Forage Selection of Native and Nonnative Woody Plants by Beaver in a Rare-Shrub Community in the Appalachian Mountains of North Carolina

Abstract

Castor canadensis (Beaver) is a selective forager that can modify the species composition and structure of plant communities. However, no studies have examined the use of woody plants by Beaver in temperate forests that contain a dominant nonnative plant. We investigated foraging of woody plants by Beaver in a riparian shrub community that is dominated by both native and nonnative species, including the federally threatened shrub Spiraea virginiana (Virginia Spiraea). We established 48 random, 25-m transects along a 12-km reach of the Cheoah River in the Appalachian Mountains of North Carolina. We sampled woody plants every 5 m using a modified point-centered quarter method to estimate relative abundance and to quantify browsing by Beaver. We used a mixed linear model to determine Beaver forage selection on the 9 most abundant plant species and Virginia Spiraea. We recorded 984 plants of 58 woody species (55 native, 3 nonnative). Beaver browsed 24% of the woody species sampled and 8% of all stems. This finding suggests that the overall effects of browsing in this community were relatively low, likely because of the high gradient and turbulent nature of the Cheoah River. Relative stem abundance and location along the river did not differentially affect local levels of browsing. However, Beaver were selective foragers at both the species and individual-plant level. Of the 9 most abundant species, Carpinus carolinana (Musclewood), Liquidambar styraciflua (Sweetgum), and Alnus serrulata (Tag Alder) were selected most often; Lindera benzoin (Spicebush), Virginia Spiraea, Cornus amomum (Silky Dogwood), and Ligustrum sinense (Chinese Privet) were moderately selected. Least frequently selected species were Rhododendron maximum (Rosebay Rhododendron), Leucothoe fontanesiana (Doghobble), and Xanthorhiza simplicissima (Yellowroot). Browsing appeared to have a positive effect on both the invasive nonnative shrub, Chinese Privet, and the rare Virginia Spiraea by stimulating asexual reproduction and inducing plants to spread through suckering. This study demonstrates the importance of understanding the reproductive strategies of woody plants when gauging the community-wide effects of foraging by Beaver, particularly when an invasive plant species is present.