1992,
 only one set of buried bags was collected in mid-summer. Data from
 that 6-week period show the mineral soil as being the region of
 greatest mineralization which follows the same pattern as seen in
 1991. Nitrification appears to be an increasingly greater portion of
 total mineralization in the pine plots. In addition, nitrification
 rates are beginning to increase in the hardwood high treatment
 plot. A full set of buried bags is being collected for 1993.  The
 soil solution chemistry results for the pine plots show a range of
 3.2 mg NO3-N*L-1 to 18.6 mg NO3-N*L-1 over the growing season in the
 high treatment plot where the low and control plots had no soil
 solution greater than 0.38 mg NO3-N*L-1. This is similar to 1991
 data. However, ammonium is beginning to show up in the high pine
 lysimeters for the first time in 1992. The hardwood plots are also
 beginning to show some leaking of NO3; the low N plot lysimeters were
 6.4 mg NO3-N*L-1 for the July collection. However, lack of water in
 the high treatment plot during that same sampling period creates a
 lack of data for comparison. Green foliage and litterfall have also
 been collected each year; tree diameter data was collected in
 November 1992. A laboratory experiment has been conducted in order to
 help determine the mechanisms behind the decrease in soil organic
 horizon mineralization rates over the course of the fertilizer
 applications. One hypothesis for the decrease is the depletion of
 available carbon for microbial metabolism, i.e., DOC. Litterfall from
 7 species was collected, air-dried, and incubated in the lab for 15
 weeks. Three treatments (DI water (control) NO3 and NH4) were added
 to the samples weekly. The litter was leached with DI water 11 times
 and the leachate analyzed for NO3-N, NH4-N and DOC. Preliminary
 values for leachate DOC concentrations show NO3 treated litter to
 have the highest DOC and a wide variety between species.

Martin, Mary E and John D. Aber.  THE USE OF NEAR INFRARED REFLECTANCE
 TO MEASURE CANOPY CHEMISTRY AT HARVARD FOREST, PETERSHAM, MA. Complex
 Systems Research Center, University of New Hampshire, Durham, NH
 03824. HFR.  The concentrations of nitrogen, lignin, and cellulose in
 canopy foliage are related to important ecosystem parameters such as
 litter decomposition rate, nutrient availability, and plant
 productivity.  Previous laboratory work with both agricultural
 products and forest foliage has shown that relationships exist
 between reflectance at selected wavelengths in the near infrared
 (NIR) spectrum and nitrogen, lignin and cellulose concentrations. In
 this project we extend this work to both the fresh leaf and canopy
 scales using data from an NIRS model 6250 spectrophotometer (leaf
 scale) and the Airborne Visible Infrared Imaging Spectrometer
 (AVIRIS, canopy scale). AVIRIS image data were acquired over the
 Harvard Forest in Petersham, MA in September 1990,1991 and June 1992.
 This instrument measures visible and infrared radiance in 224 bands
 from 400-2500nm with a spectral resolution of 10nm.  Spatial
 resolution of AVIRIS data is 17-20m.  Twenty sites (50x50m) were
 sampled at Harvard Forest within 1 week of the 1992 overflight(15
 June).  These sites were chosen to represent a wide range of species
 composition (both broad-leaved and needle-leaved species).  Foliage
 samples collected from these sites were analyzed for nitrogen,
 cellulose, lignin, and water content. Canopy biomass for each site is
 determined by litterfall collection. Both field and image data has
 been collected on an additional 30 sites at Harvard Forest in 1993
 for validation purposes.  The collection of AVIRIS spectral data and
 field data at these sites will provide the information necessary to
 determine with what degree of accuracy canopy chemistry can be
 measured by airborne (and spaceborne) sensors.  One goal of this work
 is to use algorithms to map species and nitrogen concentration from
 the AVIRIS image data.  Such maps will be used to drive a model
 predicting forest ecosystem carbon balances(PnET) at Harvard Forest.
 Martinez-Turanzas Gustavo A1 and Walter G. Whitford2. EFFECTS OF
 WATER ON CREOSOTEBUSH GROWTH AND DECOMPOSITION PROCESS IN THE
 NORTHERN CHIHUAHUAN DESERT. 1Colorado State University, Ft. Collins,
 CO., 80523, USA.; 2USEPA Environmental Monitoring Systems Laboratory,
 Las Vegas, NV, 89193, USA. JRN.  This study evaluated effects of
 precipitation on creosotebush growth and decomposition process in a
 plant community dominated by creosotebush (Larrea tridentata (DC)
 Cov.] in the Jornada LTER site (northern Chihuahuan Desert). Three
 treatments were imposed during summer period from 1987 to 1992:
 1)control plots received only natural precipitation; 2) drought plots
 received no precipitation and 3) irrigated plots received natural
 precipitation and 25mm of supplemental water applied every 15 days
 from July to September. Effects of draught and irrigation on the
 creosotebush growth and decomposition of surface creosotebush leaf
 litter bags and buried roots of the herb, senna [Cassia bauhinioides
 (Gray)] were determined by measuring dry weight of branch tips and
 mass loss respectively.  Results showed that creosotebush exhibited a
 tolerance to disturbance. The supplemental water did not result in
 significantly more biomass on the irrigated creosotebushes. Surface
 leaf litter and buried root decomposition rates were not affected by
 water. The supplemental water did not stimulate higher rates of
 surface litter and buried root decomposition. In surface litter
 decomposition, initial rapid mass loss seems to be primarily due to
 abiotic processes followed by losses due to biological activity,
 which is also the major factor in buried root decomposition.

Mason, Owen K. and James E. Beg�ét. RECONSTRUCTION OF LATE HOLOCENE
 ALLUVIAL HISTORY: GEOMORPHIC CONSTRAINTS OVER ECOLOGICAL SUCCESSION
 ON THE TANANA RIVER, ALASKA.  Univ. of Alaska, Fairbanks, AK
 99775. BNZ.  A sequence of historic and prehistoric flood deposits of
 the Tanana River is preserved on the anastomosing channel islands
 southwest of Fairbanks in the Bonanza Creek Long Term Ecological
 Research (LTER) site.  A suite of > 20 radiometric dates,
 granoulmetric differences and microstratigraphic observations
 establish the lower limiting ages on the stability of the islands for
 the establishment of spruce (Picea spp.)  forest.  Channel shifts and
 island evolution are mapped using 14C ages and dendrochronological
 inferences and will be integrated into the LTER geographical
 information system (GIS).  Most islands are less than 700 yrs old:
 older deposits are found on terraces.  Several major
 lithostratigraphic units are observed: (1) thick cross-bedded,
 pedogenically unaltered alluvial silty sands deposits 3000-2000 BP,
 recording an interval of large floods: (2) thin silty beds and
 paleosols formed after 2000 yrs ago when large floods were uncommon:
 and (3) sand units recording large floods during the last several
 hundred years.  Flood frequencies changed in response to regional
 climate changes, with more frequent flooding during times of
 widespread alpine glaciation.

Mccaig, B. C., J. L. Hamrick, and B. L. Haines.. CLONAL STRUCTURE OF
 Robinia pseudoacacia (black locust) IN THE SOUTHERN
 APPALACHIANS.University of Georgia, Athens. GA 30602 Clonal
 structure, the genotypic patchiness within populations due to
 vegetative reproduction, was investigated in Robinia pseudoacacia
 (black locust) on four watersheds in the Southern Appalachians.
 Watershed ages were 5, 13, 30, and 40 years following clear cutting.
 A total of 1200 trees and juveniles were mapped.  Foliage samples
 were analyzed by protein gel electrophoresis for 15 polymorphic loci
 to identify clones.  Average heterozygosity of polymorphic loci was
 52.3% and their was an average of 4.27 alleles per polymorphic locus.
 The number of clones in a plot ranged from 24 to 52.  In the 30 year
 old stand, 2 clones accounted for 86.7% of the ramets.  Clonal
 structure does not appear to be correlated to age, but there were
 significant differences in structure between populations.  Number of
 genotypes, population structure before a disturbance, and the history
 of succeeding disturbance events could be additional factors
 influencing the clonal structure of this species.  McKnight, D.M. and
 E.D. Andrews.  HYDROLOGIC AND GEOCHEMICAL PROCESSES AT THE
 STREAM-LAKE INTERFACE IN A PERMANENTLY ICE-COVERED LAKE IN THE
 MCMURDO DRY VALLEYS, ANTARCTICA.  U.S. Geological Survey, 3215 Marine
 St., Boulder, CO 80303 For many ice-covered lakes in the McMurdo Dry
 Valleys lake levels have risen progressively over the past 20 years,
 as a result of increases in glacial meltwater streamflow.  These
 amictic lakes have stable water columns with mixing dominated by
 chemical diffusion. During the summer, a moat of openwater forms
 between the ice edge and the lake shore.  We conducted an experiment
 using LiCl as a hydrologic tracer to determine flowpaths and
 velocities of streamwater mixing with moat water and moat water
 mixing into the lake.  Results indicate that substantial hyporheic
 (substream) interactions occur in the stream and that wind-driven
 currents in the moat are important in advecting moat-water through
 and under the moat/ice-cover boundary.  These mixing processes will
 influence the biogeochemical response to raising lake levels.
 McSwiney, Claire P. and William H. McDowell. CONTROLS ON NITROUS
 OXIDE PRODUCTION IN THE LUQUILLO FOREST.  Department of Natural
 Resources, University of New Hampshire, Durham, NH 03824.  Tropical
 areas are considered major sources in the global nitrous oxide
 budget, but factors controlling nitrous oxide production are poorly
 described for non-agricultural tropical ecosystems.  Previous work in
 the Luquillo Forest has shown that gas production rates are high, and
 show strong spatial variation as a function of landscape position in
 some watersheds.  The objectives of the proposed study are to
 determine the processes that control nitrous oxide production in
 different biogeochemical environments in the Luquillo Forest, and to
 document the effects of rainfall on production rates.  Both field and
 laboratory experiments will be conducted.  Refined estimates of
 watershed-level nitrous oxide flux will be calculated by weighting
 plot-level fluxes by spatial (landscape) and temporal (rainfall)
 variation.  Micks, Pat and John D. Aber.  SOIL RESPIRATION RESPONSE
 TO CHRONIC NITROGEN APPLICATION IN TWO STANDS AT THE HARVARD FOREST.
 Complex Systems Research Center, University of New Hampshire, Durham,
 NH 03824. HFR.  Soil respiration was measured in nitrogen-treated
 soils in the Chronic Nitrogen Addition Experiment at the Harvard
 Forest in Petersham, MA. The objective was to monitor short-term soil
 microbial response to continued nitrogen applications in soils which
 have received nitrogen applications since 1988 in an ongoing
 experiment to determine forest ecosystem response to atmospheric
 nitrogen deposition. This respiration study was designed to test the
 hypothesis that microbial immobilization is responsible for the high
 nitrogen retention in the treated plot soils.  Soil CO2 efflux was
 monitored in situ by the soda lime technique in a red pine and a
 mixed hardwood stand throughout two consecutive monthly nitrogen
 application periods during July and August 1992.  In each stand,
 measurements were made in an untreated control plot, a high-N plot
 receiving 150 Kg N ha-1 yr-1 as NH4NO3, and a plot of previously
 untreated soil which received nitrogen application identical to the
 high-N plots during the two-month study period.  In mid-August a
 third nitrogen application was made to the previously untreated
 plots. Extractable nitrogen was monitored throughout August in these
 two plots. Short term soil microbial response to individual nitrogen
 applications was evaluated by comparing changes in soil CO2 afflux
 rates among the six plots and by disappearance of the applied
 nitrogen in the previously untreated soils. CO2 afflux data revealed
 no conclusive evidence of increased soil microbial activity resulting
 from single nitrogen applications, nor any differences due directly
 to long-term nitrogen treatments. However, soil extract data showed
 rapid disappearance of the applied nitrogen. Possible explanations
 are: 1) microbial immobilization occurred without measurable increase
 in respiration; and 2) nitrogen was immobilized by abiotic as well as
 microbial mechanisms.  Millikin, Catherine and Rich Bowden.  EFFECTS
 OF PIT AND MOUND DISTURBANCE ON CO2 EFFLUXES FOLLOWING A SIMULATED
 HURRICANE BLOWDOWN IN A TEMPERATE FOREST.  Univ. of California, Davis
 CA 95616 and Allegheny College, Meadville PA.  Extensive uprooting of
 trees by hurricanes can create areas of severe soil disturbance in
 temperate forests.  In particular, uprooted trees leave shaded pits
 and mounds of exposed roots and mineral soil.  To assess the
 contribution of pit and mound microhabitats to overall CO2 emissions
 for an experimental blowdown at the Harvard Forest LTER (MA), CO2
 fluxes during summer were measured using the soda lime technique on
 pit, mound, and control plots.  Mean flux values were 45.4, 80.1, and
 99.0 mg C/m2/hr for pit, mound and control plots, respectively.
 Although CO2 emissions from pits were lower than from mounds or
 controls, total contribution (5.3%) from pits and mounds to the
 overall flux rate at the site was not important.  Therefore,
 measurements taken from undisturbed soils are representative of
 effluxes over the entire disturbed site.  Moorhead, Daryl, and Robert
 Wharton. ALGAL MAT PRODUCTION IN AN ANTARCTIC LAKE: RESULTS OF A
 PRELIMINARY MODEL. Texas Tech Univ., Lubbock, TX 79409 and The Desert
 Research Inst., Reno, NV. MCM.  The perennially ice-covered lakes of
 Taylor Valley, South Victoria Land, Antarctica, have well-developed
 benthic algal communities.  Portions of this mat tear loose (liftoff)
 from the sediments and float to the surface, where they are frozen
 within the overlying ice.  This material is transferred through the
 ice by ablation and distributed by wind throughout the valley.  The
 extremely low productivities of terrestrial ecosystems in this region
 suggest that allochthonous inputs of algal mat may be an important
 source of the organic carbon found in soils.  A mathematical model
 was developed to examine the productivities of these algal mats,
 based on previous studies of Antarctic streams and lakes.  Gross
 primary production is driven by light intensity, utilizing the
 equation for a rectangular hyperbola, given the maximum observed
 photosynthetic rate and half-saturation coefficient.  For a
 subAntarctic Signy Island lake, simulated annual net production is
 equivalent to estimates based on field observations (4 g C per square
 meter), verifying reasonable model behavior.  The 1988-1989 light
 regime beneath the ice at Lake Hoare, Taylor Valley, yields gross
 primary productivities ranging from 155 to 3 g C per square meter at
 depths ranging from 0 to 10 m, respectively.  These rates are
 comparable to production estimates based on studies of other
 Antarctic lakes and are sufficient to supply quantities of mat
 materials that are lost by liftoff, ablation and wind action from
 Lake Hoare.

