Great Basin Desert
||It has been suggested that Central Basin and Range ecoregion and Great Basin shrub steppe be merged into this article. (Discuss) Proposed since July 2015.|
|Great Basin Desert|
The Great Basin Desert is outlined in black
|Part of||North American Desert ecoregion |
|Borders on||Wasatch Range (east)
Mojave Desert (south)
|Parts||Great Basin National Park
Great Salt Lake Desert
Black Rock Desert
|Area||150,000 sq mi (388,498 km2) Approximate area derived from a GIS reproduction of the desert area of the NPS map, above. [a]|
The Great Basin Desert is the largest desert that lies completely within the US boundaries. It is a cold desert caused by the rain shadow effect from the Sierra Nevada Range  that comprises its western border. It is also bordered by the Wasatch Range on the east and the Mojave Desert to the south.[b] Rainfall within the Great Basin Desert region varies from seven to twelve inches per year and the predominant flora are "continuous shadscale and…sagebrush."
Scientists have different definitions of the Great Basin Desert, which are often defined by negatives. J. Robert Macey defines the "Great Basin scrub desert as lacking creosote bush." The Great Basin Desert includes several arid basins lacking Larrea tridentata (chaparral) such as the "Chalfant, Hammil, Benton, and Queen valleys," as well as all but the southeast portion of the Owens Valley. Conversely, the "Panamint, Saline, and Eureka valleys" have creosote bush, unlike the Deep Springs Valley which includes part of the Great Basin scrub desert.
Organizations that study and define ecoregions also do not agree on a single definition of a "Great Basin Desert". The Environmental Protection Agency divides the geological Basin and Range province into four ecoregions by geography, two of which roughly correspond to the Great Basin Desert: the Northern Basin and Range ecoregion and the Central Basin and Range ecoregion. In contrast, the World Wildlife Fund splits the Great Basin Desert by altitude: the Great Basin shrub steppe, which is arid and at low elevation; and the Great Basin montane forests, which contain Holocene refugia.
The pattern of basin and range after basin and range in this region results in incredible biological diversity. Across the high desert there are numerous sub-climates correlating to the varied elevations. Heading from the valley bottoms to the mountain peaks, one will encounter constantly changing combinations of plant and animal species making up some 200 distinct biological communities. These communities can be generally grouped into six general communities or “life zones”.
In the lower valley bottoms, where mountain run off evaporates to create saline soils, is the shadscale zone. Plants in this community are adapted to living with very little precipitation, high heat, and saline conditions. The amount of water and the soil type in any one area will determine exactly which plants will live there. Certain areas of the valley floors may harbor no life. These parched areas that flood periodically are called playas. On the shores of the playas, shadscale is the dominant plant, but is kept company by spiny hopsage, winterfat, four-winged saltbrush, and green rabbitbrush. Trees are not found in this community. Big greasewood is the dominant shrub in more saline areas or where the water table is high. These shrubs and associated grasses typically produce abundant small seeds that are harvested by rodents and insects. Ranches and irrigated alfalfa fields form mesic habitats for some non-desert species.
Up from the valley bottoms on the lower mountain slopes and alluvial fans and bajadas, the annual precipitation increases and the shadscale community gives way to the sagebrush community. Areas in this community that have wetter and less saline soils are dominated by big sagebrush. Low sagebrush or black sagebrush dominate areas with steep rocky slopes and shallow soils. Bunchgrasses such as wheatgrass and bluegrass usually co-dominate with sagebrush or play a secondary role. Bunchgrass seems to dominate over sagebrush in areas that receive more moisture. Other shrubs commonly found in the sagebrush zone are rabbitbrush, bitterbrush, snowberry and Mormon tea (ephedra).
Continuing up in elevation, you reach the pinyon-juniper community. The main plants in this community are singleleaf pinyon pine and Utah juniper, often with a sagebrush and bitterbrush understory. The elevational range of this zone varies, but it is usually found between 6,000 and 8,000 feet (1,800 and 2,400 m), with lower limits determined by lack of moisture and the upper limits determined by temperature. The pinyon-juniper community consists of short evergreen trees that rarely grow over 20 feet in height.
The trees are widely spaced and have an understory of a mixture of shrubs and herbaceous plants, often with nearly bare ground. These characteristics have led this zone to be named the “pygmy forest” by many scientists. The lower end of this zone is dominated by juniper; the middle is a combination of both species, and the upper end is dominated by pinyon.
The taller ranges of the Great Basin have a montane community. Due to the great distances created by basins between these small forest habitats, various rock substrates, and local climates, montane forests are tremendously varied across the Great Basin.
