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The Use of Cattle as a Management Tool for Wildlife
in Shrub-Willow Riparian Systems 1
Henry 0. Krueger
2
and Stanley H. Anderson
3
Abstract.--In high altitude shrub-willow riparian systems
cattle can have a beneficial effect on wildlife by creating
tunnels throughout the habitat. Mean tunnel heights for two
study areas were 0.75 and 0.95 m with 41% of the shrubs sampled
forming tunnels in each study area. These tunnels benefit
birds and mammals by opening up willows which in turn increases
the grassland habitat and structural diversity of vegetation.
INTRODUCTION
Managers of riparian communities have often
been caught in the middle of the controversy surrounding the impact of cattle grazing. Platts (1979,
1982) has given detailed reviews of this controversy
and has reported how grazing can have deleterious
effects on riparian vegetation, stream channels,
streambanks, water quality, and fish populations.
Roath and Krueger (1982) consider one of the major
problems in the grazing of riparian systems as a
dilemma between managing shrubs versus the management
of herbacious vegetation. However, as Platts (1985)
has stated the proper grazing of streamside vegetation requires controlled animal distribution.
Few studies have been performed on the interaction of cattle with shrub-willow (Salix~.)
riparian systems in mountainous regions. Lorz (1974)
conducted a fish study on the Little Deschutes River
and found that the grazing of dense willow communities had no effect on fish populations when compared
to ungrazed dense willow sites. Knopf and Cannon
(1982) found that cattle altered the structure of
shrub-willow riparian vegetation under diff~rent
grazing systems in northcentral Colorado.
In high altitude (2438 m - 8000 ft) shrub-willow
riparian systems of the North Platte River drainage
cattle have a beneficial effect on small mammal and
bird communities by creating and maintaining tunnels
throughout the willow habitat. These tunnels are
created by cattle busting out the lower branches of
1
Paper presented at the symposium on riparian
ecosystems and their management: reconciling conflicting uses. (Tucson, Arizona, April 16-18, 1985).
2
Research Assistant, Wyoming Cooperative Research Unit, Dept. of Zoology and Physiology, Box
3166, University Station, Laramie, WY 82071.
3
unit Leader, Wyoming Cooperative Research
Unit.
300
willows and appear to provide access to the interior
and lower portions of the shrubs, thus increasing
structural diversity.
The major objectives of this study were 1) to
document the extent of tunneling in a moderately
grazed shrub-willow system as well as a system that
has a history of overuse; 2) to determine shrub
densities in both sites to see if grazing practices
may have contributed to altered willow densities;
and 3) to determine if bird species respond to willow
densities.
STUDY AREAS
This study was conducted over a three year
period (1982-85) on two shrub-willow riparian communities located in the headwaters of the North
Platte River drainage of southeastern Wyoming. Both
sites were located in the mountains of the Medicine
Bow National Forest and were dominated almost exclusively by shrub-willow species (Salix~.) 0.5 m 4.2 m high (x = 2.0). Leafout of willows does not
occur until early June in both sites. Leaves begin
falling in late September or early October. Annual
precipitation averages between 51 and 64 em, most
of which is in the form of snow. Snowpack exceeds
three feet in both sites and livestock operations
are strictly seasonal.
Pelton Creek (2535-2585 m): Two sites were
established along this third order stream located
in the Medicine Bow Mountains. The stream is bordered by dense willow stands dominated by Salix
geyeriana. Sedges (Carex ~.) and grasse_s____
(Gramineae) also occur in the riparian zones interspersed with the willows. The drier upslopes are
forested with lodgepole pine (Pinus contorta). The
mid-level upslope areas between the willows and
lodgepole are occupied by big sagebrush (Artemesia
tridentata) and Idaho fescue (Festuca idahoensis).
