Influence of Sagebrush and
Grass Seeding Rates on
Sagebrush Density and Plant
Size
Laurel E. Vicklund
Gerald E. Schuman
Ann L. Hild
Abstract: Wyoming big sagebrush (Artemisia tridentata ssp.
wyomingensis) establishment on mined lands in Wyoming is a
critical element of reclamation success. Because of its importance to
wildlife, shrub density is used to assess reclamation success for
wildlife habitat in Wyoming. Research was initiated at the Belle Ayr
Mine near Gillette in 1999 to evaluate the effects of Wyoming big
sagebrush seeding rates and grass competition on sagebrush establishment. Sagebrush seedling densities demonstrated consistent
increases with increased sagebrush seeding rates. The 4 kg PLS per
ha sagebrush seeding rate resulted in significantly greater density
than either the 2 or 1 kg PLS per ha seeding rate in 1999 to 2001.
Grass competition (grass seeding rates of 0, 2, 4, 6, 8, 10, and 14 kg
PLS per ha of a mixture of C3 native species) did not significantly
affect sagebrush seedling density. However, 1999 and 2000 precipitation was above or near normal, resulting in adequate moisture for
seedling emergence and growth of all seeded species. Sagebrush
seedling density declined at the higher grass seeding rates in 2001,
but seedling density was not significantly affected by grass seeding
rates (P = 0.12). Precipitation in 2001 was well below normal, and
grass competition significantly affected sagebrush seedling canopy
volume. Sagebrush seedling canopies were significantly smaller at
grass seeding rates greater than or equal to 4 kg PLS per ha. Continued evaluation of these treatments on sagebrush seedling performance will enable development of a seeding strategy that enhances
establishment of Wyoming big sagebrush on reclaimed mine lands.
Introduction ____________________
Mined land reclamationists in the Western United States
must meet many requirements to achieve successful reclamation. In August 1996, specific shrub density require-
In: Hild, Ann L.; Shaw, Nancy L.; Meyer, Susan E.; Booth, D. Terrance;
McArthur, E. Durant, comps. 2004. Seed and soil dynamics in shrubland
ecosystems: proceedings; 2002 August 12–16; Laramie, WY. Proceedings
RMRS-P-31. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station.
Laurel E. Vicklund is Senior Environmental Engineer, RAG Coal West,
Inc., Belle Ayr Mine, Gillette, WY 82717, U.S.A. Gerald E. Schuman is Soil
Scientist, High Plains Grasslands Research Station, USDA-ARS, Cheyenne,
WY 82009, U.S.A. FAX: (307) 637-6124; e-mail: gschuman@lamar.
colostate.edu. Ann L. Hild is Associate Professor, Department of Renewable
Resources, University of Wyoming, Laramie, WY 82071, U.S.A.
40
ments were imposed on mine reclamation in Wyoming
(Wyoming DEQ 1996). This standard required that the
dominant postmining shrub on lands identified as wildlife
2
habitat be reestablished at a density of 1 shrub per m on 20
percent of the disturbed landscape. Herbaceous species can
create significant competition for shrub seedlings (Eissentat
and Caldwell 1988; Schuman and others 1998; Williams and
others 2002). However, reclamation guidelines and regulations require topsoil stabilization immediately after the
topsoil is replaced using a permanent vegetation cover that
is at least as productive as premine conditions. Establishment of a perennial vegetative cover that protects the topsoil
resource from erosion can prevent the establishment of
shrubs and other difficult-to-establish native plants. However, establishment of both herbaceous and shrub species is
necessary to provide the desired plant community diversity
and appropriate species for wildlife habitat. This study was
conducted to further evaluate the establishment of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis)
when sown at three rates with a mixture of cool-season native
grasses sown at seven seeding rates (competition levels).
