A terrestrial invader threatens a benthic community: potential effects of hemlock woolly adelgid-induced loss of eastern hemlock on invertebrate shredders in headwater streams

Abstract

The invasion of non-native species is considered among the most important causes of the loss of native biota. An example of a devastating exotic pest impacting eastern forests is the hemlock woolly adelgid (HWA) (Adelges tsugae), a xylem feeding insect native to Asia that feeds on all ages and species of hemlock (Tsuga spp.), and has the capacity to functionally eliminate eastern hemlock (T. canadensis) from the landscape. Eastern hemlock is an important component of forested riparian communities in southern and central Appalachia where it maintains stable stream conditions important for aquatic biota. We investigated differences between eastern hemlock and deciduous dominated headwater streams in eastern Kentucky to determine the extent to which HWA invasion may affect benthic invertebrate shredders. Shredders form the basis of a resource chain within headwater streams, thus they are invaluable links in stream-riparian interactions. We found that eastern hemlock contributed energy in the form of leaf litter to the riparian zone at a consistent rate throughout the growing season in contrast to the autumnal pulse of deciduous material. We also detected significant vegetation by season interactions for shredders which suggest that some shredders are more abundant in eastern hemlock streams than in their deciduous counterparts during the summer. This could be linked to the consistent addition of food resources that eastern hemlock provides. Our results indicate that stream communities will likely change following adelgid associated mortality of eastern hemlock in headwater stream riparian zones.