Chihuahuan Desert

The Chihuahuan Desert is the largest desert region in North America. The desert stretches from the southwestern United States deep into the Central Mexican Plateau, including parts of the Mexican states of Chihuahua, northwest Coahuila, northeast Durango and several others.

The Sierra Madre Occidental bounds the desert to the west, and the Sierra Madre Oriental to the east, extending as far south as San Luis Potosi and to disjunct islands of the Chihuahuan vegetation in the states of Queretaro and Hidalgo.

On the Mexican side, it covers a large portion of the state of Chihuahua, along with portions of Coahuila, northeastern Durango, the extreme northern part of Zacatecas, and small western portions of Nuevo León.

There are several more extensive mountain ranges in the Chihuahuan Desert, including the Sierra Madre and the Sierra del Carmen in Mexico and several others in the southwestern United States. These mountains create "sky islands" of more relaxed, wetter climates adjacent to or within the desert.

The desert is mainly a rain shadow desert because the two main mountain ranges block much moisture: the Sierra Madre Occidental from the Pacific Ocean to the west and the Sierra Madre Oriental from the Gulf of Mexico to the east.

Chihuahuan Desert Ecoregion

The Chihuahuan Desert ecoregion encompasses one of Earth's most biologically diverse arid regions. Moreover, the desert is unique, as it has been sheltered from the influence of other arid regions, such as the Sonoran Desert, by the large mountain ranges of the Sierra Madres.

This isolation has allowed the evolution of many endemic species; the most notable is the number of endemic plants. However, this ecoregion also sustains some of the last remaining populations of Mexican prairie dogs, wild American bison and pronghorn antelope.

The region contains a series of basins and ranges with a central highland extending south from Socorro, New Mexico, to Zacatecas, Mexico. Most of the area is at an elevation of 1,100 - 1,500 m (3,600 - 4,900 ft).

Owing to its inland position and higher elevation than the Sonoran Desert to the west, the Chihuahuan Desert has a slightly milder climate in the summer (though usually, daytime June temperatures are in the range of 35 - 40 °C or 95 - 104 °F) and cool or cold winters with occasional frosts.

The average annual temperature in the desert is 24 °C (75 °F), which varies with altitude. The hottest temperatures occur in areas of low elevations and the inter-montane depressions in the region.

The climate includes a dry summer and occasional winter rains; mild frosts occur during autumn and winter. This desert has more rainfall than other warm desert ecoregions, with precipitation ranging from 150 - 400 mm (6 - 16 in).

Flora

Creosote bush (Larrea tridentata) is the dominant plant species on gravelly and occasional sandy soils in valley areas within the Chihuahuan Desert. The other species it is found with depend on factors such as the soil, altitude and degree of slope.

Viscid acacia (Acacia neovernicosa) and tarbush (Flourensia cernua) dominate northern environs, as does broom dalea (Psorothamnus scoparius) on sandy soils in the western one. Yucca and Opuntia species are abundant in foothill edges and the central third. Arizona rainbow cactus (Echinocereus polyacanthus) and Mexican fire-barrel cactus (Ferocactus pilosus) inhabit portions near the US-Mexico border.

Herbaceous plants, such as bush muhly (Muhlenbergia porteri), blue grama (Bouteloua gracilis), gypsum grama (B. breviseta), and hairy grama (B. hirsuta), are dominant in desert grasslands and near the mountain edges including the Sierra Madre Occidental. Lechuguilla (Agave lechuguilla), honey mesquite (Prosopis glandulosa), Opuntia macrocentra and Echinocereus pectinatus are the dominant species in western Coahuila.

Ocotillo (Fouquieria splendens), lechuguilla, and Yucca filifera are the most common species in the southeastern part of the desert. Candelilla (Euphorbia antisyphilitica), Mimosa zygophylla, Acacia glandulifera and lechuguilla are found in areas with well-draining, shallow soils.

The shrubs found near the Sierra Madre Oriental are exclusively lechuguilla, guapilla (Hechtia glomerata), Queen Victoria's agave (Agave victoriae-reginae), sotol (Dasylirion spp.), and barreta (Helietta parvifolia). The well-developed herbaceous layer includes grasses, legumes and cacti.

Grasslands comprise 20% of this desert and are often mosaics of shrubs and grasses. They include purple three-awn (Aristida purpurea), black grama (Bouteloua eriopoda), and sideoats grama (Bouteloua curtipendula).

Fauna

Mammals found here include the pronghorn antelope (Antilocapra americana), mule deer (Odocoileus hemionus), grey fox (Unocyon cineroargentinus), jaguar (Panthera onca), collared peccary or javelina (Pecari tajacu), desert cottontail (Sylvilagus auduboni), black-tailed jackrabbit (Lepus californicus), kangaroo rat (Dipodomys sp.), pocket mice (Perognathus spp.), woodrats (Neotoma spp.) and deer mice (Peromyscus spp.).

The ecoregion also contains a small wild population of the highly endangered American bison (Bison bison) and scattered populations of the highly endangered Mexican prairie dog (Cynomys mexicanus), as well as the common prairie dog (Cynomys ludovicianus).

Avifauna

Common bird species include the greater roadrunner (Geococcyx californianus), curve-billed thrasher (Toxostoma curvirostra), scaled quail (Callipepla squamata), Scott's oriole (Icterus parisorum), black-throated sparrow (Amphispeza bilineata), phainopepla (Phainopepla nitens), Worthen's sparrow (Spizella wortheni), and cactus wren (Campylorhynchus brunneicapillus).

In addition, numerous raptors inhabit the desert, including the great horned owl (Bubo virginianus), elf owl (Micrathene whitneyi), burrowing owl (Athene cunicularis), Aplomado falcon (Falco columbarius), red-tailed hawk (Buteo jamaicensis), and the rare zone-tailed hawk (Buteo albonotatus).

_{Map depicting the location of the Chihuahuan Desert ecoregion (in green)}