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Title:	Impact of the hemlock woolly adelgid on radial growth of Eastern hemlock in Pennsylvania
Author(s):	Davis, Donald D.; Fromm, Matthew S.; Davis, Matthew D.
Date:	2007
Source:	e-Gen. Tech. Rep. SRS–101. U.S. Department of Agriculture, Forest Service, Southern Research Station: 157-162 [CD-ROM].
Description:	We evaluated the past 60-70 years of radial growth of old-growth eastern hemlock [Tsuga canadensis (L.) Carr] infested with the hemlock woolly adelgid (Adelges tsugae Annand) in south-central Pennsylvania. Although undocumented, the initial adelgid infestation may have occurred within the stand in the early 1990s. Increment cores were extracted during May 2003 from lightly infested and severely infested canopy hemlocks. Those hemlocks that were growing more slowly in the decades prior to adelgid infestation ultimately exhibited more severe infestation. This indicates that that slower-growing hemlocks may be inherently more susceptible to the adelgid, or that stressed trees growing on poor sites may be more susceptible. Radial growth of severely infested canopy hemlocks was below normal by the mid-1990s; growth of lightly infested trees began to decline several years later. Severely infested trees exhibited a short-term, spike in growth immediately prior to a precipitous growth decline that eventually lead to mortality.
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