User:Hike395/Ecology of the Colorado Plateau

The Colorado Plateau ecoregion is defined by the U.S. Environmental Protection Agency as southeastern Utah and parts of western Colorado. It includes the red rock desert ecosystems as well as high elevation plateaus with expanses of pinyon-juniper woodlands and shrublands, sagebrush shrublands, blackbrush-Mormon tea shrublands, salt desert shrublands, communities and isolated mountain peaks.

The Colorado Plateau itself is an uplifted, eroded, and deeply dissected tableland. Its benches, mesas, buttes, salt valleys, cliffs, and canyons are formed in and underlain by thick layers of sedimentary rock. Rugged tableland topography is typical of the ecoregion. Precipitous side-walls mark abrupt changes in local relief, often of 1,000 to 2,000 feet (300 to 600 m) or more. Juniper-pinyon and Gambel oak woodlands dominates higher elevations and is far more extensive than in the Wyoming Basin. Saltbush-greasewood and blackbrush communities are common at lower elevations but are generally absent from the higher Arizona/New Mexico Plateau ecoregion. Summer moisture from thunderstorms supports warm season grasses not found in the Great Basin Desert. Many endemic plants occur and species diversity is greater than in the Great Basin. Several national parks are located in the Colorado Plateau and attract many visitors to view their arches, spires, and canyons. Major gas and oil fields are found in the Uinta Basin.

Ecoregions

Monticello-Cortez Upland

The gently sloping Monticello Upland is blanketed by eolian material deposited in the lee of the Abajo Mountains. It receives more precipitation in a typical year than the Semi-Arid Benchlands ecoregion that surround it. Deep, silty mollisols are characteristic and are able to retain enough available moisture to naturally support Wyoming big sagebrush and associated grasses. These soils now sustain dryland farming for Anasazi beans, winter wheat, oats, alfalfa, winter wheat and pinto beans. This is the only extensive dryland farming area in the the Colorado Plateau. Shallow or stony soils occur along the rims of benches and minor escarpments and support pinyon-juniper woodland.

Shale Deserts and Sedimentary Basins

The arid Shale Deserts ecoregion consists of nearly level benches, low rounded hills, and badlands. It is sparsely vegetated with mat saltbush, bud sagebrush, galleta, and desert trumpet. Soils are mostly entisols and aridisols; they are mostly shallow and clayey and contain salts and gypsum. Clayey soils swell when moist and are slowly permeable. Surface runoff and resultant erosion occur during and after rainstorms. Scattered, gravel-capped benches occur and protrude from the present denudational surface because they are much more resistant to erosion than the surrounding shales. Deep, vertical-walled arroyos are carved where surface water concentrates. These arroyos are major contributor of sediment and salt to the Colorado River. Floodplains have alkaline soils that support greasewood, alkali sacaton, seepweed, and shadscale.

Soils that formed primarily on Mancos Shale are found in the areas northwest of Rangely, east of Meeker, in the Grand Valley, in Dry Creek Basin and Disappointment Valley southwest of the Uncompahgre Plateau, and in southwest Colorado near the Mancos River. The Mancos shale basins have the potential for high selenium levels, a particular problem in areas with irrigated agriculture. Soils formed from sandstone, limestone, shale, and gypsum are found in Paradox and Big Gypsum Valleys southwest of the Uncompahgre Plateau. Soils formed from claystone, shale, sandstone, and mudstone are found west of Meeker, and in the Colorado River valley near Rifle. Land use includes rangeland, pastureland, and dryland and irrigated cropland, with winter wheat, small grains, forage crops, and pinto beans as major crops. The valleys of the Gunnison and Colorado Rivers have areas favorable for growing apples, peaches, pears, and apricots. Shrublands provide important winter habitat for wildlife.

Semiarid Benchlands and Canyonlands

The Semiarid Benchlands and Canyonlands ecoregion is characterized by broad grass-, shrub-, and woodland-covered benches and mesas. Elevations mostly range from 5,000 to 7,500 feet (1,500 to 2,300 m) and are higher than those of the Arid Canyonlands ecoregion. Low escarpments separate remnant mesa tops and narrow canyons from surrounding benches. Bedrock exposures (e.g. slickrock and fins are common along rims, escarpments, and on steep dip slopes. Soils are mostly entisols. These deep eolian soils are composed of fine sand and support warm season grasses, winterfat, Mormon tea, four-wing saltbush, and sagebrush. Two-needle pinyon and Utah juniper occur on shallow, stony soils. Scattered areas of Gambel oak occur at higher elevations. Fire suppression and erosion have allowed this woodland to expand beyond its original range. Fire suppression and erosion has allowed this woodland to expand beyond its original range. Overall, the vegetation is not as sparse as in drier areas such as the Shale Deserts, the Arid Canyonlands, or the Sand Deserts.

