Physiognomy and Structure: Most sites are dominated by herbaceous species less than 1 m tall. In the northern portion of this macrogroup''s range, the grasses are largely C3. Deciduous shrubs are more common in the south and can dominate some stands. Vegetation density can be low, especially on heavily grazed or low-fertility sites, to dense. Some species form near monocultures.

Floristics: Abundant species vary greatly in this macrogroup, depending on the geographic location, seed sources, and nature of land use. Common species in the north include exotic and invasive Agropyron cristatum, Bromus inermis, Bromus arvensis (= Bromus japonicus), Bromus tectorum, Elymus repens (on more moist sites), Phleum pratense, Poa pratensis, and Thinopyrum intermedium. In the south, Bothriochloa ischaemum var. songarica, Dichanthium annulatum, Pennisetum ciliare, and the shrubs Baccharis neglecta, Crataegus mollis, Crataegus viridis, and Rhus lanceolata can be common. Gutierrezia texana and Amphiachyris dracunculoides (= Gutierrezia dracunculoides) are often extremely abundant on overgrazed sites in Texas. Across the range Ambrosia spp., Artemisia absinthium, Carduus nutans, Centaurea spp., Cirsium arvense, Convolvulus arvensis, Dipsacus fullonum, and Euphorbia esula can be common. Bouteloua spp., Bouteloua dactyloides (= Buchloe dactyloides) (which can dominate on overgrazed rangeland), Pascopyrum smithii, Schizachyrium scoparium, and other widespread native grasses can be found in low to moderate amounts. This macrogroup also includes native upland shortgrass prairie areas dominated by invasive Prosopis glandulosa.

Dynamics:  This macrogroup tends to replace native prairie through direct planting of exotic species, usually for forage, or through alteration of natural disturbance regimes. Native grasslands are well-adapted to moderate grazing over time or heavy grazing for short periods, but when used as long-term pasture and with high stocking rates, many of the dominant native grasses are reduced or eliminated (Branson and Weaver 1953). Heavy haying or grazing if done consistently during the mid-summer months negatively affect the dominant warm-season grasses by removing their biomass before they have flowered. Cool-season grasses and forbs which set seed earlier are favored by these activities. Native and non-native forbs, woody species, and C3 grasses increase in the absence of fire, especially when combined with grazing by livestock. Drier sites on hilltops or rocky soils persist longer, but mesic sites on lower slopes can be invaded by trees and shrubs after just several years without fire. This macrogroup is typically persistent in the absence of long-term natural disturbance regimes. More information is needed on whether succession of this ruderal type could lead to native prairie types. Annual precipitation in the region where it occurs does not allow rapid tree growth and the new disturbance regime favors the exotic species over most native prairie species.

Historically, mesquite-dominated shrublands and tree savannas probably occurred as a natural component on more fertile soils and along drainages where soils are deep in the short- and midgrass prairie, but mesquite has expanded its range into prairie uplands in recent decades (Sims and Risser 2000). Previously, periodic fire limited the development of woody cover to widely scattered large mesquite trees or possibly denser trees resembling a tree savanna (Archer 1989). Livestock grazing reduces fine fuels that carry fire and disperse seeds away from seed predators in animal dung which provides favorable conditions for germination and establishment (Archer 1989, Brown and Archer 1989). These recent invasive upland mesquite shrublands are considered ruderal or novel in th eshortgrass prairie where it did not occur historically.