ON CARBON AND WATER BALANCE
The
purposes of this workshop were to (i) identify ideas for cross-site comparison
and synthesis and (ii) explore approaches to quantifying change in carbon and
water balance in response to historic and ongoing ecosystem disturbance
resulting from land use. Workshop participants included 22 ASM attendees; an
additional 4 ASM attendees were not present at the workshop because of schedule
conflict but expressed strong interest in participating in follow-up activities
(list attached). The workshop included four presentations: Olga Krankina (Changes
in land-use and their effects on carbon stores: Examples from St. Petersburg
region, Russia), Jess Zimmerman (The
consequences of socioeconomic and land use changes for carbon dynamics in
Puerto Rico), Terry Parr (Hierarchical
approaches to LTER & land use change in the UK: Relevance to carbon balance
questions), and Ted Gragson (Land-use regimes and the legacy of
transformation in southern Appalachia).
Mark Harmon concluded the presentations by discussing strategies for
analyzing the effects of land-use change on carbon stores.
The
presentations covered a wide geographic range of sites and revealed interesting
similarities between the sites in the patterns of land use change. All presentations
outlined approaches and experiences with estimating change in carbon stores
caused by land use. Expansion of forest cover was reported in all four regions
with additional examples provided on woody encroachment in Great Plains (KNZ),
forest re-growth in Wisconsin (NTL),
Land
use and land-use change are among the major factors that shape carbon and water
balance in landscapes and ecosystems. Carbon and water are of great consequence
as synthesis topics because they are quantifiable, important at all sites (and
policy-relevant at many), and represent globally significant ecosystem
functions. Site-level studies can
greatly benefit from the collaboration and systems approach required to address
the balance of carbon and water across the network. More importantly, rigorous cross-site
comparison and synthesis is possible, can yield globally significant results,
and should therefore be central to current LTER synthesis efforts. The workshop highlighted the following ideas
and expected results from cross-site comparison and synthesis:
a. Many
LTER sites and research projects outside the network are demonstrating that
there are common patterns to the history of land use. The most significant is
the continuing expansion of forest cover or reforestation of landscapes that
began in different locations decades to centuries ago. The estimated carbon
source from tropical deforestation that was widely reported during the 90’s led
investigators to search for a large enough carbon sink somewhere in terrestrial
ecosystems to balance the global carbon budget. The processes responsible such
a sink were never identified with certainty. Although the evidence of expanding
forests and other woody vegetation in different parts of the world continues to
mount, it is unclear how much additional C storage on land this represents. Is
it large enough to explain the missing C sink? How long is this carbon store
going to last and how much is it going to expand? How is the forest expansion
related to social change in recent and distant past and will it continue? These
are important science, policy, and land management questions and answering them
requires long-term data and integrated interdisciplinary research.
b. In
many parts of the world, water availability and quality are
important issues that are clearly linked to land use and land-use change.
Understanding is nevertheless limited about how different land uses and changes
in land use cumulatively affect the water balance of landscapes and regions.
This constrains efforts to forecast future ecosystem responses or execute
management strategies that anticipate the most likely outcomes from established
trajectories of change. Furthermore, there have only been limited attempts to
derive process-based predictions of the cumulative temporal and spatial effects
of multiple land uses and land-use change on sedimentation, flow patterns, and
other attributes of water balance.
c. Land
use represents a series of decisions and actions
carried out by humans to obtain products and/or benefits by using land
resources. Current patterns of land-cover, land-use, carbon and water fluxes
reflect the cascading effects of human action across time. Immediate effects
are generally understood better than long-term or secondary effects, however
long-term effects can be just as important. The comprehensive understanding of
land use and land-use change and the ultimate explanation of the current role
of ecosystems in the global environment demands integration over large areas
and long time frames. Historical
analysis of the spatial, temporal, and decision-making components of land use
represents an important and commonly overlooked source of information that can
help explain the current role of ecosystems in the global environment and
better project future changes.
d. Through
a multitude of interactions, land use, water and carbon cycles
are intricately linked across space and time.
Large-scale examples are massive floods that have occurred in many parts
of the world following alteration of forest cover far from the location of the
floods; in other areas (South Africa, for example), afforestation with
non-native vegetation caused dramatic reductions in municipal water supplies.
Altered land use patterns also impact local and regional climate patterns,
which in turn affect carbon cycles. Research is urgently needed to address
adequately the essential feedback mechanisms and lag times within these linked
complex systems. Improved understanding is necessary to inform the water and
carbon management policy. The current lack of knowledge hampers decision making
to address the global scale problems of CO2 accumulation in the
atmosphere and fresh water supply.
e. The
large investment in research to date has led to the development of methods
for assessing the effects of land use on carbon and water balance. These
methods can easily be standardized and simplified for the task of cross-site
synthesis. The response of carbon and water balance to changes in land use is
reasonably well understood at the site level, and scaling methods for moving
from the site to the landscape and the regional level are being actively
developed at a number of LTER sites.
Much of this development is directed at meeting the needs of managers,
stakeholders, and policy-makers. The comparative analysis of response
variability across LTER sites is critical to our understanding of continental
and global-scale responses.
In summary, the effects of land use change are a major source of
uncertainty in understanding the local, regional, and global patterns of carbon
and water cycles. Reducing this uncertainly is clearly one of the Grand
Challenges in Ecology. The unique role that the LTER Network can play in
addressing this topic is defined by availability of long-term ecological and
socio-economic data sets and inter-disciplinary research teams. LTER network
(particularly in combination with I-LTER sites) covers a wide variety of
ecosystem types and historic land use patterns within an existing collaborative
framework, well poised to examine global-scale patterns in ecosystem
functioning. Carbon and water are priority topics for synthesis science and
focusing on them can serve to address significant and complex environmental
problems and generate knowledge that benefits both science and society.