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CHAPTER 10 – ANIMAL RESPONSE TO HABITAT CHANGES
Contents
11
ANIMAL INTRODUCTION
12
TIMBER HARVEST
13
13.1
13.2
13.3
SLASH DISPOSAL
Unburned Slash
Burned Slash
Piling and Burning
14
WILDFIRE
15
ANIMAL USE
16
SELECTED REFERENCE
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CHAPTER 10 – ANIMAL RESPONSE TO HABITAT CHANGES
*11 – INTRODUCTION. To maintain animal use of forest resources within
acceptable levels, resource managers must have a basic understanding of
physiological requirements, general behavior, and responses of animals to
habitat changes. Responses of animals to specific habitat changes are not
always clear-cut or the same for a given condition. Different animal species
often respond differently to similar habitat treatment. Because of these
dynamic variables, management and control planning must be site specific. No
single method of control should be universal.
All animals need food, water, shelter, and space. Significant changes in the
distribution, relative abundance, or type of food, water, and shelter
available can influence animal behavior and cause a change in population
density or use of an area by a particular species. Some species will find an
increase in the type of habitat they prefer and benefit. Other species will
find the habitat they prefer decreased, and be adversely affected.
Changes in numbers and distribution of animals and intensities of plant use
can be expected when land-management activities alter the habitat. Forest
trees and their seeds constitute a portion of the natural diet of many forms
of wildlife. For example, big-game feeding on conifers is directly related
to their preference for particular tree species and to the availability of
other preferred foods at the time.
12 – TIMBER HARVEST. Most animal species and their foods are relatively
scarce under a closed canopy. Timber harvest has the direct effect of
opening the canopy, allowing sunlight to penetrate to the ground. High
quality wildlife food develops and the carrying capacity of the land is
increased.
Animals can quickly reproduce to the carrying capacity of their habitat. As
numbers increase and exceed available food supplies, overuse of the habitat
may result. Animal feeding on trees often becomes critical when overuse
reduces supplies of other foods. Nevertheless, browsing animals often use
the succulent, highly palatable new growth on Douglas-fir and certain other
conifers even with an abundance of other foods available.
Animal movements in search of food are closely related to availability and
distribution of cover. Small forest openings are usually fully utilized by
big game. Large openings receive their greatest use near the “edge.” Use of
inner portions of large openings usually varies with the amount of escape
cover remaining within the opening or that eventually develops.
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*Big game habitat carrying capacity increases rapidly as the diversity and
volume of low-growing vegetation increases after clearcutting or wildfire.
This upward trend may continue 20 to 30 years after logging, or until tree
canopies close and begin to shade out the understory. Delays in
reforestation may extend this period of high productivity, but adjacent units
cannot be harvested creating new big game habitat until the current unit is
reforested. As the tree canopy closes, the amount, diversity, and
nutritional quality of understory vegetation decreases, and habitat carrying
capacity declines. However, by this time new adjacent or nearby units may
have been harvested creating ample browse. Changes in big-game habitat
carrying capacity may be roughly proportional to the changes in habitat
resulting from forest management.
Although the cycle of population development for deer and elk may occur in
each area of the managed forest, only small portions of the forest may be in
the same phase at the same time. Changes on one unit may be masked by
fluctuations in another in a different successional stage.
Timber management often results in quality big-game habitat, particularly on
winter ranges. As the quality of browse of the harvested area is reduced by
successional trends, new areas can be harvested. In order to keep their
chain of events in motion, animal damage protection of young conifers may be
necessary.
The type and quality of game habitat created by timber management is
determined largely by the systems of cutting and slash management.
Clearcutting sets back plant succession and usually results in temporary
production of large quantities of forage. Shelterwood cutting produces
similar but smaller increases in big-game carrying capacity than does patch
clearcutting.
13 – SLASH DISPOSAL. Slash disposal and planting site preparation practices
often have direct effects on wild and domestic animal use.
13.1 – Unburned Slash. Rabbits, hares, and many species of rodents are
extremely secretive in their behavior and depend on easily accessible cover
for protection from predators. Entire home ranges may exist in small areas
where food and cover are abundant. This is particularly true in areas with
unburned slash. Under these conditions, population density often is
controlled only by space requirements of individual animals.
Established populations of rabbits, hares, and rodents may expand due to the
favorable habitat provided by unburned slash. These species will utilize
available food, including tree seeds and seedlings.
Unburned slash provides same protection for young trees by restricting biggame and cattle movement and by reducing exposure of trees. Most of the low,
herbaceous, and shrubby vegetation responds quickly to the increased light
and moisture produced by canopy removal. This improved food source attracts
big game may, in turn, reduce browsing pressure on both natural regeneration
and planted trees.
