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Harvard Forest REU Symposium Abstract 2017

  • Title: Light availability and size-abundance scaling of saplings at Harvard Forest
  • Author: Colleen L Smith (College of the Redwoods)
  • Abstract:

    Tree size is one of the most important predictors of metabolic rates and abundance, but many gaps in our understanding remain. In particular, the idea of energetic equivalence and the relationships between body size, abundance, and light availability in forest structures are not yet fully established. Energetic equivalence asserts that collectively small trees use the same amount of energy as larger trees due to their relative abundance. Few have studied energetic equivalence in forests, and there have been no studies to our knowledge that include stems under 1 cm in diameter that may be significantly affected by light limitations. The smallest and most abundant trees are missing from analysis. To address this gap, we censused saplings under 1 cm in diameter across 50 plots within the Harvard Forest Mega-plot and quantified light availability with the use of hemispherical photography. Solar energy is a main limiting factor for the abundance and growth of trees, varying with each species as their shade tolerance differs. We hypothesized that areas with limited light would have a lower total abundance than areas where light was not a limiting factor despite the assumption of energetic equivalence. We found that sapling abundance decreased in sites with lower levels of light availability as predicted. Using preliminary measurements of our most common species, we found an inverse correlation between diameter and abundance, providing support for energetic equivalence in smaller stems. Further research may be applied to various aspects of ecology including carbon storage, succession following disturbance, and beyond.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions; Group Projects