Physiognomy and Structure: Medium to tall bunchgrass-dominated group occurring with scattered shrubs as a matrix community or interspersed among shrub-dominated communities. Cover within this group is variable from dense to less than 25% cover.

Floristics: The dominant perennial bunchgrasses and shrubs within this group are all drought-resistant plants. Dominant or codominant species are Achnatherum hymenoides, Achnatherum lettermanii, Achnatherum nelsonii, Achnatherum speciosum, Bouteloua eriopoda, Bouteloua gracilis, Hesperostipa comata, Pleuraphis jamesii, Poa cusickii, Poa secunda, and Pseudoroegneria spicata. Other graminoids may include Aristida purpurea, Carex filifolia, Elymus elymoides, Koeleria macrantha, Leymus salinus, or Sporobolus cryptandrus. Scattered shrubs and dwarf-shrubs often are present, especially Artemisia tridentata ssp. tridentata, Artemisia tridentata ssp. wyomingensis, Atriplex spp., Coleogyne ramosissima, Ephedra spp., Gutierrezia sarothrae, and Krascheninnikovia lanata. Forb cover is also sparse but can be relatively diverse. Common forbs are Gaura coccinea, Balsamorhiza sagittata, Hymenopappus filifolius, Machaeranthera canescens, Sphaeralcea coccinea, Vicia americana, Lappula occidentalis (= Lappula redowskii), Lithophragma glabrum, Lupinus pusillus, Opuntia aurea (= Opuntia basilaris var. aurea), Opuntia polyacantha, Plantago patagonica, Pediomelum argophyllum, Artemisia campestris, Artemisia dracunculus, Artemisia ludoviciana, and species of Antennaria, Astragalus, Cryptantha, Eriogonum, Gilia, and Lappula. Cryptogams are important in some stands with up to 40% ground cover on sites in the Colorado Plateau. Exotic species such as Bromus tectorum, Draba verna, Lactuca serriola, Salsola tragus, Bassia scoparia (= Kochia scoparia), Onopordum acanthium, Poa pratensis, Sisymbrium altissimum, and Tragopogon dubius are present in many of these stands.

Dynamics:  Achnatherum hymenoides is one of the most drought-tolerant grasses in the western U.S. (USFS 1937). It is also a valuable forage grass in arid and semi-arid regions. Improperly managed livestock grazing could increase soil erosion, decrease cover of this palatable plant species and increase weedy species (USDA 1937). Hesperostipa comata is a deep-rooted grass that uses soil moisture below 0.5 m during the dry summers. Burning generally kills or severely damages Hesperostipa comata plants. After fire, regeneration of this non-rhizomatous bunchgrass is through seed and may take many years to reach prefire densities. Pleuraphis jamesii is both drought- and grazing-resistant (USFS 1937, Weaver and Albertson 1956, West et al. 1972). In parts of its range it increases under grazing, and in others parts it decreases. The grass is favored in mixedgrass stands because it is only moderately palatable to livestock, but decreases when heavily grazed during drought and in the more arid portions of its range where it is the dominant grass (West et al. 1972). This grass reproduces extensively from scaly rhizomes. These rhizomes make the plant resistant to trampling by livestock and have good soil binding properties (USFS 1937, Weaver and Albertson 1956, West et al. 1972). The cool-season annual grass Bromus tectorum can be an effective competitor for winter soil moisture because it can germinate in the fall, over-winter, then begin re-growing in the early spring before it is warm enough for many perennial grasses, completing its lifecycle and depleting soil moisture before the dry summer weather begins. This annual species also produces abundant fine fuels that carry fire well and increase the frequency of fires (FEIS 1998).