Included here is North America’s Great Basin together with the Snake River Plains and the Uinta Basin. It has an interior drainage bounded prominently on the west by the Sierra Nevada and the Cascade Range, on the east and south by the Rocky Mountains and the Colorado Plateau. Its northern boundary is less distinct but gives way to the Columbia Plateau.

Great Basin Sagebrush Scrub

This vegetation is largely characterized by species of Artemisia of the Tridentatae section with Artemisia tridentata being one of the most widespread species. These formations were formerly very widespread throughout the northern Great Basin before human intervention and would have covered large parts of Nevada, Utah, northeast California, southeast Oregon and western Wyoming. It mainly occurs on deep, permeable soil free of salt, and where there is sufficient soil moisture it can reach heights of up to 2 m but it is often in a more stunted state. Grasses can be an important feature in natural stands but heavy domestic grazing often eliminates these. However, both domestic and native ruminants usually avoid sagebrush because it contains oils that inhibit microbial activity in their digestive systems and so they usually target more palatable grasses and forbs. Vegetation thought to be close to the natural condition where there has been an absence or near absence of domestic grazing can be seen, for example, on the Fishtail Mesa, a plateau in northwest Arizona, and at Boysag Point on the Kaibab Plateau. At the latter site the main shrub species include Artemsia tridentata var. tridentata, A. bigelovii, Agave utahensis, Atriplex canescens, Ceratoides lanata, Chrysothamnus greenei, Coleogyne ramosissima, Ephedra viridis, Fallugia paradoxa, Gutierrezia sarothrae, Polygala rusbyi and Yucca baccata. Typical grasses are Bouteloua eriopoda, B. gracilis, Hilaria jamesii, Poa secunda, Sporobolus cryptandrus and Stipa species. In fact, at Boysag Point the total cover of perennial grasses equals that of sagebrush and on that basis this vegetation could be regarded as a form of steppe or scrub steppe. Near natural sagebrush vegetation can also be seen on parts of the rangelands of northeastern Nevada. Here are elevation ranging from 2200-3100 m the more natural stands are largely dominated by Artemisia tridentata subsp. vaseyana and Symphoricarpos oreophilus but at least five association involving these species have been identified. In general other associated shrubs include Amelanchier pallida, Chrysothamnus viscidiflorus and Purshia tridentata, while common grasses are Agropyron spicatum, A. trachycaulon, Bromus carinatus, B. marginatus, B. tectorum, Festuca idahoensis, Poa secunda and Sitanion hystrix. The chracteristic forbs include Agastache urticifolia, Agoseris glauca, Astragalus beckwithii, Balsamorhiza sagittata, Collinsia parviflora, Crepis acuminata, Eriogonum ovalifolium, Lupinus caudatus, Mertensia oblongifolia, Penstemon hymilis, Phlox longifolia and Viola beckwithii. Endemic or near endemic species associated with this formation may include Agave utahensis (Agavaceae), Ephedra nevadensis (Ephedraceae) and Xanthocephalum sarothrae (Asteraceae).

Great Basin Shadscale Scrub

Named after the dominant species Atriplex confertifolia this is a widespread saltbush association but it is only in or adjacent to the Great Basin that A. confertifolia is a wide-ranging dominant. In the Great Basin studies of the vegetation have been carried out in Colorado and Utah. The vegetation was initially thought to be indicative of saline conditions but these studies show that is not always the case. However, it tends to grow where precipitation is lower than sagebrush areas and is considered to be characteristic of the driest Great Basin desert scrub areas. Domestic grazing has altered the natural species composition in a number of areas since in addition to the perennial grasses two of the shrub Artemisia spinescens and Ceratoides lanata are also palatable. Other important shrubs include Atriplex gardneri, A, nuttallii, Chrysothamnus greenei, C. nauseosus, Gutierrezia sarothrae, Sarcobatus vermiculatus and Suaeda fruticosa. Grasses may be present but they always tend to be widely scattered and represented by just a few species. These mainly include Hilaria jamesii, Oryzopsis hymenoides, Sitanion hystrix, Sporobolus airoides and Stipa speciosa. In spring a number of annual and perennial herbaceous species make their appearance but never in abundance. These may include Delphinium bicolor, Eriogonum hookeri, Montzelia albicaulis, Salsola pestifer, Sphaeraclea grossulariaefolia, Stanleya arcuata or the endemic or near endemic Senecio uintahensis (Asteraceae) and Sphaerostigma utahense (Onagraceae).

Great Basin Blackbrush Scrub

Blackbrush (Coleogyne ramosissima) dominates some of the southern parts of the Great Basin and largely found in southern Nevada, southeastern California, north central Arizona and southeastern Utah. It has been suggested that this vegetation represents a transition between the Great Basin and the Mohave desert scrub, but it seems to be best developed along the valleys of the Colorado and Green rivers both of which are considered to be part of the Great Basin biome. Nevertheless, it does straddle the boundary between these two biomes. Associated shrubs include Artemisia filifolia, A. parryi, A. tridentata, Atriplex confertifolia, Ephedra nevadensis, E. torreyana, Eriogonum fasciculatum, Gutierrezia microcephala, Opuntia ramosissima and Stenopsis linearifolius. In south Nevada crown coverage can exceed 50%, which is a higher percentage than any other desert scrub community. This is possible a reflection of the higher rainfall at sites it occupies.

