ASYMMETRIC BEAVER IMPACT ALONG A BEDROCK-CONTROLLED STREAM REACH, NEWTOWN CROSSING, PENNSYLVANIA

We present a new database that assesses beaver (Castor canadensis) impact during 2019-2021, which fills a gap in zoogeomorphic surveys along the Neshaminy Creek (Bucks County, PA). More than 30 signs of tree and bush cutting are confined to the left (east bank) of the stream, with only one instance of bark chew on the opposite side. Detailed measurements of 10 stumps, separated into several clusters, yielded a range of diameters of 4-17 cm, with gnaw height of 27-46 cm. Based on stump asymmetry, the majority of the trees were felled within 60° of the downslope azimuth (toward the stream), with some opposite (upslope) treefall likely directed to facilitate the drag. The ground slope ranged from 2° (terrace) to 51° (upper cutbank), with an average distance from the bank of 2.3 m, and distance to sandstone outcrops (Stockton Fm, Triassic) varying between 8.5 and 16.0 m. This distribution suggests some degree of control on focusing of the recent beaver activity into a ~100-m-long riparian buffer confined by nearby bedrock exposures. A large burrow system (entrance: 50x30 cm) has been maintained for at least three years and showed fresh signs of activity along a steep cutbank slide ramp. Several months prior to field surveys, Hurricane Ida (2021) remnants inundated the site with >3 m of water, with the burrow system acting as a conduit for water piping. Our findings highlight the role of renewed beaver activity as driving or accelerating streambank morphodynamics and vegetation, with abundant bottom-feeding fish complementing site-specific biogeomorphic cascades.