You are here

Harvard Forest >

Harvard Forest Symposium Abstract 2016

  • Title: Forest Dynamics
  • Primary Author: Rose-Marie Muzika (University of Missouri (all campuses))
  • Additional Authors: Audrey Barker Plotkin (Harvard Forest); Randall Morin (USDA Forest Service)
  • Abstract:

    Capturing the Shifting Amplitude and Dynamics of American Chestnut

    The pathogen, Cryphonectria parasitica, causing the demise of the American chestnut, swept through the natural range of its host and by 1950’s had nearly extirpated the species. Persistence through root sprouting and an occasional resistant individual allow for a continued presence in forests. In an opportunity to examine that persistence and question continued recovery of the species, we examined chestnut occurrence in permanent plots established on Harvard Forest. Of the 71 chestnut stems measured in 1969 in a 2.88 ha plot, 36 had died by 2001. Overall, however, the number of stems was nearly equal by 2011, with 41 new individuals added between 2001-2011 alone.

    To example whether this type of dynamic in pulses of American chestnut might be occurring over larger areas, we analyzed Forest Inventory and Analysis data, both current distribution of American chestnut and trends in data from the past 24 years. The greatest concentration of chestnut trees (>12.7 cm dbh) currently occurs in the central Maine foothills, southern unglaciated Allegheny Plateau, and the Blue Ridge Mts.

    Between 1990 and 2014 changes in abundance of chestnut trees were most dramatic in the Northern Ridge and Valley Ecological Section where there were increases, but abundance decreased during that time in the western adjacent Allegheny Mts. There were slight decreases in chestnut trees across all New England except for the Maine-New Brunswick foothills and lowland section, particularly the Central Maine Foothills area, which is an area north of the pre-blight distribution of American chestnut. Seedlings (>30.5 cm tall and <2.5cm diameter) and saplings (2.5-12.5 cm dbh) of chestnuts are most abundant currently in the southern ridge and valley. Saplings decreased by 31% between 1990-2014.

    Trends in size tree size class distributions reflect develop of cohorts into larger trees (Figure 1). Although number of trees in 1990 was much greater than in 2014, there were no trees in size classes over 27.9 cm in 1990 whereas, 14% of all trees were greater than 27.9 in diameter in 2014. Preliminary data shows a small shift in the diameter distribution towards larger trees indicating development of resistance in existing trees or that mature resistant trees are reproducing. Although human activity, namely planting resistant hybrids, or non-hybrids beyond the pathogen’s range, may contribute to an expansion of the geographic extent of American Chestnut, natural resistance also plays a role. Understanding the aftermath community and dynamics of the species will require long term studies.

  • Research Category: Invasive Plants, Pests & Pathogens

  • Figures:
  • Size class dist 1990-2014.pdf