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      5. Animal Damage Management
Introduction and Background
Forest vegetation and seeds are natural food items for a variety of animals, but the damage
caused to young trees can be counter to meeting management objectives for an area. In
addition, as forest managers alter the forest environment or other factors change, animals
may increase use of an area for food or cover, which may result in increased damage to a
Damage evaluation begins with knowledge of the animal – how to identify it and its
characteristics and behaviors, and how populations react to changes (Black 1994). An
integrated approach to prevention and control is the most desirable. The integrated approach
focuses on the long-term management of animal populations and habitat rather than relying
on immediate suppression and other corrective measures. Foresters must also have good
methods to monitor results.
An Activity Prescription will be completed for animal damage management activities. When
planning the activities:
 Use an integrated approach to forest protection (Walstad 1992).
 Define resource objectives and constraints.
 Establish acceptable and unacceptable thresholds of damage.
 Determine if animal damage delays reaching management objectives, or results in failure
    to reach objectives.
 Characterize potential problems.
 Develop solutions.
 Evaluate and select alternatives, considering treatment effectiveness, economic
    efficiency, and the potential effects on future yields.
 Evaluate and document effectiveness of the program.
Descriptions of different types of animal damage are found at the British Columbia Ministry
of Forests site, (Henigman et al.
A good general reference is: Animal Damage Management Handbook (Black 1994), .
Animals damage trees in many ways. They clip and browse foliage and leaders, gnaw and
girdle stems and boles, inflict trampling injuries, or completely remove trees. Browsing
refers to habits of ungulates. Browsing during the dormant season leaves a ragged, splintered
break because these animals lack upper incisors. Clipping refers to the feeding habits of
rodents, hares, and rabbits, which produce a smooth, oblique cut on woody shoots. These
animals have chisel-like incisors and tilt their heads to eat (Black 1994). Girdling occurs
when the bark and cambium are stripped from the entire circumference of the tree.

ODF Reforestation Handbook                                                                5-1

To identify damage to trees the characteristic differences must be identified. Guides are
available to help identify the cause of damage, but identifying the cause of missing trees is
more problematical.


Universal Standards
   Develop an Activity Prescription prior to initiating any animal damage management
    activity, e.g., mountain beaver trapping, pruning to reduce bear damage.
   Enter Activity Prescriptions into ROOTS.
   Complete a Notification of Operations as required by the FPA when using repellents and
    rodenticides. See;
   Use an integrated approach for the prevention and control of animal damage; relying on
    long-term management of animal populations and habitat rather than short-term
    solutions. See ORS 634.650 and 634.655 for requirements and definitions.

Specific Standards
   Because animal damage may be cumulative, a threshold needs to be established where
    further damage is unacceptable, i.e., when any further damage will result in failure to
    meet the objectives for the stand and corrective action is needed.
   When using repellents and rodenticides follow all label requirement.
   When using repellents and rodenticides, provisions of the Oregon Occupational Safety
    and Health Standards, OAR 437, Division 7, Forest Practices
    ( must be followed.
    Also see Division 4, Agriculture
   Trapping must be done in accordance with the Oregon Furbearer Trapping and Hunting
    Regulations. The regulations are found at: 2008-2010 Furbearer Regulations.pdf ;
   Deer and elk carcasses taken on damage shall be disposed of as directed by OAR
   Black bear carcasses taken on damage shall be disposed of as directed by OAR
    635-002-0007 and OAR 635-002-0008,

5-2                                                                          Animal Damage

Planning and Other Considerations
Prior to initiating any animal damage management activity, the impacted area should be
evaluated to determine if the stand is still on or will be able to reach a trajectory that will
attain management objectives. The evaluator should ask the following questions:
 Is the stand still on a pathway that will meet the DFC?
 If the stand is on a desirable pathway, will it continue on this trajectory?
 Is the cumulative damage (past, current, and projected future damage) likely to exceed
    the threshold precluding the stand from reaching the DFC?
 If the stand is on an unacceptable pathway, what needs to be done to change the
 Are environmental impacts and cost of actions needed to change an unacceptable
    pathway acceptable and reasonable?
The amount of damage acceptable in a forest stand depends on the management objectives
for the stand. The threshold is reached when the extent of the cumulative damage places the
development of the stand on a trajectory that will not meet the DFC. A hypothetical example
is where mortality from bear damage in a stand being managed intensely for timber
production begins to exceed 30% of the crop trees. If more than 30% of the crop trees are
killed, in a stand that was precommercial thinned to 220 trees per acre, opportunities for
commercial thinning may be lost or delayed. The same amount of damage might be
acceptable in a stand that is being managed to produce complex structure, because it could
still be on a pathway that will meet management objectives. There are also situations where
experience shows a high probability that damage will exceed thresholds prior to any damage
occurring. Damage from mountain beaver is an example. In most areas where mountain
beaver are present, newly planted seedlings experience unacceptable damage.
 Establish a threshold for unacceptable amounts of animal damage. When determining
     this threshold, the primary factor should be the potential effect animal damage would
     have on attaining the management objectives.
 Establish damage threshold in consultation with the Area Wildlife Biologist.
 Coordinate with local wildlife managers.
 Develop a method for measuring and monitoring threshold parameters.
 Anticipate the actions needed to prevent exceeding the threshold.
 Evaluate the consequences of no action compared to taking protection or control
     measures. This could include an economic analysis or an analysis of the consequences of
     failure to meet management objectives.
Other things to consider:
 Consider the window of opportunity to implement an activity. For example, the time
   when impacts of site preparation are effective may limit when a unit can be replanted
   without vegetation control.
 Consider how the management decisions made for one area may significantly affect the
   management objectives of adjacent areas.

