Full text of DOI:10.1672/0277-5212(2002)022[0139:SAVRTS]2.0.CO;2

WETLANDS, Vol. 22, No. 1, March 2002, pp. 139–148
2002, The Society of Wetland Scientists
᭧
STREAMBANK AND VEGETATION RESPONSE TO SIMULATED
CATTLE GRAZING
Warren P. Clary and John W. Kinney
Rocky Mountain Research Station, Forest Service
U.S. Department of Agriculture
316 E. Myrtle St.
Boise, Idaho, USA 83702
E-mail: jccwpc@aol.com
Abstract: Simulated grazing techniques were used to investigate livestock impacts on structural and vege-
tation characteristics of streambanks in central Idaho, USA. The treatments, continued over two years, con-
sisted of no grazing, simulated moderate early summer grazing, simulated moderate mid-summer grazing,
and simulated heavy season-long grazing. The moderate treatments depressed the streambank surface about
3 cm, while the heavy season-long treatment resulted in an 11.5-cm depression. There were no differences
between the no-grazing and moderate-grazing treatments for change in stream width, bank angle, bank retreat,
or root biomass. The heavy season-long treatment, however, produced significant changes in these variables.
Ϫ1
The amount of foliage biomass (i.e., kg ha ) removed by treatment was similar between the two years of
study for the moderate treatments. The foliage removed from the heavy season-long treatment plots greatly
decreased in the second year as plant growth decreased. Ten months after the last treatment application, the
average spring foliage growth was 20–43% lower on the moderate treatment plots and 51–87% lower on
the heavy season-long treatment plots than on the untreated control plots.
Key Words: riparian, mountain meadow, root biomass, stream channel, streambank deformation, simulated
grazing
INTRODUCTION
Riparian zones are major components of aquatic
vertebrate food resources and habitats (Platts 1983,
Gregory et al. 1991, Murphy and Meehan 1991). Both
research and anecdotal evidence suggest that heavy
cattle grazing negatively impacts fish habitats by re-
moving the cover of overhanging banks and vegetation
and by causing deposition of fine sediments on spawn-
ing gravels and in pools (Meehan and Platts 1978, Ar-
mour et al. 1991). The benefits of a vigorous herba-
ceous plant community, and therefore of greater root
length density and root mass, include greater resistance
to particle erosion and greater resistance to streambank
compression and shear. This is particularly true in al-
luvial meadow streambanks (Kleinfelder et al. 1992,
Dunaway et al. 1994). Greater stem and foliage length
also provide protection to the substrate surface under
conditions of inundated flow (Clary et al. 1996, Skin-
ner 1998).
Grazing animals primarily affect foraging areas by
defoliating plants, trampling soil and plants, and ex-
creting wastes that may nourish plants (Heitschmidt
1990, Matches 1992). Defoliation of plants can greatly
affect production of both foliage and roots resulting in
decreased plant vigor, biomass, and species diversity
(Jameson 1963, Kauffman and Krueger 1984, Briske
1991). A major effect of soil compaction by hoof ac-
Riparian ecosystems are normally the most ecolog-
ically productive and diverse of all terrestrial habitats
(Gregory et al. 1991, Naiman et al. 1993). In the Unit-
ed States, riparian zones have been greatly reduced in
area by human activity (Swift 1984). In addition, the
functional characteristics of the remaining areas are
often reduced through chronic impacts in or near the
riparian zone. Such impacts include stream impound-
ments, irrigation diversion, channel modification, log-
ging, pollution, recreation, and grazing (Swift 1984,
Knopf et al. 1988, Busch and Scott 1995).
Concern about the impacts of livestock, particularly
cattle, grazing in riparian zones is widespread across
the public lands of the western United States. Live-
stock grazing has reportedly damaged about 80% of
the streams and riparian ecosystems in the arid regions
of western United States (Belsky et al. 1999). Ap-
proximately 30 water quality, stream channel mor-
phology, hydrology, riparian soil, and instream vege-
tation characteristics are negatively affected by im-
proper livestock use (Belsky et al. 1999). Many re-
ductions in riparian native biodiversity have been
associated with the presence of livestock grazing (Saab
et al. 1995, Fitch and Adams 1998, Belsky et al. 1999).
