The ForSAFE-VEG model was applied to estimate changes in soil chemistry and ground vegetation of a generalized plant community in the alpine and subalpine zones of the Rocky Mountains region of the United States during the period 1750-2400 AD in response to changes in air pollution and climate. Model simulations illustrated how to operationally estimate the critical load of atmospheric nitrogen (N) deposition needed to best protect plant biodiversity. The values obtained for the critical load (critical limit for biodiversity change) of atmospheric N deposition fall in the range of about 1 to 2 kg N/ha/yr when the model inputs and response thresholds are manipulated. In a follow-up project, we used the model to simulate the impacts of N deposition on plant biodiversity, in combination with different degrees of long-term climatic shifts, to subalpine and alpine ecosystems within Rocky Mountain National Park (ROMO). This effort spanned the years 2008 – 2011.