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EFFECTS OF SIMULATED FALL
AND EARLY SPRING GRAZING ON
CHEATGRASS AND PERENNIAL
GRASS IN WESTERN NEVADA
Robin J. Tausch
Robert S. Nowak
Allen D. Bruner
James Smithson
ABSTRACT
The presence of cheatgrass decreases the productivity
of perennial rangeland grasses following fire (Melgoza and
others 1990) or without fire (Harris 1967; Wilson and others 1966). In greenhouse experiments, production of both
crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and
western wheatgrass (Agropyron smithii Rydb.) was significantly reduced by the presence of cheatgrass (Evans 1961;
Rummell1946). Much of this competitive ability appears
related to exploitative root growth patterns in cheatgrass
that deplete soil moisture down to 1.3 m (Harris 1967, 1977;
Hulbert 1955; Melgoza and others 1990; Stewart and Hull
1949). However, competitive interactions with cheatgrass
vary by species and by season (Cline and others 1977; Day
1975; Harris 1967, 1977). Thus, grazing at different times
of the year may shift the competitive balance between
cheatgrass and other species in the community.
This research investigated changes in the productivity
of cheatgrass and perennial grass species in burned and
unburned areas of a sagebrush community. Potential competitive interactions between cheatgrass and perennial
grass species were studied utilizing three simulated grazing treatments. The three grazing periods used were selected to evaluate possible differential impacts on perennial grass and cheatgrass during different portions of the
growing season.
Potential effects ofgrazing on cheatgrass and perennial
grass productivity were investigated on burned and unburned areas of a sagebrush community north ofReno, NV.
Clipping was used in fall and early spring, early spring only,
and late spring to simulate grazing for cheatgrass control.
Cheatgrass biomass did not differ between the fall plus early
spring treatment and the control over four sites with varying cheatgrass abundance over 2 years. Fall clipping increased cheatgrass production for both years. Late spring
clipping had the largest reduction in both density and biomass of cheatgrass. All three treatments significantly reduced perennial grass biomass.
INTRODUCTION
Cheatgrass (Bromus tectorum L.) has invaded and become the dominant plant species on more than 41 million
hectares in the Intermountain West (Mack 1981; Young
and others 1987; Young and Tipton 1990), including extensive areas of western Nevada sagebrush-grass rangelands
(Morrow and Stahlman 1984). In sagebrush-grass communities, cheatgrass quickly dominates on disturbed sites
(Billings 1990; Young and Evans 1973) and is capable of
invading undisturbed areas (Harris 1967; Hulbert 1955;
Hunter 1990, 1991; Klemmedson and Smith 1964; Svejcar
and Tausch 1991). Invasion by cheatgrass alters the population dynamics and fire history of sagebrush-grass communities (Klemmedson and Smith 1964; Morrow and
Stahlman 1984; Stewart and Hull1949; Young and Evans
1973; Young and others 1987). Altered fire dynamics caused
by cheatgrass convert many areas from productive, perennial communities to less reliable, annual-dominated communities with increased fire management problems.
STUDY SITE
A location on Bedell Flats, 35 km north of Reno, NV,
was selected for the study. This location was stratified
into four sites representing a range of cheatgrass abundance from over 50 percent of production to less than
5 percent. All four sites are within 0.5 km of each other,
have the same slope and aspect, and vary in elevation by
only 6 m. Soils on all four sites are fine loamy mixed mesic
xerollic haplargids. Sites I, ll, and ill had burned at least
a decade prior to the study. They are now dominated by
annual grass, perennial grasses, forbs, and rabbitbrush
(Chrysothamnus viscidiflorus [Hook.] Nutt.). Site IV is an
unburned sagebrush (Artemisia tridentata wyomingensis
Beetle) dominated community that had the lowest level of
cheatgrass abundance. For convenience, we designated
sites I through IV by their relative cheatgrass abundance:
high, medium-high, medium-low, and low, respectively.
Paper presented at the Symposium on Ecology, Management, and Restoration of Intermountain Annual Rangelands, Boise, m, May 18-22, 1992.
Robin J. Tausch is Project Leader and Allen D. Bnmer, Range Conservationist, Intermountain Research Station, Forest Service, U.S. Department
of Agriculture, Reno, NV 89512. RobertS. Nowak is Associate Professor of
Ecopbysiology, Department of Environmental and Resource Sciences, University of Nevada, Reno 89512. James Smithson is Environmental Specialist at the Newmont Gold Company, Carlin, NV 89822.
