Colorado Plateau shrublands
Kodachrome State Park, southern Utah. Source: C.Michael Hogan
The Colorado Plateau shrublands is epitomized by the Grand Canyon, an area that has been called the "land of color and canyons." The Plateau can be thought of as an elevated, northward-tilted saucer. It is characterized by its high elevation and arid to semi-arid climate. The Colorado Plateau has developed extensive topographic relief through the erosive action of high-gradient, swift-flowing rivers that have downcut and incised the plateau. Approximately 90 percent of the plateau is drained by the Colorado River and its tributaries, notably the lower catchment of the Green River, the San Juan River and Animas River. This ecoregion is classified within the Deserts and Xeric Shrublands biome, and is codified as WWF Ecoregion NA1304.
Southwest USA. Source: John Morrison
There are 416 recorded vertebrate species within the ecoregion, whose flora exhibits conspicuous but irregular vegetation zones. The woodland zone is the most extensive, dominated by what is often called a pygmy forest of Pinyon pine (Pinus edulis) and several species of juniper (Juniperus spp). Between the trees the ground is sparsely covered by grama, other grasses, herbs, and various shrubs, such as Big sagebrush (Artemisia tridentata) and Alder-leaf cercocarpus (Cercocarpus montanus).
The mountain zone extends over considerable areas on the high plateaus and mountains, but is actually much smaller than the pinyon-juniper zone. The vegetation varies considerably, from Ponderosa pine in the south to Lodgepole pine and aspen further north. Northern Arizona contains four distinct Douglas-fir habitat types. The lowest zone has arid grasslands but with many bare areas, as well as xeric shrubs and sagebrush. Several species of cacti and yucca are common at low elevations in the south.
Monoclines–local steepening in otherwise uniform, gently dipping strata–are the region’s single most distinctive structural feature. The plateau also has igneous laccoliths, flat-bottomed igneous intrusive bodies that dome up over the sedimentary rocks, such as the Henry, La Sal, Navajo, Abajo, Ute, and Carrizo Mountains of southeastern Utah and northern Arizona. The plateau is bounded on the east by the southern Rocky Mountains, on the north by the central Rocky Mountains, and on the south and west by the Basin and Range Province.
Elevations in the Plateau are generally over 1525 meters, and in some areas are as high as 3960 m. The climate is thus characterized by cold winters, and summers with hot days and cool nights. Average annual precipitation is about 510 millimeters, but some parts of the region receive less than 260 mm.
Biological characteristics
Canyon tree frog (Hyla arenicolor), southern Utah, United States. Source: Gerald and Buff Corsi, California Academy of Sciences & CalPhotos The Colorado Plateau is the only area in the United States and Canada where large mountain cutting rivers run through exposed sandstone. That unique juxtaposition created the Grand Canyon, an internationally important ecotourism zone, and other spectacular canyons in the region. There are a number of special status taxa that are found on the Colorado Plateau, denoted variously as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
Mammals
Yellow-bellied marmot. @ C. Michael Hogan Numerous mammalian species are found within the Colorado Plateau shrublands ecoregion, including the Black-tailed prairie dog (Cynomys ludovicianus); Long-eared chipmunk (Tamias quadrimaculatus); Utah prairie dog (Cynomys parvidens EN); Yellow-bellied marmot (Marmota flaviventris); and the Uinta chipmunk (Tamias umbrinus), a burrowing omnivore.
Avifauna
A large number of avian species are seen in the ecoregion, both resident and migratory. Representative of these taxa are: Chestnut-collared longspur (Calcarius ornatus NT); Greater sage grouse (Centrocercus urophasianus NT); Northern pygmy owl (Glaucidium gnoma); Cactus wren (Campylorhynchus brunneicapillus).
Reptiles
There are various snakes occurring within the ecoregion, including: Black-necked garter snake (Thamnophis cyrtopsis), usually found in riparian zones; Plains Blackhead snake (Tantilla nigriceps); Black-tailed rattlesnake (Crotalus molossus), who seeks inactivity refuge in rock crevices, animal burrows and even woodrat houses. Other reptiles found here include: Common checkered whiptail (Cnemidophorus tesselatus).