ODF Reforestation Handbook                                                                    5-3

   Use the history of animal damage problems in adjacent stands to anticipate problems and
    guide prevention and control strategies in newly established units.
   When selecting planting stock for an area, take into account the problem animal’s
    preference for seedling species and match the stock type to the problem. For example,
    when planting western redcedar, western hemlock, and Douglas-fir, the larger stock types
    generally have higher survival rates when browsed than smaller seedlings.
   Use a mix of species to provide diversity and as insurance, i.e., a diverse portfolio.
   In areas experiencing heavy animal damage, start stands at higher stocking levels to
    assure adequate numbers of surviving seedlings to meet objectives.
   Be aware of the limitations of animal damage tools (vexar tubing, repellents, vegetation
    control, etc.) and uncertainties of trying to predict animal damage problems.
   Consider the potential for adverse effects on non-target species when developing animal
    damage management prescriptions.
   In areas that typically experience damage from elk browsing, plant in spring rather than
    in fall. This provides one growing season prior to the period when elk browse damage is
    most likely to occur.

Type of Damage and Recognition
Wildlife damage problems can be localized, as in the case of mountain beaver, or they may
be pervasive over large areas, as is the case with deer and elk. Habitat modification using
silvicultural practices is often effective and economical for species with small home ranges,
because of more localized treatment areas and the relatively short duration. With species like
deer, elk, black bear, and porcupine, silvicultural practices are less effective (Black 1992).
Early awareness of animal damage occurrence and prompt action are key factors in
minimizing tree damage. Animal use or damage should be a part of all surveys. This is
especially important when doing survival checks or stocking surveys in young plantations.
Estimating the extent of damage and identification of the animals causing it are necessary to
determine if control actions are needed and in the development of treatment strategies. Once
a control treatment is initiated, follow-up is needed to monitor effectiveness.

Deer and Elk
Browse damage by deer and elk to new conifer and hardwood plantations is quite significant
in added workload and expense. Estimates for the Coast Range are that most plantations
experience some level of damage, with approximately 30% requiring additional work to
achieve adequate stocking. Experience suggests the most significant browse period is during
the winter months and during new shoot elongation in the spring. Deer are browsers, feeding
primarily on woody vegetation. Elk are grazers, utilizing grasses and other herbaceous
vegetation, but they will also utilize the new growth from young conifers.
The most widespread and economically important damage to trees is from browsing which
occurs in young plantations during the first few years after planting. Other minor damage to
young trees from deer and elk can be caused by antler rubbing and trampling.

5-4                                                                        Animal Damage

Elk and deer do not have upper incisors. This causes a jagged, splintered break when
browsing on woody plants. Browsing during the spring, when the bark is loose, can cause
the bark to peel away below the break. Elk tend to pull up small newly planted trees where
the roots are not providing adequate anchors.
Damage from elk browsing can be anticipated on flats or benches where animals tend to
congregate. Recently harvested units are often ―hotspots‖ for damage caused by elk,
especially when the adjacent areas are not providing desirable forage, e.g., a recently
harvested unit in a large area dominated by closed single-canopy stands.

