Physiognomy and Structure: The vegetation in this alliance is characterized by a moderate to dense (25-70%) cover of microphyllous evergreen shrubs, usually 0.5-1 m in height. Cespitose graminoids are usually prominent, often matching the shrubs in height and cover. Forb species may be frequent, but usually contribute little canopy cover. With increasing summer rain in the eastern portion of the range, there is a corresponding increase in the abundance of sod-forming grasses as compared to bunchgrasses. There may be significant cover on the ground surface by mosses and lichens, or a cryptogamic soil crust.

Floristics: Stands in this dry-site shrublands alliance have an open to moderately dense shrub canopy dominated by Artemisia tridentata ssp. wyomingensis. Artemisia tridentata ssp. tridentata may be present in some stands. Other shrubs have low cover, except species that increase with disturbance such as Gutierrezia sarothrae, Chrysothamnus viscidiflorus, and Ericameria nauseosa. Characteristic dry shrubland understory species include Achnatherum hymenoides, Achnatherum pinetorum, Achnatherum thurberianum, Bouteloua gracilis, Carex filifolia, Distichlis spicata, Elymus albicans, Elymus elymoides, Elymus lanceolatus, Hesperostipa comata, Leymus ambiguus, Leymus salinus, Pleuraphis jamesii, and Poa fendleriana. The non-native, invasive species Agropyron cristatum, Bromus tectorum, and Psathyrostachys juncea may be present and dominant in disturbed stands. Forbs form a minor and highly variable portion of this vegetation. Recurrent species include Achillea millefolium, Balsamorhiza sagittata, Camelina microcarpa, Erigeron spp., Opuntia spp., Phlox spp., and Sphaeralcea coccinea. Mosses and lichens, such as Selaginella densa and Tortula ruralis, may occur on bare ground, and in Washington and Idaho stands may cover up to 50% of the ground surface. Diagnostic of this dry-site shrubland alliance is the Artemisia tridentata ssp. wyomingensis-dominated shrub layer typically lacking a significant perennial graminoid layer (<20% cover).

Dynamics:  Complex ecological interactions between fire regimes, grazing history, and climate patterns result in equally complex patterns of species structure and composition in Artemisia tridentata. These present corresponding difficulties in the classification of these shrublands, which have been compounded by the influence of human settlement and agricultural patterns. What follows is a summary of some of the influences of altered fire regimes, and grazing history on Artemisia tridentata shrublands and shrub-herbaceous vegetation.

Artemisia tridentata ssp. wyomingensis shrublands may represent either drier or more disturbed examples of the Artemisia tridentata ssp. wyomingensis shrubland and shrub herbaceous alliances. Shrub densities typically increase with overgrazing of the bunchgrass component or with increasing summer drought (West 1983c). There is considerable debate over whether present shrub-dominated stands are actually degraded "steppe" (e.g., shrub-herbaceous physiognomy), and if the stands will return to steppe with changes in grazing and fire management. Artemisia tridentata is inhibited by fire, and excessive grazing may decrease fire frequency due to consumption of herbaceous forage, resulting in increased shrub density. Conversely, invasion by non-native annual grasses (e.g., Bromus tectorum or Bromus arvensis) may increase fire frequency sufficiently to eliminate the shrubs from the stands (Hironaka et al. 1983). With a change in fire frequency, species composition will be altered as well (West 1983c). With a high fire frequency (every 2-5 years), perennial grasses and shrubs are eliminated and non-native annual grasses dominate. At fire-return intervals of 10-30 years, short-lived resprouting shrubs such as Chrysothamnus or Tetradymia spp. dominate. At fire intervals of 30-70 years, a mixture of perennial bunchgrasses and shrubs is maintained. Finally, in the complete absence of fire, deep-rooted shrubs such as Artemisia tridentata become the theoretical dominants.