Average annual precipitation in the Colorado portion of the region varies from 10 to 18 inches (250 to 460 mm) in lower areas; on the highest sites, such as Mesa Verde, 20 to 25 inches can occur. Livestock grazing is a dominant land use, although stock carrying capacity is limited. On floodplains and terraces, some irrigated cropland occurs, primarily hay and grain for livestock. Oil and natural gas wells, oil shale extraction, and coal mining are also present in the region.

Arid Canyonlands

The Arid Canyonlands ecoregion includes the inner gorge of the Colorado River and its major tributaries. Much of this ecoregion is bounded by nearly vertical, canyon walls that separate it from the adjacent, higher benchlands of the Semi-Arid Benchlands ecoregion. Soils are shallower and have a drier moisture regime than those of the Monticello Uplands and the Semi-Arid Benchlands. Exposed bedrock is common. Blackbrush, shadscale, drought-tolerant grasses including galleta and Indian ricegrass occur. Blackbrush is much more common than in the Semi-Arid Benchlands, where pinyon-juniper woodland and sagebrush dominate. Some cropland and residential development occur near Moab, Utah.

The Escarpments

The Escarpments ecoregion is characterized by extensive, deeply-dissected, cliff-bench complexes that ascend dramatically from the Shale Deserts or Semi-Arid Benchlands ecoregions to the forested mountain rim. Local relief can be as great as 3,000 feet (900 m). This ecoregion includes major scarp slopes of the Tavaputs Plateau, the Book Cliffs, and the Grand Staircase in Utah. Natural vegetation ranges from Douglas-fir forest on steep, north-facing slopes at higher elevations to desert and semidesert grassland or shrubland on lower, drier sites. Pinyon-juniper woodland often dominates escarpments and benches that are covered by shallow soils. This rugged, remote, and varied landscape provides habitat for wildlife.

Unita Basin Floor

The Uinta Basin Floor ecoregion lies in a large synclinal basin that is enclosed by the Uinta Mountains and Tavaputs Plateau. Because of its topographic position, precipitation is low and soils are arid. Winters are constantly cold and often foggy due to frigid, dense air draining from the adjacent uplands and resultant air temperature inversions. This ecoregion is distinguished from other arid basins by the abundant stream runoff it receives from the mountains. Streams are often diverted for irrigation. Alfalfa, small grain and corn are grown for silage on arable, gently sloping terraces and valley floors. Stonier soils are irrigated for pasture where and when water is available. Excessive irrigation leaches salts from the underlying shale, contributing salinity to the Green River and its tributaries. Non-irrigated areas are used for livestock grazing.

North Uinta Basin Slopes

The North Uinta Basin Slopes ecoregion is a foothill area characterized by numerous mountain-fed streams that are entrenched into benches. It is warmer in winter, cooler in summer, and receives more annual precipitation than the Uinta Basin Floor. Its large number of perennial streams and extensive, stony outwash deposits set it apart from the Semi-Arid Benchlands ecoregion. Pinyon-juniper woodland is common. Mountain brush occurs at higher elevations and riparian vegetation is found along stream courses. Vegetation and climate contrast with the Douglas-fir forests of the higher and wetter mid-elevation Uinta Mountains. Land use is mostly grazing and irrigated pasture but there is also some irrigated farmland. Major gas and oil fields are located within this ecoregion.

Sand Deserts

The Sand Deserts ecoregion is nearly level and contains a mantle of sandy eolian deposits, shifting dunes, and exposed sandstone bedrock. Entisols and aridisols are common. The soils are sandy and have a low water-holding capacity. They have a drier moisture regime than the soils of the Monticello Upland and the Semiarid Benchlands. On average, they receive only 5 to 8 inches (130 to 200 mm) of precipitation annually. Vegetation is sparser than in the Semiarid Benchlands and stock carrying capacity is limited. Shifting sand is mostly devoid of vegetation while soils on stable sand blankets support drought-tolerant plants including Indian ricegrass, sand dropseed, yucca, and blackbrush.

References

Category:Colorado Plateau