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Climate Change - Terrestrial Ecosystem Science Focus Area

CO-PRINCIPAL INVESTIGATORS: Paul J. Hanson and Peter E. Thornton

PARTICIPATING STAFF: Robert J. Andres, Wilfred M. Post, Richard J. Norby, Charles T. Garten, Lianhong Gu

PROJECT START DATE: October 1, 2010


SPONSOR: US DOE, Office of Science, Office of Biological and Environmental Research (BER)

PROJECT WEBSITE: www.mnspruce.ornl.gov

Understanding ecosystem carbon cycles and responses in the context of climatic and atmospheric change is the focus of ORNL's research in the Terrestrial Ecosystem Science Focus Area. The combined efforts include large-scale manipulations, carbon cycle observations, process-level studies, and an integrating suite of modeling efforts.

Experimental work under the Terrestrial Ecosystem Science SFA focuses on the identification of critical response functions for terrestrial organisms, communities, and ecosystems. Both direct and indirect effects of these experimental perturbations are analyzed to develop and refine models needed for full Earth system analyses. ORNL's climate change manipulations are organized around a single climate change experiment focusing on the combined response of multiple levels of warming at ambient or elevated CO2 (eCO2) levels in a black spruce - sphagnum ecosystem in northern Minnesota. The experiment provides a platform for testing mechanisms controlling vulnerability of organisms and ecosystem processes to important climate change variables (e.g., thresholds for organism decline or mortality, limitations to regeneration, biogeochemical limitations to productivity, carbon evolution). The experiment will evaluate the response of existing biological communities to a range of warming levels from ambient to +9 oC. The +3 oC and +9 oC warming treatments will also be conducted at eCO2 (in the range of 800 to 900 ppm). The target ecosystem located at the southern extent of the spatially expansive boreal peatland forests is considered to be especially vulnerable to climate change and to have important feedbacks on the atmosphere and climate. Our terrestrial ecosystem science plan also includes support for core, long-term tracking of the hydrologic, biogeochemical and biological response of the Walker Branch Watershed to inter-annual climatic variations.

Carbon cycle modeling and research involves the integration of biophysical, biochemical, physiological, and ecological processes into terrestrial ecosystem models that are optimally constrained in structure and function by historical and contemporary observations, and include mechanistic results of manipulative experiments to enable projections of future responses and feedbacks to climate forcing. ORNL's TES-SFA eliminates the artificial distinction between experimental and observational studies and model building, parameter estimation, evaluation, and projection. Advancing terrestrial carbon cycle science requires observations and measurements to be integrated with spatially resolved, mechanistic process-based models of terrestrial ecosystems that represent scientific understanding from experiments and are validated and constrained by observations and revealed by experimental manipulation. Only through such integration may we produce reliable estimates of sources and sinks of CO2 and extrapolation from observations in space and time to novel environmental conditions of the future. Research will lead to an operational model framework in which observational and experimental studies and modeling activities at different spatial and temporal scales are integrated and used to estimate and mechanistically explain current carbon sources and sinks and forecast their future behavior and influence on atmospheric CO2 concentration and climate.

Accurate representation of soil carbon cycling processes, particularly the response to short- and long-term environmental changes, is needed to improve predictions of regional- to global-scale climate models. Given recent process-level advances in our understanding of the chemistry of soil carbon storage and susceptibility, the accuracy of current models in predicting soil carbon response to environmental change is uncertain. Our goal is to generate mechanistically-based rate data to resolve recent questions regarding the nature of stabilized soil carbon, and to develop a process-level model describing soil carbon response to environmental change. The resulting model and description of soil carbon dynamics will be tested at ongoing SFA field experiments and against various long-term datasets at various spatial scales.

Activities supported include the following tasks and task leads in order of overall financial investment: SPRUCE Climate Change Experiment (Hanson et al.), Carbon Cycle Modeling (Thornton & Post), a process study of carbon allocation (PITS - Norby), soil carbon cycling process studies (EBIS-AmeriFlux - Hanson, and regional soil carbon cycling assessments - Garten), the MOFLUX contribution to AmeriFlux science (Gu), and carbon emissions research and synthesis (Marland).