Amphibians
There are only a limited number of anuran taxa within the Colorado Plateau, which comprehensive occcurrence list for the ecoregion is: Red-spotted toad (Anaxyrus punctatus); Canyon treefrog (Hyla arenicolor); Woodhouse's toad (Anaxyrus woodhousii); Couch's spadefoot toad (Scaphiopus couchii); Northern leopard frog (Lithobates pipiens); Plains spadefoot toad (Spea bombifrons); and Southwestern toad (Anaxyrus microscaphus). The Tiger salamander (Ambystoma tigrinum) is the sole salamander found on the Colorado Plateau shrublands.
Fish
Humpback chub. @ Bob Corrigan/ EoL The Colorado River fish fauna display distinctive adaptive radiations. The Humpback chub (Gila cypha), for example, is a highly specialized minnow that lives in the upper Colorado. It adapted to the water’s fast current and its extremes of temperature and flow rate. Dams and water diversion, however, have created a series of placid, stillwater lakes and side streams, and the Humpback chub may not be able to adapt to these altered conditions. The species, along with other native Colorado River fishes including the Bonytail (Gila elegans), Squawfish (Ptychocheilus lucius), and possibly the Flannelmouth sucker (Catostomus latipinnis), may not survive much further in time.
Arthropods
This ecoregion is also rich in certain species of insects. The portion of the Colorado Plateau in the state of Colorado harbors 61 of the 131 species of grasshopper found in the state. The Plateau is also rich in ant species and supports several endemic leafhopper species.
Conservation status
Habitat loss and degradation
Approximately 15 percent of the Colorado Plateau remains as intact [[habitat].] While little of the remaining 85 percent has been heavily altered by human activity, all show some signs of stress. Riparian areas and areas with mineral resources have been the hardest hit. The main reason for habitat loss in the region is grazing, and there is widespread grazing damage in the ecoregion. Other important causes of habitat loss include mining for coal and uranium, agriculture, invasion of exotics following heavy grazing, oil and gas exploration, dams, and urbanization, particularly around heavily visited National Parks.
Habitat loss is concentrated along Interstate 40 in the Four Corners region, along the Colorado River, and in the coal mining region in the northwest corner of the ecoregion.
Remaining blocks of intact habitat
Several relatively large blocks of more or less intact habitat remain. Important blocks (chiefly concentrated along the Colorado River) include:
- Bryce Canyon National Park- southern Utah
- Grand Canyon National Park - northwestern Arizona
- Canyonlands National Park - eastern Utah
- Escalante-Capitol Reef-Kaiparorwits Plateau - south central Utah
- Desolation Canyon
- San Raphael Swell
- Navajo Mountain - southern Colorado
- Arches National Park - eastern Utah
- Cebolleta Mesa complex
- Sevilleta National Wildlife Refuge
- Zion National Park-Southern Utah
Degree of fragmentation
The southern and eastern parts of the Colorado Plateau have been fragmented by urbanization, mining, and agriculture. The Colorado River and Upper Rio Grande riparian corridors are also highly fragmented.
Degree of protection
This ecoregion has numerous sizable protected areas, and contains a variety of habitat types. Xeric shrubland is not well protected, but such shrubland appears to be thriving moderately well outside of the reserves. The most important protected areas in this ecoregion include:
- Grand Canyon National Park
- Bryce Canyon National Park - southern Utah
- Canyonlands National Park
- Hovenweep National Monument - southeastern Utah and southwestern ColoradoMalapei
- Arches National Park
- Dinosaur National Monument - western Colorado and eastern Utah
- Mesa Verde National Park - southwestern Colorado
- Sevilleta National Wildlife Refuge
- Capital Reef National Park
- Rio Grande NWSR
- Petrified Forest National Park - eastern Arizona
- Zion National Park - southern Utah
Type and severity of threats
While conversion of natural habitat to other land uses poses a problem for only a portion of the Colorado Plateau, urban and suburban development, strip-mining, and other activities threaten some of the most sensitive habitats in the region. Development is a particular threat in the vicinity of certain National Parks, as well as the urbanization around Moab, Utah and Santa Fe and Farmington, New Mexico. Strip-mining and the potential expansion of a coal-burning power plants threatens the Kaiparowits Plateau. There is considerable pressure to expand coal-burning power plants to support the growing use of electric vehicles; this off-site impact of electric vehicles is sometimes called the "long tailpipe".
