Impacts of Hemlock Loss on Nitrogen Retention Vary with Soil Nitrogen Availability in the Southern Appalachian Mountains

Abstract

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 decrease N retention in impacted stands. We evaluated the potential for site variation in N availability to influence the magnitude of effects of hemlock decline on N dynamics in mixed hardwood stands. We measured N 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. Nitrogen pools and fluxes varied substantially with elevation and increasing N availability. Total forest floor and mineral soil N increased (P < 0.0001, p = 0.0017, resp.) and forest floor and soil carbon (c) to n ratio decreased with elevation (p < 0.0001, p = 0.0123, resp.), suggesting that these high elevation pools are accumulating available n. contrary to expectations, subsurface leaching of inorganic n was minimal overall (

Citation

Block, Corinne E.; Knoepp, Jennifer D.; Elliott, Katherine J.; Fraterrigo, Jennifer M. 2012. Impacts of Hemlock Loss on Nitrogen Retention Vary with Soil Nitrogen Availability in the Southern Appalachian Mountains. Ecosystems 1-13. DOI: 10.1007/s10021-012-9572-9