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Biota of the Colorado Plateau

Biotic Communities

Alpine Tundra
Subalpine Conifer Forest
Quaking Aspen Forest
Mixed Conifer Forest
Ponderosa Pine Forest
Montane Chaparral/Scrub
Pinyon-Juniper Woodland
Mountain Grasslands
Semi-arid Grasslands
Mountain Wetlands
Riparian Areas
Paleocommunities
Elevational Range
Merriam's Life Zones

Changes in the Biota

Endangered Species
California Condor
Endangered Fish
Mammal populations
Megafaunal Extinction
Invasive/Exotic Species
Forest Composition
Species Range Expansion
Species Extirpations
Status and Trends of Plants
Succession
Riparian Degradation
Loss of Beaver
Wildfire History and Ecology
Ponderosa Fire Ecology
Tamarisk Invasion

Agents of Biotic Change

biotaBiotic Communities of the Colorado Plateau

Mountain Grasslands and Meadows

Mountain grasslands

Aspen groves and mountain grasslands; east slope of Thousand Lake Mountain, Fishlake Plateau, Utah. Photo 1999 Ray Wheeler.

Subalpine and montane grasslands and meadows occur on many of the high plateaus and isolated mountain ranges of the Colorado Plateau. Annual precipitation ranges from 30 to 45 inches, with almost 50% occurring during the summer monsoon season. These communities commonly form on flat areas with poorly-drained soils or on high, often east or south-facing, windswept ridges. There is commonly an abrupt transition between surrounding forests and these grasslands, producing an "edge effect" of high biological productivity. These grasslands and meadows are important to many species, including several large and small mammals, among them elk, deer, pronghorn, gophers, and voles, as well as numerous birds, including wild turkey and western bluebird.

Mountain grasslands are generally found between 7,500 and 8,500 feet in elevation on the Colorado Plateau. When healthy, they are commonly composed of abundant perennial bunchgrasses, including Arizona fescue, needlegrasses, or wheatgrasses, mixed with forbs such as yarrow, larkspur, or fleabane. While grasslands occur in uplands, mountain meadows occur in drainages, and are characterized by herbaceous plants, grasses, sedges and rushes.

Subalpine grasslands occur above 8,500 feet in the White Mountains, on the Kaibab Plateau, in the Chuska Mountains, and on the San Francisco Peaks in Arizona. The far northeastern portion of the Aquarius Plateau in southern Utah, termed Boulder Top, includes numerous lakes, wet meadows, and extensive subalpine grasslands. In the La Sal Mountains of southeastern Utah, montane grass-forb meadows are common with quaking aspen forests occurring along an elevational belt from 8500 to about 10,000 feet.

Since the late 1800s these higher elevation grasslands and meadows have been used for summer forage for cattle and sheep ranchers. Excessive stocking numbers on these once lush mountain meadows has resulted in widespread ecological degradation in many areas, predominantly from overgrazed plots and introduction of livestock too early in the season, when native grasses are vulnerable to damage. Grazing by livestock tends to lead to an increase in less palatable species, such as forbs, and a decrease in overall vegetative cover, leading to more rapid runoff of precipitation and erosion of soils. 

The suppression of wildfire combined with overgrazing has led to an overall decrease in mountain grassland habitats throughout the highlands of the Colorado Plateau. Woody species such as sagebrush in the lower montane zones and conifers and aspen at higher elevations have rapidly invaded once expansive mountain meadows throughout the region, particularly over the last 50 years. Conifers, especially blue spruce, are invading meadow margins in many areas. Arroyo cutting, caused by elimination of beavers and continued livestock grazing, has dried out many meadow sites. Increased tree densities in surrounding forests due to fire suppression and grazing may be further contributing to the problem by transpiring water that previously kept many meadows moist. 

Burgeoning elk populations are inhibiting land managers' attempts to improve grassland conditions by reducing livestock numbers. Studies in the Jemez Mountains of New Mexico have found that moist meadows are now often dominated by nonindigenous plants such as Kentucky bluegrass, white clover and dandelion.


Research:

Changed Southwestern Forests: Resource effects and management remedies. Over 150 years of occupancy by northern Europeans has markedly changed vegetative conditions in the Southwest. Less fire due to grazing and fire suppression triggered a shift to forests with very high tree densities, which in turn contributed to destructive forest fires. Options to deal with these changes include prescribed fire, thinning and timber harvest to mimic natural disturbances and conditions. However, there are barriers to implementing these activities on a scale large enough to have a significant benefit. Adapted from a published journal article by Marlin Johnson.

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.

References and Resources:

Allen, C. D. 1989. Changes in the landscape of the Jemez Mountains, New Mexico. Ph.D. dissertation. University of California, Berkeley.

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.

Bohrer, V. L. 1975. The prehistoric and historic role of the cool-season grasses in the Southwest. Ethnobotany 29: 199-207.

Branson, F. A. 1985. Vegetation changes on western rangelands. Range Monograph No. 2. Society for Range Management, Denver, CO.

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.

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

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

Mac, M. J., Opler, P. A. and Puckett, C. E. Status and trends of the nation's biological resources-grasslands. <http://159.189.96.215/resource/2000/grlands/grlands.htm> 7/24/00.

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.

McHenry, D. E. 1933. Woodland parks on the North Rim. Grand Canyon Nature Notes 8: 195-198.

Miller, F. H. 1921. Reclamation of grass lands by Utah juniper on the Tusayan National Forest, Arizona. Journal of Forestry 19: 647-651.

Moore, M. M. 1994. Tree encroachment on meadows of the North Rim of Grand Canyon National Park.Report #CA B000-B-0002. National Park Service, Washington, D.C., 86 pp.

Strahler, A. N. 1944. Valleys and parks of the Kaibab and Coconino plateaus, Arizona. Journal of Geology 52: 361-387.

Tilman, D. and Downing, J. A. 1994. Biodiversity and stability in grasslands. Nature 367: 363-365.

Wolters, G. L. 1996. Elk effects on Bandelier National Monument meadows and grasslands. Pp. 196-205 In: Allen, C. D., editor. Fire effects in southwestern forests: proceedings of the second La Mesa fire symposium. U.S. Forest Service General Technical Report RM-GTR-286, Fort Collins, CO.