Morris, James T. ESTUARINE NUTRIENT DYNAMICS AT NORTH INLET: TIDAL
 HARMONICS, LONG TERM TRENDS, AND REGULATION BY EXCHANGE WITH
 INTERTIDAL MARSHES. Univ. South Carolina, Columbia, SC 29208. NIN.
 North Inlet is an oligotrophic estuary with minimal input of surface
 water.  There is considerable drainage of tidal water into intertidal
 marsh sediments, where microbial transformations of nutrients occur,
 and subsurface return to tidal creeks.  Where salt has been used as a
 conservative tracer to calculate the turnover of water in sediments,
 I estimate that 8-10 l m-2 d-1 of tidal water drains through marsh
 sites located at mean high tide.  These exchanges appear to dominate
 the nutrient chemistry of the estuary.  Nutrients and chlorophyll
 have been monitored daily at 3 stations within the estuary for 10+yr.
 The stations are located at the mouth (M), center (C), and
 most-landward margin (L) of the estuary. The majority of nutrients
 show statistically significant increases in concentration over time.
 Furthermore, ammonium, nitrate, and phosphate have increased most
 rapidly at L and least at M, which suggests a land and/or marsh
 source.  All nutrients display harmonics with periodicities
 corresponding to the principal lunar or M2 (12.42 hr), lunar monthly
 (27.6 d), and annual solar tides, but the M2 nutrient harmonics are
 not in phase with the tides, i.e., maximum nutrient concentrations
 occur at low tide.  With few exceptions, the amplitudes increase from
 the mouth landward.  N:P atom ratios are generally less than 15,
 which indicates nitrogen limitation of phytoplankton.  These
 observations are all consistent with the hypothesis that the
 intertidal marshes function as a net source of nutrients to the
 estuary and that hydrologic exchanges between creeks and intertidal
 sediments control the nutrient dynamics of the estuary.  Mullen,
 Renee B., and Steven K. Schmidt. DYNAMICS OF PHOSPHORUS AND NITROGEN
 UPTAKE AS RELATED TO DEVELOPMENT OF FUNGAL ENDOPHYTES IN RANUNCULUS
 ADONEUS. Environmental, Population, and Organismic Biology, Campus
 Box 334, University of Colorado, Boulder CO 80309-0334. NWT.
 Phosphorus and nitrogen levels, phenology of roots and shoots, and
 development of vesicular arbuscular mycorrhizal (VAM) fungi and other
 endophytes were monitored for two years in natural populations of the
 perennial alpine herb, Ranunculus adoneus. The purpose of this study
 was to understand how endophyte development relates to phosphorus and
 nitrogen uptake in R. adoneus. This was accomplished by
 quantification of structures of VAM fungi and other root endophytes
 during maximum nutrient accumulation. Arbuscules were only present
 for a few weeks during the growing season of R. adoneus and their
 presence corresponded with increased phosphorus accumulation in both
 the roots and shoots of R. adoneus. Nitrogen accumulation appeared to
 be related to relatively high levels of a dark septate fungus. In
 addition, phosphorus accumulation and peaks in mycorrhizal
 development occurred well after plant reproduction and most plant
 growth had occurred. The late season accumulation of phosphorus by
 mycorrhizal roots of R. adoneus could be stored for use during early
 season growth and flowering the following spring. In this way
 R. adoneus can flower before soils thaw and root or mycorrhizal
 nutrient uptake can occur.

Myster, Randall and Lawrence Walker. SUCCESSIONAL PATHWAY VARIATION
 WITHIN AND AMONG 16 PUERTO RICAN LANDSLIDES. University of Puerto
 Rico, San Juan PR and University of Nevada, Las Vegas, NV. LUQ.  We
 counted the number of tree stems in 3 x 5m permanent landslide plots,
 generated successional pathways in Principal Components Analysis
 (PCA) space and explored variation within and among landslides.  We
 found that PCA separated plots well, with nitrogen-fixing,
 non-vascular and other rare species represented in early succession.
 PCA defined plant groupings implicating mycorrhizae association
 strategy as important in regeneration.  Within slides, many plots
 stayed close to the origin and did not show much community
 development in the sampling time frame of three years, but a slide in
 the Espirtu Santo watershed had the most pathway variation, defining
 the dimensions of PCA space.  PCA axis I separated plots of differing
 microhabitats (edge and center), while PCA axis II separated plots
 from different transects.  However, evidence of successional rate
 decrease and convergence over time was minimal.  Among slides,
 landslides with the most variation and most distinct pathways were
 also among the largest and oldest.  The other landscape parameters of
 elevation, landuse, slope and aspect seem to affect landslide
 occurrence more than development after disturbance.  We conclude that
 compared to other rainforest disturbances, landslide pathways maybe
 longer with more local variation, have less convergence due to
 recurrent disturbance and a slower rate of recovery.

Neff, Jason C., William D. Bowman, and Elisabeth A. Holland. FLUXES OF
 NITROUS OXIDE AND METHANE FROM NITROGEN AMENDED SOILS IN THE COLORADO
 ALPINE. Environmental, Population, and Organismic Biology, Campus Box
 334, and Institute of Arctic and Alpine Research, Campus Box 450,
 University of Colorado, Boulder CO 80309 and Atmospheric Chemistry
 Division, National Center for Atmospheric Research, P. O. Box 3000,
 Boulder CO 80307. NWT.  Fluxes of nitrous oxide and methane between
 soils and the atmosphere strongly contribute to the global
 atmospheric balance of radioactively important trace gases. In
 addition, the exchange of nitrous oxide and methane between tundra
 soils and the atmosphere may represent an important step in the
 cycling of nitrogen and carbon through alpine ecosystems. The
 microbial processes governing nitrous oxide and methane fluxes are
 sensitive to the availability of nitrogen in soils. This sensitivity,
 however, has not been quantified in alpine tundra soils. We examine
 the influence of nitrogen additions on the fluxes of nitrous oxide
 and methane from wet and dry meadow communities on Niwot Ridge. Urea
 nitrogen was added to experimental plots in June of 1990 and July of
 1991. Using flux chambers installed in the tundra from June to August
 of 1992, we measured emissions from five nitrogen-amended plots and
 five control plots in each community. Our results indicate that the
 addition of nitrogen to the dry meadow community resulted in a 60%
 reduction in methane uptake (oxidation) and a 22 fold increase in
 nitrous oxide emissions. Nitrous oxide emissions in the wet meadow
 community increased by a factor of 45 while methane fluxes were not
 significantly changed.

