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Harvard Forest Symposium Abstract 2014

  • Title: Hemlock woolly adelgid’s impact on foliar and root microbial abundance in eastern hemlock stands
  • Primary Author: David Orwig (Harvard Forest)
  • Additional Authors: Evan Preisser (University of Rhode Island); Justin Vendettuoli (University of Rhode Island)
  • Abstract:

    Eastern hemlock, Tsuga canadensis, is an integral species contributing to the ecosystem heterogeneity across many northeastern landscapes. An invasive insect, the hemlock woolly adelgid (HWA; Adelges tsugae), has been wreaking havoc in hemlock stands by draining resources from the hemlock, eventually leading to needle loss and tree mortality. The adelgid also creates a unique woolly by-product for protection of its eggs that can literally cover branches resulting in a considerable influx of wool in heavily invested stands. There is a need to better understand how the system is altered as infestation progresses, especially with regards to changes in foliar and belowground or soil processes. To assess the impact of HWA, we measured bacterial abundance on foliage and fine roots from three trees each at 10 infested and 10 control sites across central MA. We also determined carbon to nitrogen ratio of woolly by-products and fine roots to examine how that may affect bacterial abundance. We predicted to find higher bacterial abundance on infested foliage and roots based on previous research on foliage. Bacterial abundance was only slightly higher on foliage infested with HWA compared to uninfested foliage and significantly lower on roots from HWA infested saplings than uninfested saplings. Woolly by-products were found to have high nitrogen (mean of 2.6% N), which may promote bacterial growth. Fine root percent N did not differ between treatments (0.98 – 1.02%), but percent C was modestly but statistically (P<0.05) higher in control vs. infested fine roots. Reduced bacteria on roots from infested saplings may be related to reduced mycorrhizal abundance seen in prior work. Our results will contribute to an emerging conceptual model of how adelgid infestation affects above and belowground processes in hemlock stands, even before tree mortality.

  • Research Category: Invasive Plants, Pests & Pathogens