139

140
WETLANDS, Volume 22, No. 1, 2002
Table 1. Some comparative characteristics of the three study sites at the initiation of the study. Means and standard errors (in parentheses)
are presented.
Characteristic
Stanley Creek
Park Creek
Thatcher Creek
Wetted stream width (m)
1.59 (0.04)
60.06 (3.78)
1.18 (0.10)
1.51 (0.06)
109.53 (5.50)
1.05 (0.12)
1.37 (0.03)
107.81 (5.26)
1.03 (0.10)
Bank angle (Њ)
2
Soil strength (kg/cm )
Soil moisture (%)
Early summer (late June)
Mid-summer (late July)
Early fall (late August)
Graminoid heights (cm)
Forb heights (cm)
39.34 (1.07)
35.25 (2.25)
36.50 (3.42)
25.06 (1.26)
8.97 (0.67)
4.41 (0.32)
168.41 (14.62)
183.81 (11.92)
139.12 (31.74)
27.69 (1.20)
9.41 (0.57)
44.28 (3.20)
44.18 (3.69)
39.50 (4.60)
29.56 (1.16)
10.78 (0.87)
4.33 (0.37)
Root biomass (g/core)
5.18 (0.23)
tion is reduced macropore space, which reduces infil-
tration, percolation, root growth, and overall plant pro-
duction (Lull 1959, Bryant et al. 1972). The response
of plant growth to nutrient return via excreta of graz-
ing animals may be less than assumed. Much or per-
haps nearly all of the nitrogen in urine and feces can
be lost to volatilization or leaching (Watson and Lap-
ins 1969, Floate 1970, Woodmansee 1978). Ball et al.
(1979) found that only 22% of nitrogen from animal
wastes may be recovered in plant tissue. As stocking
rates increase, herbage growth decreases because the
benefits of increased nitrogen transfer are outweighed
by the negative effects of trampling and increased in-
tensity of defoliation (Curll and Wilkins 1982, 1983).
All three primary grazing effects (defoliation, tram-
pling, and nutrient return) have been shown to affect
plant growth in riparian meadows significantly (Clary
1995).
Studies of simulated livestock grazing have some
advantages over studies using actual livestock; they
cost less, require much less space, and provide an op-
portunity to examine the various individual effects of
grazing (Clary 1995). There has been some question
whether defoliation by clipping duplicates the effects
of grazing in upland situations where grazing may be
patchy (Stroud et al. 1985, Wallace 1990); however,
in meadow situations, cattle tend to graze to a rela-
tively uniform stubble height (Bartolome 1984). The
simulation of trampling combined with defoliation
should result in a plant response closely paralleling the
response to actual livestock grazing (Bryant et al.
1972), particularly when the effect of nutrient return
is added.
to a measurable degree (Trimble and Mendel 1995,
Jolley et al. 1997). In the present study, the hypothesis
was that physical and biological changes would occur
when streambanks were subjected to simulated typical
total animal impacts of cattle. A goal was to provide
information that would assist in the development of
grazing strategies designed to stay within the annual
tolerance of a site for plant and streambank/channel
impacts.
STUDY AREA AND METHODS
This study was conducted on three streams north of
Stanley, Idaho, USA in central Idaho’s Sawtooth Val-
ley. Stanley Creek and Park Creek are in the Sawtooth
National Forest, while Thatcher Creek is in the Challis
National Forest. The distance of these streams from
the town of Stanley and the elevation at the study sites
are as follows: Stanley Creek, 5.9 km and 1972 m;
Park Creek, 8.8 km and 1976 m; and Thatcher Creek,
25.0 km and 2006 m. These streams meander through
mountain meadows, average 1 to 2 m in width (Table
1), and are slightly entrenched with well-vegetated
streambanks. Rosgen stream classifications at the study
sites are Stanley Creek, C4; Park Creek, E4, and
Thatcher Creek, E4 (Rosgen 1996). Average annual
precipitation at Stanley (1912 m elevation) is approx-
imately 389 mm. Average annual temperature is 2Њ C,
while the average temperature during June, when the
root biomass and the final foliage sampling were con-
ducted, is 11Њ C (Idaho Climatic Services, personal
communication).
