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Harvard Forest Symposium Abstract 2017

  • Title: Pits & Mounds: the Charismatic Microtopography of New England’s forests
  • Primary Author: Audrey Barker Plotkin (Harvard Forest)
  • Additional Authors: David Foster (Harvard Forest)
  • Abstract:

    Pit and mound microtopography is an important structural component of most forests, influencing soil processes and habitat diversity. These features have likely diminished in New England forests since European settlement, as a result of land-clearing and repeated logging, followed by second-growth forest composed of smaller trees. The implications of land use history and forest development on pit-mound size, distribution, longevity and ecological function are unexplored. Likewise, although several studies estimate pit-mound longevity, there is scant direct information on the rates of erosion and physical alteration of these structures over time. We compare a simulated hurricane experiment initiated in 1990 in second-growth forest (the pulldown) and an old-growth forest that was blown down by a hurricane in 1938 (Pisgah) to examine these issues. Repeated measurements of individual pit-mound structures in the pulldown revealed that mound height diminished rapidly, but mound volume declined much more gradually as soil from the mound tops eroded and spread around the mound base. Although 40% of mounds in the pulldown were >1m tall immediately after the manipulation, after 25 years, maximum mound height was 0.9m. In contrast, 11% of mounds at Pisgah remained >1m tall in 1989, 50 years after blowdown. At Pisgah, fewer, larger mounds comprised a similar areal coverage as at the pulldown. Pit-mound structures are thus a diminished component of second-growth forest, and silvicultural systems designed to restore old-growth characteristics could include measures to preserve and enhance pit-mound features, as well as to cultivate large-diameter trees that will eventually become the large, long-lasting pit-mounds of the future. At both sites, trees, especially Betula spp., preferred mounds to undisturbed ground. Trees avoided pits at Pisgah, but not at the pulldown. Mounds have a greater impact on niche diversity in old-growth forests by providing opportunities for early-mid successional species in forests dominated by late-successional trees.

  • Research Category: Conservation and Management; Large Experiments and Permanent Plot Studies