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 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
on Forest Resources Research Project
Additional NWRC Resources
*All NWRC publications from 1998-present are available full-text from
this Web site. They are linked from individual yearly publication
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 Americna 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
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.
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,
on Forest Resources Research Project
Olympia Field Station Home Page
Mountain Beaver Damage and Management
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