IMPACTS OF DISTURBANCES ON ECOLOGICAL CARBON SEQUESTRATION AND GREENHOUSE GAS EMISSIONS

The U.S. Geological Survey is prototyping a methodology to fulfill requirements of the 2007 Energy Independence and Security Act (EISA) which requires an assessment of current carbon stocks and fluxes, and potential for ecological carbon sequestration under a range of climate, economic, and policy scenarios. Disturbances affect ecosystem dynamics and can introduce risk to carbon sequestration strategies, and thus, need to be accounted for. To meet EISA requirements, we developed a series of empirical and process-based simulation models to quantify disturbance impacts. Our approach forecasts future disturbance locations and severity, and the resulting impacts on vegetation dynamics. For fires, we relied on existing disturbance histories derived from Landsat time-series imagery, including the Monitoring Trends in Burn Severity (MTBS) and Vegetation Change Tracker (VCT) data, developed to update LANDFIRE fuels and vegetation layers. We used the MTBS and VCT data to parameterize models predicting the number of fires in relation to climate, land-use/land-cover change, and socioeconomic variables at an ecoregion scale. We determined the location of individual fires with an ignition probability surface and then simulated fire spread in response to weather, fuels, and topography. Following the fire spread simulations, we determined changes in biomass pools using a burn severity model. At the end of each annual simulation, vegetation dynamics were updated using LANDFIRE vegetation types and succession models. We present an overview of the modeling approach, validation results, and forecasts of disturbances and their impacts on greenhouse gas emissions, and carbon stocks and fluxes in the southeastern U.S.