The Stanley Creek and Thatcher Creek soils are
classified as loamy, cryic Fluventic Ustochrepts, and
the Park Creek soil is classified as a loamy, cryic Flu-
ventic Haplaquoll. The A horizon of Stanley Creek is
dark yellowish brown, Park Creek is black, and
Thatcher Creek is brown. Thatcher Creek had the most
rock fragments (25%), while Stanley Creek and Park
Creek had the most clay (5%). All three study sites
Although there are many anecdotal accounts and ob-
servations of cattle breaking down streambanks (Ad-
ams and Fitch 1995, Martin and Schumaker 1998),
there is little quantification of the impacts necessary to
damage streambanks. Few references provide actual
documentation of the amount of livestock use required
to change stream channel and streambank morphology

Clary & Kinney, SIMULATED CATTLE GRAZING
141
have buried soil horizons at 18 to 33 cm below the
surface (D. Gilman, personal communication). Stream-
side vegetation at the study sites was dominated by
water sedge (Carex aquatilis Wahl.), beaked sedge (C.
utriculata Boott, formerly C. rostrata Stokes), and
Baltic rush (Juncus balticus Willd.). Several of the
more abundant forbs were white clover (Trifolium re-
pens L.), American alpine speedwell (Veronica
wormskjoldii Roem.& Schult.), monkey-flower (Mi-
mulus spp.), and common willow-weed (Epilobium
glandulosum Lehm.). Adjacent moist meadow sites
were typically dominanted by the graminoids Jones
sedge (C. jonesii Bailey), small-winged sedge (C. mi-
croptera Mack.), field woodrush (Luzula campestris
(L.) DC), and Kentucky bluegrass (Poa pratensis L.).
Typical forbs included aster (Aster spp.), yarrow
(Achillea millefolium L.), rosy pussy-toes (Antennaria
microphylla Rydb.), and common dandelion (Taraxa-
cum officinale Weber). Several other characteristics of
the study sites are presented in Table 1.
Livestock use of the Sawtooth Valley began with
sheep grazing by 1879. Up to 200,000 sheep grazed
during summers in the Sawtooth Valley. Cattle grazing
began about 1899, but little attention was given to
grazing management until the 1970s. Heavy use of ri-
parian meadows apparently occurred during most of
this period (Clary 1999). The sites in this investigation
had been protected from grazing for 5 to 10 years be-
fore initiation of the study.
witnessed riparian areas subjected to severe regrazing
with residual forage lengths of 1 cm or less). The tram-
pling impact and nutrient return for the heavy season-
Ϫ1
long treatment would represent about 7.5 AUM ha
of ‘‘use’’ as animals would be expected to spend sub-
stantial time on site attempting to regraze the short
stubble heights of a streamside area.
The moderate treatments were applied to the appro-
priate subplots once in either late June (early summer)
or late July (mid-summer) in 1996 and 1997. Vege-
tation was defoliated by clipping to a height of 10 cm.
Cattle trampling was simulated by 50 random impacts
by a hoof imitator (14-kg steel weight with impact
2
surface area of 100 cm dropped from 75 cm) per sub-
plot (Clary 1995, Al Medina, Rocky Mountain Re-
search Station, personal communication). The number
of impacts was based upon the estimated animal days
of use on the site that would be required to consume
the defoliated vegetation and the likely number of hoof
prints per animal day (Scholl 1989). Animal waste was
represented by 0.8 g of urea in 0.25 liter of water
(simulated urine) and fresh manure that was applied at
Ϫ2
a rate of 66 g m per subplot. The amounts were
based upon local forage production and consumption
estimates and on excretion values from Tiedemann et
al. (1986) and Pat Moment, Caldwell Research and
Extension Center, Caldwell, ID, personal communi-
cation. The heavy season-long treatment was applied
in late June, late July, and again in late August in 1996
and 1997. Vegetation was defoliated to 1 cm in height,
120 random hoof-imitator impacts were applied, urine
was represented by 2.0 g urea in 0.25 liter of water,
The treatments applied were intended to simulate no
grazing, moderate early summer grazing, moderate
mid-summer grazing, and heavy season-long grazing.
