The role of eastern hemlock on headwater stream processes: benthic and riparian consequences of hemlock woolly adelgid invasion

The hemlock woolly adelgid (Adelges tsugae: HWA) is an invasive insect native to Asia that feeds on all species of hemlock. Eastern hemlock (Tsuga canadensis L.) is particularly susceptible to HWA and has suffered extensive mortality throughout much of its range in North America. Eastern hemlock is a critical component of eastern forests, providing food and essential habitat for wildlife and regulating key ecosystem processes. In Kentucky, eastern hemlock is primarily limited to moist coves and headwater riparian zones, playing a key role in regulating air and stream temperatures, reducing stream turbidity, and stabilizing base flows. HWA is currently spreading throughout southeastern Kentucky. Within this region, stream quality is already severely degraded from large-scale surface mining operations. Loss of eastern hemlock due to invasion by HWA populations may exacerbate the deterioration of stream quality in this area and have far reaching consequences downstream.

The objectives of my study are to evaluate the effects of HWA on headwater stream quality. I am currently investigating differences between eastern hemlock dominated and deciduous dominated headwater streams to determine the extent to which HWA invasion will affect (1) stream and riparian macroinvertebrate community dynamics, (2) stream chemistry, and (3) other stream characteristics including temperature and conductivity. Analysis of preliminary data indicates that Plecoptera and Diptera are more abundant in eastern hemlock dominated streams. My results will provide insight into the direct and indirect consequences of riparian eastern hemlock loss, and contribute to the knowledge base necessary for preservation of this imperiled ecosystem.