Assessing the Effects of Climate Change and Air Pollution on Soil Properties and Plant Diversity in Sugar Maple–Beech–Yellow Birch Hardwood Forests in the Northeastern United States: Model Simulations from 1900 to 2100

Historical deposition of nitrogen (N) and sulfur (S) over the Eastern United States has impacted ecosystem structure and function. The potential for recovery of ecosystems is relatively uncertain, with deposition paired with future climate change contributing to this uncertainty. The impacts of N and S deposition and climate change (from 1900 to 2100) on two sugar maple–beech–yellow birch sites in the Northeastern United States were evaluated using the paired biogeochemical–vegetation response model ForSAFE-Veg at two research sites, Hubbard Brook Experimental Forest and Bear Brook Watershed. Deposition was found to be the dominant stressor, causing changes in soil acid–base chemistry, N enrichment, and shifts in understory species composition. Responses of the two sites varied due primarily to differences in buffering capacity and levels of deposition. However, at both sites, recovery of soil and plant community properties to 1900 conditions was approached only when future deposition to 2100 was returned to pre-industrial levels. Policy-based reductions in deposition generally halted further damage to soils and plants and resulted in no or only partial recovery. Increased temperatures and precipitation according to Intergovernmental Panel on Climate Change (IPCC) climate futures stimulated soil and plant response, thereby accelerating changes in plant communities and N enrichment and counteracting the acidifying impacts of N and S deposition on soil acid–base chemistry.