Hemlock Susceptibility to Hemlock Woolly Adelgid Attack in the Chattooga River Watershed

Adelges tsugae (Hemlock Woolly Adelgid [HWA]), an introduced pest, is impacting Tsuga canadensis (Eastern Hemlock), and T caroliniana (Carolina Hemlock) stands throughout the eastern United States. Currently, hemlock stands in the southeast US are on the leading edge of the infestation. This study investigated HWA distributions in the Chattooga River watershed, and examined relationships between site and stand variables and hemlock susceptibility to HWA attack. The following variables were examined: latitude, longitude, elevation, slope, aspect, terrain shape index (TSI), landform index (LFI), percent infestation, quadratic mean diameter, total basal area (BA), hemlock BA, non-hemlock BA, hemlock BA(%), non-hemlock BA(%), and tree height. Multiple regression with backward selection showed statistically significant relationships of HWA infestation to latitude (P = 0.0006), longitude (P < 0.0001), and TSI (P = 0.0316). The proximity of a hemlock stand to existing HWA infestations appears to be the primary factor influencing its susceptibility to attack.