Big Creek (2430-2542 m): Three sites were
located along this third order stream in the Sierra
Madre Mountains. Two of these sites were located
on the South Fork of Big Creek while the remaining
site was located on the Middle Fork. These streams
are bordered by moderately dense willow vegetation
dominated by Salix geyeriana. Sedges and grasses
were also interspersed with the willows. Upslopes
are dominated by sagebrush (Artemesia tridentata)
with some lodgepole and aspen (Populus tremuloides)
stands on hillsides.
From both randomly selected shrubs and shrubs
in which sightings occurred, a point-centered sampling
technique was used to estimate shrub density.
Quadrants were designated as northwest, northeast,
southeast, and southwest. A new measurement not
recorded by Knopf and Cannon (1982), the tunnel
height, was also recorded for each quadrant when
appropriate. The tunnel height was defined as the
height of open space between two shrubs when the
shrubs were in contact with each other (intershrub
distance= 0).
GRAZING HISTORIES
The grazing histories on the two study areas
are quite different. Pelton Creek has a long history
of season long and semi-deferred management systems.
Records of the USDA Forest Service go back to the
1920's for Pelton Creek and show a continual decrease
in the number of animal unit months (AUM's) allocated
(1920's - 5,015 AUM's; 1940's - 2,000 AUM's; 1950
to 1967 - 1485 AUM's; and from 1967 to present 300 head at 900 AUM's). Use at Pelton Creek has
been less than or equal to permitted use. The season
of use prior to 1957 was from 6 June to 30 September
although permittees did not gain access until 1 July
or later due to snowmelt. From 1957 to present the
season of use has been from 1 July to 30 September.
Distribution of cattle had been a problem in the
past, but the permittee has used a full-time rider
since the mid-70's who has kept the cattle in small
groups which are regularly moved in the allotment.
Range condition for this allotment has improved
substantially since 1967 according to Forest Service
reports. In addition to the rider, road traffic
and fishermen also contribute to the movement of
cattle.
All sites in the Big Creek drainage also have
a long history of grazing, but range condition
indicates past overuse (Forest Service report). The
South Fork of Big Creek has just recently been
acquired by the Forest Service who has initiated a
deferred-rotation management system and also has
implemented range improvements. Currently 714
yearlings are grazed for 1750 AMU's in the allotment
with the season of use from 6 June - 30 September.
In the deferred-rotation system the season of use
has been divided into thirds.
To determine if birds showed a preference for
certain shrub: densities, densities surrounding
bird sightings and randomly located shrubs were
compared. Preference was detenmined when mean
densities from bird sightings were significantly
different from random samples (P < 0.05). Only
species with sample sizes greater than ten were
included in the analysis.
The number of sampling stakes in the two
Pelton Creek sites were 50 and 70 for a combined
total of 120 stakes. The number of stakes in the
three Big Creek sites were 70, 22, and 15 for a
combined total of 107 stakes. For the purpose of
this paper all study sites were combined in each
of the two study areas.
RESULTS AND DISCUSSION
Tunnel heights were recorded for all shrubs
that had an intershrub distance of zero in the
point-center quarter sampling scheme. The sample
size for tunnel heights at Pelton Creek was 189
and at Big Creek 177. Of the quadrants searched
in both study areas, 41% of the quadrant shrubs
were in direct contact with the center shrub which
resulted in the formation of tunnels. Thus, both
study areas had the same percentage of tunnels, even
though Big Creek has a history of overuse.
Shrub densities were calculated using a modified version of the Eberhardt technique (1967). The
formulas used in our computations were as follows:
ni
where
the density at each sampled shrub
represented as number of shrubs
found around a center shrub divided
by the area searched (i = 1, k),
METHODS
Sampling in each study site was conducted in
the same manner as Knopf and Cannon (1982). The
fundamental sampling units were willow shrubs which
were defined as clumps of stems that exceeded 0.5 m
in height. Sampling points were located using a
systematic random design with stakes positioned at
random distances from the stream at 50 m intervals.
Each sampling point served as both a census stake
and point from which random samples were selected.
