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 e