Easter Hemlock Forests Provide Habitat to a Greater Variety of Spider Taxa Compared to Non-Hemlock Forests

Eastern hemlock is a foundation species in eastern North America and plays a critical role in the local biota. This tree deeply shades the soil, creating a unique microclimate for some species. Currently, hemlocks are dying rapidly due to the invasive woolly adelgid, a nonnative phloem-feeding insect, causing alterations to the understory microclimates. Hemlocks are being replaced slowly by hardwood forests. All of these changes affect the entire ecosystem and result in the local extinction of some arthropods; for example, some spiders are very sensitive to changes in temperatures. In this study I measured the impact of hemlock loss on spider communities in hemlock stands and contrasted spider assemblages in hemlock and hardwood stands. I hypothesized that the loss of eastern hemlock and associated increase in forest-floor temperature would result in the extirpation of some spider genera. The effect of the adelgid was mimicked with four canopy-manipulation treatments: hemlock (control), girdled hemlock, logged hemlock, and hardwood (control). Pitfall traps were sampled throughout the summer in all treatments; spiders collected were identified to genus. Initial results suggest little differences among the treatments, but sample size remains small because most of the pitfall traps will not be collected until late July. Eastern hemlocks occupy large area of late successional forests in eastern North America and the effect and impact will be better observed in 20+ years, when hemlocks will be locally extinct, potentially leading to the extirpation of spiders and other species, and the alteration of local food webs and ecosystems.