REJUVENATION OF MOUNTAIN BIG
SAGEBRUSH ON MULE DEER WINTER
RANGES USING ONSITE PLANTS AS A
SEED SOURCE
Fred J. Wagstaff
Bruce L. Welch
seems a likely source of severe competition. We, along
with others, have observed that most sagebrush seedlings
are found in areas where recent soil disturbance has
occurred.
A method of increasing browse production efficiently,
and with minimum impact on the land and deer herds,
is badly needed. This study was designed to determine:
(1) whether increased seed production by mountain big
sagebrush would increase seedling establishment, (2) if
soil disturbance to reduce plant competition was needed,
and (3) whether time of tillage (soil disturbance) was
important.
ABSTRACT
In the fall of 1987 three tillage treatments were applied
to 234 mountain big sagebrush (Artemisia tridentata ssp.
vaseyana) plants. The three treatments were: early tilling,
late tilling, and no tillage. One-halfofthe treated and
control plants had been protected from browsing the previous winter (1986-1987) to enhance seed production. In
late May and again in late September of 1988 all plots
were inspected and seedlings counted to give an estimate
of initial establishment and summer survival. Plots that
had received the late tillage treatment had significantly
greater numbers of seedlings. Plots receiving the early
tillage treatment and the control plots produced no seedlings regardless of the number of seedstalks on the
mother plant. Seedling survival was excellent (May-late
September), even though the spring-summer of 1988 was
one of the driest on record.
LOCATION, MATERIALS, AND
METHODS
Study sites were located near the 5,000-foot elevation
at approximately the lower boundary of mountain big
sagebrush range in north-central Utah. Three study sites
were chosen: one near Pleasant Grove (PG), another at
the mouth of Hobble Creek Canyon (HC), and the last in
Diamond Fork Canyon (DF). Average precipitation is
about 16 inches per year at the three sites; the major
portion comes during the winter and early spring months.
All sites have soils of similar texture, parent material and
depth, and vegetation with considerable cheatgrass and
bulbous bluegrass (Poa bulbosa) cover.
In the spring of 1986, 234 mountain big sagebrush
plants were selected at these sites and tagged. Plants
were grouped into 42 plots to spread the treatments uniformly over the full range of micro habitats at each site.
In each of the plots, treated and control plants were randomly selected by the roll of dice. One-half of these
plants were caged to prevent mule deer browsing during
the 1986-87 winter. In another study, the caged plants
produced significantly greater numbers of seedstalks
(Wagstaff and Welch, in preparation). It has been documented that fallowing the soil during a growing season
reduces cheatgrass density the following year (Eckert
1983); also it has been documented that grass seedlings
cannot outcompete sagebrush seedlings if they are established at the same time (Blaisdell 1949).
Since we had observed a fall green-up of cheatgrass
for several years on the study sites, we felt a single tillage
treatment might reduce cheatgrass competition until
seedlings became established. Fall green-up of cheatgrass
INTRODUCTION
Winter browse for mule deer along the Wasatch Front
area of northern Utah continues to be a limiting factor
on herd size. Encroachment of urban land use onto the
foothills has reduced the area available for winter range
and many winter range areas are producing browse far
below site potential. Mountain big sagebrush (Artemisia
tridentata ssp. vaseyana) is an important browse species
for wintering mule deer. Along the Wasatch Front many
populations of sagebrush have been eliminated due to
heavy use and fire (McArthur and others 1988). Many
other populations are declining due to a lack of
recruitment.
Several reasons for the lack of observed recruitment
have been postulated but no clear answer has emerged.
Heavy browsing on many areas has reduced seed
production. Competition from other vegetation, particularly annual grasses, may limit establishment of sagebrush seedlings. Cheatgrass (Bromus tectorum), which
sprouts in the fall and grows rapidly in early spring,
Paper presented at the Symposium on Cheatgrass Invasion, Shrub
Die-Off, and other Aspects of Shrub Biology and Management, Las Vegas,
NV, April 5-7, 1989.
Fred J. Wagstaffis Range Economist; Bruce L. Welch is Principal
Plant Physiologist, Intermountain Research Station, Forest Service, U.S.
Department of Agriculture, Provo, UT 84627.
171
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
varies in time on our sites from early September (observed in 1980) to late October (observed in 1988) depending on when adequate moisture becomes available. In
1987 the first fall storms occurred around the first week
of October.
Treatments applied in the fall of 1987 consisted of
tillage before cheatgrass green-up (early tillage), tillage
after cheatgrass green-up (late tillage), and no tillage.
Treatments were completed with a spring-tooth cultivator
mounted on a small four-wheel drive tractor. An area
roughly 15 feet square was tilled around treated plants.
All seedheads on other big sagebrush plants for a radius
of 100 feet from all study plants were clipped to eliminate
the possibility of seeds from nonstudy plants moving into
the study plots. Goodwin (1956) showed that big sagebrush seed disperses a maximum of 33m (108ft) and
usually much less. Frischknecht (1978) stated that 90
percent of new sagebrush colonies were within 9 m (30ft)
of parent plants.
The early tillage treatment was applied to 18 plants at
the Diamond Fork site and 40 plants at the Hobble Creek
site during the third and fourth weeks of September.
Rains prevented any early treatment at the Pleasant
Grove site. The late treatment was applied during the
last week of October to 28 plants at Hobble Creek and 64
plants at Pleasant Grove. Rain and snow prevented late
tillage at the Diamond Fork site. Eighty-four plants distributed across the three sites were used as control.
