Benthic Collector and Grazer Communities Are Threatened by Hemlock Woolly Adelgid-Induced Eastern Hemlock Loss

Abstract

Eastern hemlock (Tsuga canadensis (L.) is a foundation species in easternNorth America where it is under threat from the highly invasive, exotic hemlock woolly adelgid (Adelges tsugae). Eastern hemlock is especially important in riparian areas of Central and Southern Appalachia, so we compared the spatial and temporal composition of benthic collector-gatherers, collector-filterers, and grazers in headwater streams with hemlock-dominated riparian vegetation to those with deciduous tree-dominated riparian vegetation to evaluate the extent to which adelgid-induced hemlock loss could influence composition and abundance of these two functional feeding groups. We found differences in benthic invertebrate abundance and family-level diversity based on riparian vegetation and sampling approach, and, often, riparian vegetation significantly interacted with location or season. Collector-gatherers and grazers were more abundant in eastern hemlock streams in the summer, when hemlock litter is readily available and deciduous litter is relatively sparse. Riparian eastern hemlock appears to exert considerable influence on benthic invertebrate functional feeding group composition in headwater stream communities, as expected with a foundation species. With the loss of eastern hemlock due to adelgid-induced mortality, we should expect to see alterations in spatial and temporal patterns of benthic invertebrate abundance and diversity, with potential consequences to both benthic and terrestrial ecosystem function. OPEN ACCESSForests 2015, 6 2720

The Past, Present, and Future of the Hemlock Woolly Adelgid (Adelges tsugae) and Its Ecological Interactions with Eastern Hemlock (Tsuga canadensis) Forests

“…As hemlocks have declined along streams, canopy openness and light levels have increased [11,70], often with an increase in variability of water temperature [70] and expected increases in biomass of stream periphyton [71]. Loss of hemlock should increase inputs of woody biomass (as coarse woody debris) to streams [70,72,73] and alter both allochthonous energy inputs and the community structure of benthic detrital shredders [10,74,75,76,77].…”

Basal Bark Treatment of Imidacloprid for Hemlock Woolly Adelgids (Adelges tsugae)

“…This tree is an important component of forest riparian systems. For example, riparian eastern hemlock has been shown to heavily influence benthic invertebrate functional feeding group composition in headwater stream communities [2]. Similarly, the consistent addition of woody debris and food resources that eastern hemlock provides could be linked to the abundance of macro-invertebrate shredders in eastern hemlock streams relative to their deciduous counterparts during the summer.…”