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Harvard Forest Symposium Abstract 2015

  • Title: Interacting influences of climate, land use and disturbances on regime shifts in forest ecosystems. A paleoecological perspective.
  • Primary Author: David Foster (Harvard Forest)
  • Additional Authors: Elizabeth Chilton (Not specified); Elaine Doughty (Harvard Forest); Wyatt Oswald (Emerson College); Bryan Shuman (University of Wyoming)
  • Abstract:

    This project seeks to provide background to the larger HF LTER project on Future Scenarios while yielding basic insights in ecology, climate science, and archaeology and addressing key questions concerning the conservation and management of New England landscapes. To-date the work has accomplished a number of stated objectives and answered a set of specific questions.

    Is there evidence to support the four-decades old assertion that pests/pathogens may have been involved in the regional mid-Holocene decline of hemlock? While no supporting evidence has been found, three lines of evidence run counter to this notion. First, an exhaustive search of the sediments at Hemlock Hollow that clearly document this decline contain insect parts, but none known to infest hemlock or coincident with the decline. Second, the striking congruence in the histories of hemlock and oak in coastal locations (and elm in the mid-west and Europe) argues against a species-specific cause of the decline and suggests a broader mechanism such as climate. Finally, numerous independent sources of information support the notion that climate change and disturbance (i.e., intense, prolonged droughts) are associated with these declines. Pests or pathogens may have contributed additional local stress on tree populations.

    Is there evidence that native people altered the vegetation through land-clearing, fire, or horticultural activity? This question has bearing on both the dynamics of individual tree taxa and our interpretations of the vegetation and role of disturbance at European settlement. In turn, this may help guide conservation management of vegetation ranging from forests to high priority habitats such as grasslands, heathlands, and early successional vegetation. At sub-regional and regional scales the archaeological evidence indicates substantial changes in human populations through the Holocene (peaks in the Late Archaic (6-3000 BP) and Late Woodland (last 1000 years before contact) periods) but surprisingly little change in subsistence, site selection, or broad land-use patterns. Subsistence was based on hunting, fishing, gathering, and collection of native materials with little evidence of horticulture until just before European arrival. The seasonal movement of small groups of people led to extremely modest impact on the local environment with no signal in regional or site paleoecological records. Fire, based on sediment charcoal, varies through time and physiographically and exhibits no clear pattern with human populations or abrupt vegetation changes. Increased fire activity and the origin of widespread grasslands, shrublands and early successional vegetation are linked to historical activities associated with European forest clearance and agriculture.

    The strength of the evidence at sub-regional, New England, and broader scales is that the periods of abrupt vegetation dynamics, species declines, and shifts in vegetation structure are associated with periods of rapid climate change. In the case of the mid-Holocene declines of hemlock and oak the timing of these dynamics is time-transgressive and varies with the occurrence of multi-decadal droughts. These conclusions underscore the potential for ecological surprises under future scenarios of rapid climate change.

  • Research Category: Historical and Retrospective Studies