Statistical comparisons were made using the Mini tab
Statistical procedures (Ryan and others 1985). The
Student T-test was used to test: (1) whether seedling
numbers differed significantly from zero, and (2) whether
seedling numbers on treated plots varied from those on
untreated plots. Analysis of variance procedures were
used to determine whether the mean values for sites were
different. Correlation analysis was completed using the
least squares technique.
RESULTS AND DISCUSSION
In late May and again in September of 1988 all plots
were visited and carefully inspected to locate big sagebrush seedlings. Somewhat surprisingly, more seedlings
were inventoried during the September visit. This was
probably mostly due to observational error (small seedlings are hard to see), but a few very small seedlings were
found in September, suggesting that some emergence
occurred during the summer, perhaps after a summer
thunderstorm. A summary of the results is shown in
table 1.
The only mother plants having seedlings by them
in either May or September were those tilled after
cheatgrass green-up (late October). None of the control
plants (untilled) or those tilled early had seedlings. The
difference in seedling numbers between the Hobble Creek
and Pleasant Grove sites was unexpected. This difference
might be due to two rain showers that fell only on the
Hobble Creek site during April1988 (Fred J. Wagstaff,
personal observation).
An earlier study used the same plants to determine
whether protection from one winter of browsing would
increase seedstalk production (Wagstaff and Welch, in
preparation). We found protected plants produced more
seedstalks and hypothesized they would also have more
adjacent seedlings. Table 2 shows that on plots treated
by late tilling, at Hobble Creek and Pleasant Grove,
plants that had been protected from browsing the previous winter produced significantly more seedlings (p<0.05).
Because the Hobble Creek site had more consistency in
terms of seedlings among the treated plants, a test for
correlation between seedstalks numbers and seedlings
was performed. The resulting correlation coefficient was
significant at the 0.01level. A straight line was fitted to
the data using the least squares techniques and an R 2
value of 37.3 resulted.
Table 1-Number of mountain big sagebrush (Artemisia tridentata ssp. vaseyana) seedlings counted
around mother plants. Treatments were control, early tillage, and late tillage
Sites
Treatment
Pleasant Grove
Hobble Creek
Diamond Fork
Total
Control
No. of mother plants
Seedlings
32
0
34
0
18
0
84
0
Early tillage
No. of mother plants
Seedlings
0
0
40
0
18
0
58
0
Late tillage
No. of mother plants
Seedlings - June
Seedlings- Sept.
64
117
164
28
543
557
0
0
0
92
660
721
96
102
36
234
Total mother plants
172
Table 2-Characteristics of mountain big sagebrush (Artemisia tridentata ssp. vaseyana) mother
plants receiving late tillage. Half of the mother plants were protected from wintering
mule deer grazing the previous winter. Characteristics measured were: number of
mother plants without seedlings; with seedings; and number of seedstalks. Data collected at two north-central Utah sites
Pleasant Grove
Protected
Unprotected
Total
No. without
seedlings
24
25
49
No. with
seedlings
8
7
15
Min. seedlings
Hobble Creek
Protected
Unprotected
13
Total
4
5
10
23
2
2
90
3
93
185
70
255
Total
seedlings
154
10
164
459
98
557
Total plants
32
32
64
14
14
28
Average no.
seedlings
14.81a*
0.38b*
2.56a*
32.79c*
7d*
19.89c*
977
54
1,031
2,955
593
3,548
Max. seedlings
Seeds talks
in 1987
Totals
1
Means are not significantly different (P<O.OS) with same subscripts.
"Values vary significantly from 0 at= P<0.01.
Seedlings were noted as close as 1 foot from the center
of the mother plant and up to 15 feet away. Most seedlings were within 5 to 10 feet of the mother plant, as expected from observations recorded by Frischknecht 1963,
1978). Seventy-five to 80 percent of the seedlings were
located downwind of the mother plants suggesting that
prevailing wind direction influences seed dispersal, as
Goodwin (1956) had previously documented.
Our data show that mountain big sagebrush seedling
establishment can be enhanced through use of tillage
if that tillage occurs after fall green-up of competing
annual grasses. Use of mother plants assures on-site
adapted seed, which may be an important factor in range
rejuvenation (Plummer and others 1968). We felt that the
in-place population at Hobble Creek was important to increase because this population has been shown to be a
preferred accession of vaseyana big sagebrush in wintering mule deer and sheep ratings (Welch and others 1986).
We feel confident that seedlings having survived 1 year
will be able to compete and develop as suggested by
Frischknecht and Bleak (1957), and Cook (1966). We
intend to observe these seedlings for several years to
determine their rate of growth and maturation.
This study shows the timing of tillage treatment to be
critical. Tilling before green-up of cheatgrass was not
effective in reducing competition to the degree needed to
permit sagebrush seedlings to become established. The
window of opportunity for tilling is open only from greenup until the ground freezes and this may limit acres that
can be treated and make flexible contracts necessary.
Use of on-site plants as a seed source has been demonstrated, but the needed protection to assure seed production by plants on heavily browsed range areas would be
expensive on either an individual plant basis or in larger
fenced areas. A more efficient method may be to use siteadapted seed to augment natural seed. Seeding could
then be done when monies were available. Use of certified seed of known purity and germinability would be
desirable.
REFERENCES
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Cook, C. W. 1966. Development and use of foothill ranges
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•
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174