Patterns in Beaver Herbivory in South-Central Kansas Riparian Woodlands

Abstract

Beaver (Castor canadensis) herbivory can strongly affect the physiognomy and successional dynamics of forests and woodlands near bodies of water. In the central and southern Great Plains, the riparian zones that occur in a grassland / cropland matrix are foci of biodiversity and beaver activity, but little is known about patterns of beaver damage in these areas. We conducted a regional survey of beaver girdling of trees in riparian woodlands in south-central Kansas to determine 1) how the frequency of girdling was related to distance from streams, 2) whether there were differences among tree species in the frequency of girdling and, if so, which species were damaged most and 3) how the probability of beaver girdling varied with tree diameter. The frequency of girdling of trees declined more rapidly with distance from water (< 10 m) than in most northern ecosystems where beaver foraging patterns often have been quantified. Damage occurred significantly more frequently on Celtis occidentalis, Morus rubra and Salix sp. than on Maclura pomifera, Catalpa speciosa and Ulmus sp. Beavers avoided very small-and largediameter stems, but within the range of stem diameters that beavers gnawed, the probability of girdling decreased with increasing stem diameter. Distance to the stream did not alter the distribution of girdling among tree species nor did it change the relationship between girdling probability and stem diameter. In south-central Kansas riparian woodlands, beavers have the potential to alter woodland physiognomy by reducing the density of the sapling-small adult tree layer. Further, their strong preferences among tree species suggest the potential to alter tree species composition by affecting regeneration patterns. However, at most sites these effects will be weak >10 m from streams.3