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Harvard Forest Research Project 2022

  • Title: Vegetation Dynamics in the Hemlock Removal Experiment
  • Principal investigator: Audrey Barker Plotkin (aabarker@fas.harvard.edu)
  • Institution: Harvard Forest
  • Primary contact: Audrey Barker Plotkin (aabarker@fas.harvard.edu)
  • Team members: Aaron Ellison; David Orwig; Greta VanScoy
  • Abstract:

    Eastern hemlock (Tsuga canadensis) forests are declining in abundance as they are colonized by an exotic insect, the hemlock woolly adelgid (HWA, Adelges tsugae). HWA feeds on the tree’s sap, effectively girdling the tree over time. Hemlock is then often replaced by hardwoods, causing an abrupt shift in ecosystem characteristics that is often exacerbated by salvage logging. The Harvard Forest Hemlock Removal Experiment, initiated in 2003, includes 8 plots – two replicates of each of four treatments: hemlock controls; hemlocks logged and removed from the site; hemlocks girdled and left dead on site; and hardwood controls. Logging simulates a common management response to adelgid infestation. The hardwood controls represent the expected future forest conditions after ca. 50 years of succession following hemlock death. The hemlock controls were colonized by the hemlock woolly adelgid in 2010 and their trajectory of decline and regeneration will be compared to the girdling treatment, which simulated the physical, but not chemical or biotic, impacts of the adelgid.

    This is a multi-investigator experiment with a variety of responses examined. The focus of this project is to track the short- and long-term changes in vegetation composition, structure, and productivity. We mapped and censused the overstory trees (>5cm dbh) before the manipulations in 2004, and every five years thereafter. We tally saplings (trees >1.3m tall but