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THE COMPETITIVE INFLUENCES OF
CHEATGRASS (BROMUS TECTORUM)
ON SITE RESTORATION
Stephen B. Monsen
unusually competitive and difficult to displace without
extensive remedial treatments (Stewart and Hull1949).
Stands of cheatgrass must be thinned to permit seeded
plants to become established (Hull and Pearse 1943; Platt
and Jackman 1946; Robertson and Pearse 1945). Although
treatments have been developed to restore or revegetate
areas occupied by cheatgrass, costs of site preparation and
seeding often limit treatment projects. In addition, many
sites are not accessible, limiting restoration practices. Efforts to restore cheatgrass ranges to perennial plant cover
by natural revegetation have had limited success and have
required a long time before appreciable changes have occurred (Hironaka and Tisdale 1963). Cheatgrass continues to spread and now exists in drier environments than
it did previously. These sites are more difficult to restore.
Some progress has been made in developing techniques
and practices to control this weed and to develop plants
that are better suited for seeding. This paper discusses
some ofthe competitive attributes ofcheatgrass and presents some advances in restoration.
ABSTRACT
Cheatgrass (Bromus tectorum) continues to expand its
area of occupation and dominance. The plant now exists
amid the salt desert shrublands and upper pinyon-juniper
and ponderosa pine communities. Significant increases
have been reported within the past 20 to 40 years. The
competitive features of this weedy annual prevents natural
recovery of native species and requires extensive control
measures to assure other species become established after
seeding. Some progress has been made using selected native species to restore cheatgrass-infested sites. Properly
planned seedings in the sagebrush benchlands and pinyonjuniper woodlands usuaUy can restore the native understory and prevent further spread of this weed. Remedial
treatments conducted in areas receiving less than 10 inches
of annual rainfall is hazardous, consequently restoration
is stiU quite limited.
INTRODUCTION
Cheatgrass (Bromus tectorum) has invaded and disrupted many plant communities throughout the Intermountain and Columbia Basin Regions (Hulbert 1955).
In many situations, cheatgrass has gained dominance and
exists as nearly pure stands devoid of any native species
(Morrow and Stahlman 1984). The presence of cheatgrass
has resulted in the loss of plant diversity and associated
resource values (Harniss and Murray 1973; Young and
Evans 1978). The conversion of native communities to
annual grasslands has occurred over 8.n extended period,
having a cumulative effect on existing resources (Pickford
1932). Many sites initially occupied with scattered cheatgrass plants have been converted to nearly pure stands
of annual grass (Whisenant 1990). The stands have been
converted to annual grass by the intense competition of
cheatgrass and the sequence of fires attributed to its flammability (Young and Evans 1973). As cheatgrass gains
dominance, the incidence of wildfires increases significantly. Sites are likely to bum at more frequent intervals, resulting in the perpetuation of the annual weed,
coupled with the loss of many native species (Whisenant
1990).
Measures to prevent the spread of cheatgrass or to restore infested ranges with native species or more acceptable introductions have been investigated. The plant is
DISTRIBUTION AND AREAS OF
OCCUPATION
Cheatgrass is most abundant in the Great Basin and
Columbia Basin of the Western United States, but it is
also encountered throughout the continental United
States and portions of Canada and Mexico (Morrow and
Stahlman 1984). Warg (1938) states cheatgrass was probably introduced into the eastern Coastal States prior to
its entry into the West. It may have migrated across the
country or have been introduced directly from the Mediterranean region (Novak and Mack 1993; Novak and others 1993). The earliest reported collection in the West
was made in Washington by Sandberg and Lieberg in
1883 (Warg 1938). Mack (1981) postulated that seeds arrived in contaminated grain, which may explain its rapid
spread. It was widely scattered throughout the W9st prior
to 1900 as successive collections were reported from central Utah in 1894, Colorado in 1895, and Wyoming in 1900
(Hulbert 1955). The grass expanded rapidly, and by 1928
it was reported to have reached its present distribution
(USDA 1970). Mack (1981) reported that the grass had
become the dominant species in most disturbed steppe
communities by 1930. Platt and Jackman (1946), reporting on earlier studies, concluded that cheatgrass was
present in Oregon for at least 50 years (1880), but had
abandoned its role as an ally to become an aggressor within the last 30 years (1916 to 1946). The authors report
the plant was found mostly in areas receiving between
Paper presented at the Symposium on Ecology, Management, and Restoration oflntermountain Annual Rangelands, Boise, ID, May 18-21, 1992.
