Physiognomy and Structure: No Data Available

Floristics: This association is characterized by a moderately dense herbaceous layer dominated by the perennial shortgrass Bouteloua eriopoda sometimes forming nearly pure stands. Shrubs or dwarf-shrubs may be present in low cover, including Ephedra trifurca, Gutierrezia sarothrae, or Robinia neomexicana. Common associates include Aristida purpurea, Bouteloua curtipendula, Muhlenbergia porteri, Allionia incarnata, Datura wrightii, Eriogonum spp., Opuntia phaeacantha, Senecio flaccidus, and Solanum elaeagnifolium.

Dynamics:  The abundance of Bouteloua eriopoda-dominated grasslands has declined significantly in the last 50 years (Buffington and Herbel 1965, Gardner 1950, Hennessy et al. 1983, Herbel et al. 1972, Nelson 1934). These grasslands have been replaced largely by shrublands dominated by Prosopis glandulosa in Trans-Pecos Texas, southern New Mexico, and southeastern Arizona. Studies on the Jornada Experimental Range suggest that combinations of drought, overgrazing by livestock, wind and water erosion, seed dispersal by livestock, fire suppression, shifting dunes, and changes in the seasonal distribution of precipitation have caused this recent, dramatic shift in vegetation physiognomy (Buffington and Herbel 1965, Gibbens et al. 1983, Herbel et al. 1972, Hennessy et al. 1983, Humphrey 1974, McLaughlin and Bowers 1982, McPherson 1995, Schlesinger et al. 1990). Prosopis spp. and other shrubs have extensive root systems that allow them to exploit deep soil water that is unavailable to shallower rooted grasses and cacti (Burgess 1995). This strategy works well, except on sites that have well-developed argillic or calcic soil horizons that limit infiltration and storage of winter moisture in the deeper soil layers (McAuliffe 1995). McAuliffe (1995) found Prosopis spp. invasion on these sites to be limited to a few small individuals. This has implications in plant geography and grassland revegetation work in the southwestern United States.