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*13.2 – Burned Slash. Broadcast burning of logging slash destroys some small
mammals and creates extreme changes in the habitat. Changes in the
availability of food and cover directly affect the composition, distribution,
and abundance of small mammal populations. Animals also may be affected by
minor changes in the microclimate, such as soil-surface temperature, water
penetration, and air movement.
Gashwiler (1959) studied small-mammal populations in Douglas-fir clearcutting
before and after logging. He found that deer mice increased after slash
burning, but chipmunks, hares, and redbacked voles decreased.
Burning usually produces a different plant community than if the area had not
been burned. Predicting such vegetational change or magnitude of change
resulting from fire is difficult. Pengelly’s study (1961) of broadcast
burning of slash in northern Idaho led him to conclude that “. . . fire is a
rough and largely unpredictable tool due to the following variables: time
and intensity of burn, homogeneity of burn, kind and availability of fuel and
seed source, and growing conditions during the first season after the fire.”
Steen (1966) reported significant vegetational differences between burned and
unburned slash in a study near Oakridge, Oregon. Affected were plant
composition and rates at which different plant communities reoccupied
clearcutting.
Hot burns tend to favor herbaceous plants and specific shrubs, such as red
stem ceanothus. Cold burns tend to favor shrubs present in the understory at
the time of harvest. These shrubs simply proliferate by rapid growth with
the increased light available.
Planting immediately after slash removal has been one of the main methods to
minimize damage from rabbits and hares. Piling of slash and planting small,
containerized stock have renewed rabbit and hare damage problems in many
areas.
13.3 – Piling and Burning. On many areas, especially on the more level
ground, slash is often piled using bulldozers prior to burning.
Treatment leaving 20 to 30 tons per acre of slash is generally recommended.
This favors conifer and browse shrubs regeneration. Severe treatments that
pile all of the slash reverts plant succession to the most primary stages.
In these stages grasses and herbs usually predominate. Severe site
preparation seems to stimulate pocket gopher and vole activity.
Planting immediately after slash removal has been one of the main methods to
minimize damage from hares and rabbits. Piling of slash and planting of
small, containerized stock have relieved problems of hare/rabbit damage in
many areas. Slash burning has helped reduce mountain beaver population for
short periods (Motobu et al. 1975)
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*14 – WILDLIFE. Animal populations respond to the habitat changes after
wildfire similar to changes after broadcast burning of slash. During the
revegetation period, wildlife species may be most abundant in the
successional stage with the greatest diversity of plants.
The rate at which deer and elk use a natural burn is influenced by the size
of the burn, abundance of food, and the amount of escape cover available.
15 – ANIMAL USE. The basic principles that relate to animal/forage
preference may be grouped into five categories (Heady 1964). These are
palatability; associated forge species; climate, soil, and topography; kind
of animal; and animal physiology. Understanding the nature of these factors
will help land managers recognize and possibly control some of the complex
and interrelated influences governing animal use. A brief summary of
important elements associated with each of these groups follows:
1. Palatability. Palatability has been defined as a plant characteristic
that stimulates a selective animal response. Some factors found to affect
palatability are chemical composition; proportion of leaves, stems, and
fruits; plant-growth stages; past-grazing use; climate; topography; soil
moisture; and fertility. Other items that may be related to palatability,
such as texture, odor, and external plant form, have received only cursory
attention.
2. Associated Species. Some plant species growing in one community are
preferred more than the same species growing in dissimilar plant communities.
Thus, certain plant species, such as conifers, may be used heavily when
sparsely distributed through an area of preferred forage species.
3. Climate, Soil, and Topography. These factors have been mentioned as
affecting palatability, but they probably have a more important effect by
influencing animal behavior. Changes in temperature, rainfall, soil texture,
percent slope, and moisture content of foliage often change animal
preference.
4. Forage Preference: Preferences of animal species differ among plants,
parts of plants, or plants at certain growth stages. Animal preference has
been related to animal conditions such as fatness, pregnancy, lactation, and
hunger. Senses such as sight, taste, smell, touch, instinct, and experience
also influence preference. Preferences of individual animals also may differ
from season-to-season, day-to-day, or even within a day.
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*5.