Stephen B. Monsen is a Botanist, Shrub Sciences Laboratory, Intermountain Research Station, Forest Service, U.S. Department of Agricul-
ture, Provo, UT 84606.
43
Robertson, the changes were a result of heavy grazing
coupled with the invasion of cheatgrass and the occurrence of fires.
Changes in cheatgrass distribution can be determined,
in part, by comparing previously reported studies with
current surveys. Through a review of ecological studies
by other authors, Klemmedson and Smith (1964) described
the principal areas of occurrence or habitats in which
cheatgrass was most prevalent about 30 years ago. Reports summarized in the publication concluded that cheatgrass did not tolerate saline soils well. These reports included Fleming and others 1942 and Piemeisel1932. Few
cbeatgrass plants were reported to be found in greasewoodshadscale (Sarcobatus vermiculatus/Atriple% canescens)
communities (Kearney and others 1914) and salt-desert
shrub associations (Billings 1949; Stewart and Hull1949).
Robocker (1961) reported that cheatgrass was absent from
stands ofwinterfat (Ceratiodes lanata) and Nuttall's saltbush (Atriplex spp.) communities and occurred in only
small amounts in stands of shadscale. This situation has
changed significantly as cheatgrass has expanded to occupy extensive areas once dominated by shadscale, winterfat, Nuttall's saltbush, and other woody species associated
with salt desert communities. Studies by Harper (1959)
reported little or no cheatgrass throughout the salt desert,
black sagebrush (Artemisia nova), and Wyoming sagebrush (Artemisia tridentata wyomingensis ) communities
at the Desert Experimental Range in western Utah in
1959. However, Sparks and others (1990) found that
former sagebrush- and shadscale-dominated sites in this
same area had been converted to cheatgrass and other
annual weeds on a massive scale.
Previous studies document the widespread occurrence
of cheatgrass at elevations up to 6,000 feet (Kiemmedson
and Smith 1964), with plants common in the ponderosa
pine zone throughout the West ( Daubenmire 1952; Hulbert
1955). Cheatgrass density and distribution throughout
the antelope bitterbrush ( Purshia tridentata ), mountain
brush, pinyon-juniper (Pinus/Juniperus) and ponderosa
pine communities has increased significantly in many
situations. Fire frequency has increased in these sites as
cheatgrass has gained dominance. Although the fire frequency and spread of cheatgrass has not been as evident
as that within the big sagebrush communities, the fire
cycle and changes in species composition of upland woody
communities follows the same pattern of degradation reported at lower elevations. Wildfires that ignite or originate in the lower big sagebrush-cheatgrass disturbed communities now extend to upper elevation communities,
reducing the composition of less fire-tolerant species and
creating openings for the spread of the annual grass.
The fire cycle generated by cheatgrass has eliminated
extensive stands of antelope bitterbrush in south central
Idaho, central Utah, Oregon, and southern California.
Monsen and Shaw (1994), reporting on the status and
health of stands of antelope bitterbrush within the Westem United States, indicated that many principal stands
have been lost to cheatgrass-related fires and competition.
Losses have been so critical that seed of many distinct ecotypes can no longer be collected commercially; protective
measures are recommended to retain remaining stands.
6 and 16 inches of annual rainfall. By 1946 it occupied
at least 10 million acres in eastern Oregon.