Eight main plots were randomly established per
stream–two replicates per treatment. Each main plot
Ϫ2
and fresh manure was applied at a rate of 165 g m
per subplot. Treatments were initiated in the spring of
1996 and ended in the fall of 1997. Final measure-
ments were taken in the spring of 1998.
2
had four 1-m subplots arranged in two rows perpen-
dicular to the streambank. Each row contained one
subplot centered approximately 1.75 m from the
streambank edge (meadow plot) and one subplot over-
lapping the streambank (streambank plot). A half me-
ter buffer zone was established around the subplots for
protection and access.
Changes in soil surface and bank profile were de-
termined by a bankometer patterned after a rill meter
(McCool et al. 1981). A 1.3-cm conduit pipe, 3 m long
with 0.6-cm holes drilled on 2.5-cm centers, was an-
chored to rebar stakes. Forty stainless steel rods, 0.6-
cm in diameter, were positioned through the drilled
holes in the conduit pipe and lowered to the soil sur-
face (Figure 1). The length remaining above the con-
duit was recorded for each rod position. Two banko-
meter positions on each of the 96 subplots accom-
modated 7,680 rod locations.
Determination of treatment effect on streambank el-
evation was a function of the average change in read-
ings over time. Bankometer readings were made each
spring and fall. Bank angle from water’s edge to top
of bank (Platts et al. 1987), wetted stream width, and
average existing stream depth (average of 4 measures
across the stream) were determined after spring snow
melt flow had subsided at the beginning and at the end
Grazing simulation treatments were patterned after
those in Clary (1995), with suggestions and refine-
ments contributed by Al Medina (Rocky Mountain Re-
search Station, Flagstaff, AZ) and Pat Momont (Cald-
well Research and Extension Center, Caldwell, ID).
The moderate seasonal treatments were designed to
represent the total impact that cattle would have while
grazing the foliage to a 10-cm height, an often-used
riparian grazing guideline (see Clary 1995 Table 5), or
in the case of this study, it represented a grazing in-
Ϫ1
tensity of about 1 AUM (animal unit month) ha . The
heavy season-long treatment was designed to represent
the total impact of cattle grazing to a 1-cm height at
three times during the grazing season (the authors have

142
WETLANDS, Volume 22, No. 1, 2002
Figure 1. Bankometer positioned on a study plot in central Idaho.
of the study. Bank retreat at water’s edge during the
treatment period was recorded at the end of the study.
With the exception of the bankometer measurements,
the variables discussed above had a sample size of 96
for each measurement period.
screen, drying at 100Њ C for 24 hours, and weighing.
The organic matter was burned off using denatured
alcohol as an accelerant. The ash was gently blown
away, and the residual mineral particles originally at-
tached to the roots were weighed and subtracted from
the initial gross dry weight to obtain the net root dry
biomass (modification of Lim and Jackson 1982).
Soil strength was measured by a pocket penetrom-
eter. The penetrometer method has been correlated
with unconfined strengths and zones of compaction
among similar soil types (Bradford 1986). Twelve
samples were taken at each main plot, for a total of
288 measurements each spring and fall of the study.
Moisture in the top 15 cm of soil was sampled gravi-
metrically by four 2.5-cm cores per main plot for a
total of 96 per treatment each spring and each addi-
tional treatment application. Dry weight was deter-
2
Plant data were collected from the central 0.25 m
2
of the 96 1-m treatment subplots. Plant heights, sep-
arated by graminoids and forbs, were recorded at the
beginning and end of the study. Above-ground current
year’s growth of graminoids and forbs was determined
by harvesting plants to ground level in the spring of
1998. Foliage removed during treatment and during
the final harvest was bagged, dried at 100
Њ C for 24
mined by heating samples at 100Њ C for 24 hours.
hours, and weighed.