Preventive Strategies
History of adjacent stands, remoteness of a unit from other regeneration units, amount of
forage available in the vicinity, the amount of human activity, and general number of animals
are often good indicators of damage potential. Evaluate where you are likely to get
unacceptable browse and plan preventive action accordingly. The challenge is selecting a
prevention strategy that is cost-efficient, effective, and consistent with management
Some approaches include:
   Diversify stand composition.
    Develop stands that have a variety of species. Browse preference by animals varies by
    tree species. Western redcedar and western hemlock seem to be the most palatable,
    followed by Ponderosa pine and Douglas-fir.
   Use larger stock types.
    Larger stock types will probably withstand browse better than smaller stock types.
   Plant trees in the spring.
    Trees planted in the spring tend to experience less browse damage during their first
    growing season than fall-planted trees, since they have a growing season to establish root
    systems before the winter browse period. The disadvantage of fall planting is the
    potential for browse damage during the winter, November through March, before the
    trees have established root systems that better withstand the pulling action of feeding elk.
   Use mechanical barriers.
    Mechanical barriers such as fencing and physical barriers applied to individual trees are
    effective in preventing or reducing deer damage. There are many different types and they
    provide varying levels of effectiveness. The main drawback is that they are expensive
    and require maintenance to be effective. There is a variety of physical barriers, including
    fences, plastic tubes, bud caps, netting, and fabric sleeves. Vexar tubing, made from a
    rigid degradable plastic, is the most commonly used barrier.
    A discussion of the various types of physical barriers can be found at (Duddles and Edge 1999).
   Use repellents.

ODF Reforestation Handbook                                                                  5-5

Repellents are fairly effective for short periods of time. Most research on repellent efficacy
was conducted on deer, and a lesser amount with elk. Repellents that depend on odors
produced by the degradation of proteins are the most effective (Nolte 1998). Experience and
local trials suggest one application of Plantskydd or Deer Away will protect conifer seedlings
for about 3 months. Repellents also seem to work better when alternative forage is available.
Weather conditions prior, during and immediately after application is critical to the
repellent’s effectiveness. See product label for specific information, and always follow label
requirements when using repellents.

Information about the efficacy of repellents can be found at the following sites: (Moser 2001); (Nolte 1998).

   Control vegetation.
    Intensive vegetation control may reduce the use of an area by big game animals.
    However, the effect of vegetation control on browse is not well understood. Experience
    indicates that the reduction of vegetation by means of thorough site preparation makes
    the area less desirable to elk and deer, and reduces browse damage to conifer seedlings.
    The effectiveness of vegetation control is probably related to the type and amount of
    woody vegetation that sprouts after treatment, and the expansion of the vegetation not
    affected by the treatment. In areas where there are a large number of animals, damage to
    seedlings may increase when most of the palatable vegetation is removed (Rochelle
   Manage arrangement and size of harvest units.
    The arrangement and size of harvest units, as well as the availability of forage in an area,
    are likely to affect use by elk. Harvest activities, especially heavy thinning and
    clearcutting, increase available forage and make an area more attractive to big game
    animals. It is not known whether areas with favorable forage may incur less overall
    damage because of a ―dilution effect,‖ or more damage, because more animals are drawn
    to the area. Some of today’s harvest practices, such as retention cuts, provide forage and

Control Methods
Damage control hunts that focus on harassment instead of total reduction in numbers may
have positive benefits, but this is hard to quantify. Control or special hunts are coordinated
with the local Oregon Department of Fish and Wildlife biologist.
Additional information can be found at: (Henigman et al. 2001); and (Black 1994).

Mountain Beaver
A good description and pictures of mountain beaver can be found at: New Mountain Beaver
(Aplodontia rufa) Journal (updated 4/9/09) (Steele 2004).

5-6                                                                          Animal Damage

Type of Damage and Recognition
Mountain beaver presence and damage can be recognized by the presence of burrows and the
characteristic clipping of vegetation. The burrow entrances are approximately 6 inches in
diameter, and often littered with clipped vegetation. Mountain beaver are usually found near
water or where water is readily available, either from standing water or succulent vegetation
(Carraway and Verts 1993). They are solitary and a single burrow system may occupy 0.3
acre. Wherever an active burrow system exists there is the potential for clipping young trees
(Black 1994).
An oblique cut through the stem is typical of the clipping of hares, rabbits, and most rodents,
including mountain beaver. Hare clipping can be distinguished by the presence of rabbit
―pellets‖ and the size of the stem clipped. Hares generally do not clip anything larger than
0.25 inch diameter, while a mountain beaver will clip stems as large as 1.5 inches in
diameter. Mountain beaver often leave a serrated edge on clipped seedlings because of
multiple bites. Mountain beaver can also climb, and can cause damage to lateral and
terminal branches. They usually leave stubs from 1 inch to 3 inches long. Good
descriptions of mountain beaver habits and damage can be found at: (Ministry of
Environment, Lands and Parks 1998).
Washington Wood Products Association (Wendy M. Arjo, 2006)

Control Methods
Trapping and individual tree protection using plastic-mesh tubing are currently the most
effective methods for controlling mountain beaver damage. Presently, research is being done
on the efficacy of existing rodenticides on mountain beaver, and possible registration for
forestry use (Arjo 2004). Trapping must comply with the Oregon Furbearer Trapping and
Hunting Regulations. When using repellents and rodenticides, all label requirements must be
The regulations are found at: 2008-2010 Furbearer Regulations.pdf ;
A discussion of traps and trapping methods is found starting on page 41 of the Animal
Damage Management Handbook, (Black 1994).