Nolen, Barbara.  JORNADA LTER GIS AND REMOTE SENSING DATABASES. New
 Mexico State University. Las Cruces, New Mexico 88003. JRN.  This
 poster represents the basic GIS and remote sensing data layers for
 the Jornada LTER research site.  The research area map was designed
 to include the entire Jornada basin.  Hydrology was important in
 determining the extent of the mapping area. Data layers used for the
 research area map include roads, hydrology, ownership and research
 sites. The first three data layers were converted from MOSS files
 created at the Bureau of Land Management. The digital elevation model
 was composed of 22 USGS topographic quadrangles using the 1:24000
 dems. From this model slope, aspect and contour lines are
 composed. The Landsat TM scene is a combination of path/rows 33/36
 and 33/37 from Landsat 5 taken in August and September 1992.  North,
 Malcolm and Jerry Franklin ANALYZING CANOPY STRUCTURE IN CONIFEROUS
 FORESTS College of Forest Resources, AR-10, University of Washington,
 Seattle, WA 98195.  NET.  Complex canopy structure is a
 distinguishing characteristic of old growth and is believed to
 provide unique habitat for arboreal wildlife.  In this initial effort
 at quantifying canopy structure, we used two stand-level measures:
 the percent of available canopy space occupied by foliage, and the
 diversity of vertical layering of foliage.  We compared the
 heterogeneity of foliage layers in three distinct stand types:
 managed mature (70 year old trees originating from a clearcut and
 slash burn), natural mature (70 year old trees originating from a
 wind storm) and old growth.  The analysis tested whether tree
 diameter or ocular height estimates can provide good assessments of
 these two canopy structure measures.  Tree diameter was highly
 correlated with crown volume and therefore was used to calculate the
 percentage of canopy space occupied by foliage.  Tree diameter,
 however, was not correlated with foliage layering.  Ocular height
 estimates, when analyzed with the Berger- Parker diversity index,
 provided a more robust index of foliage layering within a stand.  Old
 growth compared to managed mature showed a higher percent of
 available canopy space occupied by foliage (p<0.05) and much greater
 diversity of foliage layering (p<0.001).  Natural mature stands were
 closer to old growth in both the percent of available canopy space
 occupied (scale adjusted for height) and vertical layering.  These
 exploratory results suggest stand origin is a stronger influence on
 canopy structure than stand age.  The measures used in this pilot
 study suggest one method for comparing canopy structure between
 forested LTER sites.  O'Lear, Heather A., and Timothy
 R. Seastedt. MICROARTHROPOD DENSITIES AND IMPACTS ON DECOMPOSITION
 ACROSS THE ALPINE LANDSCAPE. Institute of Arctic and Alpine Research,
 Campus Box 450, and Environmental, Population, and Organismic
 Biology, Campus Box 334, University of Colorado, Boulder CO
 80309. NWT.  Densities of microarthropods were measured in the top 5
 cm of litter and soil in xeric, mesic, and wet alpine tundra
 habitats. Previous studies have underestimated densities due, we
 believe, to inefficient extraction techniques. High-gradient
 extraction produced densities ranging from about 70,000 to 200,000
 individuals per m2; wetter habitats had higher
 densities. Microarthropod densities were higher in moist litter. This
 litter also had the highest decay rates. A basidiocarp fungus
 decomposition experiment was conducted in summer 1993, using
 naphthalene to exclude microarthropods from this detritus. Results of
 this experiment will be reported.  O'Reilly, Mary A., and Timothy
 R. Seastedt. PLANT CONTROLS ON SOIL MOISTURE IN ALPINE
 TUNDRA. Institute of Arctic and Alpine Research, Campus Box 450, and
 Environmental, Organismic, and Population Biology, Campus Box 334,
 University of Colorado, Boulder CO 80309. NWT.  The extent to which
 plants control surface (15 cm deep) soil moisture and the extent to
 which the organic matter fraction of the soil influences soil
 moisture characteristics was studied in alpine tundra. Plots with and
 without substantial vegetation cover and with and without fertilizer
 additions were monitored over the growing season for soil moisture
 using the non-destructive Time Domain Reflectometry (TDR)
 technique. Preliminary results indicated measurable plant and
 fertilizer effects on soil moisture. Results on measurements of the
 field capacity (maximum water capacity of soil held against gravity)
 of sites denuded over 10 years ago and adjacent vegetated plots will
 be reported. Also, field capacities of wet, mesic, and xeric tundra
 will be compared and related to estimates of soil organic matter
 content and soil texture.  Osgood, D., M.C.F.V. Santos,
 J.C. Zieman. COMPARISON OF PHYSICO-CHEMICAL SUBSTRATE PARAMETERS
 ALONG THE INTERTIDAL ZONE OF A STORM-DEPOSITED SAND FLAT AND
 UNDISTURBED MARSH. Department of Environmental Sciences, University
 of Virginia, Charlottesville, VA 22903. VCR.  A tropical storm in
 Oct. 1991 destroyed dune systems on portions of the Virginia barrier
 islands and laid the foundation for future marsh development. Two
 transects were established on the storm-deposited sand flat and a
 nearby, undisturbed marsh. Three stations were established at high
 marsh, short Spartina alterniflora, and tall Spartina zones on the
 marsh transects. Identical elevations were determined for the sand
 flat transects by surveying to USGS benchmarks. Porewater at each
 station was analyzed monthly for ammonium, phosphate, sulfide, iron,
 pH, EH, and salinity. A two month pilot study initiated in July, 1992
 was continued in May, 1993. The pilot study revealed porewater
 salinity comparable to or lower than flooding water (~32 ppt) at all
 stations in both transects. Hydrogen sulfide was greatest at the
 lowest (tall Spartina) stations of the marsh transects and was lower
 than three ?mol 1-1 at the sand flat transects. Higher ammonium
 concentration was evident at the lowest station of both sand flat
 transects compared to the marsh transects. Nutrient concentrations
 were equivalent at the two highest (high marsh and short Spartina)
 stations between all transects. The data from the sand flat suggest
 that conditions are favorable for plant growth, especially at the
 lowest station in the intertidal zone where tall Spartina is
 predicted to dominate. Results from the summer, 1993, further support
 these Panov, Vadim E.  LONG-TERM ECOLOGICAL RESEARCH IN ST.PETERSBURG
 REGION, RUSSIA Zoological Institute, Russian Academy of Sciences,
 199034 St.Petersburg, Russia The main ecological research activities
 in the St.Petersburg (Leningrad) region are connected with freshwater
 sites in Lake Ladoga - the Neva River - the Neva River Estuary Water
 System.  Regular studies were started in 1956 for Lake Ladoga, in
 1961 for Lake Krasnoye in the Lake Ladoga Basin and in 1981 for the
 Neva River Estuary. Some research at the sites began over 80 years
 ago.  Scientists from a number of institutions are engaged in studies
 of seasonal and annual changes in hydrophysical and hydrochemical
 characteristics, studies of primary and secondary productivity and
 cycles of nutrients.  Future sites for terrestrial and aquatic
 long-term research are proposed to be established in areas with
 practically undisturbed nature.  One of these sites is planned for
 the north part of the Karelian Isthmus in a zone characterized by a
 high concentration of lakes.  The main topics of research will
 include studies of interactions between aquatic ecosystem structure
 and processes, top-down and bottom-up controls, and nutrient cycles
 and bottom-water interface transport processes.  Paruelo, J.M.(*) and
 W.K. Lauenroth. FUNCTIONAL CHARACTERISTICS OF NORTH AMERICAN
 SHRUBLANDS AND GRASSLANDS AT A REGIONAL SCALE. Dept. Range Science
 and CPR LTER site - Colorado State University Fort Collins, CO
 80523. (*) Permanent addresses: IFEVA - Depto. Ecolog!a - Facultad de
 Agronomia. Universidad de Buenos Aires. Av.San Mart!n 4453, (1417)
 Buenos Aires - Argentina.  We are interested in understanding how the
 functional characteristics of North American grasslands and
 shrublands differ at a regional scale.  We described the ecosystem
 function from the seasonal curve of the Normalized Difference
 Vegetation Index (NDVI), derived from the Large Area Coverage (LAC)
 data of AVHRR/NOAA satellites provided by the LTER Network
 Office. Study sites,ranging from grama-tobosa shrub steppe to
 bluestem prairie vegetation types, corresponded to areas of low
 cultural impact (National Parks, National Grasslands, Experimental
 Stations, etc.) and included four LTER sites: Konza, CPR, Sevilleta
 and Jornada. We selected several sites for each vegetation type in
 order to have replications. We processed the NDVI images using an
 ERDAS 7.5 system. Each study site was characterized as a 21 element
 vector, where each element corresponded to a date. A Principal
 Component Analysis was performed over the 46 sites x 21 dates
 matrix. The first principal component, that explained 47% of the
 total variance, was closely related to the annual integrated
 NDVI. The second axis, that accounted for 30% of the variance, was
 associated with the difference between average NDVI during the
 coldest and warmest months of the year. Our analysis suggests that at
 a regional scale grassland and shrubland functional characteristics
 differ in two main directions. The first one is related with Annual
 Net Primary Production value, and the second one with the seasonality
 of the production.

Paul, Eldor, Alvin and Harris, David.  MICROBIAL GROWTH RATES IN
 SOIL. Michigan State University. East Lansing, MI 48824. KBS.
 Knowledge of the growth rates of microorganisms is fundamental to an
 understanding of the mineralization - immobilization of nutrients and
 C cycling These processes largely control ecosystem functioning,
 agricultural soil productivity and soil inputs to the atmosphere,
 determining global change.  Estimates of the average growth rate of
 the soil microbiota can be made from C turnover if values for
 specific maintenance coefficient (m) and growth yield coefficient (Y)
 are known or assumed.  These two parameters are difficult to measure
 in soil and are frequently combined as an overall efficiency term.
 Since maintenance is independent of growth its inclusion in a yield
 efficiency parameter makes it impossible to estimate growth rate from
 C turnover data. 3H thymidine uptake into DNA is a powerful and exact
 means of directly measuring replication rates in bacteria providing
 the limiting requirements and underlying assumptions are taken into
 account.  The combined estimation of DNA synthesis and specific
 respiration rates of soil biomass allows the limits for microbial
 growth rates in soil to be defined and offers a method for the
 estimation of maintenance and yield coefficients in soil.  We used
 this combined approach to measure specific growth rates in soils from
 three treatments of the LTER site at the Kellogg Biological Station,
 conventional corn-soybean rotation, native grassland and a reversion
 to native, taken out of cultivation in 1988.  Thymidine incorporation
 showed generation times of 80 to 115 days at 25 C with the reversion
 treatment being the most active.  Specific respiration rates ranked
 the treatments in the same order.  The specific maintenance
 coefficient was estimated as 0.0005 h-1 and the growth yield
 coefficient as 0.14.  At the specific growth rates defined by
 thymidine uptake and at Q10 of 2, microbial productivity was
 calculated as 29 g C m-2 y-1 for the corn soybean treatment, 74 g C
 m-2 y-1 for the reversion treatment and 83 g C m-2 y-1 for the
 grassland.  Paul, Eldor, Tom Willson, Dave Harris and Ernesto Franco.
 SOIL MICROBIAL DYNAMICS AND CARBON MINERALIZATION KINETICS. Michigan
 State Univ. 48824. KBS.  The agronomic, grassland, and old-field
 reversion plots established at the Kellogg Biological Station
 (KBS-LTER) in 1988 provide a valuable opportunity for studying the
 effects of management on soil microbial populations and carbon
 transformations.  Over the last five years, we have documented total
 microbial C and N (CFIM), bacterial and fungal bio-volumes,
 extractable DNA, arginine deamination activity, and long term
 mineralization kinetics for each of eight management treatments as
 they diverge toward their respective equalibria.  The 6 intensively
 managed treatments (four corn based field-crop rotations, an alfalfa
 monoculture, and a Populus plantation) have tended to support lower
 levels of microbial C than either the old-field successional
 treatment or the 100 year grassland.  Short term C mineralization
 (microbial respiration) and arginine deamination rates have each been
 closely correlated with total microbial biomass across these
 treatments.  Direct microscopy suggests a fungal C : Bacterial C
 ratio of apx. 3:1 in all treatments.  On the other hand, over 90% of
 the extractable microbial DNA is associated with the bacterial rather
 than the fungal fraction.  This suggests that most hyphae contain
 little or no DNA.  Long term (200d) mineralization curves provide an
 excellent fit for the model Cm = C1(1-ek1t) + C2(1-ek2t) + C3(0)
 where Cm is the carbon mineralized over time t and C1, C2, and C3 are
 partitions of the total organic carbon such that C3 = C1 + C2 = 1/2
 CTotal .  While the CTotal is roughly identical for the old-field and
 agronomic plots (9500*g g-1soil), the Cm of the reversion plots is
 nearly twice as high as the Cm of the conventional corn and soybeans
 rotation and only fractionally lower than the Cm of the grassland.
 As a result the old-field reversion plots exceed all other treatments
 with respect to their mineralization rate constants (k1 and k2) and
 mineralization per unit microbial C.  Paustian, Keith.  THE THEORY OF
 ORGANIC MATTER DECOMPOSITION: LESSONS FROM STEADY-STATE ANALYSIS OF
 THE CENTURY AND ROTHAMSTED MODELS. Colorado State Univ., Ft. Collins,
 CO 80523. KBS Simple analytical models in ecology are routinely
 evaluated as to their steady-state properties, but this kind of
 analysis is less often conducted in the case of more complex
 ecosystem simulation models.  However, by using simplifying
 assumptions regarding stochastic driving variables, simple analytical
 steady-state solutions of multi-compartment organic matter models can
 be obtained which help elucidate several fundamental properties of
 the models.  Steady-state analytical solutions were derived for the
 CENTURY and ROTHAMSTED models, both of which have been used
 extensively in site-level and global change-related analyses of soil
 carbon.  The analyses reveal close similarities between the models
 including the linear relationship between C input rates and soil C
 levels and the influence of litter quality on soil C amounts and
 composition.  The analysis shows that predicted SOM composition
 (i.e. pool fractions) is independent of C input rates and climatic
 conditions but dependent on soil texture, litter quality and soil
 management.  The steady-state solutions provide a useful tool for
 estimating initial conditions for the simulation models and to
 analyze land use and climate change effects on potential soil C
 levels.

Paustian, Keith and Peter H. Stahl. LITTER DECOMPOSITION AND LITTER
 DECOMPOSER ACTIVITY IN THE KBS-LTER PLOTS. Colorado State Univ.,
 Ft. Collins, CO 80523 and USDA National Soil Tilth Lab, Ames, IA
 50011. KBS.  Mesh bags containing corn (Zea mays), soybean (Glycine
 max), poplar (Populus spp.), alfalfa (Medicago sativa), quackgrass
 (Agropyron repens) and chickweed (Cerastinum vulgatum) litter were
 sampled following 4, 5, 7 and 11 months incubation in no till and
 conventional till corn-soybean rotations, poplar and alfalfa
 monocultures and native successional vegetation, on the KBS-LTER
 site.  Mass losses rates of above-ground incubated litter were
 primarily controlled by litter composition rather than edaphic or
 microclimate differences between systems.  In no-till vs tilled
 plots, mean decomposition rates were the same after 5 months (just
 prior to litter burial in tilled plots) but remaining mass in no-till
 litter averaged twice that in conventional till plots after 11
 months.  Fungi accounted for 60-80%, and bacteria 20-40%, of
 metabolic activity as determined by substrate-induced
 respiration/selective inhibition on corn and soybean leaves and
 stems. There were no significant differences in decomposer dominance
 (based on relative respiratory activity) between litter type or
 litter location. The initial 5 month surface incubation in both
 systems may have allowed fungal dominance to be established and
 maintained through the first year of decomposition.

