Woodn't You Know: Beaver (Castor canadensis) Foraging Preference

Abstract

Beavers (Castor canadensis) have been defined as ecosystem engineers, playing keystone roles in wetlands including bolstering flood resiliency, storing water storage during drought, nutrient retention, and habitat creation for aquatic and terrestrial species. Much of what we understand about beaver foraging preference centers around central place foraging theory with the lodge as a safe refugia from predation risk. The selective browsing behavior of beavers shifts forest successional trajectories and increases local biodiversity. We wanted to evaluate foraging preference and habits of two beaver populations in sandstone pavement barrens versus a wildlife management area. We hypothesized that beavers would prefer trees that are more abundant and closer to their lodge. In fall 2024, we surveyed beaver ponds at two sites in Clinton County, NY, specifically a wildlife management area (Wickham Marsh) and the Altona Flat Rock sandstone pavement barrens (2018 burn). Using the Survey123 app, we recorded tree species, diameter at breast height, beaver activity (e.g., browsed, partially browsed, unbrowsed), and distance to shoreline and lodge. The average diameter of trees browsed at Wickham Marsh was twice that of the Flat Rock and beavers venture 1.6m farther out from water than at the Flat Rock to harvest. Based on the ecological setting the two different beaver populations had to forage differently, specifically at the Flat Rock beavers were forced to travel farther away from their lodge compared to at Wickham Marsh. This was due to limited availability of trees due to its early successional phase forest compared to Wickham where the forest is in later successional stages. In addition, at the Flat Rock jack pine (Pinus banksiana) trees are mostly avoided, while hardwoods are selected. At Wickham Marsh, the most heavily browsed species are eastern hemlock (Tsuga canadensis) and green ash (Fraxinus pennsylvanica), while white pine (Pinus strobus) and red pine (P. resinosa) are avoided. The largest trees browsed at Wickham Marsh were closest to the lodge, supporting central place theory. Numerous factors drive beaver foraging behaviors and include predation risk, forest composition, deer density, and drought. In the case of the Flat Rock browsed trees were smaller, in part due to low nutrients available on the barrens. Beaver complexes at the Flat Rock are expansive, likely because limited quantity and quality of browse forces them to relocate. Our research is important because it provides land managers better understanding of what a habitat may come to resemble as beavers move about their landscape, which include impacts from deforestation, ponding, and abandonment which can disrupt an entire ecosystem. Our findings demonstrate that beaver wetlands add structural and resource complexity to the ecosystem, creating a patchwork of biodiversity.