SPATIAL AND TEMPORAL ASSESSMENT OF SHORT-TERM BEAVER IMPACT ALONG PENNYPACK CREEK, MONTGOMERY COUNTY, PENNSYLVANIA

This study assessed the zoogeomorphic impact related to a recent increase in beaver activity along two reaches of Pennypack Creek in suburban Philadelphia. Key morphometric parameters – magnitude of tree damage, tree-fall orientation, and distance to stream – were quantified using field photographs compiled by scientists and local citizens during March 2019 - November 2020 (n=50). The magnitude-based typology of tree damage included: 1) chipping and stripping of tree bark; 2) partial incisions in tree trunks; 3) felling of trunks still attached to stumps, and 3) full removal of trees (chew stumps remaining). The highest two grades (3 and 4) account for >80% of the observed damage, with a likely observer bias toward a greater magnitude of impact. The beavers removed small branches of spicebush (~50%) and burning bush, with larger trees including beech, maple, and an occasional pine. Based on partially attached trunks and asymmetric chew stump indicators, the majority of the trees were felled in NNE and SSE direction, overwhelmingly toward the main stream. Over the study period, the distance of beaver impact from the stream increased from <20 to >30 m, although the ephemeral wetland segments have to be considered during spatial analysis (especially when using satellite imagery). The mapping of new sign is ongoing through trail-camera photography and video in order to assess the short-term trends in beaver activity along a dynamic riparian ecotone.