Ecoregion Based Conservation in the Chihuahuan Desert: A Biological Assessment 2000
home to fish species found nowhere else on earth.
only desert ecoregion recognized for both its freshwater and terrestrial biodiversity in the Global 200 analysis (Olson and Dinerstein 1998).
Only 2.5% (12,000 km2) of the ecoregion is under formal protection
U.S. portion holds all of the level I protected areas, even though 75% of the ecoregion is in Mexico.
glaring omission is the lack of effort to protect freshwater rivers, streams, pozas (pools), or basins, even though the Chihuahuan may be the most globally distinct arid ecoregion in terms of freshwater biodiversity (Olson and Dinerstein 1998).
restoration of flora and fauna associated with prairie dog colonies, desert springs
restoration, where appropriate, of populations of Mexican wolves, mountain lion, jaguar, bison, black bear, pronghorn antelope, and aplomado falcons
Another freshwater target would be to remove alien species where possible to prevent further extinctions in isolated pozas (pools) and other habitats such as springs where they threaten native biotas. A concerted effort to prevent the introduction of species should be made in those few freshwater sites that remain free of exotics.
stress the conservation of keystone habitats, such as riparian habitats and springs
Global 200 ecoregions study (Olson and Dinerstein 1998)
Chihuahuan as one of the most biologically diverse ecoregions, richer than even many forested units (Ricketts et al. 1999). Recent studies of cacti (Hernandez and Barcenas 1995) highlight the extraordinary richness and endemism found in this family: among the 1500 species of Cactaceae, approximately 48 genera and more than one-third of all species occur in Mexico. Many of the 345 species found in the Chihuahuan Desert are endemic to it.
Appreciation of Chihuahuan biodiversity requires a jeweler's eye because much of its unique features are cryptic. Many species of cacti, for example, are delightful miniatures. The story of cichlid evolution in the lakes and springs of Cuatrociénegas follows a similar pattern to that of the Rift Lakes of Africa, albeit on a smaller scale. Pollination of yucca and some cacti by moths and nectar-feeding bats is a wonderful tale of coadaptation in nature, but rarely witnessed by diurnal naturalists. See also https://es.wikipedia.org/wiki/Cuatroci%C3%A9negas
pine-oak and chaparral habitats
riparian habitats or springs in the Chihuahuan Desert are vitally important for maintaining vertebrate populations in surrounding habitats. Riparian forests are also essential as feeding, shelter, and resting habitat for migratory songbirds, bats, and butterflies. Other linkage habitats, migration corridors, or drought or fire refugia may also be critical habitats for maintaining ecological processes. Keystone species, such as larger mammalian predators and black-tailed prairie dogs, also have a strong influence on the structure and integrity of natural communities.
flowering cacti across whole landscapes may be important for migratory bats. Habitats or sites that may not be particularly distinctive (e.g., high richness or endemism) or intact may still act as critical habitat for migratory species.
long-term vision for conservation of the Chihuahuan Desert should consider: 1) a network of core areas that conserve intact native ecosystems and meet a suite of conservation goals, 2) linkage zones or corridors that maintain biotic interactions among core units, 3) the application of appropriate land use and wildlife practices, and 4) conservation of keystone habitats (e.g., riparian habitats, springs)
The Chihuahuan Desert (including the closely-related Meseta Central matorral to the south) is one of the three most biologically rich and diverse desert ecoregions in the world, rivaled only by the Great Sandy-Tanami Desert of Australia and the Namib-Karoo of southern Africa (Olson and Dinerstein 1998).
landscape is a series of basins and ranges with a central highland
Because of its generally higher elevation, the Chihuahuan Desert is cooler and has more rainfall than other warm desert ecoregions, averaging 235 mm annually. Shrubs dominate the landscape of the Chihuahuan, with scrub communities covering 55% of the desert.
The most common species are creosote bush (Larrea tridentata) - in many ways the defining species of the Chihuahuan Desert - tarbush (Florensia cernua), mesquite (Prosopis glandulosa), and acacia (Acacia spp.). Cacti and agave are also prominent; large, dense stands of prickly pear (Opuntia phaecantha) are common, as is lechuguilla (Agave lechuguilla). As one moves north from central Mexico, the desert grades from a landscape of cacti, yucca, and shrubs to a dry grassland ecosystem (MacMahon 1988). The grasslands, 20% of this desert, are often mosaics of grass and shrub, include side-oats grama (Bouteloua curtipendula), black grama (Bouteloua eriopoda), and purple three-awn (Aristida purpurea). Bottomlands of tobosa (Hilaria mutica) and big alkali sacaton (Sporobolus wrightii) were probably the species early Spanish explorers encountered when they excitedly reported grasses that were "belly high to a horse" (Tweit 1995).
diversity and high levels of endemism in Cactaceae, 350 of the 1500 known species of cacti occur here
Four other plant families - grasses, euphorbs, asters, and legumes - are not only speciose, but also show high levels of endemism across the desert's many basins. Less well-known is the diversity and endemism within the Nyctaginaceae (Bougainvilla family
Keystone invertebrates within the desert grasslands are the subterranean termites (order Isoptera), major consumers of dead plant material and animal dung. Fifty percent of all photosynthetically fixed carbon in desert grasslands is consumed by them (Whitford et al. 1995).
specialized freshwater assemblages of invertebrates associated with playas, such as clam shrimp (Eulimnadia texana), water fleas (Moina wierejskii), and fairy shrimp (Streptochephalus texanus), upon which migrating waterfowl depend. There are others associated with soil, such as nanorchestid and tydeid soil mites, which are essential for nutrient cycling in a dry climate.
invertebrate tied to the yucca woodlands, the yucca moth (Tegeticula yuccasella), lays her egg in the ovary of the yucca, rolls pollen into a ball, and then inserts the ball into the flower, thereby ensuring fertilization of the seeds on which her young will feed. The semi-arid Madrean region further has the richest diversity of bee species in the world (Ayala and Bullock 1993).
Chihuahuan Desert supports a large number of wide - ranging mammals, such as the pronghorn (Antilocapra americana), jaguar (Panthera onca), and collared peccary or javelina (Dicotyles tajacua). Rodent species are abundant in number and kind. Kangaroo rats (Dipodomys spp.), pocket mice (Perognathus spp.), woodrats (Neotoma spp.), and deer mice (Peromyscus spp.) are among the important burrowing and grain storing mammals that contribute to the overall structure and functioning of the ecosystem. Common bird species include the greater roadrunner (Geococcyx californianus), curve- billed thrasher (Toxostoma curvirostra), scaled quail (Callipepla squamata), and Scott's oriole (Icterus parisorum). Numerous raptors inhabit the desert and include Swainson's hawk (Buteo swainsonii), great horned owl (Bubo virginianus), and the rare aplomado falcon (Falco femoralis) and zone-tailed hawk (Buteo albonotatus).
Several lizards are endemic, including the Texas banded gecko (Coleonyx brevis), reticulated gecko (C. reticulatus), greater earless lizard (Cophosaurus texanus), several species of spiny lizards (Sceloporus spp.), and marbled whiptails (Cnemidophorus tigris marmoratus). Two other whiptails (C. neomexicanus and C. grahami) occur as allfemale parthenogenic clones in select disturbed habitats (Degenhardt et al. 1996). Representative snakes include the Trans-Pecos ratsnake (Elaphe subocularis), Mexican garter snake (Thamnophis eques), and whipsnakes (Masticophis taeniatus and M. flagellum lineatus) (Brown 1994). Endemic turtles include the Bolson tortoise (Gopherus flavomarginatus), a unique aquatic box turtle (Terrapene coahuila) and several softshell turtles.
