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Harvard Forest REU Symposium Abstract 2019

  • Title: Does Soil Nitrogen Increase Gypsy Moth Defoliation or Aid Tree Recovery?
  • Author: Emma Conrad-Rooney (Wellesley College)
  • Abstract:

    Trees’ critical roles in forest ecosystems are threatened by disturbances such as insect outbreaks. Invasive gypsy moth caterpillars (Lymantria dispar), introduced to New England in the mid-1800’s, defoliate trees which can result in mortality. Nitrogen is critical for plant recovery from defoliation and is also critical for the defoliators. I am investigating whether oak leaf nitrogen content correlates to soil nitrogen, whether there a relationship between soil nitrogen and gypsy moth defoliation intensity, and how soil nitrogen contributes to tree recovery from defoliation. Twelve red oak (Quercus rubra) street trees in Amherst, MA were monitored for percent defoliation. In ten plots in the Quabbin Reservoir watershed that had a range of defoliation intensities, trees were assessed for dieback. Soil samples of the organic horizon were collected from around the Amherst trees and in the Quabbin plots, and leaves were collected from the Amherst trees in 2018. Processed samples were run through an elemental analyzer to measure percent carbon and nitrogen in organic soil and oak leaves. Results indicated a positive correlation between soil and leaf nitrogen content (p = 0.36), less herbivory for trees with higher foliar N levels (p = 0.27), and more dieback after defoliation in areas with less soil nitrogen (p = 0.16). This study suggests that higher nitrogen promotes oak resistance to, and recovery from, gypsy moth defoliation. These results can inform predictions of the northeastern U.S. forests’ ability to act as carbon sinks that help to mitigate climate change.

  • Research Category: Soil Carbon and Nitrogen Dynamics; Invasive Plants, Pests & Pathogens; Group Projects