Impacts of Beaver Foraging on the Federally Threatened Virginia Spiraea (Spiraea virginiana) along the Cheoah River, NC

Abstract Spiraea virginiana (Virginia Spiraea) is a federally threatened shrub endemic to the southern Blue Ridge and Appalachian Plateau physiographic provinces. Observations along the Cheoah River, where the largest population of S. virginiana occurs in North Carolina, indicate that Castor canadensis (Beaver) feed on S. virginiana. However, the effects of Beaver foraging on this imperiled shrub are unknown. To address this issue, we randomly located 50 belt transects (25 m × 2.5 m) along the center of the scour zone of the Cheoah River and assessed all basal stems (<2.5 cm in diameter) of woody plants for evidence of browsing by Beaver. We recorded a total of 4963 basal stems, consisting of 59 species. Of those stems, 14.7% were browsed by Beaver. Spiraea virginiana accounted for 3.5% of the total basal stems and ranked fourth in the total number of stems browsed with 8.8%. After adjusting for transect effect, S. virginiana ranked second as a preferred forage species, with 32.0% of its stems browsed. This study suggests that overall browse levels of this community are relatively low compared to other communities inhabited by Beaver because of the high-gradient and turbulent nature of the Cheoah River. Our findings provide strong evidence that S. virginiana is an important food to Beaver, and as a consequence, Beaver foraging has the potential to affect this population. Although more information is needed to determine the long-term impacts, we suspect that in the short-term, S. virginiana may benefit from the levels of browsing found in this study. Field observations suggest that Beaver foraging stimulates asexual reproduction of S. virginiana by inducing rhizomatous growth. Beaver also may help S. virginiana with dispersal, as fresh cuttings are often left at feeding sites and then may be transported downstream for rooting.

[1]  T. Culley,et al.  Genetic variation and clonal structure of the rare, riparian shrub Spiraea virginiana (Rosaceae) , 2011, Conservation Genetics.

[2]  R. Bartel,et al.  Ecosystem engineers maintain a rare species of butterfly and increase plant diversity , 2010 .

[3]  T. Raffel,et al.  Central Place Foraging by Beavers (Castor canadensis) in a Complex Lake Habitat , 2009 .

[4]  Jessica R. Brzyski,et al.  Beaver (Castor canadensis) Impacts on Herbaceous and Woody Vegetation in Southeastern Georgia , 2009 .

[5]  J. L. Dooley,et al.  Impact by North American Beaver (Castor canadensis) on Forest Plant Composition in the Wilds, a Surface-Mined Landscape in Southeastern Ohio , 2008 .

[6]  J. Maccracken,et al.  SELECTION OF IN-STREAM WOOD STRUCTURES BY BEAVER IN THE BEAR RIVER, SOUTHWEST WASHINGTON , 2005 .

[7]  Frank Rosell,et al.  Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems , 2005 .

[8]  Paul M. Leonard,et al.  DEVELOPMENT OF AN INTEGRATED FLOW REGIME RECOMMENDATION FOR THE CHEOAH RIVER, N.C. , 2005 .

[9]  P. Curtis,et al.  HABITAT FEATURES AFFECTING BEAVER OCCUPANCY ALONG ROADSIDES IN NEW YORK STATE , 2004 .

[10]  P. Lesica,et al.  Beavers indirectly enhance the growth of Russian olive and tamarisk along eastern Montana rivers , 2004 .

[11]  T. Whitham,et al.  Central place foraging by beavers (Castor canadensis): a test of foraging predictions and the impact of selective feeding on the growth form of cottonwoods (Populus fremontii) , 1985, Oecologia.

[12]  S. H. Jenkins.  Food selection by beavers , 1975, Oecologia.

[13]  J. Fryxell.  Habitat suitability and source-sink dynamics of beavers , 2001 .

[14]  Z. Murrell,et al.  Morphological, Molecular, and Biogeographical Variation Within the Imperiled Virginia Spiraea , 2000 .

[15]  P. Busher.  FOOD CACHING BEHAVIOR OF BEAVERS (CASTOR CANADENSIS) : SELECTION AND USE OF WOODY SPECIES , 1996 .

[16]  J. M. Fryxell,et al.  Diet Choice and the Funcional Response of Beavers , 1993 .

[17]  J. Fryxell,et al.  The Effect of Nutritional Quality on Forage Preference by Beavers , 1993 .

[18]  Douglas W. Ogle.  Spiraea virginiana Britton: I. Delineation and Distribution , 1991 .

[19]  John Pastor,et al.  Interactions between woody plants and browsing mammals mediated by secondary metabolites , 1991 .

[20]  P. Beier,et al.  Beaver habitat use and impact in Truckee River Basin, California , 1987 .

[21]  R. Howard,et al.  A stream habitat classification system for beaver , 1985 .

[22]  G. Belovsky.  Summer Diet Optimization by Beaver , 1984 .

[23]  S. H. Jenkins.  A SIZE-DISTANCE RELATION IN FOOD SELECTION BY BEAVERS' , 1980 .

[24]  G. E. Svendsen.  Seasonal Change in Feeding Patterns of Beaver in Southeastern Ohio , 1980 .

[25]  B. Slough,et al.  A land capability classification system for beaver (Castor canadensis Kuhl) , 1977 .

[26]  T. Northcott.  Feeding habits of beaver in Newfoundland. , 1971 .

[27]  R. Chabreck.  Beaver-Forest Relationships in St. Tammany Parish, Louisiana , 1958 .

[28]  Robert H. Whittaker,et al.  Vegetation of the Great Smoky Mountains , 1956 .

[29]  H. Zim,et al.  American Wildlife and Plants: A Guide To Wildlife Food Habits , 1951 .

[30]  T. S. Austin,et al.  Comparison of Tree Cuttings of Six Beaver Colonies in Allegany State Park, New York , 1943 .