Perkins, Reed.  SCALING ANALYSIS OF PEAK FLOWS FROM SEMI-NESTED BASINS
 IN THE WESTERN CASCADES OF OREGON.  Department of Forest Science,
 Oregon State University, Corvallis, OR 97331.  AND.  This study
 examined the scaling properties of matched peak flow data for 400
 storms over the period 1955 to 1990 from 10 semi-nested basins
 ranging from 10 to 10,000 ha in the Andrews LTER in the Western
 Cascades of Oregon.  Empirical data showed simple scaling, implying
 that average flow frequency distributions have statistically similar
 shapes at each spatial scale.  Simulations showed that the shape of
 the scaling curve is sensitive to changes in the shape of the average
 flow frequency distribution with scale, but the scaling curve shape
 is not sensitive to variability among flow frequency distributions at
 any single spatial scale, the number of basins at any single scale,
 nor the omission of the largest storms.  This analysis suggests that
 scaling analysis may provide useful insights about averaged flow
 outing behavior from nested gauging stations, but does not reflect
 the relative variability of flows at any single spatial scale as
 previously suggested.  These results imply that scaling analyses
 using data from non-nested basins will not be able to discriminate
 the effects of flow routing behavior from climate variability effects
 on hydrologic peak flows.  We hypothesize that flow frequency
 distributions of nested basins reflect the relative importance of
 hillslope and channel processes as well as the propagation of
 clearcutting and road-related disturbances downstream.  We will test
 this hypothesis using distributed parameter modelling for the Andrews
 LTER basin and its sub-basins.

Pfeiffer, Kent, and David Hartnett. BISON SELECTIVITY AND GRAZING
 RESPONSES OF Schizachyrium Scoparium AND Andropogon Gerardii IN
 BURNED AND UNBURNED TALLGRASS PRAIRIE. Kansas State University,
 Manhattan, KS 66506. KNZ.  Two closely related grasses with
 contrasting growth form, S. scoparium and A. gerardii were studied on
 tallgrass prairie to determine how fire influences their relative use
 by bison and their responses to grazing. On unburned prairie, bison
 grazed the bunchgrass S. scoparium far less frequently than the
 rhizomatous A. gerardii, but the two species were grazed at equal
 frequencies on burned sites. Burning removes the persistent standing
 dead tillers of S. scoparium which serve as physical deterrent to
 grazing. Grazing shifted the size structure of S. scoparium
 populations toward a higher frequency of small individuals, and plant
 size (basal area/ strongly influenced its probability of being
 grazed.  On burned prairie, plants of intermediate size classes were
 the least abundant but were grazed most frequently. In the absence of
 grazing, mean plant size and densities of S. scoparium were increased
 by burning. Thus, burning favors S. Scoparium under ungrazed
 conditions but is detrimental to it under grazed conditions.  The
 results indicate that plant growth form, population size structure,
 and fire interact to influence bison grazing patterns on these
 dominant grasses and their responses to grazers on tallgrass prairie.

Phinn, Stuart , Janet Franklin, Allen Hope, Douglas Stow and Laura
 Huenneke. BIOMASS DISTRIBUTIONS OF A SEMI-ARID DESERT FROM AIRBORNE
 DIGITAL VIDEO IMAGING, FIELD SAMPLING AND SPATIAL STATISTICAL
 METHODS. Department of Geography, San Diego State University, San
 Diego, CA 92182-0381. Department of Biology, New Mexico State
 University, Las Cruces, NM, 88003. JRN.  Biomass distributions mapped
 from airborne multispectral video image data and field samples were
 compared for 70m x 70m sample sites from five vegetation types within
 the Jornada LTER, New Mexico. Normalized Difference Vegetation Index
 (NDVI) images were calculated at 0.5, 1.0, 2.0 and 4.0m pixel
 resolutions by averaging. Contoured NDVI images were compared to
 contour plots derived from field sampling of biomass at 10m
 intervals, interpolated by Kriging. Their similarity indicates that
 field sampling adequately represented the spatial distribution of
 biomass in the grassland plots and some of the shrubland plots with
 more continuous cover. However, image variograms show that a higher
 sampling intensity (5.0m or less) would capture the fine scale
 pattern of the heterogeneous biomass distribution in degraded shrub
 sites given the average diameter (5 - 7.5m) of the shrubs.  Poister,
 David, David E.Armstrong, and James P. Hurley. A SIX YEAR RECORD OF
 NUTRIENT ELEMENT SEDIMENTATION AND RECYCLING IN THREE NORTH TEMPERATE
 LAKES. North Temperate Lakes Site. Water Chemistry Program, WI
 53706.University of Wisconsin, 660 North Park Street, Madison,
 WI. NTL.  Sedimentation of C, N, and P from the water column was
 assessed during the ice-free season in three northern Wisconsin lakes
 from 1986-1991.  Seasonal trend in mass sedimentation different in
 each lake but consistent from year to year within a lake.  High rates
 of nutrient sedimentation were associated with spring and fall blooms
 of large siliceous algae.  Nutrient recycling, calculated as the
 difference between uptake during photosynthesis and loss to
 sedimentation, showed seasonal trends that were related to
 sedimentation.  Recycling was the most important source of nutrients
 to primary producers, accounting for 85-90% of phosphorus demand
 during the summer stratified period.  Porter, John H. and James
 T. Callahan. ECOLOGICAL ASSESSMENT USING REMOTELY-SENSED DATA: A
 COMPARISON OF IMAGE SOURCES.  University of Virginia,
 Charlottesville, VA 22903, USA and National Science Foundation,
 Washington, DC 20550. VCR.  We compared thematic maps, derived from
 different contemporaneous image sources using a standardized
 methodology, to assess how our perceptions of ecological landscapes
 are affected by the source of the image data. Specifically, we
 examined similarity in areal estimates, patchiness, and spatial
 coincidence of cover classes for a scanned aerial photograph and SPOT
 and Thematic Mapper satellite imagers. Images were rectified to two
 common resolutions (5 and 30 m), classified using the ISODATA
 clustering technique and recoded into cover classes. Most cover
 classes had similar areas across image sources. Changing the grain
 size of the images to 30 m had virtually no effect on the areal
 estimates. The number and character of the patches derived from the 5
 m images varied widely between image sources. However, patchiness in
 the 30 m resolution images was similar to that observed in the 5 m
 images. Spatial coincidence was highest between the SPOT and TM
 derived classifications, with an overall agreement of 75%.  Agreement
 among the both satellite images and the photo was poorer, with an
 overall agreement of only 50%.

Porter, John H. and James T. Callahan. EMERGING TRENDS IN SHARING OF
 ECOLOGICAL DATA.  LTER, University of Virginia, Charlottesville, VA
 22903, USA and National Science Foundation, Washington, DC
 20550. VCR.  Success of shared data bases depends of two primary
 qualities: (1) contributions of data to the data bases, and (2) uses
 of the data bases. There is a fundamental dilemma embedded in data
 base creation and management. At least on a perceptual level, the
 benefits derived from a data base are greater for the user of the
 data than for the contributor of the data.  Ultimately, however, the
 utility of a data base depends upon the quality of the data provided
 and the accessibility of the data to users. We examine the means by
 which LTER sites have provided for the creation, management and
 utilization of large, multi-source data bases. Also, based on a
 review of recent literature we examine the speed of consumption (the
 time between data generation and publication of results) of
 ecological data.  Reagan, Douglas and Robert Waide. PROPERTIES AND
 ORGANIZATION OF THE FOOD WEB OF A PUERTO RICAN RAIN
 FOREST. Terrestrial Ecology Division, University of Puerto Rico, Rio
 Piedras, Puerto Rico 00936. LUQ.  Multiple investigators coordinated
 efforts to define the major feeding relationships among all animal
 species inhabiting the Luguillo Experimental Forest near El Verde,
 Puerto Rico. These studies have provided a comprehensive
 understanding of the properties and organization of the forest
 community food web and included the analysis of a food web matrix
 consisting of 156 "kinds of organisms" (2,056 known species). The
 food web is characterized by low faunal richness, an absence of large
 herbivores and carnivores, and a superabundance of frogs and
 lizards. Cross predation and food loops involving large invertebrates
 and small vertebrates are distinctive features of the food
 web. Results also indicate the community food web is divided into
 day, and night compartments.  Rice, Charles W., Clarence L. Turner,
 Tracy L. Benning, and Timothy R. Seastedt.  FIRE FREQUENCY AND
 FERTILIZATION EFFECTS ON PLANT PRODUCTION AND N UPTAKE, MICROBIAL
 BIOMASS, AND SOIL N AVAILABILITY IN TALLGRASS PRAIRIE.  Kansas State
 University, Manhattan, KS 66506.  In tallgrass prairie, fire
 frequency can affect net primary production and microbial activity.
 The objective of this study was to examine the relationships between
 fire frequency, net primary production and microbial biomass.  A
 wildfire in 1991 on Konza Prairie Research Natural Area made it
 possible to estimate primary production on six watersheds last burned
 1 to 2, 4 to 5, and 10 to 11 years.  Experimental treatments designed
 to magnify the effects of fire frequency were established on these
 watersheds and included a control; added N (1.5 g/m2); and added C
 (250 g/m2).  Plant biomass and N concentration, soil inorganic N, and
 microbial biomass were measured during 1991 and 1992.  Potential
 differences in aboveground biomass attributable to fertilization or
 fire frequency were minimized by severe water stress in 1991.  Forb
 biomass responded to fire frequency with higher biomass on
 infrequently burned(4-5 y) than frequently burned watersheds.  Grass
 biomass responded to N fertilization but not fire frequency.  Plants
 quickly assimilated added N with the greatest response on frequently
 burned watersheds. Higher levels of soil inorganic N remained after
 two growing seasons with added N.  The effects of fertilization and
 fire on microbial biomass C were inconsistent while added N increased
 microbial biomass N.

Riddervold, Leif Bjorn, Tanya Furman, and Ted Hegnauer. ISLANDS OF
 FRESH WATER IN A SALT MARSH. University of Virginia, Charlottesville
 VA, 22903. VCR.  On Parramore Island (Virginia Coastal Reserve) are
 several hundred land forms known as the Parramore Pimples.  The
 pimples are typically round (<5 - 200 m diameter), elevated features
 (0.5 - 2.5 m above surrounding topography) distributed randomly
 within salt marshes throughout the island. Pimples with a diameter of
 at least 30 m have developed a fresh water lens (recharged by
 precipitation) which supports an island of terrestrial vegetation
 within a salt marsh community.  Several grass species predominate on
 the flat, sandy plain of the pimple interior, while trees and shrubs
 form a ring around the edge of the feature where the fresh water lens
 is closest to the surface. Surrounding the pimples, various marsh
 grasses define concentric rings that reflect the salinity and
 topographic gradients outward from the feature. The focus of this
 study is to determine the extent of the fresh water lens, and to
 monitor the lens following overwash events.  As the south end of
 Parramore Island is eroding quickly, several of the pimples are
 subject to frequent overwash by salt water during winter storms. Many
 of the trees and shrubs display signs of stress, including mortality
 from the saline intrusions. Normal zonation of the salt marsh
 vegetation around the pimples will be studied in order to understand
 the physical conditions responsible for supporting each zone. Several
 nests of three wells each have been installed on three pimples with
 common morphological characteristics. Two of the pimples are
 regularly subject to overwash events and their vegetation shows signs
 of stress. The third pimple is not overwashed frequently, and the
 vegetation appears healthy. Salinity profiles were determined with 5
 m depth for each pimple. Preliminary results indicate that the
 thickness of the fresh water lens varies with the elevation of the
 feature, but does not exceed 2 m. Below the fresh water, the salinity
 increases downward at a constant rate of roughly 10 ppt/m (a result
 of diffusion and mixing due to tidal oscillations), to a maximum of
 30-31 ppt (equivalent to salinities of water in surrounding marsh)
 near the center of each feature. The wells were installed during a
 relatively dry period, and therefore it is unknown whether the lens
 will expand substantially during the winter months when
 evapotranspiration is at a minimum.

