Physiognomy and Structure: The vegetation in this alliance is characterized by a sparse (<25%) cover of microphyllous evergreen shrubs, usually 0.5-1 m in height. In one association, bunchgrasses form a matrix surrounding the shrubs, occasionally matching or exceeding the shrubs in height. In another association, a sod-forming short graminoid is dominant in the herbaceous layer. Forb species are often frequent and diverse, and can be prominent in some stands.

Floristics: This alliance is characterized by a moderate to dense shrub layer in which Artemisia tridentata ssp. vaseyana or Artemisia tridentata ssp. spiciformis dominates. If other shrubs are present, they have low cover and do not codominate. Perennial graminoids typically dominate the open to dense herbaceous layer. The most widespread species are Pseudoroegneria spicata and Festuca idahoensis, which occur from the Columbia Basin to the Northern Rockies, although they may not be the most abundant species in individual stands. Other locally important species may include Achnatherum occidentale (= Stipa occidentalis), Bouteloua gracilis, Bromus carinatus, Elymus trachycaulus, Festuca thurberi, Festuca viridula, Koeleria macrantha, Leucopoa kingii (= Festuca kingii), Leymus cinereus, Pascopyrum smithii, Poa fendleriana, and Poa secunda. The forb layer is variable and can be very diverse. Balsamorhiza sagittata, Monardella odoratissima, and Phlox condensata are often prominent. Species of Astragalus, Castilleja, Erigeron, Eriogonum, Geum, Lupinus, Phlox, and Potentilla are characteristic. Non-native grasses Poa pratensis and Poa compressa may be abundant. Trees are uncommon in stands of this alliance, but Abies lasiocarpa, Cercocarpus ledifolius, Juniperus occidentalis, Juniperus scopulorum, Pinus albicaulis, Pinus ponderosa, and Populus tremuloides may occasionally occur.

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 shrublands. 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. vaseyana shrub-herbaceous plant associations may represent either more moist or less disturbed communities within the complex of Artemisia tridentata ssp. vaseyana shrublands and shrub-steppe. 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 at lower elevations) 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 may become dominant.

Artemisia tridentata ssp. spiciformis communities have a natural fire frequency averaging between 20 and 40 years. Presettlement fires burned unevenly, resulting in an ever-changing mosaic of different densities and ages of sagebrush plants (Winward 1991). However, Artemisia tridentata ssp. spiciformis resprouts vigorously after fire (Goodrich et al. 1985) and can return to pre-burn canopy cover very quickly (Winward 1991).