Monday, December 11, 2006 - 8:59 AM
0382

Influence of eastern hemlock on stream macroinvertebrate communities in Southwestern Virginia

Meredith E. Worthen, mworthen@vt.edu, Carlyle C. Brewster, carlyleb@vt.edu, and Scott M. Salom, salom@vt.edu. Virginia Tech, Department of Entomology, 216A Price Hall, MC 0319, Blacksburg, VA

Eastern hemlock, Tsuga canadensis, is under attack by an exotic insect pest, the hemlock woolly adelgid (HWA), Adelges tsuga (Hemiptera: Adelgidae). As slow-growing, shade-tolerant trees, hemlocks can be an important part of riparian vegetation in eastern forest streams. The full impact of HWA on hemlock-associated ecosystems, especially stream ecosystems, is unknown. The purpose of this study was to examine the role of hemlock in southern Appalachian streams by studying macroinvertebrate community composition and hemlock litter decomposition. In spring, summer, and fall of 2005, benthic macroinvertebrates were collected from six stream sites with varying densities of riparian hemlock cover in Giles County, Virginia. In addition, hemlock needles (litter) were placed in each stream and collected over time to evaluate litter decomposition and macroinvertebrate attraction to hemlock needles. Initial results indicate that the macroinvertebrate community composition appears to be related to hemlock tree density. Low density hemlock streams averaged fewer shredder macroinvertebrates (10% total organisms) compared to 50% shredders at a high density hemlock site. Macroinvertebrates in the scraper functional feeding group conversely were more abundant in low hemlock density streams. Hemlock litter had a slow decomposition rate (k=0.006) at all stream sites, making it available to macroinvertebrates for a longer period of time.


Species 1: Hemiptera Adelgidae Adelges tsugae (hemlock woolly adelgid)
Species 2: Gymnosperm Pinaceae Tsuga canadensis (eastern hemlock)