Great Plains Sandhill Steppe

This shrubland system is found mostly in south-central areas of the Western Great Plains Division ranging from southeastern Wyoming and southwestern Nebraska up into the Nebraska Sandhill region, south through eastern Colorado, and New Mexico to central Texas, although some examples may reach as far north as the Badlands of South Dakota. The climate is semi-arid to arid for much of the region in which this system occurs. This system is found on somewhat excessively to excessively well-drained, deep sandy soils that are often associated with dune systems and ancient floodplains. In some areas, this system may actually occur as a result of overgrazing in Western Great Plains Tallgrass Prairie (CES303.673) or Western Great Plains Sand Prairie (CES303.670). Typically, this system is characterized by a sparse to moderately dense woody layer dominated or codominated by Artemisia filifolia, but other characteristic species may be present, including Amorpha canescens, Prosopis glandulosa (southern stands), Prunus angustifolia, Prunus pumila var. besseyi (northern stands), Quercus havardii (Texas), Rhus trilobata, and Yucca glauca. Associated herbaceous species can vary with geography, amount and season of precipitation, disturbance, and soil texture. The herbaceous layer typically has a moderate to dense canopy but may include stands with sparse understory. Several mid- to tallgrass species characteristic of sand substrates are usually present to dominant, such as Andropogon hallii, Calamovilfa gigantea, Calamovilfa longifolia, Schizachyrium scoparium, Sporobolus cryptandrus, Sporobolus giganteus, or Hesperostipa comata.

This system is distinguished by a sparse to moderately dense shrub layer (15-90% canopy cover in Texas) dominated or codominated by Artemisia filifolia with Quercus havardii and Prosopis glandulosa to the south. In addition, Rhus trilobata, Yucca glauca, Prunus angustifolia, or Prunus pumila var. besseyi (northern stands) may also be conspicuous. Other common shrubs and succulents in Texas include Atriplex canescens, Penstemon ambiguus, Yucca campestris, Cylindropuntia leptocaulis, and Chrysothamnus pulchellus. Shrub cover may sometimes be sufficient to greatly reduce the cover of herbaceous species in the understory. At some sites, shrub cover may be low, and the herbaceous cover is typically dominated by grass species such as Schizachyrium scoparium and Sporobolus cryptandrus. Several mid- to tallgrass species characteristic of sand substrates are usually present to dominant within areas with low woody cover in this system, including Andropogon hallii, Calamovilfa gigantea, Calamovilfa longifolia, Cenchrus spinifex, Chloris cucullata, Hesperostipa comata, Panicum havardii, Paspalum setaceum, and/or Sporobolus giganteus. In Texas, forbs may at times constitute an aspect dominant with their prolific show of flowers, including Cnidoscolus texanus, Dalea lanata, Dimorphocarpa candicans, Eriogonum annuum, Gaillardia pulchella, Helianthus petiolaris, Heliotropium convolvulaceum, Mentzelia nuda, and Palafoxia sphacelata.

This system is found primarily in semi-arid to arid areas of the Western Great Plains Division. It occurs on somewhat excessively to excessively well-drained and deep sandy soils. This system is often found associated with dune systems and/or ancient floodplains but may occur in soils derived from sandstone residuum. In parts of Texas, this system is apparently restricted to thick sandy deposits in the Seymour Formation (a Pleistocene formation formed from ancient channel deposits of the Clear Fork of the Brazos River), and is found on rolling to level uplands. In these areas, it is restricted to Deep Sand, Sand Hills or Sandy Ecological Sites (Elliott 2011).

Fire and grazing constitute the most important processes impacting this system. Burning shrublands reduces cover of Artemisia filifolia for several years resulting in grassland patches that form a mosaic pattern with shrublands. Composition of grasslands depends on precipitation and management. Drought stress can also influence this system in some areas. In the southern range of this system, Quercus havardii may also be present to dominant and represents one succession pathway that develops over time following a disturbance. Quercus havardii is able to resprout following a fire and thus may persist for long periods of time once established, forming extensive clones. Edaphic and climatic factors are the most important dynamic processes for this type, with drought and extreme winds impacting this system significantly in some areas. Because Quercus havardii is able to resprout rapidly following fire, fire tends to cause structural changes in the vegetation, and compositional shifts are less significant in most cases. Overgrazing can lead to decreasing dominance of some of the grass species such as Andropogon hallii, Calamovilfa gigantea, and Schizachyrium scoparium. In the western extent of this system in the shortgrass prairie, more xeric mid- and shortgrass species such as Hesperostipa comata, Sporobolus cryptandrus and Bouteloua gracilis often dominate the herbaceous layer.

This system is found primarily within the south-central areas of the Western Great Plains Division ranging from the Nebraska Sandhills south into central Texas. However, examples of this system can be found as far north as the Badlands in South Dakota.