Hull and Pechanec (1947) reported that cheatgrass infestations occurred from the salt desert shrub community
through the big sagebrush (Artemisia tridentata) zone and
into the ponderosa pine (Pinus ponderosa) and Douglas-fir
(Pseudotsuga menziesii) zones. Stewart and Hull (1949)
described the distribution of cheatgrass in Idaho, concluding that the plant existed as the dominant species on approximately 4 million acres. It existed with sagebrush on
another 2 million acres as the principal understory plant.
It occurred on another 10 to 15 million acres as a component of the herbaceous vegetation. Cheatgrass was first
observed to occupy abandoned croplands, roadways, and
thin or weak fields and orchards (USDA Foresj; Service
1914). It spread to occupy dry farms and areas that were
not properly tilled. By 1915 to 1920 it had spread onto
disturbed range and wildlands. After the recession of
1920, numerous dry farms and marginal, irrigated farmlands were abandoned. The sites were quickly occupied
with the annual grass. Stewart and Hull (1949) estimated 2 million acres of abandoned farmland were converted to cheatgrass in Idaho.
Although cheatgrass invaded and quickly occupied areas throughout the West, its range and its dominance at
various sites has changed within the past 20 to 30 years.
Most noticeable has been a dramatic increase of cheatgrass density, coupled with a loss of native species. Many
sites initially invaded by cheatgrass have been burned by
wildfires or indiscriminate burning. As sites have burned,
cheatgrass, in contrast with most native species, has recovered and gained dominance. Billings (1990) reports
that without fire, cheatgrass invades overgrazed communities. As the community is burned, most shrubs and
some herbaceous species are killed, but cheatgrass seeds
are able to survive and recolonize the site. Cheatgrass increases in plant density as subsequent bums occur. The
fuel created by the annual grass provides highly flammable tinder that results in more frequent fires (Billings
1948; Young and Evans 1978). The result has been areplacement of sagebrush with cheatgrass in many sites
(Mack 1986; Pickford 1932; Piemeisel1951; Young and
Evans 1978). This cycle increases cheatgrass density and
allows it to significantly expand its area of occupation.
The conversion process has been going on since cheatgrass
was introduced. The accumulated effects becomes increasingly prevalent.
Billings (1990) reported that native bunchgrasses did
not carry fire very well, and that range fires were rare
or absent in the sagebrush-bunchgrass steppe during the
entire nineteenth century. In 1952 Robertson (1954) retraced the route and reevaluated the range-condition surveys made in northern Nevada in 1902 by P. B. Kennedy
(1903). Robertson found that bluebunch wheatgrass (Agropyron spicatum) decreased from abundant to generally absent or less than 5 percent cover within the 52-year period.
In addition, cheatgrass was not present in 1902, but had
increased dramatically by the time of Robertson's survey.
Burn scars were absent or unimportant in 1902, but by
1952 the entire route was bordered or crossed by burned
ranges that were covered by cheatgrass. According to
44
Almost complete site renovation is required to control the
weed and allow other plants to become established.
Cheatgrass has occupied many sites for nearly 100 years.
During this time, different populations have evolved that
appear site-adapted. Beckstead and others (1993) reported
differences in seed dormancy and afterripening among
collections of cheatgrass harvested from desert and mountain populations. Differences in these attributes affect
timing of germination and the ability of cheatgrass to
compete with native bunchgrasses. Cheatgrass populations differ genetically (Novak and Mack 1993; Novak
and others 1993), which contributes to the evolvement of
adapted ecotypes. The adaptability among different populations of cheatgrass is a significant problem in developing restoration measures.
Lack of Competition From Native
Species
No native species or more desirable introduced species
has been found that can compete directly with cheatgrass
throughout a broad range of sites. Most native species
that dominate bunchgrasslshrubland associations are unable to compete with cheatgrass (McKell and others 1962).
Billings (1990) found cheatgrass quickly invaded a sagebrush shrubland near Reno, NV, after a wildfire in 1947.
