Biotic Communities of the Colorado Plateau

Semi-arid Grasslands and Shrublands

Grassland north of Flagstaff, AZ. Photo by John Grahame

Below 6,000 feet in the cool-temperate region of southern Utah, northern Arizona, and northwestern New Mexico several different types of native grasslands were once common. The two most dominant were a Great Basin grassland, typical of the more western, central, and northern regions, and a Plains grassland, which is confined to the southeastern part of the region. Plains grasslands are commonly dominated by Blue Grama or other gramas that extend into the area from southern Colorado and northwestern Texas. Great Basin grasslands are dominated by Galleta Grass and Indian Rice Grass and reach down to the Colorado Plateau from the northwest. Both types intergrade downslope with semi-arid scrub communities and upslope with pinyon-juniper woodlands.

A large transitional area between the two types occurs in north-central Arizona and extreme southern Utah. Most of the cold-tolerant, cool-season bunch grasses that are native to these grasslands are most productive during spring and early summer, and once existed in a mosaic with deep-rooted shrubs. Until the late 1800s and the coming of the railroad and the cattle industry, the only large animals to graze these lands were pronghorn antelope. It took only 10-15 years of overgrazing by cattle near the end of the last century to extensively alter these ecosystems. The native bunchgrasses, not generally tolerant of grazing, sustained high mortality when grazed heavily in spring. Wildfires, once common in these grasslands, are far less frequent today as grazing has left less residual grass to carry fires and land management agencies maintain fire suppression policies. Both grazing and fire suppression favored shrub species over grasses and accelerated soil erosion. Site conditions have been permanently altered, and Eurasian annual grass species such as cheatgrass have aggressively colonized vast areas.

No visitor to these cold-temperate regions can fail to be impressed by the omnipresence of big sagebrush, a hardy, cold-tolerant shrub that shapes the ecosystems it dominates. Its expansion on the Colorado Plateau has been remarkable. Though big sagebrush tends to be widely spaced with herbaceous plants and grasses living beneath them, the intershrub spaces are barren or contain microphytic crusts composed of lichens and algae. The shrubs concentrate water and nutrients to form islands of fertility that are not easily altered. The current mosaic of shrublands dominated by big sagebrush, and grasslands dominated by cheatgrass, is in large part a reflection of continuing desertification of the Colorado Plateau. The pre-settlement mosaic of cool-season bunch grasses and deep-rooted shrubs may now be one of the rarest ecosystems in the Southwest.

Grazing continues to be widespread in these grasslands, and the colonization by cheatgrass and expansion of big sagebrush at the expense of native perennial grasses is expected to continue. Extensive amounts of land are also being converted to agricultural production, especially in the Four Corners area where Arizona, Colorado, New Mexico and Utah meet. Once these ecosystems are converted, there is only limited potential for conversion to native grasslands, either mechanically or by removal of livestock.

The social and ecological consequences of early cattle ranching in the Little Colorado River Basin. Examines the early development of cattle ranching in the Little Colorado River Basin, the various factors which contributed to overgrazing in the region, and the pervasive effects that early commercial cattle ranching had on the local environment.

Native Americans and the Environment. A comprehensive survey of twentieth century environmental issues facing Native Americans on the Colorado Plateau and throughout the Southwest, including discussions of agriculture, logging, mining, grazing, water rights, and tourism. Adapted from a published journal article by David Rich Lewis.

Where have all the grasslands gone? Numerous ecological studies across the Southwest have documented the decline in herbaceous vegetation (grasses and non-woody flowering plants) while forests thicken and brush invades. Documenting the changes in the Jemez Mountains of northern New Mexico, ecologist Craig Allen considers the evidence that these patterns are tied to changes in land use history, primarily livestock grazing and fire suppression.

Archer, S. 1994. Woody plant encroachment into southwestern grasslands and savannas: rates, patterns and proximate causes. Pp. 13-68 In: Vavra, M., Laycock, W. A. and Pieper, R. D., editors. Ecological implications of livestock herbivory in the west. Society for Range Management, Denver, CO.

Arnold, J. F. 1950. Changes in ponderosa pine bunchgrass ranges in northern Arizona resulting from pine regeneration and grazing. Journal of Forestry 48: 118-26.

Belnap, J. 1995. Potential role of cryptobiotic soil crusts in semiarid rangelands. Pp. 179-185 In: Ecology, management and restoration of Intermountain annual rangelands. Report INT-GTR-313. USDA Forest Service.

Belnap, J. and Furman, C. In press. Restoration techniques in arid lands. Technical Report. National Biological Service, Washington, D.C.

Brady, W., Stromberg, M., Aldon, E. F., Bonham, C. D. and Henry, S. H. 1989. Response of a semidesert grassland to 16 years of rest from grazing. Journal of Range Management 42: 284-288.

Buffington, L. C. and Herbel, C. H. 1965. Vegetational changes on a semidesert grassland range from 1858 to 1963. Ecological Monographs 35: 139-164.

Cottam, W. P. and Stewart, G. 1940. Plant succession as a result of grazing and meadow desiccation by erosion since settlement in 1862. Journal of Forestry 38: 613-626.

