Chihuahuan Desert

• Category: Desert Biomes.
• Geographic Location: North America.
• Summary: The vast Chihuahuan Desert, covering a large portion of the southwestern United States and northern Mexico, hosts wildlife adapted to this isolated, harsh, and extreme ecoregion in diverse and unique ways.

The Chihuahuan Desert is the largest desert in North America, stretching across about 140,000 square miles (362,600 square kilometers). This is an area larger than the state of California. The northernmost extent of the desert is in central New Mexico, while its southern extreme is in the southeastern corner of the Mexican state of Zacatecas. The desert was formed approximately 8,000 years ago due to its location in the midlatitudes, combined with the rain-shadow effect of two major mountain ranges: the Sierra Madre Occidental to the west and the Sierra Madre Oriental to the east. Elevations in the Chihuahuan Desert range from 2,000 feet (600 meters) to 8,750 feet (2,700 meters), the majority of which occur between 3,600 feet (1,100 meters) and 4,900 feet (1,500 meters).

Much of the Chihuahuan Desert is characterized by basin-and-range geomorphology, including a central highland that accounts for the relatively low mean annual temperature of 65 degrees F (18.6 degrees C). Abrupt changes in elevation often reveal unique habitats known as Sky Islands that are home to endemic species (native only to a particular biome), and also support one of the most critical migratory flyways in North America.

Precipitation in the Chihuahuan Desert varies greatly, depending on elevation and geographic location, but on average, the desert has annual precipitation of less than 9 inches (24 centimeters), most of which falls during the months of July and August. The desert is composed mainly of marine sedimentary rock, resulting from the region being underwater as part of the Cretaceous Seaway, which filled the entire region approximately 90 million years ago. The widespread rich gypsum deposits throughout this desert have resulted in the subterranean formation of expansive cave systems such as Carlsbad Caverns and Lechuguilla Cave in southern New Mexico. The largest body of water in the Chihuahuan Desert is the Rio Grande (called Rio Bravo in Mexico), which dissects the desert into northern and southern halves. Other important sources of water are seeps and groundwater springs: groundwater is the source of most surface water in this desert. Seeps and springs support complex ecosystems with multitudes of endemic plants and animals. Of special interest is the valley at Cuatro Cienegas in Coahuila, Mexico, which supports more than 500 freshwater pools and an enormous and varied amount of wildlife.

The ecosystems of the Chihuahuan Desert are very diverse and range from xeric (dry) habitat to riparian zones along major rivers. Other types include vast grasslands, savannas, and alpine habitat. The vast majority of the Chihuahuan Desert is xeric habitat categorized as desert scrub. Desert-scrub habitat tends to occur at lower elevations and tends to have the least precipitation in the desert. Grasslands and savannas occur at low to midrange elevations and tend to have slightly more precipitation than desert scrub but remain quite arid. Grasslands have been extremely modified over the past 200 years as overgrazing and water diversion have led to desertification and drastic changes in the flora and fauna of the region. The basin-and-range topography along with changes in climate over the past 10,000 years has resulted in isolated areas that support, collectively, up to 1,000 endemic species.

Flora and Fauna

The organisms of the Chihuahuan Desert are often unique, including the indicator species Agave lechuguilla, a small agave species found only in the calcareous soils of this desert. The region is home to an estimated 3,500 plant species, of which 25 to 30 percent are endemic. Among the most common are creosote bush (Larrea tridentata), various species of mesquite (Prosopis spp.), tarbush, acacia, an abundance of grasses, and hundreds of species of cacti in the Coryphantha and Opuntia genera. As many as one-fifth of the world's cacti species can be found in this desert.

Many of these plant species have evolved mechanisms to tolerate long periods of drought and intense heat. Deep root systems allow species of mesquite to tap into groundwater reservoirs, while extensive networks of shallow roots allow species like creosote bush to maximize water capture during the short, intense rainfall periods. Some species have even evolved ways to improve their photosynthetic efficiency in response to the extreme environmental conditions of the desert.

Animal species diversity is higher in the Chihuahuan Desert than in any other North American desert. Vertebrates include approximately 120 species of mammals, 300 species of birds, more than 100 species of fish, and more than 150 species of amphibians and reptiles. The diversity of habitat types in the desert provides homes for several endemic species of vertebrates and countless species of insects. The species diversity of bees, which are important pollinators here, is higher than in any other North American desert.

