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: This alliance is found on sandy sites in the central to southern Great Plains from southern Nebraska and Colorado south r south to Texas. It is dominated by tall- and midgrass species, with shortgrass species becoming important in the western portion of its range. The dominant species range from 0.5-1.5 m in height. Andropogon hallii is usually dominant or codominant. Calamovilfa longifolia is present to codominant in most stands north of the South Dakota-Nebraska border. Bouteloua gracilis, Bouteloua hirsuta, Eragrostis trichodes, Hesperostipa comata (= Stipa comata), Koeleria macrantha, Pascopyrum smithii, Schizachyrium scoparium, and Sporobolus cryptandrus are typical grasses in stands of this alliance. Upland sedges are also very common, especially Carex filifolia, Carex inops ssp. heliophila, and Carex duriuscula (= Carex eleocharis). Although graminoids are overwhelmingly dominant, several species of forbs can be found in many stands of this alliance. Some of the more common forbs are Ambrosia psilostachya, Ipomoea leptophylla, Liatris punctata, Psoralidium spp., and Tradescantia occidentalis. There are widely scattered low shrubs, including Rosa spp., Prunus pumila var. besseyi, and Yucca glauca. In west Texas, common associates on deep sands include Panicum havardii, Sporobolus giganteus, and Calamovilfa longifolia.

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 1939a, 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 1965, 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. Tolstead (1942) found that Andropogon hallii and Eragrostis trichodes are less common on pastures that receive year-round grazing. 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, Ramaley 1939a, 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) reports that in Colorado there is marginally enough precipitation to maintain this alliance. Drought causes retrogression to mixed sandhill, sand sage, or blow-out communities, which increases Muhlenbergia pungens, Artemisia filifolia, and Achnatherum hymenoides. Grazing during droughts increases the intensity of the damage (Ramaley 1939a).