Wednesday, August 5, 2009 - 2:30 PM

COS 73-4: Impacts of hemlock woolly adelgid on eastern hemlock in Great Smoky Mountains National Park

Kurt J. Krapfl1, Eric Holzmueller1, and Michael A. Jenkins2. (1) Southern Illinois University, (2) Purdue University

Background/Question/Methods Eastern hemlock (Tsuga Canadensis; hemlock) populations throughout eastern North America are threatened by an exotic, invasive insect introduced from Japan known as the hemlock woolly adelgid (Adelges tsugae; HWA).  This rapidly spreading insect has caused significant mortality to hemlocks wherever it has been found.  Hemlock woolly adelgid was first reported in Great Smoky Mountains National Park (GSMNP) in 2002, however, there have been no park wide studies conducted to assess HWA impact.  The objective of this study was to assess the impacts of HWA on hemlock populations in GSMNP.  We hypothesize that HWA associated decline is affected by hemlock size and density.  We resampled twenty-seven 0.1 ha (20 x 50 m) permanent vegetative plots established throughout GSMNP to determine the impacts of HWA following six years of infestation.
Results/Conclusions Preliminary results indicate no significant change in hemlock overstory (>9.9 cm) basal area (10.7 m² ha-1 to 10.0 m² ha-1; P = 0.37) and stem density (127 stems ha-1 to 123 stems ha-1; P = 0.71).  However, we observed a decrease in understory (≤ 9.9 cm) hemlock basal area (1.0 m² ha-1 to 0.6 m² ha-1; P < 0.01) and stem density (579 stems ha-1 to 379 stems ha-1, P < 0.01) of hemlock.  Our results suggest that currently, HWA has had a greater influence upon the forest health of understory hemlock compared to overstory hemlock.  Furthermore, signs of HWA throughout the study area indicate that all areas of the park will likely see similar dieback in the near future.