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Harvard Forest REU Symposium Abstract 2017

  • Title: White oak recruitment and growth trajectories
  • Author: Nicholas J Patel (Swarthmore College)
  • Abstract:

    The prevailing view is that, despite white oak once being a dominant species prior to the arrival of Europeans, it is failing to recruit on most sites across the eastern United States. However, this phenomenon may only be apparent when considered on a short timescale. Understanding the drivers behind this “recruitment crisis” is essential to guiding effective management solutions to this situation. Three of the four sites we sampled in Massachusetts were even-aged, 120-140 year-old stands that are likely still in the stem exclusion phase of stand development, not unlike a majority of Massachusetts forests. We cored white oaks of all canopy classes and assessed local competition. We measured cores and crossdated them using COFECHA. We determined release events and disturbance history with the TRADER R package. Ages of trees with suppressed or intermediate canopy class indicate that these trees have persisted in the understory for an average of 125 years – with one persisting for up to 230 years – under high shade with low growth rates. PCA reveals that competition and disturbance history almost independently account for the majority of the difference in growth trajectories and current canopy position of white oaks from all four sites. Recruitment analysis reveals that 82% of trees were recruited into a canopy gap at all sites, suggesting that overstory gaps are required to stimulate successful regeneration. The “recruitment crisis” may therefore not be as severe in this region because the younger forests lack the large-scale canopy disturbance events that drive white oak recruitment.

  • Research Category: Historical and Retrospective Studies