113
EXPERIMENTAL DESIGN
Each site had nine treated and control plots; three for
each treatment organized into three blocks of three paired
plots each (fig. 1). Paired plots were arranged in a 3 by 3
Latin Square design to maximize dispersion on each site
(Dowdy and Wearden 1983; Hulbert 1984). The treated
and control plots were randomly selected within each pair.
Additional treated and control areas were located acijacent
to the actual plots at each site for destructive sampling. The
treated area for all plots was 7 by 7 m in size. The area
sampled for perennial species was 5 by 5 min size centered
within the 7- by 7-m plot; this provided a 1-m buffer strip
of treatment around each sampled area.
Three simulated grazing treatments were applied: (1) late
fall and early spring, (2) early spring only, and (3) late spring
only. These periods were selected because they are those
when cheatgrass is potentially the most sensitive to grazing pressure (DeFlon 1986). Treatments were repeated__
for 2 years (fall 1986 through spring 1987 and fall1987
through spring 1988). The fall treatment was one clipping
in mid to late November. Early spring treatments included
three clippings from the end of March to the end of April.
Late spring treatments included two clippings from the
end of April to mid May and coincided with the early-boot
stage of cheatgrass. Actual dates varied between years to
match phenological stages as closely as possible. Perennial
grass phenology was 1 to 2 weeks behind cheatgrass. All
grazing treatments simulated heavy grazing.
SAMPLING METHODS
We determined total herbage production for the grasses
and forbs and total leaf biomass for the shrubs by nondestructive methods. For the shrubs and perennial grasses,
dimensional relationships between crown volume and leaf
biomass were determined by species and by year (Freedman
1984; Ludwig and others 1975; Tausch 1989; Tausch and
Tueller 1990). Plant measurements for shrub crown volume were: longest crown diameter, diameter perpendicular
to the longest, and height of the foliage-bearing portion of
the crown (Tausch 1989). For perennial bunchgrasses, the
measurements were: longest basal diameter, diameter perpendicular to the longest, and average height of the culms
(Johnson and others 1988; Tausch 1989). All measurements
were in the 5- by 5-m inner area of the 7- by 7-m plots and
were made during June of each year to coincide with the
peak standing crop of each species.
Relationships between crown volume and leaf biomass
were determined in treated and control areas that were specifically designated for destructive sampling. Twelve individual shrubs were destructively sampled for each species
present at each site for each year. Eight individual bunchgrass plants were also destructively sampled from both the
treated and untreated destructive sampling areas for each
species present at each site for each year.
Crown volume for the shrubs was computed as one-half
of an ellipsoid and for the perennial grasses as a cylinder.
Nonlinear regression (Tausch 1989; Tausch and Tueller
1990) was used to determine the relationship between
114
Fence
D .. Treated areas
~ = Control areas
0
I
I
I
I
10
I
Meters
Figure 1-Experimental design for each site
with three grazing treatments randomized within
three blocks. Treatments are: (1) fall and early
spring, (2) early spring only, and (3) late spring
only.
crown volume and foliage biomass by species and by year
for both treated and control situations.
The reference unit method was used for sampling cheatgrass and forbs (Andrew and others 1979, 1981; Cabral and
West 1986; Kirmse and Norton 1985; Tausch and Tueller
1990). Both cheatgrass and forbs were sampled in three
1-m2 plots randomly located within each 5- by 5-m sample
area. Calibration of the reference unit methods utilized a
double sampling technique by site and year (Carpenter and
West 1987) and occurred in the same destructive sampling
treated and control areas used for the dimensional methods
with the perennial species. Ten 1-m2 plots, halfofthem
treated, were randomly located within the destructive
sampling areas for double sampling at each site.
STATISTICAL ANALYSES
For the analyses in this paper, the three control plots
in each block (fig. 1) were averaged to provide a balanced
model of three replications for each of the treatments and
for the control. For analysis of variance with the full data
set, the error degrees of freedom for site and block were
partitioned off prior to the determination of the significance
between treatments and years (table 1). Interactions between treatment and site, treatment and year, and treatment, year, and site were also analyzed for the full model.
Individual analysis of variance results by year and for each
site were used to help interpret the results of the full model.
Significance was determined at the 5 percent level or better for difference between treatments, between years, and
for interaction between treatment and year.
