Abstract
The introduction of Adelges tsugae (Hemlock Woolly Adelgid [HWA]) to the eastern United States has had a devastating impact on Tsuga canadensis (Eastern Hemlock). Although much research has been done to assess HWA impacts on ecosystem processes and vegetation structure, few researchers have examined community-level changes in highly infested forest stands. Here we assess the impact of Eastern Hemlock mortality on vegetation and invertebrate diversity and community structure by comparing low-impact (healthy) stands and stands heavily impacted by HWA. We sampled the vegetative and invertebrate diversity of 8 sites (4 low impact and 4 high impact) in the summer and fall of 2008. We found a shift in the understory plant community and the canopy and subcanopy arthropod communities. Herbaceous plant species richness was significantly higher at high-impact sites, with Betula lenta (Black Birch) being the most common woody species. Overall, forest invertebrate community diversity (measured using the Shannon-Weaver diversity index) was greater in high- versus low-impact sites. Of the 21 indicator species significantly associated with a given forest type, 14 and 7 species were associated with high- and low-impact forests, respectively. Variation in arthropod community structure was driven by above-ground differences; ground-level arthropod community composition did not differ between high- and low-impact sites. These results demonstrate some of the biodiversity impacts that can result from the invasion of an exotic insect into forested systems.
Highlights
Tsuga canadensis Carrière (Eastern Hemlock) is a long-lived and shadetolerant tree that is the dominant conifer species in many forest ecosystems in the eastern United States
The introduction of Adelges tsugae (Hemlock Woolly Adelgid [HWA]) to the eastern United States has had a devastating impact on Tsuga canadensis (Eastern Hemlock)
We assess the impact of Eastern Hemlock mortality on vegetation and invertebrate diversity and community structure by comparing low-impact stands and stands heavily impacted by HWA
Summary
Tsuga canadensis Carrière (Eastern Hemlock) is a long-lived and shadetolerant tree that is the dominant conifer species in many forest ecosystems in the eastern United States. HWA is a sap-sucking hemipteran native to Japan, which was ¿UVW GRFXPHQWHG LQ WKH 86$ LQ 9LUJLQLD LQ WKH HDUO\ V +DYLOO HW DO Orwig and Foster 1998). Since its discovery, it has spread rapidly across the geographic range of Eastern Hemlock, and currently infests stands from northern Georgia to southern Maine (McClure 1987, Orwig and Foster 1998, USDA Forest Service 2010). HWA can kill mature hemlocks in as few as four years (but see Ingwell and Preisser 2011), and HWA-induced hemlock mortality has been documented in all but the most recently colonized portions of the invaded range (McClure 1991)
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