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Harvard Forest Symposium Abstract 2009

  • Title: How do changes in the canopy of hemlock forests affect litter macroarthropod communities?
  • Primary Author: Tara Sackett (University of Toronto)
  • Additional Authors: Aaron Ellison (Independent); Nathan Sanders (University of Tennessee at Knoxville)
  • Abstract:

    Litter-dwelling arthropod communities in hemlock stands attacked by the Hemlock Woolly Adelgid (Adelges tsugae) may shift in composition as deciduous species become more predominant in the canopy and litter. These changes may also affect trophic dynamics and associated ecosystem functions.

    In this experiment we tested for changes in litter macro-arthropod communities (ants, spiders, beetles, centipedes) as a result of the changing canopy composition. We used the canopy manipulations in the Simes tract of Harvard forest as four experimental treatments: girdled hemlock, control hemlock, logged hemlock, and deciduous (2 blocks per treatment).

    There were three sampling events (May 19-22, July 18-21, September 22-25), and we sampled arthropods by litter sifting and pitfall trapping. At each sampling event, we sifted five 1 m2 plots of leaf litter in each treatment block, extracting the collected litter for 10 days in Winkler sacs. At each sampling event, we also set 5 pitfalls in each treatment/block, keeping pitfalls open for ~10 days.

    We have so far analysed the data from the collected spiders. In total 6538 spiders from 14 families were collected. All individuals were identified to the family level, and 2407 individuals (37%) were mature and identified to species.

    The rarefied species richness of spiders was equal and highest in the hardwood and logged treatments, and equal and lower in hemlock and girdled treatments. Comparisons of the species composition of the treatments using the Chao-Jaccard index and non-metric multidimensional scaling showed that the intact hemlock and hardwood treatments were most dissimilar to the logged treatment. Girdled, hemlock, and hardwood treatments had very similar assemblages, but composition in the girdled treatment was also similar to logged. Compositional changes are due to shifts in hunting guilds: cursorial spiders are proportionally most common in logged blocks, least common in hemlock and girdled blocks, and intermediate in hardwood blocks. Small web-spinning spiders are relatively more common in hemlock and girdled treatments as compared to logged and hardwood.

  • Research Category: Biodiversity Studies, Conservation and Management, Large Experiments and Permanent Plot Studies