Table 1-Format for analysis of variance for four sites with three
randomized blocks within each site and four treatments
per block. Analysis parameters are the degrees of freedom (OF), sum of squares (SS), mean square (MS), and
F-test (F). Significance tests are for treatment and year
and interaction between treatment and site, treatment
and year, and among treatment, year, and site using the
cheatgrass total plot biomass results as an example
Source
Treatment
Treatment/Site
Treatment/Site/Block
(error)
Year
Treatment/Year
Treatment/Year/Site
Treatment/Year/Site/
Block (error)
1
2
ss
DF
Site
Block
SiteJBiock
(error)
MS
and April 1988 provided moisture for growth of the cheatgrass that germinated the previous fall.
Three species of shrubs and five species of perennial
grasses were common on one or more of the four sites
(table 2). One bush of smooth horsebrush (Tetradymia glabrata Gray) was also found in one plot of site
Squirreltail and two species of Stipa were the most common bunchgrasses. One rhizomatous perennial, western wheatgrass,
was present in some plots where it was sampled by the reference unit method (table 3). In addition to cheatgrass,
tansy mustard (Descurainia pinnata [Walt.] Britt.) was
a common annual (table 3).
Because analyses showed that individual bunchgrass
species had similar responses to treatment, we present
the results as a group to reduce repetition. Allometric
relationships for bunchgrasses were found to be uniform
within control areas over all four sites within each year.
The same was true within treated areas. Dimensional relationships differed between treated and control areas as
a result of the clipping. Shrub dimensional relationships
were similar among sites and between treated and control
plots within each year. Dimensional equations for the prediction of shrub and perennial grass biomass (table 2) were
comparable to the results of Tausch (1989), Tausch and
Tueller (1990), and Johnson and others (1988). The percent errors for our double sampling validation of the reference unit estimations (table 3) were comparable to the percent errors of Carpenter and West (1987).
The total leaf biomass values for cheatgrass, annual
forbs, perennial forbs, perennial grass, and shrubs were
averaged for the control plots within each site by year
(fig. 3). Although total leaf biomass for each site declined
from 1987 to 1988, reflecting the lower precipitation in
1988, the relative proportion of total leaf biomass at each
site that was represented by cheatgrass was similar in
both years.
m.
F
3
2
2.68E+6
1.24E+5
6
1.35E+5
3
9
3.55E+5
2.38E+5
1.18E+5
2.65E+4
24
1.33E+5
5.53E+3
1
3
12
1.86E+5
3.55E+4
4.95E+5
1.86E+5
1.18E+4
4.12E+4
32
2.18E+5
6.82E+3
224.41
14.79
227.35
1.74
26.05
P~0.01.
P~0.001.
RESULTS
The 1986-87 and 1987-88 winters represented drought
years with 1988 drier than 1987 (fig. 2). The lack of fall precipitation in 1986 resulted in no fall germination of cheatgrass. Spring 1987 germination occurred in late February
and early March. Fall rains in 1987 allowed fall germination of cheatgrass, and most new plants survived the winter
despite the general lack of snow. Spring rains in March
300
250
•
.
/
• •
.........
~
200
"""'
c
=
..
a.
0
as 150
A A
0
! 100
A.
50
0
J
F
M
A
M
J
J
A
Figure 2-Precipltation for the 2 study years at the Bedell Aat study location.
115
s
0
N
D
Table 2-Species sampled by dimensional methods and the results of nonlinear regression analysis (r2) and Standard Error
of the Estimate (SEE) for the combined data from four Bedell Rat study sites for 2 years
1988
1987
Untreated
,~
SEE(g)
Treated
r2
SEE(g)
Species
Treated
r2
SEE(g)
Untreated
SEE(g)
r2
Shrubs
•
0.81
.72
.74
35.31
15.09
3.15
•
•
•
•
•
•
0.92
.88
.81
14.15
12.91
5.10
0.637
1.44
.311
.610
.92
.65
.76
.82
2.32
6.12
3.36
2.11
0.50
0.925
1.23
.567
.717
.79
.59
.73
.74
2.94
2.28
2.25
1.09
Memisla tridentata wyomingensis ,.
•
Ch~so~amnuswsddffloros
Leptoclactylon pungens
Perennial grass
Agropyron cristatum
Oryzopsis hymenoides
Sltanlon hystrix
Stipa species
comata + ~urberiana
1Shrubs did
0.79
.53
.72
.62
.53
.80
.91
not receive the clipping treatment.