Forty-one years after the bum, cheatgrass and other annual weeds dominated the south and north slopes, although some native species had returned on the north
aspects. Fire-tolerant woody species, primarily antelope
bitterbrush, had recovered to occupy 17 percent of the
cover on the north-facing slopes. The fire removed both
woody and herbaceous species that were not able to recover due to cheatgrass competition. Hironaka and
Sindelar (1973) reported that squirreltail ( Sitanion hystrix)
is capable of reestablishing naturally within some sites
occupied by cheatgrass and medusahead ( Taeniatherium
caput-medusae). Sandburg bluegrass ( Poa secunda) has
also been observed to invade cheatgrass stands in some
situations, converting areas to perennial grass cover. Although natural changes have occurred, no program has
been developed for extensive conversion projects.
Robertson and Pearse (1945) concluded that cheatgrass
forms "closed communities," preventing the establishment
of seeded species unless the cheatgrass competition is
eliminated first. Similar results have been reported by
Harris (1967). Considerable success has been achieved
by planting either native or introduced species after cheatgrass has been eliminated or controlled by mechanical tillage or selected herbicides.
Various introductions have been investigated to control
and convert cheatgrass ranges to a more acceptable cover,
since few native species have demonstrated the ability to
suppress cheatgrass over extensive areas. Some progress
has been achieved in improving seedling establishment
and planting practices that increased the use of certain
introduced species, particularly crested wheatgrass
(Agropyron cristatum) (Asay and others 1986) and forage
kochia (Kochia prostrata) (Monsen and Turnipseed 1990).
Although various grass introductions compete well with
cheatgrass when the grasses are mature, the seedlings
of few species can compete with cheatgrass.
Plant communities and sites differ in their ability to
recover following occupation by cheatgrass. In general,
low elevation communities and sites receiving less than
9 inches annual precipitation are less likely to recover to
a native species complex through protection or management practices (Stewart and Hull1949). However, during
recent periods of drought from 1990 to 1994, cheatgrass
has been observed to disappear from extensive arid sagebrush ranges in Nevada, Idaho, and Utah. In some situations, perennial bunchgrasses have replaced the annual.
Klemmedson and Smith (1964) presented some preliminary
COMPETITIVE ATTRIBUTES AND
FEATURES OF CHEATGRASS
Cheatgrass possesses a number of distinct features that
contribute to its competitive ability. Like other obnoxious
weeds, this species is persistent and difficult to control. It
not only competes well with a series of native species, but
is difficult to remove from most infested areas without
significantly disrupting the plant community and soil conditions. Harris (1967) described the competitive features
of this plant. The array of characteristics is impressive,
contributing to its highly competitive nature. Any attempt to remove and replace this grass with other species,
either by artificial seeding or by management to encourage natural recovery, must consider the competitive factors controlling the ecological system. A list of principal
factors or traits that contribute to the competitive nature
of cheatgrass follows. Most features are interrelated, but
each is vital and must be addressed in any remedial treatment program.
Broad Range of Geographic
Distribution and Dominance
Cheatgrass exists as a dominant species over a broad
range of sites in the semiarid grasslands and shrublands
of the Intermountain and Columbia Basins. Within these
two broad regions, considerable variation exists in soil
features, topography, and the amount and distribution
of precipitation, yet cheatgrass maintains dominance at
all sites <Harris 1967). Few situations occur where native
species suppress cheatgrass, even in small microsites. Few
other weedy species exhibit adaptation to such a wide
range of conditions. Within these two regions, cheatgrass
occurs in quite arid environments. These sites are the most
precarious areas to artificially seed, as climatic conditions
are unpredictable and moisture is often insufficient to promote seed germination and sustain seedling establishment.
Cheatgrass is so universally abundant that it tends to
saturate almost all sites. Attempts to seed or treat cheatgrass areas are often thwarted by rapid reoccupation of
cheatgrass plants from adjacent untreated sites. Control
measures must address the weed problem of adjacent areas, particularly when small or narrow tracts are treated.
lnterseeding selected sites and managing to encourage
natural spread of the seeded species is usually not effective.