Ritchie, M. E. and David Tilman*. CASCADING EFFECTS OF BIRDS ON
 DIVERSITY OF GRASSHOPPERS AND PLANTS.  Utah State University, Logan
 UT 84322-5210, *University of Minnesota, St. Paul MN 55105. CDR..
 The effects of predators on the diversity of their prey are
 well-documented, but few studies have addressed whether predators can
 influence diversity across two lower trophic levels. With a four-year
 experiment, we addressed this question in unfertilized and fertilized
 sections of an old field at Cedar Creek Natural History Area in
 Minnesota. Specifically, we excluded birds (predators) from 9x9 m
 plots and measured responses of the biomass and species diversity of
 grasshoppers (herbivores) and plants. In general, birds increased
 grasshopper biomass and diversity, had no effect on plant biomass,
 but decreased plant diversity. These effects were similar in both
 unfertilized and fertilized plots for 1989-1991. In 1992 on
 unfertilized plots, however, birds decreased grasshopper biomass and
 increased plant diversity. For all years and plots combined, plant
 diversity was negatively associated with grasshopper
 biomass. Overall, bird predation affected grasshopper biomass and
 diversity, and increased grasshopper biomass decreased plant
 diversity. These results suggest that coupled trophic linkages can
 lead to cascading effects of predators on diversity across two or
 more lower trophic levels.

Roberts, Christine, Julia A. Jones and David Perry.  SPATIAL PATTERNS
 OF SOIL MOISTURE, NITROGEN MINERALIZATION, VA MYCORRHIZAL INFECTION,
 AND SOIL ORGANISMS IN A Juniperus occidentalis - Artemesia tridentata
 PERENNIAL GRASS COMMUNITY IN CENTRAL OREGON.  Departments of Forest
 Science and Geosciences, Oregon State University, Corvallis, OR,
 97331.  AND.  This study examined whether juniper invasion was
 associated with a change in spatial patterns of soil moisture, pH,
 nitrogen mineralization, VA mycorrhizal infection and soil organisms
 in sagebrush-grassland with and without invading junipers on the
 Island, an undisturbed area of central Oregon.  Fifty-two surface
 samples were collected in each of ten 50-m radius plots using a
 nested randomized grid design to test for spatial variation at <1m,
 1-5m, and 5-50 m scales.  Four plots were sampled in December of
 1991, two in sage-grassland and two under juniper/sage/grass.  Six
 plots were sampled in May of 1992, three each under sage/grass and
 juniper/sage/grass. Species composition of soil organisms differed
 between vegetation types and by season but biomass and functional
 groups did not.  The coefficient of variation for most properties was
 higher in plots with juniper than without.  In plots sampled in
 winter, semivariograms and correlograms showed greater short range
 variation and smaller patches for moisture and N mineralization in
 plots without juniper, and higher long-range variation and large
 patches in plots with juniper. However, soil arthropods showed the
 reverse pattern, while VA mycorrhizal infection had no spatial
 pattern.  In plots sampled in summer, spatial patterns varied
 considerably within each vegetation type depending on plot location
 under juniper canopies, but sage/grass plots generally showed greater
 short-range variation and smaller patch size whereas
 juniper/sage/grass plots had small and large patch sizes. Fractal
 dimensions for moisture and N mineralization were higher in plots
 with juniper, suggesting that juniper invasion increased long-range
 variation.  These results suggest that competition between and within
 species may produce patterns in soil resources that in turn affect
 soil ecological processes, further modifying observed soil spatial
 patterns.  Rossow, Loni. HERBIVORE EFFECTS ON Salix/Populus
 ECTOMYCORRHIZAE AND ENDOMYCORRHIZAE IN THE BONANZA CREEK FLOODPLAIN
 EXPERIMENTAL TAIGA FOREST SITES, ALASKA. Univ. of Alaska, Fairbanks,
 AK 99775. BNZ.  Mycorrhizae, a mutualistic symbiosis between plants
 and fungi, may be one of the most important and least understood
 biological associations regulating community and ecosystem
 functioning. Both animal and fungus depend on mycorrhizal plants for
 carbon. Therefore, any herbivory reduces the carbon available for the
 fungus. Herbivory has been found to suppress mycorrhizae by removing
 photosynthetic tissue which in turn reduces the photosynthate
 available for maintaining the fungus-plant mutualism. In the Alaskan
 taiga, selective mammals browse on plants in the Salicaceae family
 (Salix spp. and Populus spp.). My project involves quantification of
 both ecto- and endomycorrhizae on willow and poplar roots to study
 this effect of herbivory using the paired plots inside and outside of
 exclosures replicated along the Tanana River. Since I have recently
 started this graduate project, I have no results at present. My
 methods include taking soil cores, processing soil cores, and
 quantifying subsamples of willow/poplar roots for ecto- and
 endomycorrhizae.

Sanderson, B. L. and Thomas Frost. DINOFLAGELLATE RESPONSE TO
 MANIPULATION OF ZOOPLANKTON AND NUTRIENT CONCENTRATIONS IN TWO
 WISCONSIN LTER LAKES. Center for Limnology, University of Wisconsin,
 Madison, WI, 53706, USA. NTL.  Dinoflagellates are an integral part
 of many marine and freshwater phytoplankton communities, yet few
 investigators have evaluated the comparative importance of growth and
 loss processes in their population dynamics. We investigated
 dinoflagellate population dynamics in two Wisconsin bog lakes at the
 North Temperate Lakes Long-Term Ecological Research Site. The bogs
 have a number of common chemical features but distinctly different
 dinoflagellate populations. We tested the alternative hypotheses that
 growth processes driven by nutrient limitation or loss processes
 driven by zooplankton grazing control the populations in the bog
 lakes. Nutrient concentrations (N&P) and zooplankton density were
 manipulated in two, 12-day enclosure experiments conducted
 simultaneously in each lake. Results show no evidence of zooplankton
 grazing on dinoflagellates, suggesting that large cell size renders
 them resistant to grazing. Dinoflagellate populations in treatments
 receiving nutrients did not exhibit increased growth and in one
 experiment exhibited significantly lower densities that non-nutrient
 treatments. Pigment analysis using HPLC suggests that other algae
 were better competitors for nutrients and may negatively influence
 dinoflagellate population.  Our study highlights the importance of
 understanding algal community dynamics in order to elucidate the
 mechanisms for changes in dinoflagellate populations.

Sankovskii, Alexei and Yuri Puzachenko. SPECIES ORDINATION AS A TOOL
 FOR INTERSITE COMPARISON. Institute of Ecology, University of
 Georgia, Athens GA, 30602-2202 and Lab. of General Ecology, Moscow,
 Russia. CWT.  The objective of the current study was to compare the
 structure of a tree layer in the Southern Appalachian (Coweeta
 Hyd. Lab., USA) and Western Caucasus (Caucasus Biosphere Reserve,
 Russia) forest communities.  The comparative analysis was based on
 the following assumptions: - every species ensemble is controlled by
 the various environmental factors which can be intercorrelated, - the
 combined reaction of species to the specific set of factors creates
 an "ecological space" dimensions of which are independent; each
 dimension of this space corresponds to the combination of
 environmental factors or reflects some biotic processes such as
 competition or succession. - each species occupies a certain portion
 of ecological space - its ecological niche; ecological niche is not
 predefined a priori but is forming during the development of species
 ensemble in ecological and evolutionary time.  The structure of
 ecological space of the selected forest communities was analyzed
 using the non-metric multidimensional scaling. The results of
 analysis suggested that the tree layers in the Western Caucasus and
 Southern Appalachian forest communities are regulated by the
 different number of independent factors - 3 in the Caucasus and 4 in
 the Appalachians. Dominant tree species in both sites have the
 similar relative size of the ecological niches (based on the
 frequency of occurrence) and comparable degree of the niche overlap.

Santos, M�árcio CFV and Joseph C. Zieman. THE ROLE OF SUBSURFACE
 HYDROLOGY IN UPPER MID-LITTORAL HYPERSALINITY DEVELOPMENT. Department
 of Environmental Sciences. University of Virginia, Charlottesville,
 VA, 22903. VCR.  Porewater hypersalinity is one of the main natural
 stressors in upper mid-littorals exposed to dry or seasonally dry
 climates. It is well established that climate determines the
 potential for hypersalinity development at the regional level, while,
 at the micro-scale spatial level, salinity build-up is usually
 associated with the occurrence of upland freshwater seepage (surface
 and subsurface). Unfortunately, most of the knowledge about upper
 mid-littoral hypersalinity comes from conceptual models that lack a
 quantitative basis and field testing. In order to measure the
 relative importance of upland seepage on hypersalinity prevention at
 the VCR-LTER, twenty-three transects were established at the upper
 mid-littoral zone of sites with different sediment composition and
 upland hydrology. The transects were instrumented with piezometer and
 pressure lysimeter nests. At each transect we measured topographic
 slope, porewater salinity and upland subsurface flow. Preliminary
 data analysis revealed that hypersalinity developed only on slopes
 smaller than 0.5 degrees, suggesting the decrease in upper
 mid-littoral subsurface drainage as a potential mechanism. Upland
 seepage flow prevented salinity build-up in only one transect, and in
 the form of surface flow. We conclude that the development of upper
 mid-littoral hypersalinity, at the micro-scale spatial level, is
 governed by topographic slope, with associated changes in subsurface
 drainage as the possible mechanism. Upland seepage is restricted to
 the role of shaping the porewater salinity regime, which is
 determined by the topographic slope setting.  Schmidt, Steven K.,
 Lesley K. Smith, Melany C. Fisk, Charles H. Jaeger, Paul D. Brooks,
 Gregory M. Colores, Ann E. West, Elisabeth A. Holland, and William
 D. Bowman. TEMPORAL AND SPATIAL VARIATION IN N2O AND CH4 FLUXES
 ACROSS AN ALPINE LANDSCAPE. Environmental, Population, and Organismic
 Biology. Campus Box 334, and Institute of Arctic and Alpine Research,
 Campus Box 450, University of Colorado, Boulder CO 80309. NWT.
 Fluxes of N2O and CH4 were measured in three alpine tundra plant
 communities (3 sites per community) on Niwot Ridge. Measurements were
 taken weekly to bi-weekly from before snowmelt to well after plant
 senescence in 1992 and 1993. In addition, soil moisture, temperature
 and inorganic N levels were measured at each site on all sampling
 dates. Nitrogen mineralization, nitrification, microbial biomass
 nitrogen and plant assimilation of N were also measured periodically
 throughout the growing season at each site. N2O production was
 highest in May and June in wet and moist meadow sites and tapered off
 to almost zero for July, August and September. In dry meadow
 communities, N2O production showed a peak early in the season but
 also showed peaks of production in response to late season rainfall
 events. Moist and dry meadow sites were sinks for CH4 for all but the
 earliest sampling dates in May of 1993. Wet meadow sites were always
 a source of CH4. Overall, soil moisture was the most important
 environmental variable controlling N2O and CH4 fluxes from alpine
 tundra sites in 1992. Because moist and dry meadows are the dominant
 community types in the Colorado alpine, it appears that alpine tundra
 acts as a net source of N2O and a net sink for CH4.

