Interactive effects of hemlock mortality and nitrogen availability on nutrient pools and fluxes in the southern Appalachian mountains from 2009 to 2011

The impacts of exotic insects and pathogens on forest ecosystems are increasingly recognized, yet the factors influencing the magnitude of effects remain poorly understood. Eastern hemlock (Tsuga canadensis) exerts strong control on nitrogen (N) dynamics, and its loss due to infestation by the hemlock woolly adelgid (Adelges tsugae) is expected to affect nutrient dynamics in impacted stands. We evaluated the potential for variation in N availability to influence the magnitude of effects of hemlock decline on N and P dynamics in mixed hardwood stands. We measured N and P pools and fluxes at three elevations (low, mid, high) subjected to increasing atmospheric N deposition where hemlock was declining or absent (as reference) in western North Carolina. Specifically, this study was conducted at Coweeta Hydrologic Laboratory, a USDA Forest Service experimental forest in the southern Appalachian mountains of western North Carolina, USA from October 2009 to February 2011.