45
data summarized by Pearse that native species within the
sagebrush/antelope bitterbrushlbunchgrass communities
of south-central Idaho were capable of replacing cheatgrass
if sites were protected from grazing. The conclusions provided by Pearse were based on the response of vegetation
following 3 years of protection, 1931 to 1934. Voth (1979)
reexamined the long-term ecological exclosures that Pearse
had studied, and provided much different conclusions.
Cheatgrass remained the dominant species on most south
and west exposures after 58 years of protection. Although
native species increased in density and cover on north exposures, cheatgrass had not been eliminated and remained
an important component of the vegetation. Klemmedson
and Smith (1964) summarized the results of several investigators, concluding that cheatgrass could be replaced
by competitive natives, and that grazing and other management practices were detrimental to stands of cheatgrass (Hull and Pechanec 1947; Piemeisel1938, 1945).
Within the sagebrush communities, native species have
not demonstrated the ability to reoccupy cheatgrassdominated sites. Extensive areas exist today as evidence
of this problem. Billings (1990) concluded that little can
be done to replace cheatgrass in the sagebrush ecosystem,
to remove or to control the plant, and the only viable alternative would be to prevent it from expanding.
Lewiston, ID. Beckstead and others (1993) found
cheatgrass seeds afterripen in dry storage, thus permitting fall germination. These authors also found betweenpopulation differences in afterripening patterns were
habitat correlated. These factors were ecologically relevant and important to the survival of the species.
Seed germination features have apparently evolved to
favor establishment of cheatgrass plants under different
site or climatic conditions. Seed banking and afterripening provides sufficient seed for fall and spring germination. Although few seeds may carry over to germinate in
succeeding years, yearly renewal of the seedbank is sufficient to maintain a competitive advantage.
As cheatgrass plants invade new openings, an abundant
seed crop is quickly produced to perpetuate the plants.
First-year plants produce sufficient seeds to create highly
competitive problems. Weed seeds also spread quickly to
occupy adjacent areas and serve as a reservoir of seed for
further advancement.
Phenological Growth Attributes
of Cheatgrass
Harris (1967) described the phenological growth characteristics of cheatgrass, which contribute to its competitive
abilities. He found that once cheatgrass has germinated,
it has a distinct advantage in the rate of root elongation
over bluebunch wheatgrass. This advantage apparently
exists for other native species. Roots of cheatgrass developed about 50 percent faster than roots of the perennial
bluebunch wheatgrass. In addition, where soil conditions
remained at or near freezing throughout the \\inter months,
fall-emerging and over-wintering seedlings of cheatgrass
have an additional advantage. Roots of cheatgrass were
able to grow at temperatures as low as 3 °C, but the minimum temperature for bluebunch root growth is 8 to 10 °C.
Harris reported the inherent greater root elongation rate
of cheatgrass accounted for its dominance over bluebunch
wheatgrass. Since cheatgrass seedlings develop much
earlier than other species, the plants grow during a period
of abundant moisture. Cheatgrass effectively extracts soil
moisture regardless of plant density. Dense stands develop
both primary and secondary root systems that deplete soil
moisture as the root system advances. Sparse stands produce tillers and adventitious roots that grow faster than
roots of other plants, thereby depleting soil moisture.
Harris concluded that as growing conditions change to
favor growth ofbluebunch wheatgrass, cheatgrass has
already dominated the site. The competitive advantage
cheatgrass demonstrates over bluebunch wheatgrass is
sufficient to overcome environmental differences throughout the semiarid grasslands and sagebrush sites of the
Intermountain and Columbia Basin regions.
Seed Germination and Establishment
Cheatgrass is regarded as a winter annual. Some initial germination begins in late August coinciding with the
occurrence of fall rains, followed by a major period of germination in September and October (Mack and Pyke 1983).
Germination may occur thoughout the winter particularly
in desert conditions following winter rain (Beatley 1966).
Mack and Pyke (1983) reported cheatgrass recruitment
continued throughout the winter months, contributing 30
percent of all individuals that appear. Spring recruitment
occurs quite regularly and may be substantial, occurring
as late as mid-May (Hull and Hansen 1974). Plants that
germinate during the spring can produce a viable seed
crop. Although plants may be grazed in the spring before
seeds mature, seeds may still develop and germinate during the fall (Hulbert 1955).
Seed germination and growth of cheatgrass favor its establishment over most native herbs. Harris (1967) reports
that at moderately low temperatures with moist soils,
conditions often found in the fall at field sites, cheatgrass
has a small advantage over bluebunch wheatgrass in the
rate of germination, but the abundance of cheatgrass
seeds provides a distinct advantage. Beckstead and others (1993) evaluated different ecotypes of cheatgrass and
found that seeds of the annual grass consistently germinated earlier than squirreltail. Bum.an and others (1988)
found cheatgrass seeds germinated at lower temperatures
than perennial grasses, which was an important factor
contributing to its successful establishment.
Cheatgrass plants produce an abundance of seeds almost
every year regardless of weather conditions. Although the
amount of seed produced depends on climatic conditions,
sufficient seed is normally developed to repopulate a site.
Hulbert (1955) reported counts of between 200 and 600
seeds per square decimeter from plots located near
REMEDIAL TREATMENTS
Controlling Competition
Most weedy plants are difficult to control, and cheatgrass is no exception. Attempts to control cheatgrass under wildland conditions are extremely difficult. Failure
46
the upland sites, coupled with well designed seeding&, can
lessen the incidence of fire and restrict and limit encroachment of the annual weed.
Proactive seedings can also contain the spread of fires
from areas that frequently reburn. Greenstrip seedings
are commonly used throughout the Snake River Plain and
other large topographic regions where nearly contiguous
stands of cheatgrass occut:. In these situations, broad areas are subdivided into small units by seeding less fireprone species in strips around the border of each subunit.
This approach may not be appropriate in all situations,
but the practice can reduce the number of large fires. In
addition, the spread of fires into undisturbed areas surrounding areas dominated by cheatgrass can be prevented.
An additional advantage is the concentrated attention
given to seeding small areas. Considerably more attention and funds can be directed to seeding small strips
than is normally given to large acreages. Fire barriers
or greenstrips can normally be disked or treated to control
weed competition, increasing the assurance of attaining
a desirable stand after seeding. In addition, plantings
can normally be more easily scheduled to take advantage
of climatic conditions.
Cheatgrass can not be easily removed from all areas of
current occupation. Artificial restoration of arid regions
is extremely hazardous, but restoration of designated areas through proper management and seeding can aid weed
control.
to control cheatgrass competition is a primary factor preventing establishment of seeded species. Unlike some annual weeds, cheatgrass presents some unusual problems.
To be effective, control measures must be capable of:
• Eliminating live plants
• Preventing seed formation
• Controlling seed germination and emerging seedlings.
Controlling live plants and the existing seedbank requires a combination of treatments conducted over a 1- to
2-year period. In addition, cheatgrass competition is the
major deterrent preventing natural recruitment of new
seedlings of native species. Generally cheatgrass can be
controlled by spring tillage or by burning mature plants
before seed dispersal. Both practices reduce recruitment
of a seed crop. Fall tillage or application of a herbicide is
employed as a followup treatment to eliminate seedlings
that emerge in the fall. Artificial seeding is conducted in
the late fall or early winter.
Site Conditions
Weed control measures and seeding practices that are
used to restore cheatgrass-infested sites should be carefully designed. Techniques and methods that are used
must be functional and effective. Seeding practices must
include some means of weed control, proper seedbed preparation, and seeding. Plantings should also be conducted
at the appropriate season for the planting site.
Restoration or control measures must address the inherent growth characteristics of the plant and must be
functional within the climatic and environmental conditions of the existing communities where the plant occurs.
Recognition of climatic and environmental conditons is
critical in developing control measures. Since cheatgrass
occurs in some semiarid and arid communities, practical
control measures are frequently quite limited, as precipitation is not always adequate to assure seedling establishment. Thus, the sites in which cheatgrass occurs directly
affect the chances for restoration or site enhancement.
