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Harvard Forest REU Symposium Abstract 2012

  • Title: Eastern Hemlock Forests Provide Habitat to a Greater Variety of Spiders Compared to Non-Hemlock Forests
  • Author: YVAN A DELGADO DE LA FLOR (Humboldt State University)
  • Abstract:

    Eastern hemlock (Tsuga canadensis) is a foundation species in eastern North America and plays a critical role in the local biota. Hemlock forests deeply shade the soil and create a unique microclimate for some species. Currently, hemlocks are dying rapidly due to the invasive hemlock woolly adelgid (Adelges tsugae), a nonnative phloem-feeding insect. Hemlocks are being replaced slowly by hardwood forests and this may cause alterations to the understory microclimates. 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 and any increase in temperature may have a direct impact in their habitat. 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 30x30m canopy-manipulation treatments: 1) hemlock control, which is a forest dominated by hemlocks, 2) girdled hemlock, simulating tree mortality due to the hemlock woolly adelgid, 3) logged hemlock, mimicking the impact of the lumber companies and 4) hardwood control, in which the forest are dominated by non-hemlock trees simulating the succession event after the dead of the hemlock trees. Pitfall traps were sampled approximately every two weeks to set up and collect pitfalls. Pitfalls are small plastic cups that are placed at ground level and filled up with one-inch of soapy water. I picked up the pitfalls two days after I set them. Then, I brought them to the laboratory to proceed with the identification. I sorted all the pitfalls into three small tubes: ants, spiders and beetles. I identified spiders to genus, whereas ants and beetles were archived for future investigations. Results indicated that spiders collected in hemlock control plots are also found in other treatments. However, two out of the top three most abundant spider genera belonged to the hemlock treatment. Eastern hemlocks occupy large area of late successional forests in eastern North America and the effect and impact will be better observed in 20 or more 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.

  • Research Category: Group Projects

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