The shrub nearest the random point was used as the
random sample. When censuses were conducted from
these random points, shrubs in which sightings
occurred were flagged and later sampled. Bird
data collected from all three years of the study
were used in the analysis.
301
k
the number of sampling points in a
study area,
n.J_
the number of shrubs found at the ith
sampling point,
Y . Y , Y , Y
1
2
3
4
D
~
D.J_
i=l
k
= the distance searched
until a shrub was found
or 100 m was reached in
the NW, NE, SE, and SW
quadrants,
v(D) = ~=l (Di
n) 2
k - 1
A)
1---------1·---------tl EM FL (11) * *
1----------te-----------t(
AM RO (2. 2) *
Jt-·-----et-------11 WIWA
• II
e
WCSP(123)
LISP
~80) ••
I SOSP
(90)
**
J----..,...-------·1---------tJ
B)
•
(185)
RAN D0 M (120)
I EMFL (16)
•
I AMRO
(66)
I • I YEWA (119)
•
I GTTO (56)**
~----·--------tJ Ll s p (21)
e
J
SOSP (53)
e
0
t.OO
400
600
800
RANDOM
1000
1100
(107)
1600
1400
1800
2.000
~'ZOO
2400
2600
2.800
3000
DENSI TV
Figure 1.--Mean densities and 95% confidence intervals of willow shrubs for birds and random samples of
(A) Pelton Creek and (B) Big Creek. All densities are expressed as shrubs per hectare. Species names are
abbreviated as in appendix 1. Sample sizes are given in parentheses. * = significant difference at P(O.lO,
** = significant difference at P<O.OS.
The comparison of the shrub densities between
the two study areas are given in Table 1. A two
sided t-test assuming unequal variances was computed
to test for a significant difference between the
study area densities (Sokal and Rohlf 1981). Pelton
Creek was found to have a statistically higher shrub
density than Big Creek (P<0.05).
Table 1.--Shrub densities calculated for randomly
located shrubs in each of the two study areas.
Densities are expressed as the number of shrubs
per hectare.
n
X
sd
95% confidence
interval
Pelton Creek
120
2007
2792
1503 - 2522
Big Creek
107
897
1221
663 - 1131
on the other hand had several bird species preferring
different densities. In Pelton Creek, densities
for Lincoln Sparrows, Empidonax flycatchers, WhiteCrowned Sparrows and American Robins were significantly different from random samples (P<0.05, for
American Robin P<O.lO).
The increase in bird species preferring certain
shrub densities in Pelton Creek can be explained
by greater variation in willow densities. This is
supported by the larger confidence interval for
Pelton Creek in Figure 1 and the larger standard
deviation for density in Table 1. Thus, Pelton
Creek has a greater variety of willow densities
from which birds can, and do choose.
This study was designed to document how cattle
can affect shrub-willow riparian vegetation. Cattle
impact riparian habitats by trampling vegetation,
compacting soils, and changing plant species composition (Platts 1979). In dense stands of shrubwillow riparian habitats the major impact of cattle
is to alter the structure and de~sities of willows
within the community. Knopf and Cannon (1982) concluded that cattle in shrub-willow riparian habitats
altered the shape, size, volume, and quantities of
live and dead stems in the bushes. This influence
To examine how different bird species in each
study area responded to shrub-willow densities,
shrub densities around bird sightings were compared
to random samples using t-tests (P=0.05). The
results displayed in Figure 1 indicate that birds
of Big Creek, with the exception of Green-Tailed
Towhees (for scientific names see appendix 1), show
no preference for shrub densities. Pelton Creek
302
on structure and distribution can have both
beneficial and deleterious effects on wildlife.
Structural diversity in vegetation is also
affected by the density of willow shrubs. The
mean density of shrubs in Pelton Creek was 2007
shrubs per hectare and in Big Creek 897 shrubs per
hectare. Pelton Creek had a statistically higher
density of shrubs (P<.05) than Big Creek. Big
Creek has historically been overused which may
contribute to a lower shrub density. Knopf and
Cannon (1982) concluded that grazing practices and
pressure decreased the density of shrubs in one of
the three pastures on their shrub-willow study area.