Isolated from one mountain range to the next, montane communities inthe region have long individual histories, each one affected differently by chance factors of migration over vast expanses of desert. Smaller communities are also vulnerable to adverse affects of climate change and to genetic drift.
White fir, Douglas fir, and ponderosa pines are found in the middle elevations of some mountain ranges, while limber pine, subalpine fir, Engelmann spruce, and bristlecone pines occupy the higher elevations, continuing to the upper tree line. Mountain mahogany often dominates drier, warmer south-facing slopes. Pure stands of aspen are also common in this community.
The Bristlecone pine is an important species that is indicative of the Great Basin. Bristlecones live a long time, some for thousands of years. The harsh areas they occupy are often devoid of other plant life, so there is little competition and reduced risk of fire. The trees grow very slowly, producing very dense, disease-resistant wood. These factors contribute to the Bristlecone’s long life.
Some mountain ranges in the Great Basin are high enough to have an alpine community; a community of low growing plants above the treeline. Treeline is generally found above 10,000 feet (3,000 m) in the Great Basin, moving downslope with higher latitudes. The plants that grow above treeline are separated from other such areas by miles of foothills and valleys. This “island” phenomenon produces many endemic species - species that have evolved while isolated on a particular mountain peak or range and are found only in that one place. Grasses, sedges, low perennial herbs, and wildflowers grow above treeline.
The riparian communities of the Great Basin cut across all elevations and life zones. In the Great Basin, water is rapidly lost either to the earth or the sky. However, areas around streams where plant life is abundant constitute a riparian area. Water-loving plants like willow, narrowleaf cottonwood, choke cherry, wild rose, and aspen are found along these wet areas. The willow has a spreading root network that allows it to reach all around for water and it also helps streams by slowing erosion. These plants provide wood for beavers. In this community, Silver buffaloberry often provides shelter for North American porcupines.
The topography of the Great Basin (“island” mountain tops separated from one another by vast expanses of desert valleys) renders it vulnerable to extinctions. Populations that occupy the high peaks are isolated from one another; therefore, they cannot interbreed. Small populations are more vulnerable to the forces of extinction - generally small populations have less genetic diversity and therefore a lesser ability to adapt to changing conditions. Groundwater pumping, road and home construction, grazing, and mining are all activities that alter habitat; as more habitat is affected, the threat of extinction increases. The Great Basin is home to many threatened and endangered species:
- Least tern (Sterna antillarum athalassos)
- "Deserts". Great Basin National Park. National Park Service.
- Stoppato, Marco; Bini, Alfredo; Eklund, Linda M. (2003). Deserts. Firefly Books. p. 228. ISBN 1552976696.
- "Level I Ecoregions". US Environmental Protection Agency. Retrieved 2015-07-07.
- "What is the Great Basin?". Retrieved 2015-07-14.
- Rafferty, John P. (2011). Deserts and Steppes. The Rosen Publishing Group. p. 118. ISBN 1615303170.
- Trimble, Stephen (1999). The Sagebrush Ocean: A Natural History of the Great Basin. ISBN 0-87417-343-4. Retrieved 2010-01-13.
- Mac, M.J.; Opler, P.A.; Puckett Haecker, C.E.; Doran, P.D. (1998). "Great Basin-Mojave Desert Region" (PDF). Status and Trends of the Nation's Biological Resources. Reston, Virginia: U.S. Department of the Interior, U.S. Geological Survey.
- Macey, J. Robert (May 28, 1986). The Biogeography of a Herpetofaunal Transition Between the Great Basin and Mojave Deserts (PDF) (Report). Retrieved 2011-11-22.
Banta & Tanner (1964) felt that the Great Basin Desert [sic] deserved recognition…and defined it…as the interior drainage lying between the Sierra Nevada and the Wasatch Mountains of Utah. For the purpose of this study, I am defining the Great Basin Desert as the high elevation desert that lacks Creosote Bush.
- Soulard, C.E. "Northern Basin and Range". USGS.
- Soulard, C.E. "Land-Cover Trends of the Central Basin and Range Ecoregion" (PDF). USGS. Scientific Investigations Report 2006-5288.
- "Great Basin shrub steppe". Terrestrial Ecoregions. World Wildlife Fund.
- "Great Basin montane forests". Terrestrial Ecoregions. World Wildlife Fund.
- This article incorporates public domain material from the National Park Service document "Ecology of the Great Basin" (retrieved on 2015-07-13).
- Stoppato, Bini and Eklund stated that Great Basin Desert has an area of 190,000 square miles (490,000 km2). The derivation of the number is unclear, although it can be found in many subsequent web sources.
- The northern boundary of the Great Basin Desert is indistinct. It is commonly stated to be the Columbia Plateau, which would leave both the western and northern borders incomplete.