E&S has completed a research project for the National Park Service to apply niche models from a database of more than 1,500 statistical models previously developed by E&S to evaluate expected future changes in understory vegetation occurrence in response to air pollution and climate change across eight NPS units: Acadia NP, Glacier NP, Grand Teton NP, Joshua Tree NP, Rocky Mountain NP, Sleeping Bear Dunes National Lakeshore, Theodore Roosevelt NP, and Yosemite NP. Critical loads of atmospheric N deposition were determined to be less than 5 kg N/ha/yr for the vast majority of vegetation species and map classes represented by these eight NPS units. Protection of the most sensitive species within vegetation classes typically required N deposition to be lower than 2.5 kg N/ha/yr. Projected increases in air temperature were shown to have predominantly adverse effects on the vegetation communities considered, particularly for mountainous NPS units. Reductions in atmospheric N deposition and greenhouse gas emissions would be expected to contribute to preservation of existing biodiversity within U.S. national parks. Analyses are underway to evaluate critical loads and vegetation response across a larger set (n = 164) of National Parks.