Spatial patterns in critical loads and exceedance in forests in the northeastern U.S.: using a GIS tool for assessing effects of nitrogen deposition

Linda Pardo1, Molly Robin-Abbott2, Claire B. O’Dea3, Jennifer Pontius4 and Jason A. Coombs5

Maintaining commercially important tree species, as well as species valued for ecological, social, and cultural reasons, is becoming increasingly challenging in the northeastern U.S. due to the significant threats impacting ecosystem health and sustainability over the long term, in particular climate change and nitrogen (N) deposition. We developed a GIS-based tool, Nitrogen Critical Loads Assessment by Site (N-CLAS), to evaluate the impact of multiple stressors (N deposition and climate change) simultaneously for species of management concern on public and private forest lands. In addition to calculating species-specific critical loads, N-CLAS is designed to take into account the impact of site abiotic factors on the response of trees to N deposition.  The abiotic modifying factors include, precipitation, temperature (e.g., January T, July T, May-September T), and soil characteristics. Application of N-CLAS across the northeastern U.S. allows us to evaluate which areas and tree species are most susceptible to impacts from N deposition. We can determine the critical load and exceedance for individual tree species or all the species present. We have incorporated climate change scenarios in order to explore the interaction between climate change and nitrogen deposition. Thus, we are also able to determine the fraction of the region that is susceptible to detrimental impacts of N deposition under projected climate scenarios. Use of this tool provides resource managers with a simple way to incorporate the current state-of-the-science knowledge into their planning and management decisions.


1USDA Forest Service,
3USDA Forest Service,
4UVM/USDA Forest Service,
5U. Mass-Amherst,