Black Bear
Black bears can be a significant problem in the Pacific Northwest, causing severe damage to
young Douglas-fir stands. Bears peel the bark from the lower bole of trees and feed on the
inner bark and cambium layers. Most damage occurs in 12-25 year old coastal forests,
usually during May and June (Schmidt and Gourley 1992). Bears prefer the most vigorous,
fastest growing trees. Young stands that have been thinned or fertilized are more susceptible
than the more densely stocked stands.

ODF Reforestation Handbook                                                                 5-7

Experience shows that if peeling took place before thinning was done, then bears are usually
back within two or three years and often will do severe damage at that time (Bob Gilman).
Studies have shown that thinning increases the carbohydrate/terpene ratio in a tree’s vascular
tissue, and that bears prefer trees high in carbohydrate and low in terpene concentrations.
This data supports observations that bear damage increases in stands post-thinning (Nolte
2003). The amount of damage varies by individual stand. First year damage is generally
light, affecting less than 5% of the trees. Subsequent damage can affect up to 60% of the
stand. Bears tend to use the same stands for several seasons (Black 1992). An evaluation of
the need for corrective actions needs to include the effects of bear damage on the long-term
objectives of the stand. A good discussion on this topic can be found in Timber Damage by
Black Bears, Approaches to Control Problems,
(Nolte et al. 2003).
Bruce Kimball and others (1998a) discuss the effects of thinning and fertilization on bear
damage to trees in:

Types of Damage and Recognition
Bear presence in an area can be detected by the presence of bear-marked trees. Bears mark
trees by rubbing, clawing and biting them, most likely to define territories. Marking trees is
not usually a problem because it is limited to a relatively small number of trees. Significant
damage does not occur until the bears start feeding on the trees. Bear scats in the area are
also good indicators of bear presence and their diet. The first indication of bear damage may
be the yellowing and reddening of conifer needles in a stand. Closer examination of
individual trees will reveal the distinct vertical bite marks on the lower boles, and bark
remnants scattered around the area. Bears usually feed on the cambium and inner bark of the
lower boles of young trees, but may occasionally climb higher in the tree to feed.
There are two major options available to reduce bear damage: apply silvicultural practices
that minimize the attractiveness of trees, and control the bear population (Black 1992).

Preventive Strategies
Preventive strategies include:
 Diversify stand composition to reduce the potential impacts of bear damage. Develop
   stands that have a variety of species along with Douglas-fir.
 Postpone thinning and fertilization for stands that are in susceptible age classes or in
   areas of high bear populations.
 Prune to reduce the carbohydrate to terpene ratio, making the trees less palatable
   (Kimball et al. 1998a).
If precommercial thinning is carried out in a stand known to have bear damage, the forester
may want to consider following up immediately with pruning. Studies have shown that
pruning 40% of the live crown will reduce the carbohydrate/terpene ratio, thus making the
pruned trees less desirable to bears than unpruned trees (Nolte 2003).

5-8                                                                         Animal Damage

The Astoria District employs a variation of this tactic. Their tactic is to select 150 TPA from
the thinned stand and to prune them within one year after thinning to a height of 8 feet. This
does not reach very far into the live crown, but has been found to be successful in reducing
damage. The district also recommends monitoring stands with bear damage for 2-4 years
post-thinning to check damage levels. A discussion of pruning effects is found in Kimball et
al. (1998b),

Control Methods
The following is a summary of the control strategies found in Black (1992). Tree peeling by
bears is a learned behavior (Schmidt and Gourley 1992). The removal of individual bears
causing the damage may reduce the spread of this behavior through the general population.
Some ODF districts are members of cooperatives that pool information and resources for
bear management activities.

Hunting, where permitted by state regulations, may help reduce damage. Hunting works best
when hunters are directed into specific areas. Hunting season should start after the bears
emerge from hibernation, when trees are most susceptible to damage. Providing maps of
bear damage areas will aid hunters and help focus their efforts where damage is occurring.
 Allows recreational taking of bear.
 Reduces bear populations.
 Hunters can be directed to specific areas.
 Landowners do not have many costs.
 May not target bears causing the damage.
 Inaccessible areas are not hunted.
 The locations where bears are taken are seldom reported.
 Biological information about bears is not readily available to game management
 Some people do not like to see bears killed.
 May not reduce damage to trees.

