White Sands Gypsum Grassland

This ecological system is restricted to gypsum outcrops or sandy gypsiferous and often alkaline soils that occur in basins and slopes in the Chihuahuan Desert. Elevation range is from 1100-2000 m. These typically sparse grasslands, steppes or dwarf-shrublands are dominated by a variety of gypsophilous plants, many of which are endemic to these habitats. Characteristic species include Tiquilia hispidissima, Atriplex canescens, Calylophus hartwegii, Ephedra torreyana, Frankenia jamesii, Bouteloua breviseta, Mentzelia perennis, Nama carnosum, Calylophus hartwegii, Selinocarpus lanceolatus, Sporobolus nealleyi, Sporobolus airoides, and Sartwellia flaveriae with gypsophilous species diagnostic of this system. This system does not include the sparsely vegetated gypsum dunes that are included in North American Warm Desert Active and Stabilized Dune (CES302.744). Additional species that may be encountered in this system in Texas include Anulocaulis spp., Atriplex canescens, Calylophus hartwegii, Condalia ericoides, Ephedra torreyana, Gaillardia multiceps, Larrea tridentata, Poliomintha incana, Prosopis glandulosa, Scleropogon brevifolius, Selinocarpus spp., Sporobolus airoides, Sporobolus cryptandrus, and Yucca torreyi.

These typically sparse grasslands, steppes or dwarf-shrublands are dominated by a variety of gypsophilous plants, many of which are endemic to these habitats. Characteristic species include Tiquilia hispidissima, Atriplex canescens, Calylophus hartwegii, Ephedra torreyana, Frankenia jamesii, Bouteloua breviseta, Mentzelia perennis, Nama carnosum, Calylophus hartwegii (= Oenothera hartwegii), Selinocarpus lanceolatus, Sporobolus nealleyi, Sporobolus airoides, and Sartwellia flaveriae.

This ecological system is restricted to gypsum outcrops and strongly gypseous soils (Powell and Turner 1974, Henrickson et al. 1985, Meyer 1986, Dick-Peddie 1993). Sites occur in warm, semi-desert and desert regions with hot summers, and occasionally cold winters from the Chihuahuan Desert to eastern Mojave Desert and may extend up into the southern Colorado Plateau (Powell and Turner 1974, Meyer 1986, Dick-Peddie 1993). Elevation range is from 1100-2000 m. Some occurrences may be windswept gypsum "pavement" where much of the gypsum sand has been removed by wind, but these are not open/moving dunes dominated by eolian processes. Substrates are typically fine-textured, alkaline clay soils but include some sandy gypsiferous soils that occur in closed basins in the Chihuahuan Desert, but not gypsum dunes at White Sands National Monument (Reid 1980, Dick-Peddie 1993, Muldavin et al. 2000b). Eolian processes drive the dune system so many of the same common sand scrub plants, e.g., Atriplex canescens, may characterize vegetation on both quartz and gypsum active dunes, although some gypsophiles will occur on gypsum dunes (Shields 1956, Reid 1980, 1980, Dick-Peddie 1993). In Texas, extensive occurrences are associated with the Permian Castile Formation and alluvium within evaporative bolsons; scattered occurrences are associated with exposed gypsite and alluvium of evaporative ponds and swales receiving deposition from eroding gypsiferous formations.

Gypsophile endemism is common in the North American deserts, especially the Chihuahuan Desert where much of the region is underlain by limestone, with occasional gypsum exposures. These gypsum deposits are distributed in a discontinuous, island-like fashion that facilitates endemism. Gypsum is a difficult substrate for plants to grow on because it typically forms a hard crust when dry, erodes quickly when wet, and is relatively low in available nutrients. However, a large and diverse group of gypsophilous plants only occur on this substrate, several of which are considered rare and at risk.

This is a substrate-driven ecosystem occurring in extreme environments on chemically harsh substrates. Fire plays little to no role in this ecosystem as vegetation is generally too sparse to carry fire. Normal climate conditions are warm and arid (6-10 inches annually) with drought not uncommon. Climatic fluctuations (precipitation cycles) have been speculated to affect plant vigor and recruitment (Landfire 2007a), but this is not likely significant considering the hardiness of these plants and the harshness of the environments (E. Muldavin pers. comm.). Variation in abundance of subshrubs and grasses is likely more related to fine-scale differences in the soil environment then climatic factors (E. Muldavin pers. comm.). Some occurrences may be windswept, but these are not open/moving dunes with eolian processes. Some occurrences may be gypsum "pavement" or outcrop where much of the gypsum sand has been removed by wind.

Gypsum mining occurs in many southwestern states and is a threat to undisturbed gypsum deposits with gypsophiles. These lands are often considered "badlands" and are subject to disturbance from ORV use, which could cause direct mortality and increase rate of erosion on sites. Additionally, sites occurring on military installations may be impacted by training activities. Possible threats from fragmentation are not known because this is a naturally isolated ecosystem and the isolated nature of the ecosystem has promoted much of local species endemism. At a species level, populations of some local endemics could be threatened by fragmentation from local disturbances such as mining, roads, herbicide drift from agricultural fields, and housing developments that could eliminate or further isolate populations.

This ecosystem occurs on harsh substrates and it is not clear If invasive non-native species can tolerate these conditions enough to threaten occurrences of this ecosystem. It is believed that invasive non-native species have limited impact. Impacts from grazing by livestock from adjacent desert grasslands could impact the few palatable species such as Sporobolus nealleyi further reducing plant cover and compacting/disturbing soils.

Conversion of this type has commonly come from gypsum mining and other major disturbances such as road building, buried pipelines, and transmission lines. Common stressors and threats include gypsum mining and fragmentation and disturbance from roads, ORV or other mechanical disturbance that can increase the rate of erosion on this highly erodible substrate. Potential climate change effects will likely be minimal on this substrate-driven ecosystem that is adapted to hot, droughty conditions.

This system is found on basins and slopes in the Chihuahuan Desert at elevations ranging from 1100-2000 m.