Abstract
Eastern hemlock (Tsuga canadensis (L.) is a foundation species in eastern North 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.
Highlights
Eastern hemlock (Tsuga canadensis (L.) Carrière; Pinales: Pinaceae) is a coniferous foundation species of eastern North American forests, and is a prominent component of riparian vegetation in Central Appalachia [1,2,3]
Riparian vegetation classified as deciduous-dominated contained significantly lower eastern hemlock basal area in the overstory (3.1 + 1.3 (S.E.) versus 12.6 + 2.2 (S.E.) m2/ha), but not the understory, relative to those classified as hemlock-dominated, but eastern hemlock basal area was similar across the three study locations [16]
Eastern hemlock is prevalent in headwater riparian zones of central and southern Appalachia, and while there was some eastern hemlock present in our streams classified as deciduous dominated, eastern hemlock stem density was greater in streams that were categorized as eastern hemlock
Summary
Eastern hemlock (Tsuga canadensis (L.) Carrière; Pinales: Pinaceae) is a coniferous foundation species of eastern North American forests, and is a prominent component of riparian vegetation in Central Appalachia [1,2,3]. Eastern hemlock regulates nutrient cycling and stream base flows due to its persistent and elevated transpiration rates, and air, soil, and water temperatures beneath its dense canopy [6,7,8,9]. This canopy density significantly reduces light penetration, resulting in a paucity of understory associates [10]. Headwater streams with healthy eastern hemlock-dominated riparian zones support unique benthic invertebrate communities in New
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