Great Basin shrub steppe
Shrub steppe foreground, southeastern Utah. @ C.Michael Hogan
Great Basin National Park, Nevada, USA. (Photograph by John Morrison) The Great Basin shrub steppe ecoregion is situated in the most northerly of the four American deserts. Unlike the other three, which have almost exclusive ties to warm-temperate and tropical/subtropical vegetation types, the Great Basin has affinities with cold-temperate vegetation. The Chihuahuan and Sonoran Deserts may in fact be more closely related to the Argentine "Monte" than they are to the Great Basin.
The Great Basin is composed of a series of uplifted mountain ranges and their associated intervening valleys. There are approximately 100 internally drained basin within this ecoregion. The Basin is bounded to the east by the Colorado plateau and central Rocky Mountains, to the north by the Columbia plateau, and to the west by the Cascade-Sierra Mountains. The southern boundary is generally placed at the confluence of the Colorado River drainage and the Mojave Desert of southern California and the southernmost tip of Nevada.
Dominant species in the region include such distinctly cold-temperate species as sagebrushes (Artemisia), saltbrushes (Atriplex), and Winter-fat (Ceratoides lanata). These scrub species are much-branched, non-sprouting, aromatic semi-shrubs with soft wood and evergreen leaves. The Great Basin also contains species with evolutionary ties to warmer climates, such as rabbitbrush (Chrysothamnus), blackbrush (Coleogyne), hopsage (grayia) and horsebrush (Tetradymia). The region, however, contains few cacti species, either in numbers of individuals or species, and also lacks most characteristic desert plants in minor drainages.
Sagebrush communities are often considered steppe or shrub steppe because of the role of grasses, and in parts of the Great Basin grasses are important understory elements in distinctly shrub-steppe communities. Towards the south of the ecoregion, however, sagebrush may grow to the virtual exclusion of grasses even in the absence of grazing. The near absence of grasses may be partially explained by the fact that the peak precipitation occurs in winter.
Grazing and fire are the two most important forces in the sagebrush communities of the Great Basin. Neither domestic nor native ruminants eat sagebrush, resulting in reduction of more palatable grasses and forbs. Native annuals suffered under heavy grazing, and since approximately 1990 introduced annuals have become increasingly conspicuous throughout the region. These annuals, such as Drooping brome (Bromus tectorum) and Russian thistle (Salsola paulensii), have become important in arresting plant succession in many locales. The highly flammable Drooping brome also greatly increases the incidence of fire. After a fire, sprouting species of such genera as Chrysothamnus, Tetradymnia, and Gutierrezia may take on the role of the non-sprouting sagebrush.
The other dominant vegetation communities in the Great Basin are Shadscale (Atriplex confertifolia) and Blackbrush (Coleogyne ramosissima ). Shadscale is a wide ranging species, but it is found as a dominant only within and adjacent to the Great Basin. Blackbrush occurs primarily in southern Nevada, southeastern California, north-central Arizona, and southeastern Utah.
Most of the Great Basin lies northerly of the 36th parallel. Part of the ecoregion occurs to the south of that latitude along the Little Colorado River drainage in Arizona and New Mexico, where in some places it is referred to as the Painted Desert. The region generally receives less than 250 millimeters (mm) of precipitation per year. Mean monthly precipitation shows a strong winter-dominated pattern in the west, with a gradual shift eastward toward a stronger summer influence with wet and dry seasons less distinct than in the other deserts.
Biological distinctiveness
Gilbert Skink (Eumeces gilberti), Nevada, United States. (Photograph by Dr. Alan E. Leviton, California Academy of Sciences & CalPhotos) The Great Basin is the largest arid ecoregion in the USA. It is a true basin and range formation, with completely self-contained drainage, an endorheic landform. The region supports numerous threatened and endangered species. The state of Nevada is third in the nation in terms of numbers of listed species. In addition there is an endemic species of greasewood (Larrea) and an endemic kangaroo mouse (Microdipodops pallidus ) present in the Great Basin. Furthermore, the small lakes in the basin contain endemic shrimp and other endemic taxa.
This ecoregion also contains significant evolutionary and ecological phenomena. The size and orientation of Goshute Mountain, for example, concentrates hawk migrations. There are a number of special status organisms that are found in the Great Basin scrub steppe, denoted as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
Mammals
A number of mammalian species occur in the Great Basin, including the Utah prairie dog (Cynomys parvidens EN); Belding's ground squirrel (Spermophilus beldingi); Yellow-bellied marmot (Marmota flaviventris); Bighorn sheep (Ovis canadensis); Bushy-tailed woodrat (Neotoma cinerea); Canada lynx (Lynx canadensis); Canyon mouse (Peromyscus crinitus); Cliff chipmunk (Tamias dorsalis); Coyote (Canis latrans); Desert cottontail (Crotaphytus insularis); North American porcupine (Erethizon dorsatum)
Amphibians
Anuran taxa found in the Great Basin scrub steppe are eight in number: the Black toad (Anaxyrus exsul VU); Great Basin spadefoot toad (Spea intermontana); Northern leopard frog (Lithobates pipiens); Pacific treefrog (Pseudacris regilla); Northern red-legged frog (Rana aurora); Columbia spotted frog (Rana luteiventris); Southwestern toad (Anaxyrus microscaphus); and Woodhouse's toad (Anaxyrus woodhousii). The Tiger salamander (Ambystoma tigrinis) is the sole salamander found in this ecoregion.
