Pan, Yude (USDA Forest Service, Northern Global Change Program, 11 Campus Blvd, Newtown Square PA 19073; Phone: 610 557 4205; Fax: 610 557 4095; Email: ypan@fs.fed.us)

Forest Carbon Dynamics under Changing Atmospheric Chemistry and Climate in the Mid-Atlantic Region

Y. Pan *, R. Birdsey, J. Hom, K. McCullough

Changes in atmospheric chemistry and physics due to human activities are causing widespread impacts on terrestrial ecosystems. Besides the effects of climate change induced by greenhouse gases, elevated CO₂, O₃ and N deposition also have direct impacts on ecosystem dynamics and functioning. This study uses an ecosystem modeling approach to investigate how these multiple environmental changes interactively affect carbon dynamics in Mid-Atlantic forests that cover approximately 460,000 km² of lands. Our results indicate that elevated CO₂ increases forest productivity, but the enhanced growth was largely reduced by troposphere O₃. Currently, higher N deposition interacts with higher CO₂ to increase forest C sequestration. However, continued deposition of N at high levels will cause many areas to become saturated as other growing factors become limited. As forests become saturated with N, carbon accumulation in forest woody product will be reduced, and water quality will be degraded because of an abrupt increase in N export. Changes in interannual variability of climate during past decades add complexity to forest responses to changing atmospheric chemistry. More fundamentally, these multiple stresses together have likely altered basic forest biological processes and physiology. We validated the modeling results with observations from forest inventory and the MODIS satellite. The model-data comparison demonstrates that the ecosystem modeling approach is robust in this regional carbon study.