Table 3-Species receiving double sampling analysis and their esti·
mated average relative percent error for reference unit
method sampling of plant biomass (glm2) .. Data from five
1·m2 treated and untreated sacrifice plots were averaged
over the four Bedell Rat study sites for each of 2 years
Species
1988
Relative ~!!!:cent error
1988
1987
Treated Untreated Treated Untreated
Perennial grass
Agropyron smithii
41.18
24.17
Annual grass
Bromus tBCtorum
17.20
13.06
26.34
27.82
22.62
22.85
41.71
21.19
18.29
12.67
32.90
22.02
13.89
29.44
9.61
28.28
39.14
High MH
Perennial forbs
Astragalus lentiglnosus 40.02
Lupinus caudatus
Phlox long/folia
Annual forbs
Dsscuralnia plnnata
Erodlum cicutarium
Lygodesmla splnosa
1987
24.99
38.83
55.47
45.14
20.20
46.23
IlL
Low
Hlg!l IIH IlL
RIIISSve ctwatgrasa Dominance
Low
Figure 3-Comparison of total leaf biomass for
the control plots for each study year. averaged
over four sites of varying cheatgrass abundance.
Cheatgrass is compared with similarly pooled
data for the species groups of shrubs. perennial
grass. perennial forbs and annual forbs.
38.48
38.82
Cheatgrass Biomass and Density
The average total biomass of cheatgrass from the site with
the highest cheatgrass abundance was nearly twice the biomass of the medium-high site, over three times that of the
medium-low site, and over ten times the biomass of the low
abundance site (table 4). Average plant biomass per individual cheatgrass plant was highest on the medium-high
site and lowest on the low site. Density followed the same
trend as the total plot biomass.
Total leaf biomass of cheatgrass per plot differed significantly between treatments (tables 1 and 5) and years
(table 6). The fall plus early spring treatment biomass was
larger than that of the control, but not significantly. However, the early spring only and late spring treatment biomass levels were significantly different from each other and
significantly less than both the control and the combined
116
fall and early spring treatment levels (table 5). Total cheatgrass biomass was reduced by almost a third in the drier
year of 1988 (table 6).
Interaction between treatment and site for cheatgrass
plot biomass was significant. This resulted from a decrease in the differences between treated and control plots
as cheatgrass presence declined from the high to low abundance sites. On the low abundance site, only the difference
between the control and the late spring treatment was significant. The three-way .interaction of treatment, site, and
year resulted from the above differences, plus an overall
larger reduction in cheatgrass plot biomass in the treated
plots relative to the control plots in the drier year of 1988.
Average biomass per individual cheatgrass plant was
significantly different between treatments (table 5) and
years (table 6). Average plant size for cheatgrass from the
late spring treatment significantly differed from that of the
Table 4-Means of total biomass per plot and average biomass per plant for cheatgrass and perennial
grass, and density for cheatgrass and perennial grass on four sites with a range of cheatgrass
abundance
High
Relative cheatgrass abundance br site
Medium-high
Medium-low
Low
Cheatgrass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No.lm2)
492.7
0.0954
449.1
273.4
0.1349
323.2
174.7
0.0710
264.3
33.88
0.0461
44.51
Perennial grass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No./25 m2)
129.9
2.055
64.32
340.5
3.064
106.9
251.1
2.927
91.67
43.54
1.774
23.65
Table 5-Means1 of total biomass per plot and average biomass per plant for cheatgrass and perennial
grass, and density for cheatgrass and perennial grass from analysis of variance (table 4) for
four treatments
Control
Treatment
Fall+early
spring
Cheatgrass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No.fm2)
281.18
0.1038
291.98
310.28
0.0984a.b
326.28
233.Sa,
0.08078.b
278.68
149.50
0.0650b
184.-\,
Perennial grass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No./25 m2)
427.98
5.6018
71.348
103.9a,
110.0.,
123.~
1.38~
1Means In
each
1.3~
68.388
Early
spring
1.51~
73.298
Late
spring
73.508
row with the same letter are not significantly different by LSD analysis at the Ps O.OSievel of
significance.
Table 6-Means1 of total biomass per plot and average biomass per
plant for cheatgrass and perennial grass, and density for
cheatgrass and perennial grass from analysis of variance
(table 4) for 2 years
being significantly different from the other two treatments
on the high cheatgrass abundance site.
