Print

Lishawa, Shane C.

Forestry Program

2005

M.S.

Hemlock woolly adelgid (Adelges tsugae Annand, HWA), an introduced aphidlike insect from Asia, is threatening to eliminate eastern hemlock (Tsuga canadensis (L.) Carr.) throughout much of its range. Among its many ecological functions, eastern hemlock provides winter cover and browse for white-tailed deer (Odocoileus virginianus Zimmerman) in areas that experience harsh winter conditions. In central and southern Vermont, eastern hemlock is the basic component of many white-tailed deer wintering areas (DWA) and is thought to reduce snow depths and moderate winter temperatures. Dominant overstory species replacing dying eastern hemlock are almost exclusively hardwoods which do not provide comparable winter coverage. The objectives of this thesis were two-fold. The first was to create a spatially explicit eastern hemlock coverage model and to assess the susceptibility to HWA invasion and vulnerability to HWA impact of eastern hemlock in DWAs in southern Vermont. Ground sampled vegetation data and landscape data gathered from a geographic information system (GIS) were used to create a model representing eastem hemlock forest importance values within DWAs. Relative susceptibilities and vulnerabilities were calculated and mapped using weighting algorithms of important risk factors. This research indicates that the DWAs of southeastern VT, specifically along the Connecticut River and West River, are at highest risk and should be the focus of immediate monitoring and early management efforts. The second objective was to quantify the effects of eastern hemlock cover on winter temperature and snow depth conditions. Temperatures and snow depths were recorded in six site-paired hemlock and hardwood stands in the winters of 2003-04 and 2004-05. Temperature extremes were significantly moderated and snow depth was significantly reduced within eastern hemlock stands as compared to site-paired hardwood stands. If eastern hemlock is killed by HWA, the elimination of these areas of moderated microclimate will greatly alter local ecosystems, affecting white-tailed deer already experiencing stress from deep snow and low temperatures in the northern limits of their range.