Brown Bear Damage to Yellow-Cedar
Ursus arctos L.
Tree Species Impacted in Alaska: Yellow-cedar (Callitropsis nootkatensis)
Habitat(s): lower tree boles, often on the uphill side of tree.
General Distribution in Alaska: Admiralty, Baranof, and Chichagof Islands of Southeast Alaska.
Historic Activity
Teeth marks and stripped bark caused by brown bear feeding damage to yellow-cedar.
Photo Credit: USDA Forest Service photo by Paul Hennon.Surveys conducted in the 1980s found that over half of the yellow-cedar trees in some stands were scarred by brown bears while other tree species were unaffected (Hennon et al. 1990).
Survey Method
Most studies were conducted on Chichagof and Baranof Islands (northeast of Sitka at Peril Strait, Slocum Arm, and Kennel Creek) but also on Prince of Wales Island (near Control Lake) and Wrangell Island (near Rainbow Falls). It was important to include study locations where brown bears are rare or absent (Prince of Wales and Wrangell Islands) for comparison. The occurrence and size of basal scars were noted for 779 Alaska yellow-cedars as well as for other associated tree species. See Hennon et al. 1990 for more details.
Symptoms, Biology, & Impacts
Yellow-cedar trees on Baranof and Chichagof Islands are often wounded in the spring by brown bears. The incidence of bear damage tends to be greatest in productive stands with deep soils that are less likely to experience yellow-cedar decline. Brown bears use their teeth to rip away bark from lower tree boles, usually on the uphill side of the tree, apparently to feed on the inner bark tissue. Bear damage does not typically kill trees. Callus tissue slowly develops around wounds. Bear scars likely serve as entry points for stem decay fungi that reduce wood volume.
Additional Resources
Hennon, P. E.; McKenzie, C. M.; D'Amore, D. V.; Wittwer, D. T.; Mulvey, R. L.; Lamb, M. S.; Biles, F. E.; Cronn, R. C. 2016. A climate adaptation strategy for conservation and management of yellow-cedar in Alaska. Gen. Tech. Rep. PNW-GTR-917. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 382 p. Available here, see page 77.
Hennon, P.E.; Hansen, E.M.; Shaw, C.G., III. 1990. Causes of basal scars on Chamaecyparis nootkatensis in southeast Alaska. Northwest Science 64(2): 45–54. Available here.
Zyśk-Gorczyńska, E.; Jakubiec, Z; Wertz, B. 2016. Long-term study of damage to trees by brown bears Ursus arctos in Poland: Increasing trends with insignificant effects on forest management. Forest Ecology and Management. 366:53-64. Available here.
Content prepared by Robin Mulvey, Forest Pathologist, U.S. Forest Service, robin.mulvey@usda.gov.