Scott V. Ollinger, John D. Aber, C. Anthony Federer(*) and Jenn
 M.Ellis.  PnET-GIS: MODELING FOREST PRODUCTIVITY AND WATER BUDGETS
 ACROSS THE NORTHEASTERN U.S.  Complex Systems Research Center,
 University of New Hampshire, Durham, NH 03824 and (*) Northeastern
 Forest Experiment Station. U.S.D.A. Forest Service, Durham, NH
 03824. HFR and HBR.  Environmental perturbations such as climate
 change and atmospheric deposition can affect ecosystems at regional
 to global scales.  In order to predict their effects across real
 landscapes, site-level information must be scaled up to the levels at
 which these disturbances act.  Linking ecosystem models to geographic
 information systems allows us to accomplish this by combining the
 complexity of ecosystem processes with the spatial heterogeneity of
 driving environmental variables.  The current research involves
 linking PnET, a monthly time step model of forest carbon and water
 balances, to a GIS of the northeastern U.S. (New York and New
 England).  PnET is based on the following relationships: 1) maximum
 photosynthetic rate is a function of foliar N concentration, and 2)
 stomatal conductance is a function of actual photosynthetic rate.
 These relationships are combined with equations for photosynthetic
 response to light attenuation through the canopy, along with soil
 moisture stress and vapor pressure deficit, to predict monthly leaf
 area and carbon and water balances.  PnET has been validated against
 field data from 10 temperate and boreal forest ecosystems. PnET-GIS
 is run at 30 arc second resolution, corresponding to the elevation
 and land use maps of the northeast region.  For each grid cell,
 vegetation and soil parameters are read from existing data planes,
 and climate drivers are calculated as functions of latitude,
 longitude, elevation, and slope position.  Model predictions of net
 primary production, wood production, and water yield are output
 directly into map form.  By adding climate change scenarios to model
 runs, we use PnET-GIS to examine potential effects of climate change
 on the carbon and water balances of forest ecosystems across the
 region.  Seastedt, Timothy R., and Marilyn D. Walker. CONTROLS OF
 DECOMPOSITION IN ALPINE TUNDRA.  Institute of Arctic and Alpine
 Research, Campus Box 450, and Environmental, Population, and
 Organismic Biology, Campus Box 334, University of Colorado, Boulder
 CO 80309. NWT.  Litterbag studies were used to evaluate the
 importance of landscape position and substrate quality on
 decomposition processes. Sites of intermediate snowdepth exhibit the
 highest decomposition rates for surface litter during both the first
 and second years of decay. Such sites are neither strongly
 temperature limited (snowfield sites) or moisture limited (e.g.,
 sites blown free of ca. 80% of annual precipitation). Initial
 nitrogen content of litter was positively correlated with decay rates
 for the first year of decomposition; initial lignin content was
 inversely correlated with decay rates. Substrates with similar
 lignin:nitrogen ratios appeared to decay more rapidly in soil than on
 the surface. Wood decay, however, was similar for surface and soil
 samples.  Shelley E. Arnott. TEMPORAL VARIATION IN THE DETECTION OF
 ZOOPLANKTON SPECIES. Center for Limnology, University of
 Wisconsin-Madison, Madison, Wisconsin 53706. NTL.  Zooplankton
 species richness and abundance vary within and among seasons and
 among years. Understanding patterns of variability is of importance
 for questions of biodiversity because samples taken at a single point
 in time are frequently used in estimates of richness and diversity. A
 7 year survey of zooplankton from Little Rock Lake, North Temperate
 Lakes Long-Term Ecological Research Site was used to calculate yearly
 species diversity, richness, extinction and immigration rates and
 rates of species turnover. Patterns of species abundance and
 persistence throughout the season were compared among years to
 determine the stability of zooplankton communities and the influence
 of environmental conditions such as weather patterns. Temporal
 variation in community structure and the low probability of detecting
 rare species resulted in an underestimation of species richness by 15
 - 50 % for single samples taken at any one time during the summer. A
 sampling regime that maximizes diversity, but minimizes cost (effort)
 will be presented.

Sievering, Herman1, Lori Marquez1, Timothy Bardsley2 and Christine
 Seibold2.  ATMOSPHERIC LOADING OF NITROGEN TO ALPINE TUNDRA AT THE
 NIWOT LTER. 1 Center for Environmental Sciences, CB 136, PO Box
 173364, and 2 Institute of Arctic and Alpine Research, CB 450,
 University of Colorado, Boulder, CO.  Atmospheric gaseous nitric acid
 (HNO3) as well as particulate matter nitrate (NO3-) and ammonium
 (NH4+) concentrations have been determined for the Niwot Ridge LTER
 Saddle site on an approximately biweekly basis during the winter of
 1992-93 and on a weekly to twice-weekly basis since April 1993.
 These N species are the dominant contributors to atmospheric N
 deposition (dry and wet loading) at the Niwot LTER alpine
 tundra. Results include: -very low minimum detectable NH4+ air
 concentration measurement capability; -sufficient ambient air
 concentration data obtained to assess atmospheric N deposition during
 1993 spring snowmelt conditions and during summer peak N species
 (especially HNO3) concentration periods; -hypothesis, based on a
 comparison of average summer 1993 HNO3, NO3-, and NH4+
 concentrations, that the atmosphere over the Niwot alpine tundra is
 ammonia gas (NH3) limited; -dry deposition of N species is,
 approximately, of the same magnitude as wet deposition at the Niwot
 alpine tundra, despite the fact that wet deposition of NO3- is higher
 here than at any other location in the Colorado Rockies; -dry
 deposition of N species may be greater or less than wet deposition
 depending upon whether NH3 is emitted from or deposited to the Niwot
 alpine tundra during May-September. Conclusions: The growing season N
 dry deposition at the Niwot alpine tundra, >1 mg N m-2 d-1, plus N
 wet deposition of 1 mg N m-2 d-1 may be compared with biological N
 fixation of <0.2 mg N m-2 d-1, <0.03 mg N m- 2 d-1 by lighting
 fixation and, perhaps most interesting, N mineralization of 8-12 mg N
 m-2 d-1. It appears that new available N, about 20% as much as
 recycled N mineralization, is delivered to the Niwot alpine tundra
 yearly by way of atmospheric dry and wet deposition.  Sinton, Diana.
 RECONSTRUCTING DISTURBANCE PATTERNS FROM WINDTHROW AND FIRE IN THE
 BULL RUN WATERSHED, MT. HOOD NATIONAL FOREST, OREGON, USA.
 Department of Geosciences, Oregon State Univ., Corvallis, OR 97331.
 AND.  (Faculty advisors: J. Agee, J.A. Jones, T. Spies, F.J. Swanson;
 Andrews LTER contacts: J.A. Jones, T. Spies, F.J. Swanson). AND.
 This study examined windthrow and its historical relationship with
 fire and forest cutting in the Bull Run watershed, a 500 km2 forested
 basin which is the principal municipal water supply for the City of
 Portland, Oregon.  Although windthrow occurred in the Bull Run prior
 to 1958 when timber harvesting began, edges created by clearcutting
 and fires may have increased the incidence of windthrow and altered
 its natural spatial and temporal distribution.  The overall study
 involves (1) examining how mapped disturbance patterns are related to
 topography, vegetation, soils, exposure to wind, edges created by
 natural openings in the forest cover, road and stream networks, and
 clearcut patches based on (2) mapping and dating of pre- and
 post-harvest fire patches (J. Agee and F. Krusemark of the University
 of Washington), and (3) mapping and dating pre- and post-harvest
 windthrow patterns (D. Sinton, J.A. Jones, and F.J. Swanson).  The
 first phase was an examination of landscape-scale effects on
 windthrow disturbance produced by a large storm in December of 1983.
 Windthrow was mapped from historical aerial photography and maps and
 tabular data were created from a geographic information system
 (GIS). Northeast-facing slopes and ridgetops, and stands downwind of
 a clearcut edge, had the highest rates of windthrow.  A significantly
 higher number of windthrow patches were associated with clearcut
 edges than natural edges.  Moreover, several of the windthrow patches
 from the 1983 storm were associated with clearcut edges which had
 been created by salvaging timber from previous windstorms, suggesting
 a pattern of disturbance propagation across the landscape.  Continued
 work will include spatial modeling based on random (no spatial
 pattern) and landscape-controlled conceptual models of disturbance
 spread to assess the relative importance of landforms and human
 actions on the spatial and temporal propagation of disturbance in
 this forested basin.  Smucker, Alvin, Kurt Pregitzer and Liisa
 Pietola. ALFALFA AND POPLAR ROOT DYNAMICS IN LTER EXPERIMENTS AT
 KELLOGG BIOLOGICAL STATION. Michigan State University East Lansing,
 Michigan. KBS.  Root development, distribution and turnover rates of
 alfalfa and poplar fields were evaluated by the minirhizotron (MR)
 and microvideo camera methods during a four-year study on a
 stratified loam soil. Clear plastic MR tubes were installed at 45
 degrees at planting. Video recordings were taken to depths of 110 cm
 at 1 - 3 week intervals during the most dynamic growth periods or
 following each cutting of the alfalfa fields. Root images were
 quantified into numbers of total, new and senescent roots. Root
 growth and death rates of alfalfa were highly dynamic during their
 first three years. Roots of both species accumulated at the soil
 horizon interfaces between the Ap, B, and Bt horizons of the soil
 profile. Nonuniform development and death of roots, in these horizon
 interface regions, suggest possible accumulations of nutrients and
 water at soil horizon interfaces. Root development and distribution
 were modified more by the seasons and ages of the alfalfa than by
 defoliation. Storage carbon in the taproots appeared to be
 remobilized and transported to the fibrous branched roots following
 each cutting of the alfalfa. Poplar roots were most dynamic during
 the first 3 to 4 months following the spring planting. During
 subsequent years, root growth was most active in the early spring and
 late autumn. Evaluations of alfalfa root dynamics became less
 effective as the depth of active root growth increased to depths
 greater than the MR tubes. This problem could be resolved by
 installing longer MR tubes or by installing horizontal MR tubes at
 depths greater than 110 cm.  Spaulding, S.A., D.M. McKnight and
 R.L. Smith. PHYTOPLANKTON POPULATION DYNAMICS IN PERENNIALLY
 ICE-COVERED LAKE FRYXELL, ANTARCTICA.  U.S. Geological Survey, 3215
 Marine St., Boulder CO. 80303 Phytoplankton were collected over 5
 austral summers to examine seasonal and annual fluctuation in species
 composition and biomass in Lake Fryxell, a perennially ice-covered
 lake in southern Victoria Land, Antarctica.  The lake is amictic and
 has perennial and dramatic gradients of salinity, dissolved oxygen,
 and nutrients. Algal species diversity was low (58 total taxa and
 between 18 and 26 taxa within a given year), confirming the results
 of previous short term studies.  The phytoplankton consisted
 primarily of cryptophyte and chlorophyte flagellates and filamentous
 cyanobacteria.  Each year one dominant species contributed over 70%
 of total biovolume; Chroomonas lacustris was dominant in one year
 while Cryptomonas spp. dominated in the following 4 years.  Several
 species of filamentous cyanobacteria were abundant in the plankton;
 only one species had previously been reported, and it was not
 abundant.  Some common taxa were strongly vertically stratified
 (Oscillatoria limnetica, Phormidium anqustissimum, Pyramimonas spp.,
 Oscillatoria spp.), while others showed no distinct vertical
 stratification (Chlamydomonas subcaudata, Cryptomonas spp.).
 Phytoplankton stratification reflects gradients of nutrients and
 light, and water column stability.

Stammerjohn, Sharon.  VARIABILITY IN SEA ICE AREAL COVERAGE ALONG THE
 WESTERN ANTARCTIC PENINSULA.  Computer Systems Laboratory - Girvetz
 1140, Center for Remote Sensing and Environmental Optics (UCSB),
 Santa Barbara, CA 93106. PAL.  The Antarctic Marine Ecosystem Long
 Term Ecological Research (LTER) project proposes that interannual and
 annual variability in sea ice extent may be the major physical
 determinant in spatial and temporal changes in Antarctic marine
 biota.  Research presented here focuses on the annual and interannual
 variability in sea ice areal coverage in the LTER study area along
 the Western Antarctic Peninsula and compares the variability to other
 regions in the Antarctic.  A 12.5 year time series (from 10/78 to
 3/91) of surface ice concentrations was obtained from passive
 microwave temperature brightnesses recorded by NASA's Scanning
 Multi-channel Microwave Radiometer (SMMR) and DMSP's Special Sensor
 Microwave/Imager (SSM/I) using the NASA algorithm.  Ice areal
 coverage was calculated from the percent surface ice
 concentrations. The time series of ice areal coverage shows that the
 interannual variability in the LTER study area is distinct from other
 regions in the Southern Ocean.  This is confirmed by cross spectral
 analysis.  The mean annual cycle also shows that the timing of
 maximum/minimum ice area, as well as the period of ice advance and
 retreat, are different for each region, in particular for the LTER
 study area.  Lastly, this historical ice record quantifies the
 magnitude of a low and high ice year for the LTER study area,
 facilitating better characterization of ice coverage during current
 LTER research. A future objective of this LTER project is to model
 the links between ecosystem processes in the LTER study area and the
 interannual and annual variability of sea ice.  The historical sea
 ice record presented here will aid in such modelling efforts.
 Stevenson, Mark J.and Frank P. Day. FINE ROOT PRODUCTION ALONG A
 CHRONOSEQUENCE OF BARRIER ISLAND COMMUNITIES. Old Dominion
 University, Norfolk Va, 23529. VCR.  Fine root production was
 quantified by an ingrowth core method along a chronosequence of dune
 communities on Hog Island, a Virginia Coast Reserve LTER site. The
 dune communities are dominated by Ammophila breviligulata, Spartina
 patens, and Aristida tuberculosa. Production estimates for fine roots
 ( < 2 mm) were estimated using biomass ingrowth into root-free soil
 volumes for one growing season. Fine root production was greater in
 N-fertilized plots than unfertilized plots. The most substantial
 level of fine root production for unfertilized plots occurred in the
 upper 0-10 cm depth in R120. The unfertilized plots showed no real
 differences in production between communities at 10-20 cm, 20-30 cm
 and 30-40 cm depths. R24 and R36 produced similar the root production
 measurements in their N-fertilized plots. There was no substantial
 increase in total phosphorus concentrations in any of the dune
 communities. There was an increase in total nitrogen concentrations
 in fine roots from all dune communities in N-fertilized plots.