Methods _______________________
The study site was located at the RAG Coal West, Inc.,
Belle Ayr Mine, 29 km southeast of Gillette, WY. Climate at
the site is continental, elevation is 1,460 m, mean air
temperature is 6.7 ∞C and the average annual precipitation
is 376 mm (Belle Ayr Coal Mine 2001). The premine vegetation of the area is a northern mixed-grass prairie primarily
comprised of cool- and warm-season grasses and Wyoming
big sagebrush. Soils are derived from Tertiary and Upper
Cretaceous shale, limestone, and sandstone. The topsoil was
a sandy clay loam, with a pH of 7.6, EC of 2.0 dS per m, total
nitrogen concentration of 700 mg per kg, and a soil organic
carbon content of 1.0 percent.
Topsoil replacement (56 cm) was completed in December
1997 to January 1998, and the area was seeded to barley
(Hordeum valgare var. “Steptoe”) in April 1998 to establish
a stubble mulch. In December 1998, seven grass seeding rate
treatments (0, 2, 4, 6, 8, 10, and 14 kg PLS [pure live seed]
per ha) were randomly drilled into 6.5 by 27 m main plots
within each of four replicate blocks. The grass mixture
(approximately equal seed numbers of each species) was
USDA Forest Service Proceedings RMRS-P-31. 2004
Influence of Sagebrush and Grass Seeding Rates on Sagebrush Density and Plant Size
Results and Discussion __________
Sagebrush seedling density data (1999 and 2000) and
aboveground plant biomass data (2000) were reported earlier by Williams and others (2002) but will be included in this
paper to demonstrate longer term trends and responses over
a wider range of climatic conditions. Precipitation in 2001
was considerably less than in 1999 and 2000, which were
near-normal or above-normal precipitation years (fig. 1).
Grass Seeding Rate Responses ___
Biomass of planted grasses in 2000 and 2001 showed
similar trends (fig. 2). In 2000, aboveground biomass of
planted grasses was significantly lower for grass seeding
rates of 0 and 2 kg PLS per ha and did not differ among grass
USDA Forest Service Proceedings RMRS-P-31. 2004
100
Monthly total
Precipitation data (mm)
25 Year avg.
80
60
40
20
0
J F M A M J J A S O N D
J F M A M J J A S O N D
1999
J F M A M J J A S O N D
2000
2001
Figure 1—Monthly precipitation for 1999 to 2001
and long-term average annual precipitation, Belle
Ayr Mine, RAG Coal West, Inc., Gillette, WY (Belle
Ayr Coal Mine 2001).
1200
2000
Grass biomass (kg / ha)
composed of three cool-season native perennials: western
wheat grass (Pascopyrum smithii [Rydb.] A. Love), thickspike
wheatgrass (Elymus lanceolatus [Scribner & J.G. Smith]
Gould), and slender wheatgrass (Elymus trachycaulus [Link]
Gould ex Shinners). Each grass seeding treatment plot was
subdivided into three, 6- by 9-m plots, which were randomly
seeded to one of three Wyoming big sagebrush seeding rates
(1, 2, or 4 kg PLS per ha) in March 1999.
2
Six 1-m quadrats were permanently marked in each
sagebrush seeding rate subplot in early 1999 before seedling
emergence. Sagebrush seedlings were counted within each
of these quadrats on June 30, August 3, August 31, and
October 25, 1999; June 5 and September 18, 2000; and June
20 and September 27, 2001. In 1999, a high density of
colonizing forb species (Kochia scoparia, Melilotus officinalis,
Salsola kali) were present on the site. To mimic reclamation
practices and to aid in the counting of sagebrush seedlings
the plots were mowed at about 15 to 18 cm in height and the
material removed from the plots. In July 2000 and 2001
herbaceous plant biomass at peak standing crop was deter2
mined by clipping four 0.18-m quadrats within each of the
84 sagebrush by grass seeding rate subplots. Aboveground
biomass was separated into planted grasses, exotic grasses
(Bromus japonicus, B. tectorum, E. junceus), and forbs.
Volunteer barley from the stubble mulch was included with
the exotic grasses but comprised a very small portion of the
total biomass.
In 2001, sagebrush seedling volume was estimated on all
of the seedlings counted within the permanent quadrats.
This parameter was included because of the visual perception of differences in sagebrush seedling size among grass
seeding rates. Sagebrush seedling volume was determined
by using a caliper to measure the plant canopy diameter at
its widest point, crown diameter perpendicular to the first
measurement, and the plant height. Plant volume was
calculated with the assumption that plant shape most closely
resembled an ellipse cone.
