REGIONAL ASSESSMENT OF RESURGENT BEAVER ACTIVITY IN SUBURBAN PHILADELPHIA COUNTIES

During the period of 2018-2021, there has been a substantial resurgence in beaver (Castor canadensis) activity in Philadelphia suburbs (e.g., Fairmount Park, Cobbs Creek) and surrounding counties. Most research has been carried out in Bucks County (Neshaminy Creek and its tributaries), with additional sites in Montgomery County (Pennypack Creek, Green Lane Park), Delaware County (Tinicum), as well as new locations along the Delaware River (e.g., Newbold Island). This study presents the first regional geo-located database of beaver activity hot spots. Along the Neshaminy Creek, the majority (>80%) of heavily affected riparian sites occur along the left bank of the main channel, with streambank exposures varying from south (>40%) to west. Dendrogeomorphic impact includes bark stripping (most recently extended to mature oaks), gnawing of saplings and prop roots, and varying degrees of tree chews, most resulting in distinct cone-shaped stumps. Zoogeomorphic impact varies from small bank lodges, to larger pond lodge complexes, and massive bank burrows. The combined impact places beaver as initiating or accelerating biogeomorphic and sediment transport cascades, especially where a reduction in watershed area makes it increasingly vulnerable to treefall and bioturbation by non-native fish and semi-fossorial aquatic reptiles. Complementary surveys focused on partially decayed “relict” stumps aid in assessing the long-term spatial and temporal patterns of beaver activity, with potential applications to reconstructing past extent of riparian ecotones in a heavily developing metropolitan region. Quantitative analysis of individual trace metrics (e.g., tree species preference, treefall azimuth, burrow metrics, geomorphic context, incisor width, etc.) will complement the growing neoichnological and zoogeomorphological database of this keystone landscape engineer.