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 results appear reasonable compared with past model applications in northern Europe. 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. This range might expand further, depending on selection of critical site-specific parameters (rainfall, temperature, soil chemistry, plant uptake of nutrients, and any eventual harvest of biomass) for the hypothetical site, and also depending on the maximum change allowed for specification of the critical load.
In a recent follow-up project, we used the ForSAFE-VEG model to simulate the impacts of nitrogen 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).