Cheatgrass density also significantly differed between
treatments (table 5) and years (table 6). Cheatgrass density significantly differed only between the control and the
late spring treatment. Cheatgrass density significantly
differed between years with the density much higher in the
drier year of 1988 (table 5). Only the interaction between
treatment and year was significant because the differences
between the late spring and the control treatments were
significant only in 1988.
Year
1987
1988
Cheatgrass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No./m2)
287.78
0.1538
69.868
470.7b
Perennial grass
Plot biomass (g/25 m2)
Plant biomass (g)
Density (No./25 m2)
183.78
2.578
69.978
198.88
2.348
73.28a,
199.~
0.020~
Perennial Grass Biomass and Density
Total plot biomass for perennial grass was highest on
the medium-high cheatgrass abundance site, followed by
the medium-low site, the high site, and finally the low site
(table 4). Average plant biomass and density for perennial
grass both followed the same trends over the sites as the
total plot biomass.
Perennial grass plot biomass significantly differed among
treatments (table 5), but not between years (table 6). Perennial grasses consistently had significantly less total foliage
biomass in the treated than in the control plots. The late
spring treatment had slightly higher perennial grass foliage
In each row with the same letter are not significantly different by
LSD analysis at the P s 0.05 level of significance.
1Means
control plots, but not the other two treatments (table 5).
Average plant biomass in 1988 was almost one-eighth that
of 1987 (table 6). The interactions between treatment and
both site and year were not significant, but the three-way
interaction among them was significant. This resulted from
the control and combined fall and early spring treatments
117
biomass than the other two treatments. Only the interaction between treatment and year was significant. Differences between the control and all three treated plots were
greater in 1987 than in 1988, although significant in both
years.
Average leafbiomass per plant for perennial grass significantly differed among treatments (table 5), but not between
years (table 6). Perennial grass consistently had significantly less average plant biomass in the treated than in
the control plots (table 5). The early spring treatment had
the highest average plant foliage biomass of the three treatments. Significant interaction again occurred only between
treatment and year for the same reasons as for the total
plot biomass interaction.
Perennial grass density for the full model significantly
differed only between years (table 6), but not between treatments (table 5). Only the three-way interaction among
treatment, site, and year was significant. This resulted
primarily from an increase in density of crested wheatgrass on the medium-high and medium-low cheatgrass
abundance sites in 1988. Unlike the total and average
plant biomass analyses, there were some density response
differences among the perennial grass species. The combined fall and early spring treatment significantly reduced
crested wheatgrass. density compared to the other two treatments. Both the Stipa species and crested wheatgrass increased overall, and squirreltail decreased, in density in
1988 compared to 1987. The squirreltail density decrease
was the greatest on the high cheatgrass abundance site.
Shrubs were not clipped and only small, nonsignificant
changes occurred between treatments or years over the
period of the study.
DISCUSSION
Late spring clipping (early boot stage) consistently had
the largest negative impact on both total foliage biomass
and density of cheatgrass. This treatment also had a .
slightly less negative impact on the total biomass of the perennial grass species. Removal of fall regrowth on the perennial grasses by late fall clipping consistently boosted
the production of cheatgrass over all sites and over both
years of data. Fall clipping apparently reduced the ability
of perennial plants to compete with cheatgrass the next
spring, even in the presence of the early spring clipping
treatment. This reduced competitive ability occurred both
when cheatgrass germinated in the spring and in the previous fall. A similar negative impact of mowing on perennial grass growth was observed on a nearby site by Young
and Evans (1978).
The reduction of the total biomass of the perennial
grasses by the three treatments was less in 1988 compared
to 1987. The reverse was true for cheatgrass plot biomass.
Density for the perennial grasses also increased in 1988
primarily from recruitment of new, small crested wheatgrass plants in 1988. The 2 years were substantially different in the average biomass and density of cheatgrass
plants. Even though the much smaller cheatgrass plant
size in 1988 was compensated for by a much higher density in 1988, the 1987 total leaf biomass was still only just
over two-thirds of the 1988 level. The greater suppression
of cheatgrass by the treatments, compared to perennial
grass, in 1988 than in 1987 may indicate cheatgrass control by grazing is possible. Additional studies of this type
over longer periods of time will be needed to verify this
possibility.
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