Snaring is the most common method used to trap bears. Spring-activated foot snares are the
most effective. Trapping of problem bears is done by contract through the Animal Damage
Cooperative. The disposition of bears taken in this manner is outlined in a Memorandum of
Understanding between the Animal Damage Cooperative’s contractor and the Oregon
Department of Fish and Wildlife.
 Targets specific areas where bears are damaging trees.

ODF Reforestation Handbook                                                                5-9

   Is the most selective lethal control method.
   Is cost-effective.
   Provides control efforts in areas that are not accessible to hunters.
   Provides game management agencies with biological information and take locations.
 May not be acceptable to some people.

Supplemental feeding of bears during the critical spring time period is an attempt to lure the
bears away from the inner bark and cambium of conifers to something more desirable. The
feeding ends and the feeders are removed in June or early July, when the trees become less
palatable and other natural foods are available.
 Feeding is more acceptable to some people than killing.
 Feeding may reduce damage.
 High costs and labor intensive.
 Long-term effects on tree damage and bear behavior are uncertain.
 Incompatible with hunting.
 Once feeding is started, it is difficult to stop.
 Bears often become destructive when feeding stations are empty, peeling trees and
   damaging the station.
   May not be acceptable to some people.

Relocation of problem bears to other areas has not been successful because it just moves the
problem to another area.
 Relocation is more acceptable to some people than some other bear damage control
 High management costs.
 Bears are often injured, sometime fatally.
 Bears often return.
 May not reduce damage.
 There is no place to take captured bears because most suitable habitat is already

5-10                                                                        Animal Damage

Snowshoe Hares and Rabbits
In localized areas, hare damage may be greater than damage caused by big game animals.
Fluctuations in populations are cyclic, and it is not known if increased damage to plantation
is related to population fluctuations or the suitability of good habitat. A study in Utah
estimated that 6 jack rabbits can consume as much forage as one sheep on winter sheep range
(Black 1994)

Types of Damage and Recognition
Clipping of seedlings by hares and rabbits has a similar appearance. Generally these animals
do not clip branches larger than .25 inch. The clipping is characterized by a clean oblique
cut, at about a 45 degree angle, made by their incisors. This is in contrast to the ragged edge
made by ungulates, which lack upper incisors and tear the twig. Rabbits’ and hares’ teeth are
relatively small, with 0.09-0.10 inch wide incisors. When a hare or rabbit strips bark the
damage is characterized by horizontal tooth marks. Rabbit ―pellets‖ are often evident in
areas with high rabbit use. See Henigman et al. (2003),

Preventive Strategies
   Use larger planting stock that is less affected by rabbit damage, and can grow quickly
    beyond the size where rabbits are no longer a problem.
   Reduce the amount of food and cover (vegetation).
   Use mechanical protection, such as plastic tubes or fencing.
   Use repellents.

Control Methods
Hunting is used to control hare and rabbit populations. However, these animals are resilient
and populations recover quickly

Pocket Gophers
Pocket gophers are very adaptable rodents occupying a wide range of plant communities and
environmental conditions. They are herbivorous and adaptive in their feeding habits. They
spend most of their lives underground and get their name from the external fur-lined cheek
pouches. The availability and quality of forage and the type of habitat affect the density of
gophers in an area (Black 1992).

Types of Damage and Recognition
Gophers feed on a wide variety of plants, preferring fleshy or succulent roots and stems of
herbaceous plants. They injure tree seedlings by root pruning, stem girdling, and stem
clipping. Damage occurs all year, but most damage takes place in winter. Most above-
ground damage occurs under snow. Root damage generally becomes evident during the

ODF Reforestation Handbook                                                               5-11

summer when the foliage starts to turn brown. See
(Black 1994).
Gopher mounds produced from burrowing activities are fan or horseshoe-shaped in
appearance, unlike the volcano-shaped mounds produced by moles (Arjo 2003).

Preventive Strategies
Gopher damage can be reduced by using practices that reduce suitable habitat:
 Minimize disturbance of understory vegetation during harvest to reduce herbaceous
 Reduce herbaceous vegetation with herbicides.
 Use a silviculture system that will protect advanced regeneration and minimize
   understory disturbance.
 Schedule early planting before gophers have a chance to get established in an area,
 Use of larger planting stock, 2-1 or 3-0, that are less susceptible to gopher damage.
 Protecting seedlings with plastic tubes may reduce damage.

