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Harvard Forest Symposium Abstract 2018

  • Title: White oak recruitment and growth trajectories: is there a crisis?
  • Primary Author: Nicholas Patel (Swarthmore College)
  • Additional Authors: Ross Alexander (Illinois Mathematics and Science Academy); David Orwig (Harvard Forest); Neil Pederson (Harvard Forest)
  • Abstract:

    Although white oak has been 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. We sampled white oak at 4 locations in Massachusetts. Three of the sites sampled were even-aged, 120-140 year-old stands that are likely still in the stem exclusion phase of stand development, like many Massachusetts forests. The fourth site we sampled is an old-growth stand in the Mohawk Trail State Forest. 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 indicated that these trees had 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 ordination analysis revealed that competition and disturbance history accounted for the majority of the difference in growth trajectories and current canopy position of white oaks from all four sites. Recruitment analysis revealed that 82% of trees across sites recruited into a canopy gap, 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 will continue to age and likely experience more large-scale canopy disturbance events that will facilitate white oak recruitment.

  • Research Category: Historical and Retrospective Studies; Physiological Ecology, Population Dynamics, and Species Interactions