Reptiles
The Great Basin holds numerous reptilian taxa: Bluntnose leopard lizard (Gambelia sila EN); Common kingsnake (Lampropeltis getula); Sierra gartersnake (Thamnophis couchii); Black-collared lizard (Crotaphytus insularis); Desert horned lizard (Phrynosoma platyrhinos); Desert spiny lizard (Sceloporus magister); Western gopher snake (Pituophis catenifer); Ground snake (Sonora semiannulata); Long-nosed leopard lizard (Gambelia wislizenii); Long-nosed snake (Rhinocheilus lecontei); Milk snake (Lampropeltis triangulum); Panamint alligator lizard (Elgaria panamintina), a California endemic found only in the following desert mountains: Panamint, Inyo, Nelson, White, Cosos and Argus; Yellow-bellied racer (Coluber constrictor); Ringneck snake (Diadophis punctatus); Sagebrush lizard (Sceloporus graciosus); Pygmy short-horned lizard (Phrynosoma douglasii); Side-blotched lizard (Uta stansburiana); Striped whipsnake (Masticophis taeniatus); Western banded gecko (Coleonyx variegatus); Western patch-nosed snake (Salvadora hexalepis); Western pond turtle (Emys marmorata); Western terrestrial garter snake (Thamnophis elegans); Tiger whiptail (Cnemidophorus tigris); Zebra-tailed lizard (Callisaurus draconoides); Rubber boa (Charina bottae); and Night snake (Hypsiglena torquata).
Avafauna
A large number of bird species occur within the Great Basin, either as resident or migratory taxa. Example avian species found here are: Lewis's woodpecker (Melanerpes lewis); Phainopepla (Phainopepla nitans); Pinyon jay (Phainopepla nitans VU), a specialist found in pinyon-juniper woodlands; Greater sage grouse (Centrocercus urophasianus NT); Sandhill crane (Grus canadensis).
Conservation status
Habitat loss and degradation
Virtually the entire basin has been grazed and browsed, and less than 10 percent remains as intact habitat. Exotic species have become established across the ecoregion. Irrigation for alfalfa has increased salinization in the region while mining has led to pollution by heavy metals. Urban areas in the region, particularly Las Vegas, Reno, and Salt Lake City, are growing rapidly.
Remaining blocks of intact habitat
The Great Basin contains several substantial intact habitat blocks. The most important are:
- Black Rock Desert - northwestern Nevada
- Sheep Range - southern Nevada
- Desert National Wildlife Range - southern Nevada
- Nevada test site - southern Nevada
- Great Basin National Park - eastern Nevada
Degree of fragmentation
High elevation, lush [[habitat]s] in the Great Basin are badly fragmented, but low elevation habitat is relatively intact. Much of the fragmented area can be restored.
Degree of protection
The most significant protected areas in the Great Basin are:
- Desert National Wildlife Reserve - southern Nevada
- Dugway Proving Grounds - northwestern Utah
- National Electronic Warfare Center
- Hill Air Force Base; Wendover Range - northwestern Utah
- Arc Dome Wilderness Area
- Still water National Wildlife Refuge
- Important lakes of conservation significance: Pyramid, Walker, Mono, Topaz
Type and severity of threats
West Stewarts Valley, Nevada, USA. (Photograph by David Olson) Overgrazing by domesticated livestock poses the greatest conversion threat to the Great Basin; the U.S. Federal Government is currently pursuing policies disadvantageous to rangeland protection, by artificially stimulating the grazing of livestock, through below market lease rates for grazing. Currentovergrazing creates on-going opportunities for invasion by non-native species (Invasive species). The expansion of cities like Salt Lake City and Provo also may to lead to increased development and further conversion of habitat.
Invasive species and fires are degrading the habitats of the Great Basin, while hunting threatens populations of fur-bearing mammals.
Suite of priority activities to enhance biodiversity conservation
- Protect the desert experimental range near Milford, Utah. This range has the most detailed historical grazing records in the USA. These provide the opportunity for research to determine the impact of grazing, the return of native species, and so on.
- Large scale solar energy projects should be discouraged on intact habitat areas.
- The U.S. Department of Interior should increase grazing lease rates to market levels.
- The Department of Defense should increase stewardship activities in Dugway Proving Grounds and Hill Air Force Range, Utah.
- Restore riparian areas.
- Find and protect representative pinyon-juniper vegetation association sites.
Conservation partners
- Sierra Club
- Southern Utah Wilderness Alliance
Neighboring ecoregions
- Sierra Nevada forests, to the west
- Mojave Desert, to the south
- Wasatch and Uinta montane forests, to the east
- Snake-Columbia shrub steppe, to the north
References
- J.M. Hoekstra, J. L.; Jennings, M.; Revenga, C.; Spalding, M. D.; Boucher, T. M.; Robertson, J. C.; Heibel, T. J.; Ellison, K. (2010). Molnar, J. L., ed. The Atlas of Global Conservation: Changes, Challenges, and Opportunities to Make a Difference. University of California Press. ISBN 978-0-520-26256-0.
- C. Michael Hogan, Marc Papineau, et al (1987). Development of a dynamic water quality simulation model for the Truckee River. Environmental Protection Agency Technology Series. Washington D.C. Earth Metrics Inc.
- U. S. National Park Service. "Great Basin". Geologic Provinces of the United States: Basin and Range Province. nature.nps.gov
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