Numerous mammal species can damage trees in Pacific Northwest ecosystems. Voles, like many small rodent species, can produce many litters in a single year (every 21 days) and females are mature 30-40 days after they are born. Average litter size is 3 pups.
With this type of reproductive capability, it is easy to see why vole populations can rapidly expand in ideal habitats. Voles can be especially damaging on small tree farms where the understory is mostly comprised of grasses. Small holes and runways through grass often signify voles. Voles feed on young tree roots, usually stripping them and leaving pointed tips. In addition, they will also feed on stems and cause some girdling of seedlings. Circular marks on girdled seedlings are characteristic. Barriers around trees, and rodenticides, have both been used to reduce vole damage. However, with rodenticides, it is important to first reduce the vegetation so that the rodenticide can reach the runways. The best means of vole control is through habitat modification. Reduction of grasses and vegetation through mowing, plowing, or herbicides, reduces the attractiveness of an area for voles.
Hares, rabbits, and pikas also damage trees. Pikas are restricted to the eastern drier areas of the western United States, generally occurring in rock outcrops. Small piles of grass and other forbs in rockslides are good evidence of pika presence. In the Pacific Northwest, the snowshoe hare is the most widely distributed rabbit species. Hares leave large angular toothmarks and sometimes wood chips at the base of damaged trees. Seedlings less than ¼ inch are preferred; however, in winter, hares will feed on the bark of trees. Several methods of control have been tried including hunting and employing Vexar tubing to protect seedlings, both of which can be costly. Removing cover with herbicides is another potential method to reduce damage; however, this may affect habitat use by other wildlife. Success in reducing damage has been shown when larger seedling stock has been used. Additionally, repellents show promise, and the NWRC field station continues to investigate this tool.
Porcupines are the second largest North American rodent (stream beavers are the largest) and they have modified dorsal hairs better known as quills. With their muscular tails and long claws, porcupines are well-adapted for climbing trees. Porcupines feed on herbaceous foliage on the ground in the spring and summer, and in fall and winter can be found foraging on trees. Clipped needles, bark chips, and quills at the base of trees are prime indicators of porcupine activity. Porcupines strip the bark from trees and leave horizontal teeth marks, in addition to clipping stems. Young pole-trees are preferred in the winter, and crowns of trees are the most susceptible. Porcupine damage becomes evident in the summer when the crowns appear dead. Although fencing does work to protect areas, it is time-consuming and expensive. Trapping and hunting are the most reliable methods for reducing damage by porcupines.
The legal status of wildlife species and subspecies may vary by state. Some wildlife damage management methods mentioned here may not be legal, permitted, or appropriate in your area. Please check with personnel from your state wildlife agency and local officials to determine if methods are acceptable and allowed.
*the above discussion is summarized from the following article by Wendy M. Arjo. Click on the link to see the full-text of the article.
03-3 ARJO, W. M. 2003. From seedlings to crowns: these species cover it all. Western Forester 48(4):15. 64K
Additional NWRC Resources
*All NWRC publications from 1998-present are available full-text from this Web site. They are linked from individual yearly publication lists.
NOLTE, D. L., AND M. DYKZEUL. 2002. Wildlife impacts on forest resources. Pages 163-268 in Larry Clark, Jim Hone, John A Shivik, Richard A. Watkins, Kurt C. VerCauteren, and Jonathan K. Yoder, editors. Human conflicts with wildlife: economic considerations. Proceedings of the Third NWRC Special Symposium. National Wildlife Research Center, Fort Collins, CO. 123K
FELICETTI, L. A., L. A. SHIPLEY, G. W. WITMER, AND C. T. ROBBiNS. 2000. Digestibility, nitrogen excretion, and mean retention time by North American porcupines ( Erethizon dorsatum) consuming natural forages. Physiological and Biochemical Zoology 73(6):772-780.
FELICETTI, L. A., L. A. SHIPLEY, AND G. W. WITMER. 1998. Dry matter, nitrogen, and energy digestibility in the North American porcupine ( Erethizon dorsatum). Pages 47-52 in C.L. Kirk Baer. editor. Banff Centre, Banff, Alberta, Canada). Comparative Nutrition Society, Silver Spring, Maryland.
MASON, J. R., HOLLICK. J., B. A. KIMBALL, AND J. J. JOHNSTON. 1999. Repellency of Deer Away Big Game Repellent® to eastern cottontail rabbits. Journal of Wildlife Management 63(1):309-314.
STERNER, R. T. 1998. The bait surcharge program: research improves zinc phosphide use for vole control in alfalfa. Proceedings of the Vertebrate Pest Conference 18:176-180.
STERNER, R. T., D. A. GOLDADE, AND R. E. MAULDIN. 1998. Zinc phosphide residues in gray-tailed voles ( Microtus canicaudus) fed fixed particles of a 2% grain bait. International Biodeterioration & Biodegradation 42(2-3):109-113.
STERNER, R. T. 1999. Pre-baiting for increased acceptance of zinc phosphide baits by voles: an assessment technique. Pesticide Science 55:553-557.
WAGER-PAGE, S. A., J. R. MASON, E. ARONOV, AND G. EPPLE. 1997. The role of sensory cues and feeding context in the mediation of pine-needle oil's repellency in prairie voles. Pages 301-311 in J. R. Mason, editor. Repellents in wildlife management. Denver Wildlife Research Center, Denver, Colorado.
WAGNER, K. 1997. The problem with voles. Northwest Woodlands 18-19.
WITMER, G. W., AND M. J. PIPAS. 1998. Porcupine damage and repellent research in the interior Pacific Northwest. Proceedings of the Vertebrate Pest Conference 18: 203-207.
WITMER, G., AND K. VERCAUTEREN. Understanding vole problems in direct seeding--strategies for management. Pages 104-110 in R. Veseth, editor. Proceedings of the Northwest Direct Seed Cropping Systems Conference. Spokane, Washington).
WITMER, G. W., AND A. A. HAKIM. 2001. Investigations of methods to reduce damage by voles. Pages 357-365 in M C. Brittingham, J. Kays and R. McPeake editors. Proceedings of the Ninth Wildlife Damage Management Conference. Pennsylvania State University, University Park, PA.
Mammalian Impacts on Forest Resources Research Project
Olympia Field Station Home Page
Mountain Beaver Damage and Management
Bear Damage and Management
Pocket Gopher Damage and Management
Deer and Elk Damage and Management
Fencing for Deer and Elk