Spatial Distribution and Pattern of HWA Induced Hemlock Mortality in the Southern Appalachians

The hemlock woolly adelgid (Adelges tsugae, HWA) is a significant mortality agent of Eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) in the eastern United States. These hemlock species play important roles in the vegetation dynamics of Southern Appalachian forest landscapes. Spatially explicit inventory information on HWA herbivory at landscape scale does not exist. The goal of the study was to employ remote sensing technologies to inventory Eastern and Carolina hemlocks and to quantify the extent of HWA herbivory. The specific objectives of this study were 1) to detect dead hemlocks from high resolution aerial imagery, 2) to estimate potential forest gap sizes in the canopy surface, 3) to study relationship between hemlock dieback and topography and 4) to study spatial pattern of hemlock mortality. The study, site was located in Linville River Gorge, Southern Appalachians, NC (35°56’N, 81°55’W). The results indicate that dead hemlocks were more abundant close to Linville River, at higher elevations, and on northern and northwestern aspects. Spatial pattern of the dead trees was mostly clustered at all spatial scales. Although hemlocks represent only a small percentage of plant biomass in Southern Appalachian forest landscapes, impact of HWA is significant as these trees are considered to be foundation species. This study provides quantitative information on distribution, abundance, and location of hemlocks and HWA herbivory and provides the means for quantitatively assessing impact of the insect on Southern Appalachian forest landscapes.