Many of the species have adapted to the extreme desert environment by modifying their behavior (such as nocturnal activity) and evolving physiological adaptations that maximize water retention and allow organisms to function for long periods without food or water. Large mammals that can still be found in the Chihuahuan Desert, though in small populations, include: brown bears, pronghorn antelope, American bison, wolves, peccaries, and even jaguars and mountain lions. Common birds of this desert include several species of hummingbirds, owls including the great horned owl (Bubo virginianus), hawks, vireo, migrating sparrows, and quail. Also commonly found here are roadrunners and other ground birds.

Human Impact

Native Americans have occupied the Chihuahuan Desert throughout its entire history. The Mogollon people occupied much of the desert for more than 1,000 years and eventually were displaced by Ancestral Pueblo, Pueblo, and Apache cultures. The Tarahumara people of the highlands of Chihuahua, Mexico, still occupy much of the harshest mountainous terrain of the Chihuahuan Desert and have adapted to the area with unique hunting and agricultural practices. Urban, agrarian, and industrial development over the past 200 years, especially along the United States-Mexico border, has led to major threats to the ecological balance in the desert: overgrazing (and the related invasion of nonnative species); depletion of water sources due to irrigation and pumping of groundwater; soil erosion; mining; and off-road vehicle use in some fragile areas.

The effects of humans have impacted native species of the region. Many of the large desert vertebrates of the area are rare and isolated. Large mammals, such as bison, pronghorn, and large cats have almost disappeared from the desert due to a loss of habitat. Brown bears have been extirpated. Conservationists have tried to garner protections for species of the desert threatened by the effects of urban sprawl. The Center for Biological Diversity petitioned to add the sagebrush lizard to the Endangered Species Act in 2002. Almost successful in 2010, the campaign was thwarted by fears of the effects on oil and gas jobs if the lizard gained protected status. The Center sued in 2013, and in 2023 the U.S Fish and Wildlife Service declared sagebrush lizards may warrant protection. The lizard is just one of a number of species on the verge of endangerment with the increased threats to their natural habitat.

Conservation and protective measures have been put in place in the United States in the regions that fall under National Park Service jurisdiction, and in Mexico with the creation of the National Commission for the Knowledge and Use of Biodiversity (CANABIO).

Such agencies will have to contend with changes wrought by global warming, such as wider opportunities for invasive species as both droughts and floods become more severe. It is expected that salt cedar (Tamarix ramosissima) and Russian olive (Elaeagnus angustifolia), for example, will spread through riparian areas by crowding out native species and reducing diversity as groundwater supply declines.

A lengthening of the frost-free season and higher minimum temperatures will expand the desert to the north and east, while higher elevations are likely to be colonized by arid savanna vegetation; some sky island communities will be severely stressed and may disappear as the warming climate alters their fundamental temperature, humidity, and snowpack regimes.

Bibliography

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"Chihuahuan Desert Network." National Park Service, 30 Aug. 2017, science.nature.nps.gov/im/units/chdn. Accessed 7 Oct. 2024.

"Chihuahuan Desert, US and Mexico." WWF, 2017, wwf.panda.org/knowledge‗hub/where‗we‗work/chihuahuan‗desert/. Accessed 7 Oct. 2024.

"Chihuahuan Desert." World Wildlife Fund, 2018, www.worldwildlife.org/places/chihuahuan-desert. Accessed 7 Oct. 2024.

Dodson, Carolyn, and Robert DeWitt Ivey. A Guide to the Plants of the Northern Chihuahua Desert. U of New Mexico P, 2012.

Peters, Debra P. C., et al. "Plant Species Richness in Multiyear Wet and Dry Periods in the Chihuahuan Desert." Climate, 13 Aug. 2021, doi.org/10.3390/cli9080130. Accessed 7 Oct. 2024.

Skroch, Matt. “Sky Islands of North America: A Globally Unique and Threatened Inland Archipelago.” Terrain.org, 2008. . Accessed 7 Oct. 2024.

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Tweit, Susan J. Barren. Barren, Wild, and Worthless: Living in the Chihuahuan Desert. U of Arizona P, 2003.