Control Methods
   Trapping effectively controls populations when numbers are low and the area is small.
    Trapping is labor intensive.
   Baiting with rodenticides is effective in reducing populations over large areas.
   Fumigants such as aluminum phosphide can also be used in appropriate situations to
    reduce gopher populations.

Porcupines are large rodents, up to 30 pounds, identifiable by the stiff quills that cover much
of the upper body and tail. They can damage trees of all ages, but young trees are most
susceptible. Porcupine damage occurs during late summer through winter, when mature
herbaceous vegetation becomes dry. Porcupines prefer to feed on the dominant and the
codominant trees in a stand. East of the Cascades, porcupines prefer Ponderosa pine. In
western Oregon, Ponderosa pine, Douglas-fir and hemlock are the preferred tree species.

Porcupines utilize caverns in road ballast rock, culverts, old log landings, lava flows, stumps,
or hollow logs for dens. See:
(BC Ministry of Environment, Lands and Parks 1998).

Types of Damage and Recognition
Porcupines feed selectively on trees, selecting individual trees to feed on and leaving nearby
trees undamaged. Damage to smaller trees is usually by basal girdling, while debarking of
the upper stem is more common on larger trees. Damaged trees may have dead tops or

5-12                                                                         Animal Damage

multiple tops resulting from girdling. The bark is gnawed from trees, not stripped, with
horizontal or diagonal toothmarks (vertical toothmarks are also described as an identifier in
some publications). The bark removed by porcupines is more in the form of chips rather than
the strips removed by squirrels. Porcupine incisors are slightly larger in width than those of
most gnawing mammals, approximately 0.14 inch wide. See (Black 1994), and (Henigman et al. 2001).
Tracks are evident in the snow in winter, in the form of trails or furrows in deep snow. Fecal
droppings may also be present beneath damaged trees. They are usually about an inch long,
slender and fibrous.

Preventive Strategies
   Individual high-value trees can be protected by placing a metal sleeve around the bole to
    prevent porcupines from climbing the tree. The flashing should be at least 24 inches
    wide and placed high enough on the tree to be above the maximum expected snow depth.
   Reducing the number of open grown stands and planting a mixture of tree species may
    reduce porcupine damage. Porcupines prefer open grown trees.
   The reduction of artificially created den habitat may be beneficial in some areas (Dodge
    and Borrecco 1992).

Control Methods
Trapping, generally used in conjunction with drift fences, may be effective if travel routes
can be determined and the fences used to intercept and direct the animals. Traps may also be
baited with a fetid scent or apples (Black 1994).
Hunting is probably the most effective method for controlling porcupines. During winter,
daytime hunting can be successful where snow allows tracking. During the summer and
early fall, night hunting is a good technique, especially around wetlands and agricultural
areas. Road hunting during the breeding season, late summer and early fall, can also be
productive (Black 1992).

Woodrats and Squirrels
Woodrats are widespread and adaptable. The dusky footed woodrat is semi-arboreal and is
the species most likely to cause damage to trees (Sullivan 1992). Their large nests, 3-6 feet
high and the same in diameter, are found in trees or sheltered spots on the ground in young
dense stands of Douglas-fir. Woodrats are an important prey for the northern spotted owl,
and this needs to be considered prior to any control activity (Sztukowski and Courtney 2004).
See (Ministry of
Environment, Lands and Parks 1998).
Squirrels do not usually cause major problems. However, both ground and tree squirrels eat
significant amounts of conifer seeds, and tree squirrels have the potential to cause
unacceptable damage to trees. The Douglas squirrel, western gray squirrel, and the red

ODF Reforestation Handbook                                                              5-13

squirrel cause the most serious damage to conifers. Protection is usually needed only on high
value trees, e.g., in progeny sites or selected seed trees.

Types of Damage and Recognition
Damage to trees from woodrats is characterized by the absence of the bark that was stripped
from the trees. Woodrats remove the bark and transport it to their nest site, in contrast to
squirrels, who discard strips of bark beneath the damaged tree. Woodrats do not eat the
cambium, as squirrels and porcupines do. The damage caused by woodrats has a smooth
appearance, in contrast to the rough texture caused by the toothmarks of other gnawing
animals. See
(Ministry of Environment, Lands and Parks 1998).

Preventive Strategies
Silvicultural methods, such as vegetation manipulation to reduce favorable habitat and
thinning, may reduce the amount of tree damage from woodrats.

Control Methods
Trapping, using live traps or snap traps, can be used to remove individual woodrats.

