Interactions between the invasive hemlock woolly adelgid, eastern hemlock, and benthic macroinvertebrates: cascading effects of foundation species mortality in headwater stream riparian zones

Invasive species impact the environment along a spatial continuum from individual to ecosystem both directly and indirectly, ultimately disrupting ecosystem processes. One example is the hemlock woolly adelgid (Adelges tsugae: HWA) an invasive insect native to Asia that feeds on all Tsuga species. Eastern hemlock (T. canadensis) is particularly susceptible and has suffered catastrophic mortality throughout much of its range. Eastern hemlock is widely recognized as a foundation species, and an important component of riparian zones. It provides food and essential habitat for wildlife and regulates and stabilizes important ecosystem characteristics such as air and stream temperatures, stream turbidity, and base flows. HWA is spreading rapidly throughout southeastern Kentucky, where stream quality is severely degraded from large-scale surface mining operations and logging practices. Adelgid-induced hemlock mortality will potentially exacerbate deterioration of stream quality in this region.

The objective of my study is to evaluate the effects of HWA on headwater stream quality. I am investigating differences between eastern hemlock and deciduous dominated headwater streams to determine the extent to which HWA invasion will affect aquatic macroinvertebrate community composition and stream chemical and physical characteristics. Eastern hemlock significantly influences stream parameters including sulfate, calcium, total carbon, total organic carbon, and conductivity. Two benthic macroinvertebrate families within the gatherer functional feeding group are significantly more abundant in streams with corresponding eastern hemlock dominated riparian zones. Further, eastern hemlock affects the abundance of benthic macroinvertebrate shredders. My results suggest changes in stream function will likely follow HWA associated mortality of eastern hemlock in headwater stream riparian zones.