Root sampling was conducted by extracting 4.5-cm-
diameter, 15-cm-deep soil cores. Twelve samples were
taken at each main plot, for a total of 288 cores, both
at the beginning of the study in the spring of 1996 (in
buffer areas) and at the end of the study in the spring
of 1998 (in treated plots). Gross root biomass was de-
termined by washing the samples over a 1.6-mm
A mixed-model analysis of variance was used to
analyze data with one date of measurement or to an-
alyze the change in variables between the beginning
and end of study. A protected Fisher’s LSD multiple
range test was used to differentiate treatments. A
mixed-model analysis of variance with AR(1) error
structure (Littell et al. 1996) was used for the repeated

Clary & Kinney, SIMULATED CATTLE GRAZING
143
measures analysis of bankometer data. Effects of soil
moisture content were examined through correlation
with response variables. Probability values of 0.05 or
less were considered significant in all tests.
RESULTS
Streambank surface elevations were significantly af-
fected by the treatments (F3, 6
ϭ 33.05, P Ͻ 0.01). The
streambank plots receiving simulated grazing treat-
ments had a cumulative reduction in average surface
elevation as the surface structure became progressively
more deformed and broken (Figure 2a). The two mod-
erate intensity treatments had about 3 cm of average
surface depression, while the heavy season-long treat-
ment had about 11.5 cm of average surface depression
as the edge of the bank became severely deformed. In
contrast, the meadow plots experienced relatively little
change from the simulated grazing (F3, 6
ϭ 2.68, P ϭ
0.14) (Figure 2b). Bank retreat, or the retreat of the
streambank face at water’s edge, was also affected by
treatment (F3,
ϭ 10.02, P ϭ 0.01). The no-grazing
6
and moderate-grazing treatments were comparable, av-
eraging about 3.5 cm of bank retreat at the water’s
edge, but the heavy season-long treatment resulted in
substantially greater bank retreat of about 12 cm over
the study period (Table 2). Stream discharge on the
study areas was less in 1998 than in 1996. This gen-
erally resulted in reduced wetted stream width. The
wetted stream width at the plot locations, however,
Figure 2. Mean depression of soil surface related to time
and four simulated grazing treatments: a. streambank, b.
meadow. Treatments with different letters have significantly
different population means at the P
Ͻ 0.05 level.
responded differentially with treatment (F3, 6
ϭ 19.44,
P
Ͻ
0.01). The no-grazing and moderate-grazing treat-
Table 2. Changes in streambank characteristics and standard errors (in parentheses) in response to simulated grazing in central Idaho.
Simulation
treatment
Bank retreat
(cm)
Stream width
(m)
Bank angle
Penetrometer
2
(Њ)
(kg/cm )
1
No grazing
1.96 (0.39)a
2.00 (0.91)
1.75 (0.70)
2.12 (0.44)
Ϫ0.22 (0.05)a
Ϫ0.33 (0.06)
Ϫ0.30 (0.07)
Ϫ0.04 (0.09)
Ϫ7.71 (4.62)a
Ϫ3.75 (7.25)
Ϫ6.87 (9.57)
Ϫ12.50 (7.76)
0.13 (0.11)a
0.22 (0.19)
0.08 (0.21)
0.10 (0.20)
Stanley Creek
Park Creek
Thatcher Creek
Early summer moderate
Stanley Creek
5.54 (1.17)a
1.75 (0.94)
11.00 (2.40)
3.87 (0.35)
Ϫ0.28 (0.05)a
Ϫ0.33 (0.07)
Ϫ0.37 (0.07)
Ϫ0.15 (0.11)
8.75 (5.77)ab
12.87 (9.78)
12.75 (9.27)
0.62 (11.51)
0.24 (0.16)a
0.86 (0.22)
Ϫ0.60 (0.22)
0.48 (0.10)
Park Creek
Thatcher Creek
Mid-summer moderate
Stanley Creek
2.96 (0.53)a
1.50 (0.63)
4.87 (0.52)
2.50 (1.10)
Ϫ0.24 (0.05)a
Ϫ0.22 (0.06)
Ϫ0.35 (0.10)
Ϫ0.17 (0.06)
Ϫ10.68 (9.50)a
9.62 (8.87)
Ϫ9.31 (20.36)
Ϫ32.34 (16.44)
0.37 (0.14)a
0.77 (0.24)
Ϫ0.20 (0.13)
0.55 (0.22)
Park Creek
Thatcher Creek
Season-long heavy
Stanley Creek
Park Creek
Thatcher Creek
1
12.38 (1.14)b
9.87 (1.08)
18.12 (1.75)
9.12 (1.19)
0.01 (0.06)b
Ϫ0.06 (0.03)
Ϫ0.07 (0.14)
0.15 (0.08)
34.42 (7.69)b
71.37 (9.52)
6.87 (8.18)
0.08 (0.07)a
0.36 (0.12)
Ϫ0.24 (0.12)
0.13 (0.06)
25.00 (10.43)
Values followed by different letters within a column are significantly different at the P Ͻ 0.05 level.

