Physiognomy and Structure: No Data Available

Floristics: This is often a somewhat sparse community, with total perennial vegetation cover rarely exceeding 30%. In wet years, weedy and native annual herbaceous species may provide more than 50% cover. Opuntia polyacantha and Opuntia phaeacantha are the most common dominant cacti in this alliance, occurring in patches or clumps throughout the community. Scattered individuals of other shrub species may also occur in this community, particularly Atriplex canescens. Other shrubs present may include Artemisia tridentata ssp. wyomingensis, Atriplex confertifolia, Chrysothamnus viscidiflorus, Ephedra spp., Gutierrezia sarothrae, Grayia spinosa, and Sarcobatus vermiculatus. The exotic annual grass Bromus tectorum frequently dominates the herbaceous layer along with weedy and exotic forbs such as Astragalus nuttallianus and Erodium cicutarium; however, even in the most disturbed sites, some native forbs and grasses may persist, including Achnatherum hymenoides, Bouteloua gracilis, Hesperostipa comata, Pleuraphis jamesii, and Sphaeralcea spp.

Dynamics:  In all but the most xeric habitats, dominance by Opuntia species generally indicates heavy, chronic disturbance, such as grazing by domestic livestock (Rice and Westoby 1978). However, in some extremely xeric habitats, such as sandsheets or coarse dark metamorphic gravels, Opuntia will dominate a community that otherwise shows few signs of disturbance and may have a well-developed cryptobiotic soil crust.