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2005 Harvard Forest REU Student Symposium Abstracts

Author:
Bennet Leon - Bates College

Title:
Evolution of pit and mound microtopography 15 years after a simulated hurricane.

Abstract:

Microenvironments of tip-up mounds and pits are significant locations of tree regeneration after wind disturbance. In this study, I surveyed sapling growth and pit-mound erosion fifteen years after a simulated hurricane manipulation in a New England red oak-red maple dominated forest. I measured three dimensions for each pit and mound to compare to initial data taken in 1990. I also recorded all saplings (defined as stems taller than 30cm) growing on pit-mound complexes.

Between 1990 and 2005, mound area increased 37%, while pit area decreased 9%. Mound height decreased an average of 36%, with greater decrease found on taller mounds. Pit depth decreased 39%. Pit and mound dimensions were found to strongly correlate with the original diameter at breast height of the fallen tree. Sapling abundance was highest on mound tops, and lowest in pits. While all sapling species were distributed evenly across microenvironments, birch (Betula) species were the most abundant.

Significant weathering and erosion has occurred since 1990, possibly affecting sapling distribution and abundance. No correlation was found between pit-mound area and number of saplings. I believe that this is in part due to erosion, which in many places has created an unstable substrate. The material eroded from mound tops has caused a number of effects: mound basal area increased while pit area and depth decreased, and has resulted in sapling mortality. The results support that pit-mound topography is a dynamic environment for forest regeneration after a significant windthrow.


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