Analysis of variance was conducted on plant biomass,
sagebrush seedling density, and sagebrush seedling volume
using a split-split plot randomized block design (SAS Institute 1999). Mean separation was accomplished using Fisher’s
protected least significant difference procedures. All statistical analyses were evaluated at P < 0.05.
Vickland, Schuman, and Hild
2001
1000
a
800
0
a
a
a
400
200
a
a
600
a
a
a
a
a
b
c b
0
2
4
6
8
10
14
Grass seeding rate (kg PLS/ha)
Figure 2—Aboveground grass biomass for 2000
and 2001 at seven grass seeding rates. Belle Ayr
Mine, RAG Coal West, Inc., Gillete, WY (means
within a year across grass seeding rates with the
same lower case letter are not significantly different,
P < 9,95).
seeding rates of greater than or equal to 4 kg PLS per ha. In
2001, planted grass aboveground biomass did not differ
among grass seeding rates greater than or equal to 2 kg PLS
per ha. These data indicate that grass seeding rates of 2 to
14 kg PLS per ha can produce similar aboveground production in the second and third year after establishment. Therefore, grass seeding rates could be lowered considerably from
rates typically used by mine reclamation specialists and still
achieve the mandated production standards (equal to or
greater than premine). Reducing grass seeding rates could
aid natural recruitment of native grass, forb, and shrub
species that are less competitive (Fortier 2000; Stevenson
and others 1995). Because the grass species planted in this
41
Influence of Sagebrush and Grass Seeding Rates on Sagebrush Density and Plant Size
Sagebrush Seeding Rate Responses
Sagebrush seedling densities differed among the three
sagebrush seeding rates within each sampling date. Sagebrush seedling density for all three seeding rates was greatest on the June 2000 count and generally declined throughout the growing season due to seedling mortality (fig. 5). In
both years (2000 and 2001) sagebrush seedling density was
greater with increased sagebrush seeding rate. Highest
densities occurred at the 4 kg PLS per ha seeding rate. Even
the 1 kg PLS per ha seeding rate resulted in sagebrush
2
seedling densities greater than the 1 seedling per m shrub
standard. However, considering the long-term survival for
big sagebrush reported by Kiger and others (1987) and
Schuman and Belden (2002), seedling densities observed at
the 1 kg PLS per ha seeding rate in our study would not meet
the shrub standard after years 9 and 10, when the standard
is assessed. Kiger and others (1987) reported survival rates
160
Sagebrush volume (cm2)
study were a mixture of bunchgrass and rhizomatous species, soil protection was adequate to ensure soil stability.
Sagebrush seedling density after three growing seasons
was not significantly different among grass seeding rates
(fig. 3), although, sagebrush seedling density within the 14
kg PLS per ha grass seeding rate was less than half that
observed at the lower grass seeding rates. Grass seeding
rate did not affect sagebrush seedling density even though
precipitation (221 mm) in 2001 was below the long-term
average (336 mm) for the site. Therefore, it appears that
sagebrush seedling density did not respond to grass competition in the first 3 years of the study.
Aboveground sagebrush seedling size (canopy volume)
differed among the grass seeding rates (fig. 4). Canopy
volume of sagebrush seedlings was significantly smaller at
grass seeding rates of greater than or equal to 4 kg PLS per
ha than at the 0 and 2 kg PLS per ha grass seeding rate. No
differences in sagebrush seedling volume were observed for
grass seeding rates of 4 to 14 kg PLS per ha.
140
120
100
Sagebrush density (seedings / m2)
June '01
Oct '01
5
4
bc
60
40
cd
cd
cd
d
10
14
0
0
4
2
6
8
Grass seeding rate (kg PLS/ha)
Figure 4—Influence of grass seeding rate on Wyoming
big sagebrush canopy volume in 2001, Belle Ayr
Mine, RAG Coal West, Inc., Gillette, WY (means with
the same lower case letters are not significantly
different, P > 0.05).
