Forest health is affected by multiple factors, including climate change, nitrogen deposition, insect pests, and forest pathogens. We are developing a GIS-based tool to evaluate the impact of multiple stressors on forest health and critical loads of nitrogen (N). In the first phase of this project, we have created a framework to evaluate the effects of abiotic modifying factors on species specific critical loads of N. Tree species of management concern were identified by resource managers in VT and NH: American beech, American chestnut, quaking and bigtooth aspen, balsam fir, paper and yellow birch, butternut, eastern hemlock, red, white, and chestnut oak, red and pitch pine, red and black spruce, sugar maple, and white cedar. Ranges for critical loads of N were determined based on empirical responses to N deposition as reported in the literature. For each species, we have created a table of abiotic modifying factors that influence the response of trees to N deposition, including elevation, aspect, precipitation, average January and July temperature, and soil characteristics. For each factor, we identify thresholds that affect the species’ response to N deposition. These tables will be used in concert with GIS data to generate site and species specific critical loads of N, and can also be used to generate critical loads of N under various climate change scenarios.