Stem size selectivity is stronger than species preferences for beaver, a central place forager

Abstract

The North American beaver (Castor canadensis) is a classic ecosystem engineer, creating and expanding wetlands throughout their vast range. As important as their impacts on aquatic ecosystems, beaver as central place foragers restructure the surrounding forest community by their selective cutting of preferred woody species and size classes. These effects, which have been studied in several regions of North America, are still poorly understood within forests of the northeastern United States, where beaver populations are rebounding following regional extirpation. Here, beaver represent a key disturbance agent in a region where other drivers such as fire and timber cutting have been greatly reduced over the last century. Understanding their specific impacts on forest composition and structure is needed to manage these forests and their multiple ecosystem services.In this context, we assessed beaver foraging preferences throughout New York’s Adirondack State Park, a vast northern wooded region, to model their impacts on forest structure and composition. Across 19 sites distributed throughout the Park, beavers preferentially harvested stems < 10 cm diameter, with the 2–5 cm size class most preferred overall. Mixed-effects logistic regression models showed greater probability of harvest for stems closer to the impoundment for all species and taxonomic groups modeled, consistent with central place foraging theory. Broadleaf deciduous tree species were browsed at rates 33% greater than coniferous species, with American beech (Fagus grandifolia) among the most utilized species, contrary to other regions where it is typically avoided. Though stem diameter preferences and spatial gradients of foraging intensity were consistent with those found in other regions, species preferences differed greatly, suggesting that selectivity for a deciduous species expressed on the landscape is primarily a function of the size distribution of its available stems.