Voles and Mice
There are several species of voles, often called meadow mice, found in Pacific Northwest
forests. Damage by voles and mice is generally not a significant problem. However, in some
situations damage can be extensive. Most of the damage occurs in the winter when they feed
on conifer seedling roots. Voles also feed on newly germinated seedlings, and can girdle
older seedlings, especially when the seedlings are covered by snow.
While conifer seeds can be a part of both animals’ diets, seed-eating is generally not a
problem unless artificial seeding or natural regeneration is being considered.

Types of Damage and Recognition
Gnawing damage caused by voles is characterized by a fuzzy appearance with indistinct
tooth marks. Unlike other small gnawing animals, voles leave a pointed tip when seedlings
are clipped. Voles also strip the cambium from roots and leave pointed root tips (Black
1992). Distinct runways are visible in the matted vegetation.
Deer mice destroy seeds by gnawing a small opening in the hull and eating the seed (Black

Preventive Strategies
Reducing suitable habitat for voles, that is, grasses, is an effective method of preventing
damage from voles. Grass control may be either mechanical or chemical. Before habitat

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manipulation is undertaken, it is important to verify if the problem still exists. Vole
populations are cyclic and can crash very suddenly (Black 1994).

Control Methods
Currently there are no control methods for voles or deer mice.

The beaver is the largest rodent in North America, and is well-known for its tree felling and
dam building abilities. Beavers prefer habitat with hardwood tree species, primarily red
alder, aspen, cottonwood, and willow. They will eat conifers where more desirable food is
not present, but it is not their preferred diet. The falling of individuals trees is generally not a
major problem except in administrative areas such as campgrounds. Beavers may plug
culverts during beaver dam construction, which increases the risk of road damage from
flooding. Tree mortality from flooding caused by their dams can also be significant. See (Oregon Department of Fish and

Types of Damage and Recognition
Beaver feed on herbaceous plants during the summer, but they primarily eat tree bark during
the winter. Characteristic dams and cone-shaped stumps with large wood chips piled around
the base are indicators of beaver activity. Beaver teeth are large, with incisors almost 0.24
inch wide. Peeled branches are usually present in or near the water. See (Henigman et al. 2001).

Preventive Strategies
Individual trees can be protected with a 3 foot fence made from small wire mesh or solid
sheet metal material.
Beaver dam modification may be an alternative where it may be desirable to have beaver, but
minimize their adverse impacts on improvements. See Michigan State University’s
Extension Bulletin E- 2045 (Randall 2000) for details of beaver dam modification,

Control Methods
Trapping is the most common method of removing problem beaver. The results are usually
temporary because the site is soon recolonized.

Arjo, W. M., and D. L. Nolte. 2004. Assessing the Efficacy of Registered Underground
Baiting Products for Mountain Beaver (Aplodontia rufa) Control. Crop Protection

ODF Reforestation Handbook                                                                    5-15

Black, Hugh C., ed. 1992. Silvicultural Approaches to Animal Damage Management in
Pacific Northwest Forests. Gen. Tech. Rep. PNW-GTR-287. Portland, OR: U.S. Department
of Agriculture, Forest Service, Pacific Northwest Research Station: 187-204. (Not available
on line.)
Black, Hugh C., tech. ed. 1994. Animal Damage Management Handbook. Gen. Tech. Rep.
PNW-GTR-332. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific
Northwest Research Station. 236 p.
British Columbia Ministry of Environment, Lands and Parks. 1998. Inventory Methods for
Mountain Beaver, Bushy-tailed Woodrat & Porcupine. Standards for Components of British
Columbia's Biodiversity No. 27. Prepared by Ministry of Environment, Lands and Parks for
the Terrestrial Ecosystems Task Force, Resources Inventory Committee, October 6, 1998,
Version 2.0.
Carraway, L.N., and B.J. Verts. 1993. Aplodontia rufa. Mammalian Species 431:1–10.
Dodge, W.E., and J.E. Borrecco. 1992. Porcupines. In: Black, H.C. tech. ed. Silvicultural
approaches to animal damage management in Pacific Northwest forests. Gen. Tech. Rep.
PNW-GTR-287. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific
Northwest Research Station: 253-270. Chapter 12.
Duddles, Ralph E., and W. Daniel Edge. 1999. Understanding and Controlling Deer Damage
in Young Plantations. Extension Circular 1201, reprinted June 1999. Oregon State
University Extension Service, Corvallis, OR.