144
WETLANDS, Volume 22, No. 1, 2002
change for the moderate treatments, but decreased by
an average of 43% for the heavy season-long treatment
(Streambank F3, 6
11.52, P 0.01) (Tables 1 and 3). A similar but non-
ϭ 10.35, P ϭ 0.01; Meadow F3, 6 ϭ
ϭ
significant trend of decrease in height growth with in-
creasing treatment stress occurred for the forb species
(Streambank F3, 6
1.97, P 0.22).
ϭ 1.94, P ϭ 0.22; Meadow F3, 6 ϭ
ϭ
Total foliage removed as part of the treatments dif-
fered substantially. The values varied from 0 (no graz-
Ϫ2
ing) to 107.2 g m (heavy season-long) (Figures 4a
and b). There were significant interactions between
treatment and year (Streambank F3,
ϭ 17.18, P Ͻ
0.8081). The amount
0.01; Meadow F3,88
ϭ
11.43, P
Ͻ
Figure 3. Change in root biomass in response to four sim-
ulated grazing treatments. Treatments with different letters
of foliage removed in the second year of the season-
long treatment was reduced by as much as 73% com-
pared to the first year. This occurred because of the
decrease in plant growth in response to the severe
treatment.
Total above-ground biomass produced in the spring
of 1998 differed significantly among treatments
are significantly different at the P
Ͻ 0.05 level.
ments had about 0.25 m narrower stream wetted-
widths. The heavy season-long treatment differed sig-
nificantly from the other treatments and resulted in no
reduction in stream wetted width even in the face of
the reduced flow (Table 2). The bank retreat increase
with this treatment (described above) apparently coun-
tered the effects of the lower flow, resulting in a mea-
sured wetted stream width similar to that at the initi-
ation of the study. Bank angle also experienced a sig-
(Streambank F3, 6
ϭ 12.41, P ϭ 0.01; Meadow F3, 6 ϭ
5.13, P 0.04). The strongest effect occurred in the
ϭ
streambank location. The moderate-grazing treatments
yielded biomass values of about 57% of the no-grazing
plots, and the heavy season-long treated plots yielded
only about 13% of the no-grazing plots (Table 4).
Equivalent values for the meadow plot locations were
80% and 49% of the no-grazing treatment.
nificant change related to treatment (F3, 6
0.04). All treatments but season-long heavy had statis-
tically similar changes in bank angle that averaged
ϭ 4.90, P ϭ
Ϫ3
degrees. Season-long heavy had an increase in bank
angle of 34 degrees, producing a substantial flattening
of the bank face (Table 2).
DISCUSSION
Excessive grazing along streams removes protective
vegetation and tramples banks into sloping profiles.