Stottlemyer, Robert, Charles A. Troendle and Raymond
 Herrmann. COMPARISON OF A DECADE OF CHEMICAL INPUT/OUTPUT BUDGETS IN
 FIRST ORDER WATERSHEDS: FRASER EXPERIMENTAL FOREST, COLORADO, CALUMET
 AND WALLACE LAKE WATERSHEDS, MICHIGAN.  National Park Service and
 National Forest Service, Rocky Mountain Forest and Range Experiment
 Station, Ft. Collins, CO 80526.  Streamwater samples have been
 collected for 10-12 y from watersheds in the Fraser Experimental
 Forest, Colorado, and the Calumet and Wallace Lake watersheds,
 Michigan, to compare surface water chemistry and watershed budgets at
 ecotonal sites receiving moderate (Michigan) and low (Colorado)
 inputs of anthropic atmospheric inputs. Precipitation inputs are
 dominated by snow.  No site retains 5042-inputs.  Midwinter thaws
 often result in streamwater NH4 ion "pulses".  During spring melt,
 streamwater No3 pulses are common, but >88% of NO and >95% of NH4 is
 retained in the watersheds.  Streamwater H pulses are not common.
 Watersheds with an elevation change >100 m show a significant
 increase in snowpack ion load as a result of higher input and better
 retention.  Over-winter N mineralization in soils coupled with late
 spring snowpack release account for the streamwater mineral N pulses.
 The increase in N inputs with elevation, good retention in the
 snowpack, late spring release in snowmelt, and strong ecosystem
 incorporation suggest probable effects on site biodiversity.

Su, Haiping, and Geoffrey M. Henebry. LANDSCAPE TRAJECTORIES USING
 AVHRR DATA. Division of Biology, Kansas State University, Manhattan
 KS 66506-4901. KNZ.  We demonstrate a novel decomposition of
 satellite images into spatial dependence, spatial heterogeneity, and
 spectral intensity.  This procedure defines a 3-space within which to
 plot trajectories, i.e. time series of vectors derived from multidate
 imagery.  Trajectories of different landscapes can thus be
 visualized, quantified, and compared.  We derive landscape
 trajectories of grazed grasslands in the Kansas Flint Hills from the
 biweekly composites of AVHRR NDVI data available from EROS Data
 Center for 1988, 1990, 1991, and 1992.  The trajectories capture 1)
 the seasonality of reflectance associated with canopy development and
 senescence, 2) patterns of spatial structure associated with
 available soil moisture, and 3) interseasonal variations due to
 climatic forcings.  Landscape trajectories constitute an important
 analytical concept for global and synoptic ecology.  Su, Haiping,
 Alan K. Knapp, John M. Briggs. EFFECTS OF FIRE AND TOPOGRAPHY ON SOIL
 MOISTURE MEASURED BY TIME DOMAIN REFLECTOMETRY. Kansas State
 University, Manhattan, KS 66506. KNZ.  Soil moisture is one of the
 important factors governing the growth and development of a tallgrass
 prairie canopy. Fire and topography can affect the distribution of
 soil moisture across a watershed or landscape. On the Konza Prairie
 Research Nature Area (KPRNA), near Manhattan, Kansas, we used a Time
 Domain Reflectometry (TDR) system to monitor soil moisture on an
 annually burned and a long-term unburned watershed during the early
 Spring and Summer months (March to September). For each watershed,
 eleven sites were selected along a transect that spanned
 upland-lowland-upland topographic positions. TDR soil moisture was
 measured for each transect at 15 and 30 cm depths (where
 possible). Measurements were made weekly or biweekly depending on
 weather conditions. Preliminary results from this year's measurements
 have shown a strong topographic redistribution of soil moisture from
 upland to lowlands at 15 cm depth. Relatively high soil moisture also
 was measured at the unburned transect relative to the annually burned
 transect. The results indicate that redistribution of soil moisture
 can be an important factor influencing landscape patterns in
 aboveground production. Long term measurement of soil moisture are
 planned to more clearly understand the importance of soil moisture
 redistribution as affected by fire and topography.

Theodose, Theresa A., and William D. Bowman. THE EFFECTS OF NEIGHBOR
 AND NITROGEN AVAILABILITY ON BIOMASS AND NITROGEN ACCUMULATION AND
 ALLOCATION IN TWO ALPINE GRAMINOIDS, Deschampsia caespitosa AND
 Kobresia myosuroides. Environmental, Population, and Organismic
 Biology, Campus Box 334, and Institute of Arctic and Alpine Research,
 Campus Box 450, University of Colorado, Boulder CO 80309. NWT.  Two
 dominant alpine tundra graminoids, Kobresia myosuroides from a low
 resource environment and Deschampsia caespitosa from a more resource
 rich environment were subjected to high and low N treatments in the
 absence and presence of inter- and intraspecific neighbors to
 investigate how each species responds to N and if that response is
 influenced by neighbors. Deschampsia accumulated significantly more
 biomass and N than Kobresia, regardless of N or neighbor
 treatment. Deschampsia responded significantly to N availability with
 increases in root and shoot biomass and nitrogen concentration and
 decreases in biomass and N root: shoot ratios in the high N
 treatment. Neighbor had no effect on Deschampsia biomass
 accumulation, but presence of a neighbor resulted in increased
 biomass and N allocated to shoots relative to roots. Kobresia biomass
 accumulation and N and biomass allocation did not respond
 significantly to N availability, but root nitrogen concentration
 increased in the high N treatment. When grown with Deschampsia,
 Kobresia increased N and biomass allocation to shoots relative to
 roots. Under high N, this response to Deschampsia resulted in
 increased tillering, biomass per tiller, total shoot biomass and
 possibly total plant biomass in Kobresia. Thus Deschampsia, a
 dominant of resource rich moist meadows accumulated more biomass and
 N and was more plastic in its response to N availability than
 Kobresia. Although Kobresia, a dominant of resource poor dry meadows
 had the more conservative growth response, allocation patterns
 shifted so that growth was not inhibited by the presence of
 Deschampsia, even under high N conditions.  Tirrell. Rebecca and
 Linda Blum.  RHIZOSPHERE ENHANCEMENT OF BELOWGROUND DECAY IN A
 Spartina alterniflora MARSH. Univ. Virginia, Charlottesville VA
 22903. VCR.  The potential for live roots of Spartina alterniflora to
 enhance below round decomposition was investigated over an 18 month
 period on the Eastern Shore of Virginia. Three clipped (no live
 roots) and 3 vegetated (live roots) plots were established in both
 the creekbank and interior sections of Phillips Creek marsh in May
 1991. One month later, litter bags containing dead Spartina roots and
 rhizomes were buried in the marsh sediments.  Every 2 months a litter
 bag was removed from each treatment plot and examined for decay and
 root in-growth. Samples for bacterial abundance and acetate
 mineralization were collected from each plot. Only 20% of the
 starting litter-bag root material was lost after 18 months of decay
 regardless of location in the marsh or the presence of vegetation.
 Little root production was observed even in the vegetated plots.
 Noticeably greater numbers of bacteria were evident in the vegetated
 plots of both creekbank and interior marsh locations. Greater acetate
 mineralization rates were measured in creekbank than in interior
 sediments regardless of the presence or absence of live
 roots. Acetate mineralization was greatest in the spring and Summer,
 and was minimal during fall and winter. A rhizosphere effect was
 demonstrated: bacterial cells were more abundant in the vegetated
 plots than in the clipped treatments. These weight loss data are not
 inconsistent with the hypothesis that decay is enhanced by the
 presence of live roots since few live roots grew into the litter bags
 throughout the study. However, the effect of live roots on decay and
 microbial activity is not clear.  Torgerson, Christian, and Mike
 Lemaster.  SPATIAL HETEROGENEITY OF SOIL INVERTEBRATES AND EDAPHIC
 PROPERTIES IN AN OLD-GROWTH FOREST PLOT IN THE ANDREWS LTER, WESTERN
 OREGON.  Research Experiences for Undergraduates, Andrews LTER, 1992
 and 1993.  (Faculty advisors and Andrews LTER contacts: J.A. Jones,
 A. Moldenke, D. Perry). AND.  This study examined how spatial
 patterns of living, dead, and downed trees in old-growth forest
 canopies are related to spatial patterns of soil arthropods,
 nematodes, O-horizon depth, soil pH, soil moisture content, and soil
 temperature in an old-growth forest plot in the Andrews LTER.
 Fifty-two surface samples were collected in each of six 50-m radius
 plots using a nested randomized grid design to test for spatial
 variation at <1m, 1-5m, and 5-50 m scales.  Two plots were sampled in
 the hot dry summer of 1992, one centered under a living old-growth
 Douglas fir (Pseudotsuga menziesii) in a cluster of remnant Douglas
 firs that survived a fire about 70 years ago, the other centered on a
 stump of a tree killed in that fire.  Four plots were sampled in the
 cold wet summer of 1993: one replicated the 1992 plot centered under
 the remnant Douglas fir, a second was centered on an isolated remnant
 Douglas fir, a third was centered on a Douglas fir snag estimated to
 have died 20 years ago, and a fourth was centered on a young (<30
 year old) Douglas fir.  Data were subjected to standard parametric
 statistical analysis and spatial analysis using semivariograms and
 correlograms.  Means and standard deviations of soil properties and
 organism counts were similar between plots within each year but
 differed by year, with much higher moisture contents and lower
 temperatures in summer 1993.  Spatial analysis revealed more
 pronounced short-range variation and smaller patches in plots lacking
 remnant trees, whereas plots containing remnant trees had greater
 long range variation and larger patches.  We hypothesize that
 litterfall, root crowns, and downed trees in remnant Douglas fir
 stands gradually produce a spatial pattern of large patches which
 becomes more pronounced as the trees age, and that this long-range
 pattern is lost within a few years of old-growth tree removal or
 death.  Tremmel, David C., James F. Reynolds, Ross A. Virginia, and
 Amrita G. De Soyza. MEASUREMENTS OF ROOT GROWTH AND WATER USE OF
 CREOSOTE BUSH AND MESQUITE IN THE CHIHUAHUAN DESERT.  Duke
 University, Durham, NC, 27708, Dartmouth College, Hanover, NH, 03755,
 and New Mexico State University, Las Cruces, NM, 88003.  JRN.  We are
 measuring in situ root growth and sap flow of creosote bush (Larrea
 tridentata) and mesquite (Prosopis glandulosa) plants at the Jornada
 LTER site near Las Cruces, NM, in order to obtain a better
 understanding of the coordination between above- and below-ground
 function in these species.  Root counts are made in 10 cm segments
 from three 1.2 m long minirhizotron tubes inserted around eight
 replicate plants of each species in both a summer rainfall exclusion
 treatment and control plots.  Our results show that creosote bush and
 mesquite differ in rooting density and patterns of root growth, and
 that plants denied summer rainfall maintain and produce fewer roots
 than control plants over the same time interval.  The magnitudes of
 the differences between species, and the effects of the rainout
 treatment, vary with depth in the soil profile and time of year.  We
 are measuring the diurnal course of water movement through stems of
 these species (a proxy for transpiration rate) using a heat-balance
 sap flow measurement system.  Sap flow rates in four plants of each
 species, along with several micrometeorological parameters, have been
 monitored continuously from the end of the spring dry season to the
 middle of the summer rainy season.  Preliminary results indicate that
 mesquite responds more markedly and rapidly than does the more
 xerophytic creosote bush to both changes in cloud cover throughout
 the course of a day and to rainfall events.

