You are here

Harvard Forest >

Harvard Forest REU Symposium Abstract 2005

  • Title: Mid-Holocene vegetation and climate change in New England
  • Author: Sarah A Truebe (Stanford University)
  • Abstract:

    Lake sediment records across northeastern North America feature a decline in abundance of eastern hemlock (Tsuga canadensis) ~5400 years before present (BP). The decline is usually attributed to a pest or pathogen, but recent evidence points to a potential climate signal. I investigated the hemlock decline at Benson Pond in western Massachusetts by analyzing organic content (via loss-on-ignition, LOI) and pollen preserved in the sediments. LOI showed two sustained periods of high organic content, with the hemlock decline occurring at the beginning of the more recent period. These sections of the Benson core were quite peaty, perhaps indicating low lake levels between 6500-6000 BP and then again at the hemlock decline at 5400 BP. When I compared the hemlock abundance record from Benson with those from nineteen other New England lakes, however, I noticed many records often demonstrated two peaks in hemlock abundance, one ~6600 BP and another just before 5400 BP (see Figure 1). These peaks in hemlock abundance never co-occur with the Benson LOI peaks, implying that conditions may have been too dry for hemlock populations to sustain themselves between 6500-6000 BP and after 5400 BP. This suggests a possible climatic forcing for Mid-Holocene hemlock abundance and the hemlock decline in New England. Further investigation into ponds like Benson will aid us in interpreting the climate/pest/disturbance history of New England vegetation. Ideally, that knowledge can then be applied to current climate change and the Hemlock Wooly Adelgid infestation impacting hemlocks today.

  • Research Category: