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An Assessment of Exotic Plant Species of Rocky Mountain National Park

Bromus tectorum L. (Anisantha tectorum)
Downy brome, downy chess, cheatgrass (Poaceae)


Current level of impact
Known locations in RMNP: South facing slopes, lateral moraine near Hollowell Park, Moraine Park museum, Headquarters area.
Assessment: Appears to be spreading on south facing slopes, lower elevations, and in recently disturbed areas. If all populations were added together, would cover an estimated area of 11-50 hectares. Populations are widespread and dense and are likely inhibiting natural secondary succession.

Distribution
Origin: Mediterranean region and Eurasia, introduced in packing materials first found near Denver, Colorado.
Geographic distribution: Widely distributed throughout North America. Abundant in Great Basin and Columbia Basin of the U.S. Very common in western states and in Colorado from 4000 to 9000'.
Ecological distribution: Common along roadsides, waste areas, misused pastures, rangelands, and cultivated crop areas. Open slopes, salt desert shrub, sagebrush, pinyon juniper, and less commonly in aspen and conifer communities. Found primarily in the 15-56 cm precipitation zones' although is found in many climatic areas.
Soils: Sandy or gravely soils, does not grow well on heavy soils, or soils with high salts.

Reproduction
Annual or winter annual, reproduces by seeds. Germinates in fall, overwinters as a seedling and flowers in the spring (from April-June). Plants are self-fertile.
Number of seeds/plant: Capable of producing in excess of 300 seeds/plant, and plants as small as 2.5 cm are capable of producing seed.
Seed longevity: Seeds may remain viable in soil for 2 to 5 years.
Seed dispersal: Seeds may be dispersed by wind, attachment to animal fur, or by small rodents. Seed is often a contaminant in hay, grain, and straw and is difficult to separate from crop seed.
Germination: Germination is increased by moistening of stratum. Litter also promotes germination and establishment of seedlings. Seeds will germinate regardless of whether they are in contact with soil. However, germination is enhanced when in contact with soil. Seeds germinate best in dark or diffuse light. Adequate fall or spring moisture seems to be primary factor which inhibits germination.

Competition Competes for soil moisture with perennial grasses because of its early spring growth habit. An excellent competitor for soil moisture and is capable of reducing soil moisture levels to permanent wilting point in upper soil layers. Capable of invading perennial bunchgrass communities that have been protected from grazing and fire in the Columbia Basin.
Response to shading: Although a competitive plant, generally does not tolerate shading.

Level of impact Strong invader, has potential to inhibit natural succession processes. Can become a fire hazard after plants have reached maturity. Although considered an invader, cheatgrass is an important forage on certain inter-mountain ranges.

Control An important consideration for control is that cheatgrass produces a large amount of seed which remains viable for 2-5 years.
Mechanical: Mowing can help to reduce seed production. However, plants continue to develop during growing season, and late developing plants may be capable of producing seed after mowing. Grazing may also help to reduce plant numbers, but is not an effective method of control.
Chemical: Most chemical control methods developed have been related to control in agricultural crops. Herbicides that have been used to control cheatgrass include: AAtrex (atrazine), Hyvar (bromacil), cynazine, chloropropham, diclofop, Roundup (glyphosate), metribuzin, Cyclone (paraquat), promamide, propham, simazine, terbacil and trifluralin. Research on chemical control in natural area (prairies) has been primarily limited to atrazine. Young (1991) found that atrazine applied at 1.1 kg/ha over one year-old bitterbrush seedlings controlled cheatgrass and promoted the establishment of big sagebrush and bitterbrush seedlings.
Biological: There is limited information on the potential of biological control of cheatgrass. Animals such as rabbits and mice will feed on cheatgrass, as will some migratory grasshoppers.
Other: Prescribed burns could be a useful method of control. However, the prescribed burn should occur in early spring to kill seedlings. Burning may also help to reduce the surface seed bank. Caution should be exercised with the timing of prescribed burns because fires later in the growing season may only reduce competition from other warm season species and promote re-establishment of cheatgrass. Young and Evans (1978) found that fire reduced the number of seeds, but those that survived the fire produced seed more vigorously and more prolific plants. McLendon and Redente (1992) reported that sucrose treatments may also be an effective method for controlling annual plants such as cheatgrass. In this study, soils that received sucrose treatments of 1600 kg C/ha/yr had significantly higher amounts of shrubs and perennial grasses than plots that received nitrogen treatments or no treatments.

References

Harris, G.A. 1967. Some competitive relationships between Agropyron spicatum 
    and Bromus tectorum. Ecological Monographs 37:89-111.

Hulbert, L.C. 1955. Ecological studies of Bromus tectorum and other brome-
    grasses. Ecological Monographs 25:181-213.

Lee, W.O. 1965. Selective control of downy brome and rattail fescue in irrigated 
    perennial grass fields of Central Oregon. Weeds 13:205-208.

Mack, R.N., and D.A. Pyke. 1984. The demography of Bromus tectorum: The role 
    of microclimate, grazing, and disease. Journal of Ecology 72:731-748.

McLendon, T. and E.F. Redente. 1992. Effects of nitrogen limitation on species 
    replacement dynamics during early succession on a semiarid sagebrush site. 
    Oecologia 91:312-317.

Morrow, L.A., and P.W. Stahiman. 1984. The history and distribution of downy brome 
    (Bromus tectorum) in North America. Weed Science 32: Supplement 1:2-6.

Peeper, T.F. 1984. Chemical and biological control of downy brome (Bromus 
    tectorum) in wheat and alfalfa in North America. Weed Science 32:Supplement 
    1:18-25.

Stubbendieck, J., C.H. Butterfield, and T.R. Flessner. 1992. Bromus tectorum L. 
    pp. 183-188. In An Assessment of Exotic Plants of the Midwest Region. Final 
    Report. Department of Agronomy, University of Nebraska, Lincoln.

Thrill, D.C., K.G. Beck, and R.H. Callihan. 1984. The biology of downy brome 
    (Bromus tectorum). Weed Science32:Supplement 1:7-12.

Upadhyaya, M.K., R. Turkington, and D. Mcilvride. 1986. The biology of Canadian 
    weeds. 75. Bromus tectorum. Canadian Journal of Plant Science 66:689-709.

Young, J.A. 1969. Population dynamics of downy brome. Weed Science 17:20-26.

Young, J.A., and R.A. Evans. 1978. Population dynamics after wildfires in sage-
    brush grasslands. Journal of Range Management. 31 :283-289.

Young, J.A. 1991. Cheatgrass. In James, L.F., J.O. Evans, M.H. Ralphs and R.D. 
    Child (eds.) Noxious Range Weeds. Westview Press, Boulder Colorado. 466 pp.

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