The Rio Grande (Río Bravo del Norte), fed by its major tributaries the Pecos River and the Río Conchos, is the only major through-flowing stream in the Chihuahuan. The larger Río Grande system is home to native minnow, sucker, catfish, killifish, and sunfish species, two species of gar (Lepisosteus oculatus, L. osseus), and a rare sturgeon (Scaphirhynchus platorhynchus). Rivers draining into the interior, such as the Río Nazas located north of Durango, contain unique assemblages of minnows, suckers, and pupfish. Isolated basins, such as the Tularosa in New Mexico and Cuatrociénegas in Coahuila, have given rise to numerous endemic fish species including several pupfish (Cyprinodon spp.), cichlids (Cichlasoma spp.) and poeciliids (Gambusia marshi and G. longispinis) (Miller 1977, Minckley 1977). What most strongly distinguishes the freshwater biota of the Chihuahuan Desert is not the number of species, but the high degree of local endemism, a globally outstanding feature.
At the time of this writing (2000-2001), a survey of the entire ecoregion is not yet complete, but the U.S. portion of the Chihuahuan (which makes up less than a third of the desert's total area) contains approximately 2263 species of vascular plants, over 100 species of mammals, over 100 species of reptiles, 250 bird species, 20-25 amphibian species, and 250 species of butterflies
Forested mountain ranges, rise abruptly like sky islands on a desert sea, each home to a unique mix of desert and montane plant and animal species. These mixed conifer forests and oak woodlands comprise approximately 7% of the Chihuahuan Desert. In the northern desert, Spanish explorers marveled at the vast grasslands of black grama, blue grama, and big alkali sacaton. In New Mexico and Coahuila, windblown gypsum soils form dunescapes of white sand, a rare and seemingly inhospitable habitat type that has given rise to plant species found nowhere else. In the isolated basin of Cuatrociénegas, spring fed pools of warm freshwater nurture communities of endemic stromatolites, fish, and snails, resembling coral reefs in the heart of the desert. In parts of the Meseta Central matorral, minute changes in moisture or temperature from one valley to the next give rise to distinct plant communities.
the ecoregion is heavily degraded. Historical accounts report that in the mid-1800s the native grasslands were lush and relatively free of shrubs. Riparian areas were lined with gallery forests and unchanelled streams often spread out to form wetland systems (ciénegas). Pronghorn, black-tailed prairie dog (Cynomys ludovicianus), and Mexican wolf (Canis lupus baileyi) were abundant. Today, native shrubs dominate throughout, including former grasslands, savanna, and riparian and wetland areas. Populations of native grasses, overgrazed and deprived of their natural, fire-based disturbance regime, are disappearing. In southern New Mexico, around Las Cruces, for example, the desert floor is covered with little more than creosote and fluffgrass (Dasyochloa pulchella). Most of the riparian forests and ciénegas have disappeared, victims of over-grazing, heavy erosion, and excessive water diversion for agriculture. Many perennial streams and springs are now only seasonally wet as a result of degraded soil and upland vegetation conditions (Dick-Peddie 1993). Pronghorn and prairie dogs are scarce, and the Mexican wolf and grizzly bear are extirpated (Bahre 1995).
Before introduction of domestic livestock, desert scrub was more limited in range, contained a more diverse assemblage of species, and supported a dominant grass layer. Between 25-50% of current scrublands may have once been grasslands. Today, the landscape is characterized by shrub communities of creosote bush, mesquite, and acacia that occur either in vast expanses or pockets within other communities of grassland or yucca woodland. At least 40% of the ecoregion is a matrix of these shrub-dominated communities. Currently, around 20% is dominated by grasslands, often with a strong shrub component. Drastic alteration in species composition of the grasslands has occurred, with native species often replaced by a few species of low-growing or unpalatable grasses (Brown 1995). In some areas, little grass cover remains. Approximately 5% of the ecoregion is yucca woodland and crasicaule, a habitat rich in agaves, yucca, and cacti.
Fields cleared for irrigated agriculture have destroyed thousands of hectares of native grassland and floodplain. Over-pumping of groundwater for agriculture and use by growing urban areas is severely affecting flows of Chihuahuan Desert rivers, including the San Pedro, Pecos, Río Grande, Río Conchos, Río Nazas, Río Extorax, and Río Aguanaval. De-watering of rivers and streams, coupled with damage from grazing, has severely degraded much of the freshwater and riparian habitats in the ecoregion. These weakened riparian communities have subsequently become invaded by salt cedar (Tamarix ramosissima), a highly aggressive exotic shrub. This shrub will also invade intact, healthy riparian communities.
high degree of endemism in specialized habitats such as gypsum dunes;
Globally, only the Namib-Karoo of southern Africa and the Great Sandy-Tanami Desert ecoregion of central Australia may match or exceed the richness and endemism of the Chihuahuan's biota (Olson and Dinerstein 1998).
More thorough inventories of the Mexican portion will probably elevate the Chihuahuan desert to second place among xeric ecoregions for reptile diversity just behind the Namib-Karoo. In terms of diversity at the family level, we know that the Chihuahuan exceeds the Great Sandy-Tanami.
diverse ecoregions-subtropical conifer forests, subtropical thickets, and temperate grasslands
the most distinct priority sites are complexes of mountains, valleys, and rivers that often occur along ecoregion boundaries.
Taxa exhibiting high levels of local endemism include cacti, spurges, asters, cichlid and cyprinid fishes, aquatic pulmonate snails, aquatic reptiles, butterflies, spiders, scorpions, ants, lizards, and snakes.
The Cactaceae, a conspicuous component of the Chihuahuan flora, is restricted to the New World (with exceptions in Sri Lanka, West Africa, and Madagascar). With perhaps one-fifth of all the world's cacti occurring here, the Chihuahuan Desert is an arena for a prolific evolutionary display in this family of succulents. Among the 22 plant genera that contain at least 20 species, four are cacti (Table 4.2); two cacti genera, Coryphantha and Opuntia, are among the five most speciose in the entire flora.
The replacement of cacti species from one basin to another offers an instructive rule for conserving Chihuahuan Desert biological diversity: incorporate patterns of beta-diversity into the design of a comprehensive conservation strategy. Some valleys support the highest concentrations of endemic cacti in the world.
sky islands typically harbor biotas characteristic of more northern climes or adjacent mountainous ecoregions.
The isolation and challenging conditions of the region's limited freshwater springs and streams has promoted a high degree of endemism in aquatic groups. The extraordinary freshwater species radiations and local endemism of Cuatrociénegas represent a globally outstanding phenomenon, the freshwater "Galapagos" of the Americas. Local endemism can be extreme with fish and snail species being restricted to only a few small pools. High endemism of obligate freshwater taxa is found elsewhere in the Chihuahuan Desert complex as well; in the Mapimí area, defined by the Río Nazas, 50% of the fish fauna may be endemic.
Table 4.1 A comparison of reptile diversity among the three richest desert ecoregions of the world
Table 4-2. Chihuahuan plant genera which contain over 20 species.
The Chihuahuan Desert still harbors some areas that support relatively intact landscapes, primarily in montane regions. However, many degraded lowland habitats have good potential for restoration
Wolves (Canis lupus) and grizzly bears (Ursus horribilis) were extirpated in this century and no truly intact vertebrate assemblages remain. However, several sites do retain the remaining complement of larger vertebrates, including top predators such as puma, jaguar, and golden eagles. Extant prairie dog colonies also serve as keystone habitats for eventual restoration of native grassland ecosystems, complete with pronghorn, golden eagles, aplomado falcons, coyotes, badgers, and wolves.
Migratory routes for a broad range of taxa depend upon seasonal availability of resources in the Chihuahuan Desert. Many migratory bird species continue to use riparian and montane habitats in the Chihuahuan as feeding and resting habitats, and several bat species track flowering cacti over large areas in early summer. Monarch butterflies rely on the riparian vegetation of several Chihuahuan passes to rest during their migration.
distinctive habitat types in the Chihuahuan include yucca woodlands, playas, gypsum grasslands, gypsum dunes, scrubs dominated by arborescent cacti, and a diverse array of desert freshwater habitats, best illustrated by the unique Cuatrociénegas springs. Cuatrociénegas is home to the only aquatic box turtle (Terrapene coahuila), a local endemic, and the only known fish (Cichlasoma minckleyi) to have two co-occurring morphs which feed on algae and snails, respectively. The Madrean coniferous forests once supported populations of the world's largest woodpecker, the Imperial, now believed extinct.