Impact of Use: Browsing animals, such as big game, can greatly
affect their own food supply. Deer and elk thrive in the shrub stage of
succession that develops after logging or fire. Heavy use of these subclimax
forests may retard plant succession, which prolongs the productivity of the
habitat for big game and the exposure of trees to browsing. Little is known
about the cumulative effects of animal use on forest succession and animal
damage. The interaction of animals with their habitat has been demonstrated
on the Olympic National Forest where small study plots were fenced to exclude
deer and elk. The exclusion of browsing animals permitted low shrubs to
develop rapidly. This, in turn, provided excellent cover for rabbits and
rodents. Under these conditions, destruction of Douglas-fir trees inside the
big-game exclosure by rabbits, mice, and mountain beavers exceeded losses on
the outside. Average tree heights were 30 percent greater outside the
exclosure where big-game browsing had reduced small-mammal cover and
vegetative competition.
Pocket gophers were observed by Moore and Reid (1951) to adversely affect
plant composition in several ways: favored foods were gradually removed and
replaced by those of lower palatability; soil excavated from runways
suppressed plants on which it was deposited; soil mounds were quickly
occupied by annuals that were usually less desirable than the original
perennial vegetation; and unused runways provided refuge for other
herbivorous rodents such as deer mice and meadow mice. Gophers also
prevented natural improvement of mountain meadows that were in pool
condition, but did not limit improvement of meadows in fair or better
condition.
A long-term cooperative study between the Forest Service and University of
Idaho is being conducted on the Nez Perce, Idaho Panhandle, and Clearwater
National Forests. The general objectives of this study are to quantify and
qualify the affects of animal use and physical factors on tree establishment
and growth in selected clearcut areas with normal succession disrupted by
cattle grazing.
Uncontrolled grazing by big game or livestock greatly influences soil
compaction and range condition. With time, plant communities may be
completely altered. The more obvious effects are changes in plant
composition, density, vigor, soil structure, and rate of soil erosion.
All wildlife species are responsive to both subtle and dramatic modifications
of their habitat. Thus, the type of land use practiced will influence their
distribution and density.
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*16 – SELECTED REFERENCES.
Asherin, Duane A. 1976.
Changes in elk use and available browse production on North Idaho winter
ranges following prescribed burning. In Elk-Logging-Roads Symp. Proc.
(Moscow, ID, December 16-17, 1975) Univ. of Idaho. Moscow, ID. PP. 122134.
Black, H. C., ed. 1974.
Wildlife and Forest Management in the Pacific Northwest.
Univ., School of Forestry, Symp. Proc. 236 pp.
Oregon State
Black, H., R. J. Scherzinger, and J. W. Thomas.
Relationships of Rocky Mountain elk and Rocky Mountain mule deer to timber
management in the Blue Mountains of Oregon and Washington. In Elk-LoggingRoads Symp. Proc. (Moscow, Idaho, December 16-17, 1975), Univ. of Idaho,
Moscow. pp. 11-31
Gashwiler, J. S. 1959.
Small mammal study in west-central Oregon, J. of Mammal.
40(1):128-138.
Hagar, D. C. 1960.
The interrelationships of logging, birds, and timber regeneration in the
Douglas-fir region of northwestern California, Ecol. 41(1):116-125.
Heady, H. F. 1964.
Palatability of herbage and animal preference.
J. Range Manage.
17(2):
Hooven, E. F. and H. C. Black. 1976.
Effects of some clearcutting practices on small-animal populations in
western Oregon. Northwest Science 50(4):189-208.
Irwin, Larry L.
Effects of intensive silviculture on big game forage sources in Northern
Idaho. In Elk-Logging-Roads Symp. Proc. (Moscow, ID, December 16-17,
1975), Univ. of Idaho. Moscow, ID. pp. 135-142.
Lawrence, W. H. 1967.
Effects of vegetation management of wildlife. In Herbicides and vegetation
management in forests, ranges, and non-crop lands. Symp. Proc. Oregon
State Univ., School of Forestry, Corvallis. pp. 88-93.
Moore, A. W. and E. H. Reid. 1951.
The Dalles pocket gopher and its influence on forage production of Oregon
mountain meadows. USDA Circular No. 884. 36 pp.
Motobu, D., J. Todd, and M. Jones. 1975.
Effects of slash burning on mountain beaver populations and movements.
Weyerhaeuser Forestry Res. Tech. Rep. 40/4600.75.24. 7.
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*Pengelly, W. L. 1961.
Ecological effects of slash-disposal fires on the Coeur d’Alene National
Forest, Idaho. Printed by Northern Region, Forest Service, USDA, Missoula,
Montana.
Steen, H. K. 1966.
Vegetation following slash fires in one western Oregon locality.
Science 40(3):113-120.
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Northwest