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Harvard Forest Symposium Abstract 2014

  • Title: New analyses of the middle-Holocene hemlock decline in southern New England
  • Primary Author: Wyatt Oswald (Emerson College)
  • Additional Authors: Elaine Doughty (Harvard Forest); David Foster (Harvard Forest); Bryan Shuman (University of Wyoming)
  • Abstract:

    The abrupt, range-wide decline of eastern hemlock ~5500 years ago is one of the most-studied events in North American paleoecology. However, despite decades of study, key aspects of the hemlock decline remain poorly understood. Recent analyses of sediment cores from sites in north-central and western Massachusetts provide new insights into the cause, rate, and geographic pattern of this event. The hemlock decline has been attributed to an insect outbreak, but analyses of Hemlock Hollow, a vernal pool in north-central Massachusetts that has been surrounded by eastern hemlock for the past ~10,000 years, did not yield insect remains in sediments dating to the hemlock decline. On the other hand, reconstructions of lake-level history at sites across southern New England reveal dry events at 5500, 5000, and 4200 years ago, suggesting that the hemlock decline was initiated and sustained by major droughts. Detailed radiocarbon dating of the middle-Holocene interval of lake-sediment cores from the Berkshires of western Massachusetts indicate that hemlock declined rapidly, with sizable population reductions occurring in less than a century. Moreover, it appears that the hemlock decline in the Berkshires took place later in upland areas than at lowland sites, perhaps because cool and moist conditions at higher elevations allowed hemlock to survive for a period of time despite severe drought across the region.

  • Research Category: Historical and Retrospective Studies