Sites in the salt desert and lower big sagebrush communities normally are often the most arid and difficult to restore. Areas throughout the sagebrush benchlands, pinyonjuniper, and ponderosa pine communities can be planted
without much difficulty. Once disturbances occur within
these communities, openings should be seeded if an adequate understory does not exist and weed invasion is imminent. In many situations, the herbaceous understory
has been removed from sites occupied by these woody species. Cheatgrass invasion can be expected as the overstory is removed or weakened. Measures to reestablish
the native understory are recommended in these sites
before natural disturbances such as fire or disease may
weaken the overstory. Managers may be reluctant to recommend large-scale chaining and seeding of some communities, yet seeding can reduce the potential spread of cheatgrass. Areas surrounding large, dense stands of cheatgrass
are prime areas for fires and invasion of cheatgrass. In
many situations cheatgrass has invaded low valley bottoms and with the assistance of fire is spreading to dominate more upland communities. Proper management of
Development of Adapted Species
In many situations weeds have been controled by planting a more competitive and desirable species capable of
containing or preventing the spread of the target weedy
plant. Cheatgrass occupies a number of native communities, and the primary goal in site restoration is to reestablish the native composition. Planting a single species to
control cheatgrass rarely results in the recovery of the
native community. Plantings of various wheatgrasses,
particularly crested and desert wheatgrass (Agropyron
desertorum) have been effective in controlling annual
weeds (Asay and Johnson 1983). In addition, some selections are able to compete directly with cheatgrass and can
be planted with little site preparation. Established stands
of these perennial grasses provide adequate ground cover,
reduce the incidence of fires, and prevent cheatgrass from
becoming more than a minor part of the community.
However, the introduced perennials are not compatible
with most native species and do not facilitate or allow
recovery of the natives (Monsen and Shaw 1983; Walker
and others 1993). The perennial grasses are very useful
in controlling annual weeds and can be used where recovery of the native community is not a primary goal.
Ecologists have recognized that cheatgrass seedlings
are able to suppress seedling growth of most native species. Although cheatgrass is able to invade some climax
communities (Daubenmire 1942; Poulton 1955), the plant
is unable to gain dominance of mature, established plants
(Daubenmire 1942; Young 1943). Ifthe native composition has been destroyed, cheatgrass can restrict natural
recruitment of new seedlings required to reestablish the
47
requires a long time and is not a common occurrence. Consequently, artificial seeding is required to reestablish most
plant communities. Cheatgrass competition can be controlled sufficiently by mechanical tillage, application of
herbicides, and fires to allow seeded species a chance to
establish. Seeding of native and introduced species can
be successful once cheatgrass competition is diminished.
Although cheatgrass has become a serious problem, control and restoration measures are not entirely adequate
to treat all sites. In addition, the cost and resources required to restore large areas are not currently available.
As additional resources are lost and fire-related costs continue to escalate, the need for cheatgrass control and restoration measures will become more critical.
native vegetation. Consequently, most native species have
not been considered potentially capable of competing initially with weeds unless they demonstrate unusual seedling vigor. Some attention has been given to the use of
native pioneering species to compete directly with cheatgrass. Hironaka and Sindelar (1973) reported that squirreltail competed well with cheatgrass, and suggested the
plant be used as a pioneer species to convert weedy sites
to a perennial cover. Harris (1967) suggested selecting
ecotypes of native grasses that have the ability to grow
rapidly at low temperatures, thus providing plants that
are capable of competing with rapidly growing cheatgrass
seedlings. Kitchen and Monsen (1994) found that germination and establishment of bluebunch wheatgrass could
be enhanced through selection, allowing more aggressive
and competitive materials to be developed. Hardegree
(1994) found that native seeds could be primed to initiate
early germination, increasing the competitive ability of
young seedlings.