12
2 kg PLS / ha
1 kg PLS / ha
11
4 kg PLS / ha
10
9
a
a
8
7
a
6
a
b
b
5
b
4
b
3
2
c
c
c
c
June '00
Sept '00
June '01
Oct. '01
1
Figure 5—Wyoming big sagebrush seedling density
at three sagebrush seeding rates averaged across
grass seeding rates, 2000 to 2001, Bellel Ayr Mine,
RAG Coal West, Inc., Gillette, WY (means within a
sampling date with the same lower case letter are not
significantly different, P > 0.05).
3
2
1
0
0
2
4
6
8
10
Grass seeding rate (kg PLS/ha)
Figure 3—Influence of seven grass seeding rates on
Wyoming big sagebrush seedling density in 2001,
Belle Ayr Mine, RAG Coal West, Inc., Gillette, WY
(sagebrush seedling density did not differ among
grass seeding rates, P > 0.05).
42
b
80
0
6
a
20
Sagebrush density (seedings / m2)
Vickland, Schuman, and Hild
14
of 28 to 32 percent after 11 years on a volunteer stand at a
coal mine in northwestern Colorado (believed to be mountain big sagebrush, Artemisia tridentata ssp. vaseyana).
However, Schuman and Belden (2002) reported a 59 percent
average survival rate across several cultural treatments
after 8 years in the Powder River Basin of Wyoming in a
Wyoming big sagebrush stand seeded at 2.2 kg PLS per ha.
Summary and Conclusions _______
Based on the observed sagebrush seedling densities as
affected by grass seeding rate it would be difficult to make
USDA Forest Service Proceedings RMRS-P-31. 2004
Influence of Sagebrush and Grass Seeding Rates on Sagebrush Density and Plant Size
foolproof recommendations for a grass seeding rate that
would provide a sagebrush density that meets the shrub
standard after 10 years. However, if one assesses the effect
of the grass seeding rate on sagebrush seedling density and
canopy growth in the context of the sagebrush seeding rates
and planted grass aboveground biomass, we suggest that
sagebrush seeding rate of 2 kg PLS per ha and a grass
seeding rate of 4 kg PLS per ha will likely meet management
goals on comparable sites. This recommendation is based on
the lack of differences in planted grass aboveground biomass
in the 6 to 14 kg PLS per ha grass seeding rates, while grass
seeding rates greater than or equal to 4 kg PLS per ha
greatly reduced canopy size of the sagebrush seedlings.
Early results indicate a trend (nonsignificant) of fewer
sagebrush seedlings above the 6 kg PLS per ha grass seeding
rate in 2001. We know that as grass seeding rates increase,
natural recruitment and establishment of difficult-to-establish native species are significantly reduced, particularly
desired forbs and shrubs (Bergelson and Perry 1989;
Eissenstat and Caldwell 1988; Richardson and others 1986).
We believe this recommendation should result in adequate
cover, provide adequate forage production, reduce vegetative competition, and enable establishment of Wyoming big
sagebrush to meet the shrub density standard required for
successful mine reclamation.
Acknowledgments ______________
We would like to thank Mary (Fortier) Williams, Rich
Vincent, and Darrell Ueckert for their review of this paper.
We also acknowledge the assistance of Mary Williams, Matt
Mortenson, Cliff Bowen, Kristene Partlow, Jennifer (Boyle)
Muscha, Leah Burgess, Krissie Peterson, Larry Griffith,
Pam Freeman, Ernie Taylor, Doug Miyamoto, Kelli Sutphin,
and Wes Brown and other technical support staff for help in
collecting the field data. We acknowledge support of RAG
Coal West, Inc., Belle Ayr Mine, Gillette, WY; the USDA
ARS High Plains Grasslands Research Station, Cheyenne,
WY; and the Department of Renewable Resources, University of Wyoming. This research was supported in part by the
USDA Forest Service Proceedings RMRS-P-31. 2004
Vickland, Schuman, and Hild
Wyoming Abandoned Coal Mine Land Research Program,
administered by the Office of Research, University of Wyoming, and the Abandoned Mine Land Division, Wyoming
Department of Environmental Quality, Cheyenne.
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Soil Components and
Microsites
Eriogonum exilfiolium
45
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