Figure 4-2. Chihuahuan Desert ecoregion complex with subregions
3. Biological distinctiveness of the subregions
urban growth and rural subdivision
Tucson, Arizona suffers from urban and industrial air pollution. The Chiricahua- Animas-Sierra Madre Complex (1.20) and Upper San Pedro (1.10) is vulnerable to groundwater contamination created by copper mines and mills.
agriculture were significant in 42% of the Apachean sites
All of these sites are associated with playas, wetlands, rivers and streams. Water diversions from channels and groundwater pumping reduce soil moisture available to riparian and wetland species and alter habitat
Thirteen of the sites (50%) are subject to the impacts of urban development or subdivision
Timber extraction occurs in six (23%) of the sites
fire suppression are evident in 23% of the sites
Livestock grazing effects 85% of the priority sites
Several of the sky islands are popular recreational sites (26% of all sites). Facilities such as campgrounds, trails, roads, stores, and parking lots reduce and fragment habitat
has the highest proportion of grasslands (45%) among the subregions and the highest percentage of montane chaparral, forest, and woodland habitats (10%). The desert scrub component covers approximately 33% of the landscape. Rivers and springs arise from the waters of the Sierra Madre Occidental ecoregion and the sky islands, however riparian habitat is less than 1% of the total land cover.
Local endemism in the Apachean subregion is most pronounced in the sky islands and playas. Some reptiles and amphibians restricted to sky island habitats include the ridge-nosed rattlesnake (Crotalus willardi), twin-spot rattlesnake (C. pricei), cat-eyed snake (Leptodeira septentrionalis), Yarrow's spiny lizard (Sceloporus jarrovii), Chiricahua leopard frog (Rana chiricahuaensis), and canyon spotted whiptail (Cnemidophorus burti). Within the playas, several endemic plants and invertebrates are uniquely adapted to seasonal inundation and alkaline conditions such as Griffith's saltbush (Atriplex torreyi var. griffithsii).
Sycamore Canyon, a riparian area within the Pajarito-Atasco Mountains (1.02) contains at least 593 species of plants and 200 species of butterflies. A rich assemblage of reptiles along Antelope Pass in the Peloncillo Mountains (1.20) contains the highest documented lizard diversity in the United States. Willcox Playa (1.17) is the highest recorded site diversity of tiger beetles (family Cincindelidae) in the world.
Several of the sky islands have escaped extensive resource exploitation. The Galiuro Mountains (1.15), the Whetstone Mountains (1.07), Peloncillos and Animas Mountains (1.20), and the Dragoon Mountains (1.18) contain examples of Madrean evergreen woodland and grama grassland habitats, despite many decades of timber extraction and grazing. Although the Chihuahuan Grasslands in site 1.20 are heavily grazed and degraded, a remarkable assemblage of vertebrates is associated with the black-tailed prairie dog colony at Janos, Chihuahua. This is the largest remaining prairie-dog colony in North America. Ferruginous hawk (Buteo regalis), long-billed curlew (Numenius americanus), burrowing owl (Athene cunicularia), swift fox (Vulpes macrotis) and pronghorn (Antilocapra americana) are among a number of species that rely on the prairie-dog colony for prey, habitat, or forage.
Large scale migrations of waterfowl, shorebirds, raptors, and cranes depend upon shallow playa waters as migratory stopovers. Willcox Playa (1.17), Lordsburg Playa (1.24), Upper San Pedro River (2.10), and Playas Playa (within site 1.22) are critical links for birds on both northern and southern migration routes. Perhaps the critical stopover hotspot of the ecoregion is the riparian woodland of the Upper San Pedro (2.10) which serves as a corridor for up to four million neotropical migrants and is also important for nesting and wintering habitat. Locally, riparian woodlands help regulate other processes, such as river temperature, flooding intensity, soil retention, and evaporation rates.
Riparian and wetland habitats are increasingly rare in the Apachean subregion because of human activities
many invertebrate species dependent on riparian vegetation, including the viceroy butterfly (Limenitis archippus), and a local lycaenid butterfly (Apodemia phyciodoides).
Conservation apachean less than 6% of the subregion has been converted to agricultural uses
vast majority of non-cultivated lands are subjected to livestock grazing
Woodland and montane sites have lost habitat primarily because of timber harvest and road construction. Riparian sites are in serious trouble.
direct consumption of vegetation and the shearing of steambanks by cattle.
playa sites are largely intact but their associated ciénegas are often pumped dry or grazed. Woodlands are chiefly degraded by roads, mining, and livestock grazing
large expanses of grass-dominated blocks have shifted to mosaics of desert scrub dominated by creosote bush and acacia.
Natural habitats in the subregion as a whole are highly fragmented
Corridors among the sky islands are patchy, narrow, or lacking. Recreation and home-building in the sky islands reduces habitat, increases fire risk, and fragments former expanses of higher elevation communities. A U.S. Interstate bisects the subregion, which is a major barrier to movement of larger vertebrates.
Rivers and springs arising from the waters of the Sierra Madre Occidental and its satellite sky islands to the north support intensive agriculture in bordering valleys. Apple orchards in Casas Grandes, Chihuahua, cotton and alfalfa near Safford, Arizona, and chile peppers grown in the Playas Valley near Lordsburg, New Mexico are among the most intensive water users and these areas are the most heavily altered of the subregion.
copper mine in Cannanea, Sonora, is the largest in Mexico. Mining operations, tailings, and high water use of the headwaters of the San Pedro have heavily altered this area
industry uses lots of water, even though on 6% ag.
Many of the sky island forests in the U.S. Coronado National Forest and Bureau of Land Management lands have U.S. Wilderness Areas and Area of Critical Environmental Concern status. However, grazing is still allowed under these designations.
Reptile and invertebrate collecting occurs in the Chiricahua-Animas-Peloncillo-Sierra Madres complex (site 1.20). Prairie dog poisioning is also a serious threat. Overall, exploitation is low in the subregion
only three examples of subalpine coniferous forest, characterized by the presence of Engelmann spruce (Picea engelmanni) and corkbark fir (Abies lasiocarpa) have been documented: the Pinaleño Mountains [not too threatened, observatory, some development/logging] (1.16), the Santa Catalina Mountains (1.05), and the Chiricahua Mountains
Upper San Pedro (1.10) is one of the most important remaining riparian forests in the ecoregion, but it has been substantially altered by a variety of uses during the last 150 years. Felling of cottonwoods, heavy concentrations of livestock in the channels and wetlands, upland erosion from mining, timber harvest, and livestock grazing have degraded this keystone habitat. USA 60% side protected, mexico 40% not.
Chiricahua-Peloncillo-Sierra Madre Complex
Highly degraded grasslands occur in the intervening valleys. Woodlands and forests are connected by relatively intact corridors. Ciénega and riparian habitats in Mexico appear to have had fewer alterations than the same habitat types in the U.S.. Wetlands surrounding Ascension, Chihuahua, are associated with the Río Casas Grandes and are an important wintering ground for ducks, geese, and cranes. Most of the wetlands in the area are drained for agriculture. Groundwater levels have dropped significantly in U.S. wetlands from agricultural uses as well, including the San Simon Cienega. The largest remaining black-tailed prairie dog colony is found near the village of Janos, Chihuahua. This colony is highly threatened by potato farming and overgrazing of cattle.
Peloncillo Range supports an oak-pine woodland that has experienced lighter degradation. [good example for conservation]
higher elevations of the Chiricahua Mountains, a montane coniferous forest with relict populations of corkbark fir (Abies arizonica) and Engelmann spruce (Picea engelmanii). Inaccessbility has protected this rugged area from large-scale timber harvest
The Hatchita Grasslands (1.23) were once extensive and dominated by prairie dogs. After their eradication, modern ranching techniques were brought in (including fencing and fire suppression). Tobosa swales, of low palatability to livestock, are still a dominant feature in basins. However, the uplands surrounding the swales are near monocultures of creosote bush. The processes and species that once dominated these grasslands can be restored if they are better protected and connected to the more intact, species-rich grasslands of the Animas and Playas Valleys.