The sloping of a streambank, which is normally steep,
vertical, or undercut, represents a fundamental change
in channel morphology that is detrimental to most na-
tive biota (Bohn 1986). Such channel morphology is
strongly influenced by the stabilization contributed via
riparian vegetation (Fitch and Adams 1998). Herba-
ceous roots and rhizomes provide much of the com-
pressive strength and soil stability for streambanks in
meadow situations (Kleinfelder et al. 1992, Dunaway
et al. 1994). Streambanks on our sites were well-veg-
etated with a variety of plant species. The most prom-
inent plants near the water’s edge were water sedge,
beaked sedge, and Baltic rush, species known to be
strongly-rooted (Manning et al. 1989, Platts and Nel-
son 1989, Kleinfelder et al. 1992, USDA Forest Ser-
vice 1992, Dunaway et al. 1994). Thus, our study sites
should not have been particularly susceptible to
streambank damage. Our season-long, heavy simulated
grazing treatment, however, did result in a significant
increase in streambank surface depression, bank re-
treat, and bank angle within a two-year period.
Penetrometer readings, although showing a short-
term increase from the heavy season-long treatment
(F3, 6
ϭ 3.65, P ϭ 0.02), did not appear to retain the
change over winter. There were no differences in soil
penetrability among treatments when comparing
spring 1998 readings to that of spring 1996 (F3, 6
ϭ
0.57, P 0.65) (Table 2). Root biomass changed little
ϭ
during the study for the no-grazing and the moderate-
grazing treatments, whereas the heavy season-long
treatment produced a 32.5% decrease following the 2
treatment years (F3, 6
ure 3).
ϭ
5.20, P
ϭ
0.04) (Table 1, Fig-
Significant correlations (r
ϭ
0.44–0.62, P 0.01–
ϭ
0.03) occurred between bank retreat and streambank
moisture on treated plots but not on controls (r
ϭ
0.17,
0.04,
P
ϭ
0.41). No soil moisture correlations were found
with changes in elevation of the soil surface (r
0.74), stream width (r 0.26, P
angle (r 0.29, P 0.17).
ϭ
P
ϭ
ϭ
ϭ 0.20), or bank
ϭ
ϭ
The height of graminoid plants at the vegetative/
boot phenological stage was greater in 1998 than in
1996 for the no-grazing treatment, showed little

Clary & Kinney, SIMULATED CATTLE GRAZING
145
Table 3. Change in average vegetation heights and standard errors (in parentheses) between beginning of study June 1996 and end of
study June 1998 in central Idaho.
Graminoid
Forb
Simulation
treatment
Streambank
Meadow
Streambank
Meadow
1
No grazing
6.92 (1.40)b
0.17 (1.68)b
7.75 (2.63)b
4.58 (1.86)b
3.67 (1.96)b
Ϫ8.92 (2.31)a
2.66 (1.66)a
Ϫ1.25 (0.95)a
Ϫ1.50 (1.28)a
Ϫ3.42 (1.49)a
2.83 (1.55)a
Ϫ2.67 (1.21)a
Ϫ1.92 (1.16)a
Ϫ3.17 (1.15)a
Early-summer moderate
Mid-summer moderate
Season-long heavy
1
Ϫ1.58 (1.40)b
Ϫ12.42 (2.16)a
Values followed by different letters within a column are significantly different at the P Ͻ 0.05 level.
Another factor affecting the vulnerability of stream-
banks to trampling damage is soil moisture content.
Montana researchers found a substantial correlation
between changes in stream-channel area and stream-
bank soil moisture, and little correlation between chan-
nel area and observed cattle presence in the riparian
area (Marlow and Pogacnik 1985, Marlow et al. 1987).
They suggested that a primary guideline for grazing
riparian areas would be to limit livestock use to the
Conversely, we found relatively limited correlation be-
tween variations in streambank soil moisture and
streambank damage in the present study. Perhaps one
reason was that the banks of the study streams re-
mained well above the 10% moisture threshold for
bank toughness suggested by Marlow and Pogacnik
(1985). Average early fall streambank moisture was
36% at Stanley Creek, 39% at Thatcher Creek, and
over 100% at Park Creek.
Livestock grazing in many locations has been
shown to increase soil compaction, decrease soil infil-
tration, increase runoff of surface water, and increase
soil erosion (Alderfer and Robinson 1949, Warren et
al. 1986, Usman 1994, Trimble and Mendel 1995).
