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Harvard Forest Symposium Abstract 2005

  • Title: Comparison of hemlock cutting following HWA infestations in urban vs. rural forests
  • Primary Author: David Orwig (Harvard Forest)
  • Additional Authors: Peter Del Tredici (100th EN Co); David Foster (Harvard University); Heidi Lux (Harvard Forest); Richard Schulhof (Arnold Arboretum of Harvard University)
  • Abstract:

    Hemlock Hill at Harvard University’s Arnold Arboretum is located in Jamaica Plain and has long been considered a remnant of the forest primeval in the heart of Boston. Eastern hemlocks have dominated the flanks and crest of this hill for centuries, despite experiencing many past disturbances. Following the 1997 snowstorm, the introduced hemlock woolly adelgid (HWA) was discovered on downed branches. Since the discovery of HWA at the Arboretum, an action committee was formed to develop plans for managing Hemlock Hill to meet the new threat. Over 1800 hemlock trees were tagged, measured for diameter, assigned a crown health rating, and mapped with GPS coordinates. Various chemical and biological control treatments were attempted to control the spread of HWA at the arboretum, with mixed success. From 1998 to 2002, 263 trees have died or were removed due to poor health. Of the remaining 1600+ trees, 70% are rated as being in poor condition. Since this is a heavily used portion of the Arboretum, which is part of the Boston Parks Department, the decision has been made to remove many of the dead and dying trees to reduce risks posed to the general public by falling limbs. The presence of HWA at the Arboretum provides us with an unusual opportunity to examine the environmental impacts of hemlock death and hemlock removal in an urban environment, including soil nutrient cycling, microclimate changes, and vegetation succession, especially the spread of invasive species. During 2004, six 15 x 15 m plots were fenced off, and baseline data on soil nutrient cycling, microclimate, and vegetation information was collected from each. Analyses of these baseline data are underway. Hemlocks are currently being removed from 4 plots, and 2 will remain untouched as control plots. Slash in the cut plots is either being chipped and left on site or removed so that we can investigate what impact these post-cut inputs have on ecosystem and vegetation trajectories. We will continue with data collection on vegetation and ecosystem parameters following harvesting, especially the spread of invasive plant species. Data from this project will provide a nice comparison to the rural cutting and girdling that is ongoing at HF this winter (see Barker-Plotkin et al. abstract). Simultaneously, we are investigating the resistance of Chinese hemlock (Tsuga chinensis) to HWA. This species, which was planted on Hemlock Hill in 1999, continues to demonstrate a high degree of resistance to HWA as well as a tolerance for the stressful growing conditions of the hill.

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