Henigman, John, and Tim Ebata, Eric Allen, Joan Westfall, Adriane Pollard, editors. 2001.
Field Guide to Forest Damage in British Columbia. March 2001, Second Edition
MOF/CFS Joint Publication Number 17. Crown Publications, Inc., Victoria, B.C., Canada.
Information Ventures, Inc. 1995. Putrescent Whole Egg Solids: Pesticide Fact Sheet.
Prepared by Information Ventures, Inc. under U.S. Forest Service Contract. November 1995.
Adapted from Insecticides, Brooks, H.L., et al. (1973) Cooperative Extension, Kansas State
University, Manhattan, Kansas.
Kimball, Bruce A., and Eric C. Turnblom, Dale L. Nolte, Doreen L. Griffin, Richard M.
Engeman. 1998a. Effects of Thinning and Nitrogen Fertilization on Sugars and Terpenes in
Douglas-Fir Vascular Tissues: Implications for Black Bear Foraging. Forest Science
Kimball, Bruce A., and Dale L. Nolte, Doreen L. Griffin, Steve M. Dutton, Steve Ferguson.
1998b. Impacts of Live Canopy Pruning on the Chemical Constituents of Douglas-Fir
Vascular Tissues: Implications for Black Bear Tree Selection. Forest Ecology and

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Management 109 (1998) 51-56.
Moser, Brian W. 2001. An Evaluation of Chemical Repellents and Vexar Bud Caps to
Reduce Winter Deer and Elk Browsing on Conifer Seedlings in Northern Idaho. Brian W.
Moser, Potlatch Corporation, Lewiston, ID.
National Wildlife Federation. 2005. eNature: Online Field Guides: Dusky-Footed Woodrat.
Nolte, Dale L. 1998. Efficacy of selected repellents to deter deer browsing of conifer
seedlings. International Biodeterioration and Biodegradation 42:101-107.
Nolte, Dale L. 2003. Developing Approaches to Reduce Wildlife Damage to Forest
Resources. Western Forester, Vol. 48, No. 4 (July/August 2003). Society of American
Foresters, Portland, OR.
Nolte, Dale L., and Kimberly K. Wagner, Andy Trent. 2003. Timber Damage by Black
Bears: Approaches to Control the Problem. 3E32E84—Animal Damage Management.
USDA Forest Service Technology and Development Program and APHIS, 0324-2832-
Oregon Department of Fish and Wildlife. Living with wildlife. Oregon Department of Fish
and Wildlife, Salem, OR.
Randall, Carolyn. 2000. Forest Pest Management. Chapter 9, Vertebrate Pests. Extension
Bulletin E- 2045. Michigan State University, E. Lansing, MI.
Rochelle, James A. 1992. Deer and Elk. In: Black, Hugh C., ed. Silvicultural Approaches to
Animal Damage Management in Pacific Northwest Forests. Gen. Tech. Rep. PNW-GTR-
287. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest
Research Station. p. 333-349.
Schmidt, Wyman, and Mark Gourley. 1992. Black Bear. In: Black, Hugh C., ed.
Silvicultural Approaches to Animal Damage Management in Pacific Northwest Forests. Gen.
Tech. Rep. PNW-GTR-287. Portland, OR: U.S. Department of Agriculture, Forest Service,
Pacific Northwest Research Station. p. 309-331.
Steele, Dale. 2004. Mountain Beaver (Aplodontia rufa) Journal (latest update 10/04/04). Dale
Steele, Stockton, CA.
Sullivan, T.P. 1992. Tree Squirrels, Woodrats, and Beaver. Pages 271-287 in Black, H. C.
(tech. ed.), Silvicultural approaches to animal damage management in Pacific Northwest
forests. Gen. Tech. Rep. PNW-GTR-287. Portland, OR, U.S. Dep. Agric., For. Serv., Pac.
N.W. Res. Sta. 422 pp.
Sztukowski, Lisa, and S.P. Courtney. 2004. Chapter 4, Prey. In: Scientific Evaluation of
the Status of the Northern Spotted Owl. Sustainable Ecosystems Institute, Portland, OR.

ODF Reforestation Handbook                                                               5-17

Walstad, John, and Logan Norris. 1992. Animal Damage Management in the Context of
Integrated Forest Protection. In: Black, Hugh C., ed. Silvicultural Approaches to Animal
Damage Management in Pacific Northwest Forests. Gen. Tech. Rep. PNW-GTR-287.
Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research
Station. Pp. 57-66.

Web Sites
Oregon Occupational Safety and Health Standards
       OAR 437, Division 7, Forest Practices,
       OAR 437, Division 4, Agriculture,
Oregon Department of Forestry, Forest Practices, Notification of Operation – Application for
Oregon Forest Practices Act
       Notification of Operations
Administrative Rules, Department of Fish and Wildlife
       Disposal of Wildlife, OAR 635-002
       Oregon Furbearer Trapping and Hunting Regulations, OAR 635-050;

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