PS 107-209 - Vegetation and invertebrate community response to Eastern hemlock decline in southern New England

Friday, August 10, 2012
Exhibit Hall, Oregon Convention Center
Laura L. Ingwell, Plant, Soil and Entomological Sciences, University of Idaho, Moscow, ID, Mailea R. Miller-Pierce, School of Biological Sciences, Washington State University, Vancouver, WA, R. Talbot Trotter III, USDA Forest Service, Hamden, CT and Evan L. Preisser, Biological Sciences, University of Rhode Island, Kingston, RI
Background/Question/Methods

The introduction of Adelges tsugae Annand (Hemlock woolly adelgid; ‘HWA’) to the eastern United States has had a devastating impact on Tsuga canadensis Carrière (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. We assessed the impact of Eastern hemlock mortality on vegetation and terrestrial invertebrate diversity and community structure in heavily HWA-impacted stands in southern Connecticut with nearby (~50 km) northern Connecticut stands with little HWA-related damage. We sampled the vegetative and invertebrate diversity of eight sites (four low -impact and four high -impact) in the summer and fall of 2008. We used six invertebrate sampling methods and collected 8787 specimens of 623 morphospecies belonging to five different arthropod classes: Arachnida, Malacostraca, Diplopoda, Chilopoda, and Hexapoda.

Results/Conclusions

We found a shift in the understory plant community and the canopy and subcanopy arthropod communities. High-impact sites had more herbaceous and shrub species than low-impact sites (37 ± 3.7 and 27 ± 3.6 species respectively), and almost twice the species richness (14.25 ± 2.6 and 7.75 ± 0.8 species respectively). The most common species at high-impact sites in the herbaceous and shrub layers were Betula lenta L. (Black birch; 18% of individuals), Acer rubrum L. (Red maple; 17%), Maianthemum canadense Desf. (Canada mayflower; 8%), Hamamelis virginiana L. (Witch-hazel; 7%), Quercus rubra L. (Red oak; 7%) and Quercus prinus L. (Chestnut oak; 7%). A single hemlock seedling was found in the understory (<1m) at one high-impact site. Vegetation in the herbaceous and shrub layer at low-impact sites was dominated by T. canadensis (44% of individuals), A. rubrum (13%), and Quercus alba L. (White oak; 13%). Overall, forest invertebrate community diversity was greater in high- impact sites. Of the 21 indicator species significantly associated with a given forest type, 14 and seven species were associated with high- and low-impact forests, respectively. The most abundant indicator species was a Geophilomorpha sp. Centipede; all 223 individuals were collected in low-impact stands. The rarest indicator species were all found in high-impact sites and included species from the Leiobuninae, Nabidae, and Anthicidae families. 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.