Dr. Charles Curtin, Biology Department, University of New Mexico.
outstanding biodiversity features of the Apachean are the Madrean Sky Islands (particularly the Chiricahua and Peloncillo mountains), the playas, and the wetlands complexes of the Gila River.
The subdivision has very high mammal, reptile, and arthropod diversity, with many endemics. Habitats range from Chihuahuan desert scrub to subalpine. Extremely high levels of beta-diversity occur due to elevation and topography, ranging from desert scrub and ciénegas in lowlands, to woodlands and grasslands in mid-elevations, to montane forest in the highest elevations. Threats to biodiversity in the Apachean subdivision include altered fire regimes, exotic species (particularly salt cedar in the riparian areas), home construction, and ground water depletion
restoring the ecological role of fire throughout the area, re-watering wetland complexes, maintaining habitat linkages in the core areas, stopping subdivisions for housing,
The Nature Conservancy, Santa Fe, NM
New Mexico Natural Heritage Program, Albuquerque, NM
Animas Foundation, Animas, NM
Wildlands Project, Tucson, AZ
Quivera Coalition, Santa Fe, NM
Southwest Environmental Center, Las Cruces, NM
Malpai Borderlands Group, Animas, NM
Southwestern Center for Biological Diversity, Tucson, AZ
Forest Guardians, Santa Fe, NM
Center for Ecologia, Sonora
GilaWatch, Silver City, NM
Society for Range Management NM Chapter
People for the West
New Mexico Cattlegrowers
<P>Northern Chihuahuan subregion
Livestock grazing, fire suppression, and urban development appear to be the primary causes of biodiversity loss in the Northern Chihuahuan subregion. Riparian habitats have been particularly effected.
Municipal wastes, agricultural run-off, industrial pollutants, and mining contaminants are found scattered in nine of the eighteen sites. All three Rio Grande sites (2.02, 2.03, 2.18), the Pecos River (2.10), Conchos River (2.15), and Alta Bavicora (2.11) carry high levels of contaminants. The three sites associated with the Big Bend area, Big Bend (2.07), Davis-Chinati Mountains (2.05), and Marathon Basin (2.16), all suffer from air pollution.
The impacts of agriculture range from complete loss of natural communities and associated species, fragmentation of landscape through habitat conversion, roads, fences, and vehicular traffic, pumping groundwater or diverting river water, and river channelization. Eleven of the eighteen sites in this subregion are directly impacted by agriculture
Ten of the eighteen sites are threatened with development, which includes urban expansion in the region of El Paso/Ciudad Juárez
Within two Rio Grande sites, (2.02) and (2.18), invasions of two exotics, salt cedar (Tamarix sp.) and Russian olive, create dense understories of highly volatile fuels
Grazing practices incompatible with native grassland or shrubland phenologies are found on [almost] all
waterfowl are illegally hunted at Alta Bavicora (2.11) and black bear are taken from the Sierra del Nido (2.01). Reptiles and cacti are illegally removed from Big Bend (2.07) and Marathon Basin (2.16).
Oil and gas exploration and pumping causes fragmentation within Pecos River (2.10) and Mescalero Sands (2.13) sites, as well as habitat loss along drilling pads
introduction of non-native plant species to the riparian areas of this subregion has resulted in a shift in community composition, from cottonwood-willow dominated woodlands to thickets and strands dominated by introduced salt cedar and Russian olive Soil salinity levels typically increase after these invasions
Vertebrate exotics include feral sheep and pig populations within the Northcentral Chihuahuan Grasslands (2.08), burros in Big Bend (2.07), and oryx in the Tularosa Basin
Campgrounds, roads, and trails eliminate patches of habitat. The presence of humans disrupts wildlife movements
Airforce bombing ranges, missile launch sites, and army roads However, in some military areas, incendiary activities often help maintain relatively natural fire regimes.
most populated subregion and includes a number of major urban areas: El Paso, Texas; Las Cruces, Alamogordo, and Socorro, New Mexico; Ciudad Chihuahua, Ciudad Juarez, Ciudad Camargo, Jimenez, Ciudad Delicias, and Parral, Chihuahua, and Torreon, Coahuila. Development in urban areas has led to habitat loss, degradation, and fragmentation of surrounding terrestrial and freshwater habitats.
Remaining natural habitats in priority sites are surrounded by a matrix of degraded grama grasslands and desert scrub. Approximately 50% of the subregion is Chihuahuan desert scrub and approximately 25% is semi-desert grassland and Plains-Great Basin grasslands. Woodlands and mixed-conifer forests occupy about 10% of the subregion.
Intensive agriculture is dependent on groundwater pumping around Deming, New Mexico, Fort Stockton and Pecos, Texas, and Villa Ahumada and Gomez Farias, Chihuahua. Water diversions along the Rio Grande, Pecos River, and Río Conchos also support intensive agriculture. Water diversion has had a devastating effect on freshwater biodiversity.
A gridwork of roads and drill pads created by oil and gas companies has resulted in habitat loss and fragmentation. Riparian sites and other lowlands areas are heavily altered throughout the subregion, their associated water sources tapped for municipal and agricultural needs
Degradation in the upland priority sites is widespread because of livestock grazing. Seven of the ten upland sites show moderate levels of degradation where historic semi-desert grasslands were heavily grazed and converted to scrub communities
Estimates of the original extent of grassland cover for the subregion range from 40-70%. Historic accounts of black grama and other grass species dominating the region indicate that the 25% grassland cover today
Restoration of many degraded grassland habitats is possible; however, former grama grasslands now degraded to mesquite dunes should be considered permanently altered.
riparian sites have lost substantial amounts of habitat and are subjected to damming and water diversions. In this century, irrigation systems and flood control have permanently altered the riparian character of the Rio Grande, sites [(2.02), (2.03), and (2.18)], and the Río Conchos (2.02).
All but the Marathon Basin (2.16), North-Central Chihuahuan Grasslands (2.08), and La Perla (2.12) contain some degree of state or federal protection within the site
Exotic species such as salt cedar (Tamarix ramosissima) threaten riparian areas
is a landscape dominated by Chihuahuan desert scrub, representing approximatley 50% of the total cover. This subregion may have once supported up to 50% more grasslands than it does today. Only 25% of this subregion is currently grassland.
Less then 5% of the ecoregion consists of montane and woodland habitat types,
complex basin and range physiography promotes isolation, Localized endemism commonly
Intact habitats are surprisingly frequent in this subregion. The Northcentral Chihuahuan Grasslands (2.08) are an unusual example of relatively intact grama grasslands that have supported decades of livestock grazing. Nesting aplomado falcon (Falco femoralis), frequent wildfire, and an abundance of kangaroo rats (Dipodomys spp.), are evidence of low human impacts and a functioning native ecosystem. Stream and springs, however, are highly degraded in this site. Many of the montane and woodland sites in protected areas, such as the Guadalupe Mountains-Carlsbad Escarpment (2.04), Chisos Mountains (2.07), Organ and San Andres Mountains (2.09), and Davis-Chinati Mountains (2.05) retain intact habitats of pine-oak woodlands and coniferous forests. United States federal and state parks protect these sites from logging, as do military installations and other protective designations.
The reptile assemblages of Big Bend (2.07) are truly remarkable. Intact desert scrub, woodland, and grassland habitats are occupied by a wide array of species including 34 species of snake, 21 species of lizard, and five species of turtle.
The lesser prairie-chicken (Tympanuchus pallidicinctus), sand dune lizard (Sceloporus graciosus arenicolous), swift fox (Vulpes macrotis), and pronghorn antelope (Antilocapra americana) create an unusual and threatened assemblage of grassland dependent vertebrates.
