Impacts of the Hemlock Woolly Adelgid (Adelges tsugae) on Headwater Stream Large Woody Debris Loads in the Southern Appalachian Mountains

The hemlock woolly adelgid (HWA; Adelges tsugae) is responsible for widespread mortality of eastern hemlock (Tsuga canadensis) throughout its range. Models suggest that HWA-induced mortality could serve as a disturbance event that will increase large woody debris (LWD) loads in head-water streams. The objective of this research was to investigate the extent to which HWA infestation has impacted in-channel LWD loads in southern Appalachian headwater river systems. We surveyed 26 sites within the Blue Ridge Mountains with varying degrees of eastern hemlock composition, and HWA-induced decline. We combined these into a Hemlock Decline Index (HDI) that served as an explanatory variable for analyses. Results revealed that high HDI values were associated with higher LWD loads, higher frequency of LWD jams, and larger diameter LWD. These findings indicate that the HWA is significantly impacting LWD loads in streams, and subsequently impacting stream ecology. Additionally, the HDI developed here could be a useful tool for making regional comparisons of the impacts of the HWA on forest ecosystems.