Pelton Creek on the otherhand, has had use below the
permitted level and good control over the distribution of cattle in the allotment. We believe that
this management practice has produced the high
density of shrubs in Pelton Creek. We also believe
that overgrazing has contributed to reduced shrub
density in Big Creek.
One benefit to wildlife in dense shrub-willow
communities is the formation of tunnels throughout
the shrub-willow habitat. Both study sites were
found to have 41% of the shrubs that were sampled
forming tunnels. The formation of tunnels occurs
when cattle move through willows busting out lower
branches. The concept of tunnels is an extension
of an idea proposed by Knopf and Cannon (1982),
who described the alteration of shrub structure
by cattle as a "notching" effect. When two shrubs
are in contact with each other, the two notches
form the sides and roof of a tunnel. In most cases
tunnel width increased as tunnel height increased.
Tunnel floors were covered by a mat of grasses
and/or sedges. Tunneling therefore had the affect
of increasing the amount of grassland habitat.
Heights of tunnels in the two study areas
varied from 0.1 to 1.8 m with the mean height for
Pelton Creek being 0.75 m
(s=0.32) while the
mean height for Big Creek was 0.95 m
(s=0.37).
The means and standard deviations (s) of tunnel
heights tend to correspond closely to heights one
would expect for cows, calves, steers, and yearltngs.
Of course not all tunnels are created by cattle,
some are formed by deer and elk while others may
be formed by beaver or phenomena we have not yet
observed. However, when one considers the large
number of cattle that have historically been
grazed in the two study areas it seems logical to
conclude that cattle have been the major contributor
to tunnel formation.
Biologically, tunnels are important to both
small mammals and birds because they create structural diversity as well as increase the amount of
grassland habitat (grasses and sedges) within the
shrub-willow community. Birds are particularly
responsive to the structural diversity of vegetation
(MacArthur and MacArthur 1961, Roth 1976). Small
mammal diversity was found to increase in channelized
streams becaus~e of the increase in grassland vegetation in these habitats (Geier and Best 1980). The
increase in grassland vegetation contributes to
habitat diversity which in turn can increase the
diversity of the insect community (Price 1975).
Insects are important to birds as a valuable food
source. Another potential advantage of tunnels
for both birds and small mammals is the cover they
provide from aerial predators such as Sharp-Shinned
Hawks. Birds were frequently observed flying through
the tunnels to forage and move through the shrubwillow vegetation. This was particularly true for
birds traveling to and from nests.
The benefit gained from grazing dense shrubwillow sites is the formation of tunnels throughout
this habitat. This can be achieved when a manager
can control the distribution of cattle in his
allotment to prevent the detrimental effects of
overgrazing. These tunnels benefit birds and
mammals by opening up the willow habitat which in
turn increases the grassland habitat and stru.ctural
diversity of vegetation.
303
Cattle appear to affect bird species by altering
shrub-willow structure and density. The logical
conclusion from our bird results is that different
grazing practices can be used to create a wide
spectrum of willow densities that in turn should
lead to a diverse avifauna. However, this conclusion
is not a sound one. Enough riparian habitat has
been overgrazed to create plenty of low density
shrub-willow habitats. Another consideration is
the fact that all the species in Figure 1 for Big
Creek and almost all the species for Pelton Creek
are generalists, which means they are not dependent
on shrub-willow habitat. Still another consideration
is the fact t·hat once structural changes have been
made by grazing practices, recovery of high shrubwillow densities will take a very long time (Knopf
and Cannon 1982).
The most important consequence of grazing in
riparian systems is the impact it may have on the
aquatic ecosystem. Meehan and Platts (1978) reported
that sedimentation from streambank erosion, removal
of vegetative and bank cover, and animal wastes all
contribute to the degradation of water quality and
fish populations. These perturbations may not be
as severe in dense shrub-willow riparian communities.
