Included here is North America’s Great Basin together with the Snake River Plains, the Uinta Basin and a large part of the Colorado Plateau. It has an interior drainage bounded prominently in the west by the Sierra Nevada and the Cascade Range and in 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 Shadscale Associations

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 Greasewood Associations

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 Associations

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 Associations

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.

Great Basin Saltmarsh

These are largely confined to saline wet depressions and often dominated by the desert salt grass Distichlis stricta, but species composition can vary from place to place depending on levels of salinity and water availability. In hyper saline zones with seasonal water supplies, very few additional species occur, but may include other well developed halophytes such as Cordylanthes maritimus, Salicornia europaea, Sporobolus airoides, Suaeda depressa, Triglochin maritima and the endemic or near endemic Salicornia utahensis (Chenopodiaceae). Examples are found at Goshen Playa, Utah County, and Plover Playa, Tooele County. In less saline situations where water supplies are more consistent more diverse communities can develop. Here additional species may include Allenrolfea occidentalis, Eleocharis palustris, Juncus balticus, Puccinellia nuttaliana, Scirpus americanus and the endemic or near endemic Centaurium exaltatum (Gentianaceae). Around the Great Salt Lake in Utah there are some remarkable saltmarsh strandline zonations. At Garfield and Saltair beaches the pioneer zone is dominated by Salicornia rubra and S. utahensis. Moving landward this is followed by a further four zones: a Suaeda erecta zone, a Distichlis spicata zone, a zone that includes Abronia salsa, Bromus tectorum, Eriocoma cuspidata, Puccinellia nutalliana, Spartina gracilis and the endemic or near endemic Sphaerostigma utahensis (Onagraceae), and finally a zone with Atriplex hastata, Distichlis spicata and Sporobolus asperifolius. Other species that may be present are Atriplex rosea, Chrysothamnus pulcherrimus, Gutierrezia microcephala, Iva axillaris, Pachylophus marginatus, Poa nevadensis and Sporobolus cryptandrus.


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