Effects of climate, site and soil characteristics on critical loads and exceedance in forests in the northeastern U.S.

Linda Pardo1, Molly Robin-Abbott2, Claire O'Dea3, Jennifer Pontius4 and Jason Coombs5

Assessing the impacts of the multiple threats impacting ecosystem health and sustainability over the long term, in particular climate change and nitrogen (N) deposition, remains a critical challenge for resources managers and policy makers. To facilitate such assessments, we used 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 forest lands in the Northeast and Upper Midwest. 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. We conducted our analysis for the full region and at the Ecoregion levels 2 and 3. 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. In this analysis, we determined the critical load and exceedance for individual tree species and all the species present. We also evaluated the extent and magnitude of the CL exceedance and how that would change under future deposition scenarios. N-CLAS facilitates analysis of the extent of the area impacted by N deposition which provides resource managers with a simple way to incorporate the current state-of-the-science knowledge into their planning and management decisions.


1US Forest Service, lpardo@fs.fed.us
2US Forest Service, mjrobina@gmail.com
3US Forest Service, cbodea@fs.fed.us
4UVM/US Forest Service, japontiu@uvm.edu
5US Forest Service, jcoombs@cns.umass.edu