Among the challenges to maintaining ecosystem health and sustainability over the long term are climate change, nitrogen (N) deposition, pest outbreaks, and land use change and fragmentation. In this project, we are developing a GIS-based tool to evaluate the impact of multiple stressors (N deposition, climate change, pests) simultaneously for species of management concern on public and private lands. The regional tool that we are developing for the Northeast serves as a pilot project for national-scale implementation. Our approach is to: (1) develop critical loads (CL) for individual species of trees and herbaceous plants; (2) develop a framework to evaluate the effect of landscape characteristics and other abiotic factors on N CLs for species of management concern; (3) assess the interacting effects of climate change and N deposition on forest health and how this will affect the CL; (4) incorporate impacts from insect pests into the forest health and CL assessment. The abiotic modifying factors include elevation, latitude, precipitation, temperature (e.g., min winter T, max summer T), and soil characteristics. The impact of each abiotic modifying factor on the response to N deposition for a given species is determined by the weight of evidence (weak, moderate, or strong) which is based on the certainty associated with the data and response reported. For each location and species/community, an assessment is made about the certainty (likely, possible, unlikely) of the effect on the CL based on the weight of the evidence. The systematic approach we developed, in which the basis for each decision is made explicit, allows users to understand the reliability of the CLs presented.