Jornada Bat Caves, within the Tularosa Basin (2.09) site, is a migratory stopover for at least four million Mexican free-tail bats (Tadarida brasiliensis). Neotropical migratory birds utilize remaining riparian corridors along the Pecos River
Alta Bavicora (2.11) is the only large, natural lake in the subregion, and is a critical migratory stopover for cranes, waterfowl, shorebirds, and raptors. Human-made impoundments along the Rio Grande have become important wintering habitats for migratory waterfowl.
Sierra Blanca (2.17) is an example of a vast grassland with low fragmentation, a relatively natural fire regime, and an assemblage of burrowing rodents, including prairie dogs. Combined, these factors regulate such important processes as water infiltration, soil development and productivity, species diversity, and microbiotic crust formation.
Along the Devil's River of site (2.06) are northern range limits of two subtropical species, Mexican white oak (Quercus polymorpha) and the jaguarundi (Felis yagouaroundi). This riparian corridor blends biota representative of the Chihuahuan Desert, Tamaulipan, and Edwards Plateau ecoregions. The occurrence of fireflies (Lampyridae) and other eastern North American invertebrates in the Davis Mountains
the riparian forests of the Pecos River (2.10). Blue Jay (Cyanocitta cristata), Yellow-throated Vireo (Vireo flavifrons) and White-eyed Vireo (V. griseus) are among the eastern songbirds found in the cottonwood-willow forests.
Two rare habitats-the gypsum dunes of White Sands National Monument within the Tularosa Basin (2.09) and the mineral outcrop of Caballos Noviculite in Marathon Basin (2.16)-both support unusual assemblages of plant and vertebrate species and several endemic soil invertebrates. Saline-adapted species occur in playas of Tularosa Basin (2.09) and Salt Flat, east of the Guadalupe Escarpment (within site 2.04).
John Karges, The Nature Conservancy of Texas
outstanding biodiversity features of the Northern Chihuahuan include riparian areas/gallery forests, montane habitats, springs-ciénegas, grasslands, headwaters of watersheds, range limits and boundaries of many species, migratory and wintering birds, and flyway boundary interfaces with Central Plains and Rocky Mountains flyways.
Threats include air pollution, agriculture, lack of surface water quality and quantity, overgrazing, fuel wood collection, altered fire regimes, exotic game introductions, and urban expansion
better environmental education and technology transfer in rural areas, effective monitoring of keystone species and the suite of species dependent on
improved monitoring of migratory bird species
Some information gaps include knowledge of concentrated food resources for migratory birds, missing keystone species, an information exchange across the border, a mollusk inventory, and a Big Bend to Juárez inventory of the Rio Grande (Río Bravo).
PROFAUNA, A.C. Chihuahua
The Nature Conservancy of Texas and New Mexico, Santa Fe, NM & San Antonio, TX
National Park Conservation Associations for Big Bend, Guadalupe Mountains, White Sands, and
Southwest Environmental Center, Las Cruces, NM
Rio Grande Restoration, Taos, NM
El Paso Audubon Society, El Paso, TX
Rio Bosque, Center for Ecological Restoration, El Paso
Forest Guardians, Santa Fe, NM
Peregrine Fund, Boise, ID
Ducks Unlimited Mexico
Unidos para Conservacion Barrengo
Texas Organization for Endangered Species
Chihuahuan Desert Nature Park
Colorado Bird Observatory, Brighton, CO
El Paso Native Plant Society
NM Native Plant Society, Las Cruces, NM
Mesilla Valley Audubon Society, Las Cruces, NM
Central Chihuahuan subregion
Livestock grazing practices that alter natural communities are widespread. Agricultural effects such as habitat loss, water diversion, and salinization are most prevalent in the Cuatro ciénegas basin. Mining of gypsum and other minerals occurs throughout the region, with varying degrees of impact. The mining of gypsum dunes can quickly lead to species extinctions because of the extreme local endemism in plants.
Runoff and drift of agricultural chemicals contaminates the soil and groundwater
Within Mapimí (3.01) and Cuatro ciénegas (3.03) agricultural practices have converted grasslands and shrublands to crops. Water use for agriculture in Cuatrociénegas (3.03) has reduced surface and groundwater supplies and reduced water quality. Water diversions into canals and ditches and the pumping of groundwater have altered wetland habitats and caused fragmentation
The harvesting of wood in an unsustainable manner occurs in half of the subregion sites. In the Sierras del Carmen and Santa Rosa Complex (3.02), intensive wood exploitation results in loss of woodlands, erosion, and habitat fragmentation. The Sierra de la Madera surrounding Cuatrociénegas suffers from erosion and poor water retention, impacting the basin below. Timber extraction in Sierra de la Gloria (3.07) and Sierra de la Paila (3.04) fragments wooded communities and disrupts wildlife populations
intensive livestock grazing
All eight sites are subjected to poaching of mammals and the trade of cacti and wildlife. In Sierras del Carmen and Santa Rosa (3.02), birds and reptiles are harvested and sold. The unsustainable harvest of guayule, candelilla, and lechuguilla is practiced here
Gypsum mining occurs in five of the sites
Fires have increased in frequency
Cuatrociénegas (3.03), primarily in wetland habitats, have displaced native species and altered habitat composition. Water hyacinth, an aggressive invader, was recently documented in the basin.
Central Chihuahuan Desert is one of the driest subregions. The valleys are lower (700 m - 1,400 m) than the other subregions, and the mountain ranges are not as high, resulting in less orographic precipitation. Most of the soils are derived from limestone. Only a few perennial streams or lakes are known and most basins drain internally. Desert scrub covers 60% of the subregion, including yucca woodlands and cactus scrub habitat types. Semi-desert grasslands constitute just 8% of the subregion but are believed to have once been more extensive. Grasslands have been replaced or become dominated by scrub because of centuries of frequent grazing and changes to fire regimes. Agricultural lands account for 14% of the land cover, and woodlands a sparse 3%. Playas constitute a surprising 8% of the land, concentrating in the La Laguna region.
The Sierra de Parras, Sierra Guadalupe and the Río Nazas separate the Central Chihuahuan subregion from the Meseta Central to the south. The mountain ranges and river create a dispersal barrier for some mammals and mark the limit of the range for others. For example, the western mastiff bat (Eumops perotis), yellownose cotton rat (Sigmodon ochrognathus) and whitetail antelope groundsquirrel (Ammospermophilus interpres) have their southern distributional limits in the Central Chihuahuan, whereas other mammals (Sigmodon leucotis, Sorex saussuri, and Dipodomys phillipsi) reach their northern limits. At least 100 endemic plant species have been recorded. Plant endemism in the subregion is highest within Cuatrociénegas
This unusually high number of endemic species may be due to the complex soil and microclimate conditions, the long-term stability of conditions, and isolation of the bolsón.
crasicaule - cacti dominated shrublands - and yucca woodlands occur throughout the subregion.
gypsum dunes of Cuatrociénegas
northern goshawk (Accipiter gentilis)-a species more typical of northern conifer forests-the Montezuma Quail (Cyrtonyx montezumae) of Madrean oak woodlands, and Audubon's oriole (Icterus graduacauda), a subtropical species that typically nests in dense, humid evergreen forests but found here in semiarid pine-oak woodlands.
The spectacular phenomenon of the monarch butterfly migration occurs within the forests of the Sierra de La Paila (3.04) and in riparian scrub of several mountain passes just north of Saltillo. Extremely high numbers of butterfies congregate at these sites. The Sierra Santa Fe del Pino (3.05) provides an important corridor for bat migrations. Bird migration routes within the Sierras del Carmens and Santa Rosa (3.02) run along corridors of woodland and forested habitats.
retain large tracts of intact desert scrub, grassland, woodland, and montane habitats. The Sierra de la Menchaca (3.06) has also had little human disturbance and contains intact pine and oak woodland forests. Their remoteness and inaccessibility has protected them to date from heavy grazing or mining. The Central Chihuahuan subregion has a higher proportion of intact habitats than the other three subregions.
large complexes of mountains, valleys, grasslands, and scrublands
wintering grassland birds, abundant burrowing rodents and associated predators, and relatively natural fire regimes. Cuatrociénegas (3.03) was identified as a globally important site for pronounced radiations and other complex evolutionary phenomena.
