VISUALIZING BIOGEOMORPHOLOGICAL IMPACT OF RIVERBANK BARK STRIPPING BY BEAVERS

This research focuses on zoogeomorphological impact of an anomalous activity by the North American beaver (Castor canadensis) in eastern Pennsylvania. In addition to traditional tree felling as part of foraging and bio-construction, there has been an increase in partial or full bark stripping (girdling) of large live trees, without any indication of deep incision. At a number of sites in Tioga and Bucks Counties, as well as along the islands on the lower Delaware River, recently live trees with diameters >30 cm (some > 1 m) have been partially or completely stripped along their lower trunk section by the resurgent beaver population. Girdling has been particularly detrimental to white oak (Quercus alba). Some partially stripped trees show evidence of healing, while many (some >100 years old) along stream banks have succumbed to extensive bark loss. This activity, including similar behavior by the Eurasian beaver (C. fiber), has the potential long-term impact on bank stability due to the reduction in canopy cover (increased rain-splash impact) and soil-stabilizing capacity. Image color-intensity analysis was used for rapid assessment and quantification of the damaged area. This study has potential paleoichnological implications, with sub-fossil tree stumps bearing castorid incisor marks ~0.2-0.8 m above the paleo-surface.