Turner, Clarence L., Alan K. Knapp and Timothy R. Seastedt. MECHANISMS
 OF PERSISTENCE OF LONG-LIVED PERENNIAL FORBS IN TALLGRASS PRAIRIE: A
 COMPARISON OF PHYSIOLOGICAL RESPONSES AND LONG-TERM DATA SETS ON
 PRODUCTION.  Kansas State University, Manhattan KS 66506 and
 University of Colorado, Boulder CO 80309.  KNZ.  Relatively little is
 known about the mechanisms by which long-lived forbs (non-woody,
 perennial herbs), maintain themselves in the face of competition from
 the dominant grasses in tallgrass prairie.  We investigated the roles
 of light and nitrogen limitation, as affected by burning and
 topographic position, on gas exchange responses in big bluestem (a C4
 grass) and 5 co-occurring forbs at Konza Prairie Research Natural
 Area in 1992 and 1993.  Unusually high rainfall amounts in both years
 reduced the potential for higher water stress typical of uplands
 (vs. lowlands) and burned (vs. unburned) areas in this system.  In
 1992, photosynthetic rates of forbs were 10-50% lower than big
 bluestem, were higher on burned areas than on unburned areas, but
 were not affected by topographic position.  In 1993, photosynthetic
 rates of forbs were higher following nitrogen additions.
 Photosynthetic rates of forbs peak at light levels equivalent to
 approximately half full sunlight.  Forbs appear to maximize their
 leaf area within the surrounding grass canopy at that light level,
 which is determined primarily by factors controlling production of
 the dominant grasses.  Analysis of long-term data on biomass
 production suggests that NPP of grasses is reduced to a greater
 degree than that of forbs in low light (unburned) conditions
 (reducing the competitive advantage of grasses), resulting in greater
 relative forb production.  This agrees with observations of greater
 forb abundance in unburned prairie and suggests that competition for
 light is a significant factor controlling year-to-year variation in
 forb production, distribution and abundance.  Turner, P.A.,
 E.F. Benfield, and J.R. Webster. PATTERNS OF MACROINVERTEBRATE DRIFT
 ALONG AN ELEVATIONAL AND STREAM SIZE GRADIENT IN A SOUTHERN
 APPALACHIAN STREAM. Dept. of Biology, VPI&SU, Blacksburg, VA
 24061. CWT.  The downstream movement of macroinvertebrates in drift
 has been shown to be important in stream ecosystems in terms of
 colonization and distribution, as well as being a vital energy link
 between upstream and downstream reaches. Drift was collected from
 each off our 100m reaches along an elevational and stream size
 gradient in a southern Appalachian stream in order to investigate the
 role of drift along the gradient. Preliminary results, based on 24h
 drift densities, suggest no elevational trends, except that highest
 drift densities occur at the highest, first order site (WS27).  A
 distinct diel periodicity was found for the lower three sites. These
 results may actually be an artifact of incomplete analysis because
 organisms have not yet been identified.  Uliassi, Daniel D.,
 R. W. Ruess, and K.M. Klingensmith. SUCCESSIONAL PATTERNS OF NITROGEN
 FIXATION AND DENITRIFICATION IN A TAIGA FLOODPLAIN FOREST. University
 of Alaska, Fairbanks Alaska, 99775 USA. BNZ.  Nitrogen fixation by
 Alnus tenuifolia is the major contributor to the nitrogen budget of
 taiga floodplain forests in interior Alaska.  Acetylene reduction and
 acetylene inhibition assays were used to measure root nodule nitrogen
 fixation rates and rhizosphere denitrification rates of A. tenuifolia
 within successional forests along the Tanana River floodplain.  Rates
 were measured in dense alder, alder/balsam poplar, balsam poplar, and
 white spruce stages during early, mid, and late growing season.
 Fixation rates were highest in the dense alder (38.41 �± 13.43 ?Mole
 C2H4 g Nodule DWT -1 hr -1), declined with increasing abundance of
 balsam poplar, and increased in white spruce stands. Significant
 intraseasonal variation in fixation rates were found, with peak
 fixation occurring during mid-summer (48.46 �± 11.48 ?Mole C2H4 g
 Nodule DWT -1 hr -1). Rhizosphere denitrification losses were highest
 in September (81.47 �± 16.43 ?g N g DWT Root -1 hr-1) and lowest in
 August (0.32 �± 0.16 ?g N g DWT Root -1 hr-1). Taken together, our
 estimates of nitrogen fixation inputs (68.9 g N m-2 yr-1) and
 denitrification losses (24.9 g N m-2 yr-1) for early successional
 stands yield a net ecosystem nitrogen input of 44.0 g N m-2
 yr-1. Given the potential uncertainties associated with these
 estimates, this value is similar to the ranges of values (15.6 to
 36.2 g N m-2 yr-1; Van Cleve et al. 1971;1993) estimated from
 nitrogen mass accumulation, and emphasizes the dynamic nature of
 nitrogen cycling processes in this ecosystem.

Wagener, Stephen M.1, J.M. Anderson2, Mark W. Oswood1, and Joshua P
 Schimel1. RIVER AND SOIL CONTINUA: PARALLELS IN CARBON AND NUTRIENT
 PROCESSING . 1lnstitute of Arctic Biology, University of Alaska
 Fairbanks, Fairbanks, AK 99775; 2Rothamsted Experimental Station,
 Harpenden, Herts AL5 2JQ, Great Britain. BNZ.  Both soil and stream
 ecosystems receive inputs from leaf litter and living primary
 producers. Despite this functional similarity, soil and stream
 ecologists have dissimilar views of trophic processes. Soil
 ecologists usually see decomposition as a process that mineralizes
 carbon from plant residues and provides nutrients for plant uptake,
 with invertebrates playing little role in carbon dynamics. In
 contrast, aquatic ecologists view litter decomposition in a forest
 stream as a series of transformations mediated by specialized
 invertebrates. Soil ecologists often underestimate the role of
 invertebrates in litter processing because they are mostly concerned
 with CO2 flux, little of which is directly a result of invertebrate
 respiration. In contrast, the stream ecologist's measure of carbon
 loss includes not only CO2 lost to the atmosphere, but leachates and
 fine particulates lost downstream as well. Stream ecologists
 underestimate the importance of microbes because much of the carbon
 is transported downstream to be eventually respired by microbes. Both
 a forest soil profile and a stream can each be divided into three
 analogous regions: an upper region where carbon is predominantly from
 leaf litter, a middle region where a significant proportion of carbon
 is derived from living primary producers in the form of roots (in
 soil) or macrophytes and algae (in running water), and a lower region
 dependent on fine particulate or dissolved carbon from higher in the
 soil profile or upstream. The differences in perspective of the soil
 and stream ecologists is likely due to the very different spatial and
 temperal scales in soils and streams. Soil process takes place over
 very small distances (cm), over long time periods (years), in the
 dark. In contrast, decomposition in a stream occurs over much longer
 distances (hundreds of km), over shorter time periods (months), and
 in daylight. What the stream ecologist fails to see is the entire
 river (analogous to a soil core) as an ecosystem. Despite great
 differences in the perceived importance of invertebrates in
 decomposition processes between streams and soils, invertebrates play
 very similar roles in carbon mineralization.

Wagener, Stephen M.1, J.M. Anderson2, and Joshua P
 Schimel1. BIOLOGICAL CHARACTERISTICS OF BIRCH LITTER
 COHORTS. 1lnstitute of Arctic Biology, University of Alaska
 Fairbanks, Fairbanks, AK 99775, 2Rothamsted Experimental Station,
 Harpenden, Herts AL5 2JQ, Great Britain. BNZ.  In the forest floor of
 Alaskan taiga, annual layers of Equisetum (horsetail) litter are a
 naturally occurring marker of birch litter cohorts. Equisetum litter,
 because of its texture and the presence of silica, leaves a
 long-lasting residue that provides a sharp contrast with birch
 litter. Due to the absence of macroinvertebrates, there is little
 bioturbation and litter cohorts generally maintain their location
 relative to surrounding litter. We collected box core samples of the
 forest floor in early September 1992. Forest floor material was
 separated into the following strata: Stratum 1, the 1991 year class;
 Stratum 2, the 1990 year class; Stratum 3, the 1989 year class;
 Stratum 4, the fermentation layer, 1988 year class and older; and
 Stratum 5, the upper white-colored zone of the fibrous root layer
 which made up the rest of the forest floor. Short-term respiration
 potential decreased with depth, as generally did the nitrogen content
 of the litter. Immobilization of nitrogen exceed mineralization in
 Strata 1 and 2, but net mineralization of nitrogen occurred in Strata
 3-5, with mineralization increasing with depth.  Some invertebrate
 taxa (such as Oribatida: Liodidae and Collembola: Entomobryidae) were
 found associated with upper strata, some taxa (such as Diptera larvae
 and Collembola: Onychiuridae) were found in deeper strata, and some
 (Oribatida: Nothridae) were evenly dispersed in all strata.

Walker, Donald A., William B. Krantz, Brad E. Lewis, Erik T. Price,
Ronald D.Tabler, Marilyn D. Walker, and Carol A. Wessman. MULTI-SCALE
STUDIES OF SNOW-VEGETATION INTERACTIONS IN THE ALPINE ZONE. Institute
of Arctic and Alpine Research, Campus Box 450, Environmental,
Population, and Organismic Biology, Campus Box 334, Chemical
Engineering, Campus Box 424, and Cooperative Institute for Research in
Environmental Sciences, Campus Box 216, University of Colorado,
Boulder CO 80309 and Tabler Associates, 7505 Estate Drive, Longmont
CO. NWT. The Niwot Long-Term Ecological Research (LTER) has begun a
snow-fence experiment to examine the consequences of altered snowpack
regimes in alpine ecosystems. This poster describes the principal
questions that are being addressed, the design of the experiment, an
update on the status of the fence construction and experimental plot
layout, and the results of the first winter's snow-depth and
ground-temperature observations. Snow depths are reported for a 350 x
500-m grid surrounding the experimental site and for more intensive
measurements in the 60 x 125-m snow-fence experiment study area. The
period November 1992 to April 1993 had 183% of average snowfall at
D-1, and April was the wettest month on record, so patterns of snow
distribution reported here may be representative of conditions that
could be expected with increased snow fall.  Walker, (Skip) D.A.,
William B. Krantz, Brad E. Lewis, Erik T. Price, Marilyn D. Walker,
and Carol A. Wessman. MULTI-SCALE STUDIES OF SNOW-VEGETATION
INTERACTIONS IN THE COLORADO ALPINE ZONE. Niwot LTER Project,
University of Colorado, Boulder, CO, 80309 NWT Alpine ecosystems are
thought to be particularly sensitive to climate change, and research
at the Niwot Long-Term Ecological Research (LTER) site in the Indian
Peaks of the Colorado Front Range is focusing on the consequences of
changed temperature and precipitation regimes.  We are particularly
interested in the effects of altered snowpack because of the known
importance of snow to the distribution of alpine plant and animal
communities.  The distribution of snow patches and windblown areas,
duration of the snow-free period, and position of melt water drainages
strongly affect the patterns of alpine plant communities.  Two of the
goals of the Niwot LTER project are to understand (1) how current
snowpack distributions affect patterns of vegetation and primary
production from species to regional scales, and (2) how will altered
snowpack regimes change the existing ecosystems.  We focus on making
fine- and intermediate-scale databases that provide linkages between
species-level studies and remotely sensed information in order to
develop a broad understanding of environmental and edaphic controls on
vegetation patterns.  A standardized method makes our approach useful
for multiscale and intersite comparisons.  At the plot level, the
abundance of key taxa in a Braun-Blanquet classification are closely
correlated with snow distribution.  At the landscape level, over 78
percent of the mapped areas are covered by communities typical of
snowbeds or windblown sites, an indication of the importance of wind
and snow cover to the vegetation of this alpine site.  Finally, at the
regional level, analysis of SPOT satellite data reveal strong negative
correspondence between elevation and the Normalized Difference
Vegetation Index (NDVI, an index of green biomass) on all slope-aspect
combinations except for west-facing slopes east of the Continental
Divide, where strong westerly winds control vegetation production at
all elevations.  The relationship may have general appl