Central Chihuahuan subregion supports large areas of izotal. Approximately 60% of the subregion is characterized by these sotol-yucca-agave scrublands as well as creosote bush and tarbush (Larrea sp. and Flourensia sp.). Only 8% of the subregion is semi-desert grasslands and less than 5% is woodland and forest.
Mining and other heavy industrial activities are concentrated on the periphery of the two large urban centers in Monclova and Torreon, Coahuila
groundwater pumping in Monclova may have far-reaching impacts to Cuatrociénegas. Water diversion from the Río Nazas in Torreon has completely eliminated the shallow lakes that once characterized the basin known as La Laguna. The landscape matrix adjacent to priority sites, izotal and desert scrub is degraded but provides some linkages between priority sites
Low human population and limited resource extraction have helped to conserve biological and landscape integrity.
although goat and cattle grazing and water diversion have had widespread and pervasive effects
Most sites have been spared appreciable habitat loss (Table 5.3), however, localized, intensive resource use has dramatic impacts. Mining of gypsum and timber harvest in Sierra de la Gloria are poorly regulated and some areas have become deforested. Gypsum mines dot the subregion. Although the total area affected is quite small, the implications for biodiversity are large because of the high number of narrow endemics found in these specialized habitats. The limited agriculture in the Central Chihuahuan Desert is concentrated within riparian zones. Clearing of riparian woodlands and wetlands has had a substantial impact on wildlife, and is often a source of invasive species. Diversion of springs and streams may cause total loss of many freshwater habitats. Torreon, Coahuila, was established along a complex of large shallow lakes fed by the Río Nazas. These lakes, or lagunas, once supported high numbers of migrating shorebirds, including the endangered Whooping Crane (Grus americana) (Rod Drewien, personal communication). Diversions of the Río Nazas for agriculture has left these lakes completely dry.
Sierra de las Minas Viejas is degraded primarily by goats, whereas cattle and goats affect the other sites.
Many of the priority sites have been recognized as important for conservation by state and federal agencies, but widespread formal protection is lacking. Cuatrocíenegas and Cañon Santa Elena are protected areas established by the Mexican government for the protection of flora and fauna, and are classified as IUCN category IV. Curiously, Maderas del Carmen, also an area established for the protection of flora and fauna, is considered IUCN category VI by the United Nations Environment Programme World Monitoring Conservation Centre (http://www.wcmc.org.uk). Hunting and poaching has eliminated pronghorn, javelina, bighorn, bears, and large cats from most of the subregion. Illegal collection of cacti and reptiles threatens many species with limited ranges and small populations.
The desert scrub, yucca woodlands, grama grasslands, woodlands, and forests are connected by corridors and contain diverse species assemblages. Ecological processes like fire and large-scale movements of species also appear to be relatively intact. Cattle grazing and gypsum mining have degraded some habitats and agricultural crops have eliminated portions of some grassland habitats
Lower elevations, however, have been subjected to greater amounts of livestock grazing and the poaching of deer, cacti, and reptiles
The terrestrial component of Cuatrociénegas (3.03) is considered relatively intact
Dr. Tom Wendt, Herbarium Curator, University of Texas, Austin
tobosa grasslands, pine forest, gypsum flats, and montane
Sierra del Carmen-Sierranillos Burros-Valle Encantada complex, approaches Cuatrociénegas in distinctiveness. The complex is characterized by high species richness and an interesting phytogeography. Species of the eastern deciduous forests, northern grasslands, and western pine forests converge in this complex.
threats and habitat alteration are relatively low compared to subregions with higher urban densities.
Coahuila and Nuevo Leon are the greatest threats.
Exotic species, salt cedar in particular, threaten the area. Illegal hunting and collection of reptiles and cacti are also problems. Mining and human-caused fires
vision of success might be to keep the sites looking like they do today
keep urban growth from affecting the surrounding natural resources
Improved grazing management
emphasize restoration of benign grazing regimes, protection and maintenance of freshwater habitats and riparian areas, and the development of corridors and linkages among priority sites
public education and involvement at the local level
PROFAUNA, A. C. Coahuila
Ducks Unlimited of Mexico
Institute Nacional Ecologia
Friends of Mesquite
The Nature Conservancy
National Parks and Conservation Association
Museo de las Casas in Monterrey, NL
Desert Fishes Council
Meseta Central subregion
Six of the eight priority sites are evaluated as highly threatened. Pollution and agricultural impacts appear to be more severe in this subregion. Livestock grazing effects are similar to other subregions
Agricultural runoff contaminated with pesticide and insecticide residues cause soil and groundwater contamination. The waters of the Laguna de Santiaguillo (4.06) contaminate birds, fish and invertebrates
Eight of the nine sites are impacted by agricultural activities
Grasslands, shrublands, and shore lines of lakes are converted to croplands in some areas, such as the Laguna de Santiaguillo
Groundwater pumping for irrigation also reduces the lake level here. Wind erosion removes soil from abandoned or fallow fields in Chihuahuan Querétaro Desert
Órganos-Malpais (4.05) has lost forest habitat and is fragmented by roads and mill sites. Within the Chihuahuan Querétaro Desert (4.03), careless illegal harvests result in wind caused soil erosion and habitat fragmentation and new access roads for poachers
Fires have increased in frequency
Seven of the nine sites are used extensively for cattle or goat grazing
Illegal extraction of wildlife and plant life is a significant problem in six of the nine priority sites
wildlife trade and poaching animals for food is a serious problem. Within Huizache-Cerritos (4.02), cacti are removed for trade, as are small mammals and birds. In the Chihuahuan Querétaro Desert (4.03), both cacti and reptiles are removed for trade. Small mammals, mountain lions (Felis concolor), black bear (Ursus americanus), and white-tailed deer (Oidecoileus virginiana) are illegally hunted. Laguna de Santiaguillo (4.06) is a tremendously important lake for wintering waterfowl in the region. Illegal hunting of birds is a threat to populations.
off road vehicle use by recreationists damages flora and soils
Timber harvesting occurs in eight sites (22%).
Agricultural activities affect 31 sites (84%) if floodplain conversion, water diversions such as dams, canals, irrigation ditches, and groundwater pumping are considered
streams, lakes, and springs that have been converted from riparian and wetland habitats to croplands
groundwater for agricultural purposes affects 23 (62%) of the freshwater sites. Groundwater pumping has reduced subterranean flows that traditionally fed channels, and in some cases, has eliminated entire springs and wetland systems - pumping of water for municipal and agricultural purposes
Water is diverted in 73% of the sites and all diversions are used to some degree for agricultural purposes. Channel drying, reduced water flows, channelization, altered seasonal flows, reduced flooding, modification of habitats at ditch heads, and drowning of riparian habitat at dams and reservoirs
Three of the sites (8%) have been channelized for flood control: the Rio Grande-Southern New Mexico (5.11), the Pecos River (5.15), and the Upper Gila (5.37). The sites can no longer support aquatic species adapted to slower waters that result from increased sinuousity, backwaters, and side channels
(38%) suffer from the alteration and encroachment of floodplains for development
Exotic, or non-native, plant and animal species currently affect twenty-three (62%) of the sites. Salt cedar (Tamarix ramosissima)
Salt cedar is an aggressive phreatophyte, reducing water availability as well as altering water quality by concentrating salts
Organic inputs to the channel are also reduced by salt cedar. Bullfrogs (Rana catesbiana.) in Upper Yaqui (5.02) and Pecos River (5.15) prey upon native fish. Non-native fish, such as predatory bluegill (Lepomis macrochirus) and carp (Cyprinus carpio), are a problem
West of the continental divide, red shiner (Notropis lutrensis), channel catfish (Ictalurus punctatus), flathead catfish (Pylodictis olivaris), and small-mouth bass (Micropterus dolomieu) pose wide-spread threats to native fish. Non-native fish have been planted into many systems for human use
exotic fish species outcompete natives or hybridize with congeners. In the Pecos River, the exotic sheepshead minnow (Cyprinodon variegatus) hybridizes with the Pecos pupfish (C. pecosensis), a fish proposed as endangered in the U.S.. In Cuatrociénegas, the Rio Grande cichlid (Cichlasoma cyanoguttatus pavonaceus) and largemouth bass (Micropterus salmoides) are known to prey on native fish.