Great Basin Greasewood Scrub

Associations dominated by greasewood (Sarobatus vermiculatus) usually require good soil moisture levels. They can occur in saline situations but are not a particularly good indicator of high salt levels. In the White Valley, Utah, for example, virtually all the valley floor is occupied by this formation. Here the associated shrubs include Artemisia spinescens, Atriplex confertifolia and Suaeda fruticosa, while other species are Kochia vestita and the salt grass Distichilis stricta. However, when soil salt content exceeds about one percent, salt grasses like Distichilis spicata and D. stricta become more conspicuous together with other salt tolerant species like pickleweed (Allenvolfea occidentalis) and samphire (Salicornia utahensis).

Great Basin Winterfat Scrub

Winterfat (Krascheninnikovia lanata) associations were probably much more widespread before human intervention. The dominant species is palatable and has been described as a superior winter browse for livestock and wildlife. Consequently it is very susceptible to overgrazing and often fails to re-grow or reproduce under these conditions. The association also has a high water requirement and is intolerant of high concentrations of salt. The best stands, which can grow to about 0.5 m in height, occur on permeable, sandy soil that absorbs at large proportion of the available precipitation. Associated species typically include Atriplex confertifolia, Hilaria jamesii, Oryzopsis hymenoides, Sphaeralcea grossulariaefolia and Tetradymia glabrata. These formations often occur as ‘islands’ in a ‘sea’ of extensive shadscale and are clearly discernable due to their lighter colour.

Great Basin Iodinebush Scrub

The dominant plant here, Allenrolfea occidentalis, is very tolerant of salt and largely found in areas where the concentration is too high for other desert shrubs such as the greasewoods. Because of this it is seldom accompanied by many other species. The main ones may include shrubs like Sarcobatus vermiculatus, grasses like Distichlis stricta, Leymus cinereus, Sporobolus airoides and succulent forbs like Suaeda suffrutescens and species of Nitrophila and Salicornia.  If greasewoods are present they are invariable unhealthy looking with a stunted, yellow appearance.  The association is often confined to marginal areas and occurs, for example, as a narrow fringe around the barren playa adjacent to the greasewood associations at Tula Springs, Utah.

References

Brown, D. E. 1982. Great Basin Conifer Woodlands. In: Desert Plants.  Biotic communities of the American southwest United States and Mexico. Ed. D. E. Brown. University of Arizona.

Brown, D. E. 1982. Plains and Great Basin Grasslands. In: Desert Plants.  Biotic communities of the American southwest United States and Mexico. Ed. D. E. Brown. University of Arizona.

Brown, D. E. 1982. Great Basin Montane Scrubland. In: Desert Plants.  Biotic communities of the American southwest United States and Mexico. Ed. D. E. Brown. University of Arizona.

Fautin, R. W. 1946. Biotic communities of the northern desert shrub biome in western Utah. Ecological Monographs, 16: 251-310.

Flowers, S 1934. Vegetation of the Great Salt Lake Region. The Botanical Gazette, 95: 353-418.

McKell, C. M. & Garcia-Moya, E. 1989. North American Shrublands. In: The Biology and Utilization of Shrubs. Ed. C. M. McKell. Academic Press, Inc.

Ricketts, T. h. et al. 1999. Terrestrial Ecosystems of North America - a conservation assessment. World Wildlife Fund, USA and Canada. Island Press, Washington.

Turner, R. M. 1982. Great Basin Desert Scrub. In: Desert Plants.  Biotic communities of the American southwest United States and Mexico. Ed. D. E. Brown. University of Arizona.

Tueller, P. T. & Eckert, R. E. 1987. Big sagebrush (Artemisia tridentata vaseyana) and longleaf snowberry (Symphoricarpos oreophilus) plant associations in the northeastern Nevada. Great Basin Naturalist, 47: 117-131.

Welsh, S. L., Atwood, N. D. & Reveal, J. L. 1975. Endangered, threatened, extinct, endemic, and rare or restricted Utah vascular plants. The Great Basin Naturalist, 35: 372-376.

Welsh, S. L., Atwood, N. D. & Murdock, J. R. 1978. Kaiparowits Flora. The Great Basin Naturalist, 38: 125-179.

West, N. E. 1983a. Western Intermontane Sagebrush Steppe. In: Ecosystems of the World 5-Temperate Deserts and Semi-Deserts. Ed. N. E. West. Elsevier Scientific Publishing Company.

West, N. E. 1989a. Intermontane Deserts, Shrub Steppe and Woodland. In: North American Terrestrial Vegetation. Eds. M. G. Barbour & W. D. Billings.  Cambridge University Press.

West, N. E. 1989b. Intermontane Deserts, Shrub Steppe and Woodland. In: North American Terrestrial Vegetation. Eds.  M. G. Barbour & W. D. Billings.  Cambridge University Press.

Young, J. A., Evans, R. A. & Major, J. 1977. Sagebrush Steppe. In: Terrestrial Vegetation of California. Eds. M. G. Barbour & J. Major. John Wiley & Sons.