Physiognomy and Structure: Vegetation included in this alliance has a moderate to dense herbaceous layer (0.5-1.5 m tall) that is dominated by tall grasses and mid grasses, with short grasses common in the western portion of its range. There is usually a sparse forb layer. Widely scattered low shrubs may also be present.

Floristics: Stands have a medium to tall herbaceous layer dominated by widely spaced bunchgrasses 0.6-1.5 m tall. This layer is dominated by Calamovilfa longifolia. Other species present include Achnatherum hymenoides (= Oryzopsis hymenoides), Andropogon hallii, Hesperostipa comata (= Stipa comata), Koeleria macrantha, Pascopyrum smithii (clayey sites), Schizachyrium scoparium, and Sporobolus cryptandrus. Many of these stands also have a second herbaceous layer dominated by short graminoid species, forbs, and some small shrubs. Graminoids make up the majority of this layer, especially upland Carex spp. Among the most frequent are Carex duriuscula (= Carex eleocharis, = Carex stenophylla), Carex inops ssp. heliophila, and Carex filifolia. Bouteloua gracilis is prominent in some stands, especially in the western portion of this alliance''s range. Forbs and shrubs do not usually contribute greatly to the vegetation cover, although forb species diversity can be moderately high (Hanson and Whitman 1938, USFS 1992). The forbs that are present typically include Artemisia spp., Chenopodium leptophyllum, Lathyrus spp., Liatris punctata, Lygodesmia juncea, and Phlox hoodii. Psoralidium lanceolatum and Rumex venosus are most common on the least stabilized locations. Shrubs are uncommon, but when they are present, short shrubs such as Artemisia filifolia, Artemisia frigida, Rhus trilobata, Rosa spp., and Yucca glauca are the most likely to occur.

Dynamics:  Wind is a dominant factor that shapes the landscape where this alliance occurs. Wind sometimes scours sand and vegetation from small areas and creates blowouts. These bare spots are initially colonized by species that are relatively uncommon in this alliance, such as Redfieldia flexuosa, Muhlenbergia pungens, Yucca glauca, and Achnatherum hymenoides. Eventually, these blowouts succeed to other communities (Savage 1937, Ramaley 1939b, Tolstead 1942, Harrison 1980). Tolstead (1942) cites Nebraska pioneer accounts that dunes were less vegetated than at present, and blowouts and stands were more common before cattle ranching. Fire frequency and extent are also thought to have declined since settlement because of fuel removal by livestock grazing and fire control (Burzlaff 1962, Wolfe 1973). Consequently, active dunes and large blowouts are less common now, as are the pioneer plant species Redfieldia flexuosa, Andropogon hallii, and Yucca glauca (Harrison 1980).

These grasslands provide excellent summer forage and need careful management to prevent grazing out desirable species. Generally, overgrazing this alliance decreases the cover of species of Andropogon, Calamovilfa, Eragrostis, and Hesperostipa, and increases the cover of Bouteloua gracilis, Bouteloua hirsuta, Muhlenbergia pungens, Achnatherum hymenoides, and Sporobolus cryptandrus (Savage 1937, Tolstead 1942, Harrison 1980). Overgrazing also kills out desirable shrubs, especially Amorpha canescens and Prunus pumila var. besseyi (Ryan et al. 1994). This grassland responds rapidly to management. Deferment of grazing in the late spring and summer favors warm-season grasses such as Andropogon hallii, Bouteloua hirsuta, Bouteloua gracilis, Calamovilfa longifolia, Eragrostis trichodes, Koeleria macrantha, and Schizachyrium scoparium.

Drought also causes declines in cover of all species, especially tall grasses, and can make the grassland more vulnerable to blowouts. Savage (1937) found large declines in tallgrass cover on sandy sites during drought in 1935. He ranked the cause of damage by decreasing effect: heat, drought, and, to a much lesser extent, grazing and then soil blowing. Ramaley (1939a, b) reports that in Colorado there is marginally enough precipitation to maintain this alliance. Drought causes retrogression to mixed sandhill, sand sage, or blowout communities, which increases Muhlenbergia pungens, Artemisia filifolia, and Achnatherum hymenoides. Grazing during droughts increases the intensity of the damage (Ramaley 1939a, b). Many of these stands, especially those disturbed by wind and grazing, are vulnerable to invasion by exotic annual species of Bromus such as Bromus arvensis, Bromus squarrosus, or Bromus tectorum (Comer et al. 1999).