CASTORID DENDROGEOMORPHIC IMPACT ON CUTBANK STABILITY AND PLANT COMMUNITY COMPOSITION, SOUTHEASTERN PENNSYLVANIA

This study focused on riparian morphodynamics subjected to intense selective cutting of trees and bushes by the North American beaver (Castor canadensis), a keystone zoogeomorphic agent. Continuing research at Tyler State Park (Bucks County, PA) is aimed at assessing the cumulative impact of the resurging beaver activity on plant community composition and cutbank stability along a section of Neshaminy Creek. Hurricane Ida floodwaters inundated our study site in early September 2021, undercutting large trees and creating overhanging root systems. Exacerbated by extreme flood events, the exceptionally narrow riparian buffer is in need of restoration due to legacy sediment transport, as well as increased vulnerability to erosion due to the geomorphic cascade now involving beaver activity. At the study site, where many trees are now protected by metal wire tree fencing, C. canadensis preferred native deciduous trees (Acer, Platanus, Quercus, etc.) with circumferences ranging between 10-15 cm within a 3 m distance to the stream bank. The azimuth of most felled trees ranged from 202°-260°, mainly downslope toward the stream (bank-normal azimuth: 235°). Treefall away from the stream included 25% of samples, involving the farthest distance to the stream at 2.8 m. There is evidence that beyond foraging for consumption, C. canadensis were also transporting these trees down river to a small bank lodge. Due to the protected nature of the park grounds, some foot traffic is routed close to the stream, further exacerbating bank erosion.