35% of sites show livestock grazing
Significant pollution occurs in eighteen sites (49%). Municipal and industrial pollution
Salt accumulation and increases in nitrogen are also a result of intensive agriculture
lakes contaminated by runoff from agricultural chemicals.
Six sites (16%) are affected by recreational activities
Catchment scale alterations such as widespread clearcutting and livestock grazing, which cause increased runoff and sedimentation, as well as the expansion of agriculture, were identified as widespread and significant threats. Future threats include degraded water quality through increased salinization, altered flow regimes and water levels, dams, non-native species, and the loss of organic inputs
dominated by a large plateau, with internally drained basins from 1,550 m to 2,100 m in elevation, and is generally higher and cooler than the Central Chihuahuan subregion
biota of the Meseta Central is poorly known
56% of the subregion is dominated by desert scrub communities. Playas cover 3% of this subregion and grasslands are found over 13%. This subregion contains the highest proportion of agriculture at 23% of land cover. Woodlands are limited to just 2.5% of the total area.
within the Altiplano Mexicano Nordoriental (4.01), 8 % of 72 cacti species are endemic, and Huizache-Cerritos (4.02) has at least 14 species of endangered species of cacti including several local endemics. The cacti diversity of the Querétaro Desert (4.03), an arid zone disjunct from the Chihuahuan Desert, also supports a wealth of cacti species.
Río Nazas (4.07) supports an exceptional set of long disjunct plant genera, among them Siphonoglossa,Justicia, and Henricksonia. A new plant family, the Setchylonthusaceae, has recently been described.
Yucca woodlands and crasicaule, two distinctive Chihuahuan habitats, reach their widest distribution in the Meseta Central.
Jaguars (Panthera onca), mountain lion (Felis concolor), and bobcat (Lynx rufus) inhabit canyons and foothills of the Sierra Madre Oriental. South of Saltillo and within the Altiplano Mexicano Nordoriental (4.05) occur some of the last remaining Mexican prairie dog (Cynomys mexicanus) colonies. Associated vertebrate species include mountain plover (Charadrius montanus), ferruginous hawk, swift fox (Vulpes macrotis), aplomado falcon, golden eagle, and the rare Worthens sparrow. Bats are known to migrate through the pine-oak woodlands of Órganos-Malpais (4.05). The long-tongued bat (Leptonycteris spp.) and California myotis (Myotis californicus) have been recorded at this site. The Laguna de Santiaguillo (4.06) is a critical migratory and wintering stopover for shorebirds, waterfowl, and raptors.
Most of the Meseta Central is highly altered because of intensive agriculture in its southern half
The subregion is approximately 55% desert scrub, including yucca woodlands and crasicaule. Just 13% is grassland, and less than 5% woodland and montane habitats. Agricultural lands constitute a full 23% of the total land coverage.
one site has experienced high losses due to timber harvest
Livestock grazing is the major cause of degradation. Habitat fragmentation, caused largely by roads, timber harvest, and agricultural fields
Cacti poaching is a severe problem in the subregion
potato farms have fragmented grama grassland habitats. Agricultural chemicals pollute ground and surface water supplies
Intensive timber extraction, an altered fire regime, and the building of roads have fragmented the landscape and degraded habitats
Julian Trevino Villareal, Universidad Autonoma de Tamaulipas
Outstanding areas for biodiversity include: the Altiplano Mexicano, which covers numerous habitat types of the Chihuahuan Desert including grasslands, halophytes, scrub, and gypsophiles; the canyons of Sierra Madre Oriental with endemic gypsophyllous plants; prairie dog towns in grasslands; and endemic cacti throughout. Huizache-Cerritos has many freshwater resources and is high in cacti endemism
Queretaro has high cacti diversity
corridor between Monterrey and Saltillo has a great diversity of plants
great data gaps in Zacatecas and Durango. These areas, including Rio Nazas, need inventories.
Threats include agriculture, goat grazing, cattle grazing, cacti removal, and pressures from increasing human population.
The biodiversity vision for this subregion includes: conservation of the richest foci for endemism of cacti in the world, protection of extensive desert scrub, and conservation of freshwater assemblages
Universidad Autonoma Nuevo León
Associacion de Ecología de Sierra Madre
Freshwater 3 and conservation
The aquatic species present today are the survivors of a more diverse biota that flourished before climate shifts transformed the Chihuahuan region into its present desert state (Smith and Miller 1986). As a result of this desiccation, combined with complex tectonic events, many freshwater habitats are isolated and reduced in size, and display high levels of endemism.
Despite its xeric nature, the Chihuahuan Desert has many perennial and ephemeral rivers and streams, their waters originating in large part at high elevations or in distant places (Smith and Miller 1986). Many Chihuahuan running waters experience a biannual cycle of flooding, with high flows occurring in the spring due to run-off from high-elevation snowmelt and then in the summer due to monsoons. In general, headwater streams tend to have more predictable and less fluctuating flow regimes than larger downstream tributaries (Smith and Miller 1986). Especially where flow is more erratic, flows may be dampened or cease altogether between often torrential wet periods, leaving behind intermittent pools.
cyprinids (minnows) and catostomids (suckers) dominate in these habitats
The Rio Grande is considered one of North America's most endangered rivers as a result of degraded water quality and water withdrawals. The river still supports pockets of native fauna along the 835-km reach located within the Chihuahuan Desert. Because 80% of instream flow is diverted for agricultural use
The Río Mezquital, a perennial river that flows to the Pacific Ocean, supports seven endemic fish species, some with affinities with the Rio Grande fauna. The Mezquital is also the northern range of some southern Mexico species (Minckley et al. 1986). The headwaters of the Río Conchos (5.35) is a refuge for an endemic fish assemblage (8-10 fish), and also supports populations of river otter (Lutra canadensis) and beaver (Castor canadensis). Overgrazing and introduced species in this region have imperiled all fish species at the site.
Xeroriparian areas have been shown to support 5 to 10 times the avian population densities and species diversity of surrounding desert uplands (Johnson and Haight 1985).
ephemeral and perennial reaches of the Upper Yaqui harbor assemblages of restricted fish species, including Yaqui chub (Gila purpurea), Yaqui topminnow (Poeciliopsis occidentalis sonoriensis), Yaqui catfish (Ictalurus pricei), and Yaqui and Bavispe suckers (Catostomus bernardini, C. leopoldi).
upper Gila River system contains several endemics, including the Gila trout (Onchorhynchus gilae), Gila chub (Gila intermedia) and two endemic spring snails.
Fig 4.4 freswater map
Pupfish of the genus Cyprinodon, and livebearers of the genus Gambusia, dominate the endemic fish fauna of springs in North America's desert Southwest. Extraction of water from springs and underlying aquifers has caused the wholesale elimination of habitat, and industrial and agricultural runoff have led to water quality degradation. Exotic species are more easily able to thrive in disturbed spring habitats and have excluded natives. Thus, the aquatic fauna inhabiting springs is often vulnerable due to both its own highly endemic nature and the susceptibility of spring habitats to disturbance.
in San Diego Springs (5.36), the bighead pupfish (Cyprinodon pachycephalus) and an undescribed Gambusia species survive in water temperatures as high as 43o to 44o C, the highest known temperatures inhabited by freshwater fish in the world.
La Concha harbor two local endemic fish derived from the Río Nazas fauna, and several basin endemics including Etheostoma spp. and Cyprinodon nazas.