The Animas-La Plata project, were it constructed, would destroy the river system and create agricultural land. Air pollution from uranium and coal mining poses a potential threat to the ecoregion, along with off-road vehicles, overgrazing, and excessive impacts of recreation around Moab. The greatest threat to wildlife on the Colorado Plateau is the destruction of native fish by dam-building and other forms of development.
Priority activities to enhance biodiversity
- Repeal RS 2477. This federal law allow counties to establish rights of way across old cattle trails and horse trails on federal lands. Counties have made thousands of claims to rights-of-way within the Colorado Plateau. By exercising these rights, counties fragment public lands and thus disqualify them for wilderness designation, often leading to development.
- Control the impact of livestock overgrazing. Such grazing causes severe impacts to riparian areas, which are the biological corridors of the plateau. An important element of this mitigation is to raise all grazing fees on public lands to market rates. The use of taxpayer subsidies for private grazing places great pressure on preservation of grasslands and prairies.
- Control exotics. Tamarisk, cheat-grass, and other alien species threaten native plants and animals. This will require management plus research into the most cost-effective control methods.
- Protect Colorado River endangered fishes: Change reservoir operations to benefit fishes. For example, manage flows so as to mimic the natural hydrograph (floods), and release water from the top rather than the cold bottom of Glen Canyon reservoir (certain fishes require warm water).
- Inventory and monitor biodiversity. Too little is known about biodiversity in this region. In particular, there is a need to determine why amphibians are declining.
- Protect neotropical migratory birds. We need to protect their nesting habitat in this region, but we also need to know what is causing their population decline.
- Protect threatened and endangered species. The Colorado Plateau has some localized threatened and endangered species. The Mexican spotted owl (Strix occidentalis lucida) tends to occur in areas where people like to recreate, leading to conflicts.
- Repeal the salvage logging rider. A number of southern Utah forests have been targeted for logging under the provisions of the salvage rider.
Non-government conservation partners
- Grand Canyon Trust
- The Nature Conservancy of Arizona
- The Nature Conservancy of Colorado
- The Nature Conservancy of New Mexico
- The Nature Conservancy
- The Nature Conservancy of Utah
- The Nature Conservancy - Western Region
- Navaho Nation Natural Heritage Program
- Southern Utah Wilderness Alliance
- Utah Wilderness Coalition
Neighboring ecoregions
- Wyoming Basin shrub steppe, to the northeast
- Western short grasslands, at the southeast
- Chihuahuan Desert, at the south-southeast
- Arizona mountains forests, south-southwest and some disjunct pieces within the ecoregion
- Sonoran Desert, with a small contact zone at the extreme southwest
- Mojave Desert, to the west
- Great Basin shrub steppe, with a small contact zone at the west
- Wasatch and Uinta montane forests, at the northwest
References
- Michael G. Barbour and William Dwight Billings. 2000. North American Terrestrial Vegetation. Cambridge University Press. ISBN 0-521-55986-3.
- Donald L. Baars. 2000. The Colorado Plateau: a geologic history. Donald L. Baars. 2000. The Colorado Plateau: a geologic history. University of New Mexico Press. 254 pages
- Arthur C. Benke and Colbert E.Cushing. 2005. Rivers of North America. 1144 pages
- Eugene P. Kiver and David V. Harris. 1999, Geology of U.S. Parklands, Wiley, 5th ed. ISBN 0-471-33218-6
- Taylor H. Ricketts. 1999. Terrestrial ecoregions of North America: a conservation assessment. 485 pages
- Richard Cannings. 2007. The Rockies: A Natural History. 304 pages
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