Little attention has been given to the selection and
use of some key native species for initial weed control
and secondary successional recovery. Natural recovery
of some cheatgrass sites by native species has been observed. Sandburg bluegrass, squirreltail, Thurber needlegrass, (Stipa thurberiana), western wheatgrass (Agropyron
smithii), and streambank wheatgrass (Agropyron riparian) have been observed to invade and gain dominance of
sites once infested by cheatgrass (personal observations).
The recovery process has been evident throughout the
Intermountain Region during recent periods of drought.
The natural recovery process certainly suggests that these
same species can be effectively used in artificial seedings
if seed were available and planting requirements were
better understood.
REFERENCES
Asay, K. H.; Johnson, D. A. 1983. Genetic variability
for characters affecting stand establishment in crested
wheatgrass. Journal of Range Management. 36:
703-706.
Asay, K. H.; Dewey, D. R.; Gomm, F. B.; Horton, W. H.;
Jensen, K. B. 1986. Genetic progress through hybridization of induced and natural tetraploid& in crested
wheatgrass. Journal of Range Management. 39: 261-263.
Beatley, J. C.1966. Ecological status ofintroduced brome
grasses (Bromus spp.) in desert vegetation of southern
Nevada. Ecology. 47:548-554.
Beckstead, J.; Meyer, S. E.; Allen, P. S. 1993. A comparison of the effects of afterripening on cheatgrass (Jlromus
tectorum) and squirreltail (Elymus elymoides) germination. In: Abstracts of papers, eighth wildland shrub
symposium, arid land restoration; 1993 19-21 October;
Las Vegas, NV. Provo, UT: Shrub Research Consortium: 7.
Abstract.
Billings, W. D. 1948. Preliminary notes on fire succession
in the sagebrush zone of western Nevada. Bulletin of
the Ecological Society of America. 29: 30. Abstract.
Billings, W. D. 1949. The shadscale vegetation zone of
Nevada and eastern California in relation to climate
and soils. American Midland Naturalist. 42: 87-109.
Billings, W. D. 1990. Bromus tectorum, a biotic cause
of ecosystem impoverishment in the Great Basin. In:
Woodwell, G. M., ed. The earth in transition: patterns
and processes of biotic impoverishment. New York:
Cambridge University Press: 301-321.
Bum.an, R. A.; Monsen, S. B.; Abernethy, R. H. 1988.
Seeding competition between mountain rye, "Hycrest"
crested wheatgrass, and downy brome. Journal of
Range Management. 41: 30-34.
Daubenmire, R. F. 1942. An ecological study of the vegetation of southeastern Washington and ac:ljacent Idaho.
Ecological Monographs. 12: 53-79.
Daubenmire, R. F. 1952. Forest vegetation of northern
Idaho and ac:ljacent Washington, and its bearing on
concepts of vegetation classification. Ecological Monographs. 22: 301-330.
Fleming, C. E., Shipley, M. A.; Miller, M. R. 1942. Broncograss (Bromus tectorum) on Nevada ranges. Bull.159.
Reno, NV: University of Nevada, Agricultural Experiment Station. 21 p.
CONCLUSIONS
Cheatgrass is an extremely tenacious and competitive
weed. Since being introduced into the Western United
States over 100 years ago, it has spread to occupy extensive areas. It is particularly well suited to semiarid environments. It continues to spread and colonize additional
plant communities. This species is able to encroach onto
new sites as openings are created. Once established, it
may persist as a minor component of the community for
a considerable period of time. Its presence can restrict
natural seedling establishment of most native species. If
sites are burned or native plants are otherwise weakened,
cheatgrass can flourish and may eventually gain dominance. Semiarid shrublands and associated plant communities that are naturally slow to recolonize following a disturbance are the primary sites where cheatgrass has increased. Once cheatgrass is in place, wildfires become
more common as the plant produces highly flammable
foliage. Less fire tolerant species are further weakened
or eliminated by successive fires.
Cheatgrass provides such intense competition to new
emerging seedlings that few native plants are able to become established. Natural succession is slow under these
circumstances. Although some native species can reoccupy sites that were dominated by cheatgrass, the process
48
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