Disequilibrium and Transient Dynamics: Disentangling Responses to Climate Change versus Broader Anthropogenic Impacts on Eastern Forests

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U.S. forests face an unprecedented array of threats. Scientists have typically studied these threats in isolation, but it is clear that changes in the distribution and abundance of tree species over the next century will depend on the cumulative impacts of a wide range of human impacts. The proposed research will link an existing, well documented and tested model of forest dynamics to the continental-scale forest inventory data maintained by the U.S. Forest Service Forest Inventory and Analysis Program. The new framework will expand the model to assess the effects of a broad suite of human impacts on eastern U.S. forests, including (1) climate change, (2) changes in logging regimes, (3) introduced pests and pathogens, and (4) increasing nitrogen (N) deposition and CO2 concentrations. Preliminary results suggest that the direct effects of climate change alone on the distribution and abundance of tree species in the eastern U.S .will be relatively small over the next 50-100 years, in part because direct climate impacts on adult tree survival are relatively small. However, processes that increase the natural mortality rates of adult trees, such as harvesting or the spread of pests or pathogens, are expected to interact with the effects of climate change by opening the forest canopy and allowing the establishment of new species. This research addresses a clear need of resource managers and policy makers for transparent, data-driven models that can be used to understand and predict forest response to a broad range of human impacts. For instance, the new model will be able to project the effects of proposed increases in forest harvest rates for production of energy biomass on subsequent forest productivity, and how the effects could change in combination with other human-caused impacts such as the accidental introduction of pests and pathogens. The project will also provide training and workshops for students and management professionals in the use and application of this new tool for sustainable use of the nation's forests.