Loss of a foundation forest species due to an exotic invader impacts terrestrial arthropod communities

The hemlock woolly adelgid (Adelges tsugae) is an invasive insect native to Asia that feeds on all species of hemlock (Tsuga spp.), and is rapidly spreading throughout the range of eastern hemlock (T. canadensis). Eastern hemlock is an essential component of forested communities, is particularly susceptible to the adelgid, and has already suffered extensive mortality throughout much of its range. Hemlock dominated forests in the central Appalachians are expected to shift to deciduous species following adelgid-induced hemlock mortality, leading to shifts in epigeic macroinvertebrates. In a 2-year study using pitfall traps, we compared abundance, diversity, and composition of ground dwelling arthropod taxa and feeding guilds associated with riparian zones dominated by eastern hemlock to those associated with deciduous trees in the southern Appalachians. Differences were detected for the Diplopoda (millipedes) and Isopoda (pillbugs and wood lice), and for Formicidae (ants) and Staphylinidae (rove beetles). Each was more abundant beneath deciduous canopies than eastern hemlock canopies. Our comparative evaluation of eastern hemlock and deciduous riparian zone arthropod communities depicts the potential end point of a likely successional trajectory of eastern North American forests invaded by hemlock woolly adelgid. Our results indicate probable shifts in arthropod communities as the hemlock woolly adelgid invasion progresses through the Central Appalachian region.