Lorz (1974) found that the presence or absence of
grazing in dense willow habitats had little effect
on fish populations on the Little Deschutes River.
This could be attributed to the anchoring of the
stream banks by root systems, and dense structure
preventing easy access to streams.
The responsible management of riparian habitats
are in the hands of land managers. Sound management
of riparian habitats is essential if we are to
maintain fisheries and wildlife communities in the
western United States. In the management of shrubwillow riparian habitats found in the higher elevations of the Rocky Mountains, cattle can be used
as a management tool to benefit small mammal and
bird communities by creating tunnels in dense vegetation. However, managers must be able to control
the distribution of cattle in allotments to prevent
the detrimental effects of grazing.
Roath, L. R. and W. C. Krueger. 1982. Cattle
grazing influence on a mountain riparian
zone. Journal of Range Management 35:100-103.
Roth, R. R. 1976. Spatial heterogeneity and bird
species diversity. Ecology 57:773-782.
Sakal, R. R. and F. J. Rohlf. 1981. Biometry.
Second edition. W. H. Freeman and Company,
San Francisco, CA. 859 p.
ACKNOWLEDGEMENTS
We thank USDA Forest Service Rocky Mountain
Forest and Range Experiment Station for funding
this study. Also George Menkens and Cherry Keller
of the Wyoming Cooperative Research Unit for their
comments on various forms of this manuscript.
LITERATURE CITED
APPENDIX 1
Eberhardt, L. L. 1967. Some developments in
'distance sampling'. Biometrics 23:207-216.
Geier, A. R. and L. B. Best. 1980. Habitat
selection by small mammals of riparian
communities: evaluating effects of habitat
alterations. Journal of Wildlife Management
44:16-24.
Lorz, H. W. 1974. Ecology and management of brown
trout in Little Deschutes River. Oregon
Department Fish and Wildlife Fisheries Research
Report 8. 49 p.
Knopf, F. L. and R. W. Cannon. 1982. Structural
resilience of a willow riparian community to
changes in grazing practices. in Peek, J. M.
and P. D. Dalke (Ed.). Wildlife-livestock
relationships symposium: Proceedings 10.
University of Idaho, Forest, Wildlife, and
Range Experiment Station, Moscow, Idaho.
614 p.
MacArthur, R. H. and J. W. MacArthur. 1961. On
bird species diveristy. Ecology 42:594-598.
Meehan, W. R. and W. S. Platts. 1978. Livestock
grazing and the aquatic environment. Journal
of Soil and Water Conservation 33:274-278.
Platts, W. S. 1979. Livestock grazing and
riparian/stream ecosystems - an overview.
p. 31-34. ln Grazing and riparian/stream
ecosystems forum proceedings. Trout Unlimited,
Vienna, Va.
1982. Livestock and riparian fishery interactions: what are the facts?
Transactions of the 43rd North American
Wildlife and Natural .Resource Confei:-ei1ce.
p. 507-:515.
--------------- and R. L. Nelson. 1985. Streamside
and upland vegetation use by cattle. Journal
of Rangelands 7:5-7.
Price, P. W. 1975. Insect Ecology. John Wiley
and Sons, NY. 514 p.
304
Common Name
Scientific Name
Abbreviation
Sharp,;..Shinrled
Hawk
AcciEiter
striatus .
SSHA
Empidonax
Flycatchers
EmEidonax
EMFL
American
Robin
Turdus
migrator ius
AMRO
Yellow
Warbler
Dendroica
Eetechia
YEWA
Wilson
Warbler
Wilsonia
pusilla
WIWA
Green-Tailed
Towhee
PiEilo
chlorurus
GTTO
Song
Sparrow
MelosEiza
melodia
SOSP
Lincoln
Sparrow
MelosEiza
lincolnii
LISP
White-Crowned
Sparrow
Zonotrichia
leucoEhr;ys
WCSP
~·