Impacts of Hemlock Woolly Adelgid Infestation on Decomposition: An Overview

Hemlock woolly adelgid (HWA), Adelges tsugae Annand, a small aphid-like pest, is initiating rapid and widespread changes in composition and structure in southern New England hemlock forests. Rapid HWA expansion and extensive eastern hemlock (Tsuga canadensis) salvage logging threaten a region-wide reduction of this ecologically unique, culturally and economically important forest type. The purpose of this paper is to describe the major results from a series of ongoing decomposition studies comparing the direct impacts of HWA feeding (damage to foliage, changes in soil microclimate) with indirect effects of forest harvest and community change. HWA canopy thinning rapidly alters soil temperature and moisture, retarding surface soil decomposition in stands suffering heavy damage and immediately following forest harvest. Fungal establishment and litter N retention at the most open sites were reduced. Regenerating stands had increased decomposition relative to noninfested hemlock forests, whether they where initiated after logging or by HWAhemlock mortality. Initial results suggest that feeding by HWA did not alter foliar chemistry and only weakly influenced N retention in decomposing foliage. Replacement of hemlock by high foliar N black birch (Betula lenta) is likely to have persistent impacts on decomposition in these forests. These changes probably enhance N mobility in infested hemlock stands and potentially increase N export to forest streams.