The Chihuahuan : by Cathryn A. Hoyt Diversity at Risk

block mountains Spanish ranchers and, later, American separated by down- settlers were drawn to the Chihuahuan faulted basins. Typically, Desert region by the lush grasslands and the basins are internally potential for grazing. Once, grasses in drained, resulting in the the Big Bend region of were said formation of saline to have been tall enough to brush the ephemeral lakes known bellies of horses. Ranchers believed that as playas. Dune fields, the supply of grass to feed livestock was composed of quartz or unlimited. By the mid-19th century, the gypsum sand, are stocking of desert grassland ranges with common throughout the cattle, sheep, and goats was progressing desert, while volcanic at a phenomenal rate. In 1900, the desert Photo by Michael Bender features add additional grasslands of supported over The Chihuahuan Desert is a land of complexity to the landscape. 9 million herd animals, up from 500,000 superlatives. Covering nearly 250,000 The varied geology of the head in 1830. The ranges of the south- square miles (647,500 square kilome­ Chihuahuan Desert supports a mosaic of west were soon stocked to capacity with ters), it is the largest of the North vegetation communities, ranging from no overflow ranges in case of drought. American . Jutting mountains and desert shrubs such as creosote (Larrea What ranchers could not know is that low basins form a range of habitats tridentata) and tarbush (Flourencia the luxuriant grasslands of the 19th suitable for a broad spectrum of terres­ cernia) at lower elevations to conifer century were the expression of a cooler, trial and freshwater species. In fact, the woodlands at higher elevations. Two wetter period that was to end abruptly at Chihuahuan Desert is considered to be features make the Chihuahuan Desert the turn of the century. After 1900, one of the most biologically diverse arid region unique: the vast temperate droughts became more frequent, and regions in the world. It is also one of the grasslands that skirt the mountain flanks grass cover on heavily grazed ranges most endangered. at mid-elevation and the diversity of declined by up to 70 percent. As and agaves. One of the agaves, warmer, drier conditions prevailed and The Landscape lechuguilla (Agave lechuguilla), is heavy grazing continued, thousands of The Chihuahuan Desert stretches from considered the primary diagnostic acres of Chihuahuan Desert grasslands southern New through the Rio species of the Chihuahuan Desert. were converted to desert shrubland, a Grande drainage of west Texas/northern process that continues to this day. Mexico and spreads southward over the Modification of the Environment In addition to change and into the states of While some of the inaccessible, overgrazing, certain water-use practices , , southwestern montane parts of the Chihuahuan Desert are having significant impacts on the Nuevo Leon, northeastern , and region have floral and faunal communi­ desert. The Chihuahuan Desert is San Luis Potosí. The desert is bounded ties that are at least relatively intact, punctuated by large lake basins and to the east and west by the ranges of the much of the desert has been heavily crisscrossed by drainages—indicators of and the Sierra disturbed by human land use. Overgraz­ a time thousands of years ago when Madre Occidental, respectively. The ing, water diversion, aquifer “mining” water was more plentiful and lakes and northern and southern boundaries, more (pumping at an unsustainable rate), and flowing rivers were abundant. With difficult to define, are usually based on overcollecting of native plants and climatic warming and drying over the such diagnostic indicators as climate, animals are considered the greatest past 10,000 years, water sources dried vegetation, or animal communities. threats to biodiversity in the Chihuahuan up, tributaries became isolated from the Basin and range topography predomi­ Desert . main rivers, and headsprings that once nates the Chihuahuan Desert, with fault- supported interconnected pools and

16 ENDANGERED SPECIES BULLETIN MARCH/JUNE 2002 VOLUME XXVII NO. 2 species are found in Mexico, with many about Chihuahuan Desert research. of the 345 Chihuahuan Desert species Research data are presented to the found only in small areas. Because the general public through interpretive entire range of a particular cactus programs centered at the CDRI’s 507- species may be confined to a single rock acre (205-hectare) site. Here, visitors can outcrop, species can be rendered extinct participate in seminars or stroll through all too easily because of overcollecting, the 20-acre (8-ha) arboretum, where over especially for the commercial trade. 100 species of Chihuahuan Desert trees and shrubs—representing communities Some desert grasslands have survived overgrazing. Conservation and Education from the desert lowlands through the CDRI photo Conservation efforts in the conifer highlands—are grown. One of perennial streams shrank to form small, Chihuahuan Desert are complicated by the highlights of a visit to the CDRI is a isolated pools and marshy wetlands the fact that the ecoregion extends tour of the Cacti and Succulent Green- known as cienegas. Water, once rela­ across an international border and house, which houses over 300 species of tively abundant in the Chihuahuan numerous state boundaries, both in Chihuahuan Desert cacti and succulents. Desert, is now a precious—and very Mexico and the . Nonethe­ The more energetic visitor can hike into limited—resource. less, attention is being focused on the a protected canyon where permanent Problems arise as urban areas in the Chihuahuan Desert through the interna­ springs and pools support a diverse desert continue to expand and fertile tional, multidisciplinary efforts of freshwater ecosystem, or climb to the desert soils are put into agricultural organizations such as the World Wildlife top of an igneous outcrop to enjoy production. Up to 99 percent of the Fund, the Nature Conservancy, the spectacular views of the surrounding water in the perennial rivers of the Instituto de Ecología in Mexico, and desert grasslands. Chihuahuan Desert is diverted to federal agencies such as the National municipal water supplies or to irrigate Park Service and the U.S. Fish and fields. The consequences of current Wildlife Service. water-use practices include the loss of In addition, private organizations like native fish populations and the replace­ the Chihuahuan Desert Research Institute ment of diverse riparian forests with (CDRI) are devoted to promoting an monocultures of tamarix (Tamarix spp.), awareness of the desert through research an invasive tree introduced in the 1800s. and education. Founded in 1973, the In addition to water diversion, mining CDRI encourages student research of aquifers is a serious threat to freshwa­ through scholarships and the W. Frank For more than 20 years, the Chihuahuan Desert ter species. Groundwater pumping can Blair Student Paper competition, main­ Research Institute has propagated endangered significantly lower the water table, tains a regional research library, and species of cacti for revegetation. reducing—or often completely eliminat­ serves as a clearinghouse for information CDRI photo ing—spring flow. Many cienegas of the Chihuahuan Desert once supported an Coordinated efforts of public and amazing array of endemic fish, snail, and private organizations in both Mexico and other invertebrate species. However, the United States is leading to a broader these hotspots of biodiversity are rapidly understanding of the Chihuahuan Desert being lost as groundwater pumping and the threats to its ecosystems. With lowers the watertable, reduces this understanding will come a greater springflow, and significantly decreases appreciation of the desert and new ways the number of intact cienegas. of addressing human needs while Some inhabitants of the Chihuahuan maintaining the biodiversity characteris­ Desert are imperiled simply because tic of the Chihuahuan Desert. people want to possess their own little piece of the desert in the form of a wild Dr. Hoyt is Executive Director of the plant or animal. The Chihuahuan Desert Chihuahuan Desert Research Institute in is recognized for the extraordinary Fort Davis, Texas. For more information, diversity of cacti and succulents found call Dr. Hoyt at 915/364-2499 or email there. According to the World Wildlife The endangered Chisos Mountain hedgehog cactus her at [email protected]. You can access Fund, more than one-third of all cacti Photo by Tom Alex the CDRI website at www.cdri.org.

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