Grazing season impacts on surface soils can be sub-
stantially reversed due to the action of freeze-thaw and
wet-dry cycles (Tollner et al. 1990, Weigel et al.
1990). Our data and those of Wheeler (1998) from
moist riparian areas suggest a similar result because
the growing season treatment differences in soil char-
acteristics were lost over winter.
seasonal periods of dry (Ͻ10% moisture) streambanks.
Benefits to plant composition of using rotational or
other specialized grazing systems are cited for many
conditions (Holechek et al. 1989, Heitschmidt and
Taylor 1991). However, the actual grazing system
used seems to have little effect on the total trampling
impact (Abdel-Magid et al. 1987, Guthery and Bing-
ham 1996, Holechek et al. 2000). The specific grazing
system used (i.e., timing and frequency of grazing)
probably would not have great importance in our study
area because the streambanks did not dry to the level
that could potentially allow seasonal protection from
trampling damage. The primary way to control stream-
bank deformation on our sites is apparently to concen-
trate on controlling the total animal use of streambank
areas rather than manipulation of the type of grazing
system. Control of livestock activity on streambanks
is often easier to accomplish in the spring when live-
stock prefer the floodplain and upland sites compared
to the wetter streamside areas (Siekert et al. 1985,
Clary and Booth 1993, Del Curto et al. 2000).
Figure 4. Foliage biomass removed under four simulated
grazing treatments for two consecutive years for: a. stream-
bank and b. meadow. Note severe reduction in harvested
foliage under the heavy season-long treatment suggesting
large reduction in biomass growth in the second year of the
study (also see Table 4). Interactions between treatment and
There has been little quantification of the amount of
livestock use required to change stream channel and
year were significant (P
Ͻ 0.01).

146
WETLANDS, Volume 22, No. 1, 2002
Ϫ2
Table 4. Above-ground current year’s growth (g 0.25 m ) and standard errors (in parentheses), spring 1998 in central Idaho.
Graminoid
Streambank Meadow
Forb
Total
Simulation
treatment
Streambank
Meadow
Streambank
Meadow
1
No grazing
71.83 (6.95)c
80.08 (13.84)a
78.83 (10.03)a
69.12 (13.31)a
45.83 (5.64)a
9.42 (2.23)a 20.92 (5.08)b
81.25 (7.42)c 101.00 (11.89)b
Early summer moderate
Mid-summer moderate
Season-long heavy
1
42.67 (5.56)b
43.25 (4.40)b
6.45 (2.67)a
3.91 (1.34)a
3.12 (0.44)a
4.25 (2.71)a
7.50 (1.79)a
6.62 (1.58)a
3.66 (1.32)a
46.58 (6.23)b
46.37 (4.13)b
10.70 (3.18)a
86.33 (9.81)b
75.75 (13.08)ab
49.50 (5.17)a
Values followed by different letters within a column are significantly different at the P Ͻ 0.05 level.
bulk density and water infiltration as affected by grazing systems.
Journal of Range Management 40:307–309.
streambank morphology (Trimble and Mendel 1995,
Jolley et al. 1997). Treatment levels that have com-
paratively little effect on meadow plots can literally
crush the streambanks at the water’s edge. The poten-
tial loss of livestock forage supplies and, perhaps more
importantly in these narrow streamside zones, fish and
wildlife habitat and general channel stability is signif-
icant. Although the most severe treatment reduced
1998 above-ground plant biomass production by 87%
at the streambank location, the retention of substantial
plant growth and the comparatively little change in
streambank characteristics under moderate levels of
simulated grazing are encouraging. This suggests that
careful grazing management can result in harvest of
riparian forage without severe environmental impacts.
Other studies involving actual grazing tests support
this contention (Clary 1999).
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ACKNOWLEDGMENTS
The authors wish to thank Daniel W. Uresk, Rocky
Mountain Research Station, USDA Forest Service, and
Wayne C. Leininger, Department of Rangeland Eco-
system Science, Colorado State University and two
anonymous reviewers for their insightful and helpful
reviews of earlier drafts of this paper.
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Manuscript received 1 December 2000; revisions received 20 July
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