Cottam, W. P. 1947. Is Utah Sahara bound? University of Utah Bulletin 37: 40.

Dick-Peddie, W. A. 1993. New Mexico vegetation: Past, present and future. University of New Mexico Press, Albuquerque, 244 pp.

Dwyer, D. D. and Pieper, R. D. 1967. Fire effects on blue grama-pinyon-juniper rangeland in New Mexico. Journal of Range Management 20: 359-362.

Edwards, T. C. 1995. Protection status of vegetation cover types in Utah. Pp. 463-464 In: LaRoe, E. T., Farris, G. S., Puckett, C. E., Doran, P. D. and Mac, M. J., editors. Our living resources: a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. U.S. Department of the Interior, National Biological Service, Washington, D.C.

Edwards, T. C., Jr., Homer, C. G., Bassett, S. D., Falconer, A., Ramsey, R. D. and Wight, D. W. 1995. Utah gap analysis: An environmental information system.Technical Report 95-1. Utah State University, Cooperative Fish and Wildlife Research Unit, Logan.

Evans, R. D. and Belnap, J. 1999. Long-term consequences of disturbance on nitrogen dynamics in an arid grassland ecosystem. Ecology 80: 150-160.

Gross, F. A. and Dick-Peddie, W. A. 1979. A map of primeval vegetation in New Mexico. Southwestern Naturalist 24: 115-122.

Hall, D. O. and Scurlock, J. M. O. 1991. Climate change and productivity of natural grasslands. Annals of Botany 67: 49-55.

Herbel, C. H. 1986. Vegetation changes on arid rangeland of the southwestern United States. Cambridge University Press, New York, NY.

Hull, A. C., Jr. 1976. Rangeland use and management in the Mormon West. Symposium on agriculture, food and man--a century of progress. Brigham Young University, Provo, UT.

Hull, A. C. and Hull, M. K. 1974. Presettlement vegetation of Cache Valley, Utah and Idaho. Journal of Range Management. 27: 27-29.

Jameson, D. 1966. Pinyon–juniper litter reduces growth of blue grama. Journal of Range Management. 19: 214–217.

Johnsen, T. N., Jr. 1962. One-seed juniper invasion of northern Arizona grasslands. Ecological Monographs 32: 187-207.

Johnsen, T. N., Jr. and Elson, J. W. 1979. Sixty years of change on a central Arizona grassland-juniper woodland ecotone. Agricultural Reviews and Manuals ARM-W-7. U.S. Department of Agriculture Science and Education Administration, 28 pp.

Kleiner, E. F. 1983. Successional trends in an ungrazed, arid grassland over a decade. Journal of Range Management 36: 114-118.

Mast, J. N., Veblen, T. T. and Linhart, Y. B. 1998. Disturbance and climatic influences on age structure of ponderosa pine at the pine/grassland ecotone, Colorado Front Range. Journal of Biogeography 25: 743-755.

McCarthy, M. M. 1981. The past and future of southwest grasslands: changing issues in land planning. Pp. 99-113 In: Southwest grasslands; past, present and future. Bureau of Land Management, Washington, D.C.

Milchunas, D. G. and Lauenroth, W. K. 1989. Plant communities in relation to grazing, topography, and precipitation in a semiarid grassland. Vegetatio 80: 11-23.

Potter, L. D. and Krenetsky, J. C. 1967. Plant succession with released grazing on New Mexico range lands. Journal of Range Management 20: 145-51.

Rice, B. and Westoby, M. 1978. Vegetation responses of some Great Basin shrub communities protected from jackrabbits or domestic stock. Journal of Range Management 31: 28-33.

Rogers, G. F. 1982. Then and now: A photographic history of vegetation change in the central Great Basin Desert. University of Utah Press, Salt Lake City, 152 pp.

Schlesinger, W. H., J. F. Reynolds, G. L. Cunningham, L. F. Huenneke, W. M. Jarrel, R. A. Virginia, and W. G. Whitford. 1990. Biological feedbacks in global desertification. Science 257:1043­1048.

Shaw, H. G. and McCrosky, M. L. 1995. Historic photographs of central Arizona grasslands and associated habitats. Sharlot Hall Museum, Prescott, AZ.

Stoddard, L. A. 1946. Some physical and chemical responses of Agropyron spicatum to herbage removal at various seasons. Utah State Agricultural College, Agricultural Experiment Station Bulleti 324: 24.

Turner, R. M., Applegate, L. H., Bergthold, P. M., Gallizioli, S. and Martin, S. C. 1980. Arizona range reference areas. General Technical Report RM-79. USDA Forest Service, 34 pp.

West, N. E. 1983. Great Basin­Colorado Plateau sagebrush semi-desert. Pp. 331-349 In: West, N. E., editor. Temperate deserts and semi-deserts. Volume 5. Ecosystems of the World. Elsevier Scientific Publishing, Amsterdam and New York.

West, N. E., Provenza, F. D., Johnson, P. S. and Owens, M. K. 1984. Vegetation change after 13 years of livestock grazing exclusion on sagebrush semidesert in west central Utah. Journal of Range Management 37: 262-264.