Zona Carbonifera (5.06), a subterranean aquifer with associated caves and springs, is suspected to contain many unknown species in addition to the Devil's River minnow (Dionda diaboli), platyfish (Xiphophorus meyeri), sand shiner (Notropis stramineus), and endemic isopods and amphipods.
endemic fish species such as Media Luna killie (Cualac tessellatus), bluetail splitfin (Ataeniobius toweri), flatjaw minnow (Dionda mandibularis) and bicolor minnow (D. dichroma) inhabit the springs
world's only known population of the Leon Spring pupfish (Cyprinodon bovinus) in Diamond Y Spring. Rattlesnake Springs, which is also found within the Pecos River (5.15) site, is a migration stopover for and home to about 250 species of birds.
two endemic and critically imperiled fish in the splitfin (Goodeidae) family, as well as a rare freshwater shrimp, inhabit springs
springs and a lagoon that once supported four endemic species of fish and three endemic species of shrimp. All are now extinct. The site still contains eight endemic species of snails in monophyletic groups and three endemic crayfish. Restoration of the original springs by limiting groundwater extraction
Laguna de Santiaguillo (5.20) has rare Cyprinodon and Gila species, along with three endemic fish species
A ciénega is a marshy area created by the presence of seepage or springs, often with standing water and abundant vegetation
Cuatrociénegas (5.30), unparalleled in its aquatic species richness, is a globally outstanding site that takes its name from its dominant habitat type. The basin supports at least sixteen native fish, including eight endemic species. Fishes occupy springs, spring-fed rivers, marshes, playa lakes, ephemeral pools, and artificial canals (Minckley 1984).
Twelve crustaceans are known from the Cuatrociénegas basin. Many are endemic, including the cirolanid isopods (Speocirolana thermydronis, Sphaerolana interstitialis, and Sphaerolana affinis), one stenasellid isopod (Mexistenasellus coahuila), and two endemic hadzioid (weckeliid) amphipods, (Mexiweckelia colei) and the monotypic Paramexiweckelia particeps (Cole 1984).
Five of the nine hydrobiid snail genera in Cuatrociénegas are endemic - a degree of higher-level endemism that is extraordinary. These nine genera represent thirteen species, of which nine are endemic (Hershler 1984).
Riparian, semiaquatic, and aquatic reptiles and amphibians comprise 40% of the basin's herpetofauna. Thirteen riparian lizards, skinks, snakes, and toads occur here. Six semi-aquatic species are also found, including the ground skink (Sincella lateralis); the world's only aquatic box turtle (Terrapene coahuila); three garter snakes, including Thamnophis proximus; and the massasauga (Sisturus catenatus). The six aquatic species are the endemic black softshell turtle (Apalone ater), spiny softshell turtle (Apalone spiniferus), pond slider (Trachemys scripta), plain-bellied water snake (Nerodia erythogaster), diamondback watersnake (Nerodia rhombifera), and a species of frog within the Rana pipiens complex. While only two of the mesic-adapted species are endemic, the richness and taxonomic diversity of the assemblage is remarkable within the desert environment (McCoy 1984).
Fig 4.6 freshwater features table
At least eight species of freshwater fish are now extinct as well as four species of invertebrates.
at least 77% of the highly diverse freshwater sites in the Chihuahuan Desert either altered or heavily altered
heavy municipal demands as well as water withdrawals for agriculture
Dr. Salvador Contreras-Balderas, Facultad de Ciencias Biologias, Universidad Autonoma de Nuevo Leon
Almost the entire ecoregion was once drained by the Rio Grande, and the outstanding freshwater biodiversity in the ecoregion is a result of natural fragmentation of the pluvial basin, which has led to speciation within many small areas. More than 170 species of fish occur in the Chihuahuan Desert. There are at least thirty-five undescribed species. In the last ten years, ten more species have been discovered. There are seventeen extinct species of fish, six having gone extinct in the last ten years.
all water in the ecoregion must be effectively managed. This includes groundwater, a resource that is difficult to monitor. Underground fauna should be used to assess aquifer health
increases in industrial development, agriculture, and logging. Threats stemming from agriculture include pumping of groundwater, extraction of surface water, and dams on rivers and streams
Maquilas (factories) pollute surface and groundwater and must have restrictions put on them. Logging, in addition to causing increases in sedimentation and other pollutants, is leading to a loss of rainfall through deforestation. Furthermore, exotic species outcompete native fish.
vision of conservation success must include no more extinctions, sustainable water use, and less aggressive development
Southwestern Center for Biodiversity
New Mexico Riparian Council
Pecos River Native Riparian Restoration Organization
Instituto Nacional de Ecologia
Desert Fishes Council
North America Wetland Conservation Council
The Nature Conservancy
Changes in grazing and fire regimes and depletion and diversion of water sources are the major drivers in this process. Relatively intact habitats, those in a pristine state, are now rare and primarily restricted to montane areas, inaccessible slopes, the harsh environments of gypsum dunes and saline playas, and undisturbed springs.
Desert grassland quality and area have been drastically reduced since the onset of European settlement in the ecoregion (Dick-Peddie 1993). While bison inhabited this region within the past 1000 years, evidence that large grazing herbivores played a dominant role in maintaining these grasslands, as they did in the Great Plains, is not strong (Parmenter and Van Devender 1995, Monger et al. 1998).
Overgrazing can be defined as the repeated removal of above-ground biomass and disturbance of the soil surface leading to reduced plant vigor and increased mortality. Overgrazing is often associated with increased soil erosion, further reducing the potential for re-establishment of grassland species. Concurrent with the loss of grasslands has been increased erosion and reduction in grassland dependent species (MacMahon 1988).
Fragmentation of habitats through urban development, roads, fences, and conversion has curtailed the seasonal and nomadic movements of ungulates and their associated predators.
Intensive harvesting and poaching of rare cacti, birds, and reptiles for the wildlife trade
Fortunately, the original terrestrial habitats have high restoration potential if source pools of native species persist, water sources are renewed, and grazing and fire regimes are brought back within natural ranges of variation.
Irreversible impacts do occur, such as when high stocking rates are coupled with drought over an extended period of time, forcing a shift to mesquite or creosote bush dominance. The loss of montane forests because of logging, burning, and grazing is also more difficult to reverse.
Some of the best examples of larger blocks of intact ecosystems are the Chiricahua Complex (1.20), Tularosa Basin (2.09), Sierras del Carmen and Santa Rosa (3.01), and the Altiplano Mexicano Nordoriental (4.02) (Figure 5.1). If properly conserved, these are the foundations upon which future restoration efforts can build.
The Apachean subregion had the highest number of priority sites, but it had the fewest Level 1 areas (highest priority) (Table 6.1). This result is partly attributable to the degree of resolution used by the different subregion experts. The Apachean group separated disjunct mountain ranges into smaller discrete sites. The Central Chihuahuan and Meseta Central groups tended to aggregate disjunct sites into larger complexes. The Northern Chihuahuan group aggregated some and retained some smaller disjunct sites. Regardless, the Meseta Central had the highest proportion of level 1 sites followed by the Northern and Central Chihuahuan subregions. The large number of freshwater sites in the highest priority category is a reflection of the high endemism of the naturally fragmented aquatic systems of the Chihuahuan and the degree of threat to those systems.
Fig 6.1 priority site map
Mixed conifer and riparian habitats account for nearly 50% of priority sites, reflecting high levels of endemism in the former and keystone habitats in the latter.
strong latitudinal trend with mixed conifer, riparian, and grassland habitats dominant in the north and desert scrub more common in the southernmost subregion (Meseta Central).
high salinity cool springs nor high gradient ephemeral streams were represented at any sites, due to the extreme rarity of their occurrences. similar reasons, only one site contained a temporary laguna
Large rivers were represented by only two sites, both as a result of the fact that these habitats are rare in the Chihuahuan, and because they have been highly degraded.
subterranean habitats, which are likely important within the Chihuahuan, were only represented by two sites, due to the fact that there was not sufficient expertise among the workshop experts to identify biodiversity hotspots for that habitat type.
isolation of many freshwater habitats, particularly those associated with springs, has led to the evolution of distinct forms in a large number of habitats
3.6% (22,411 km2 ) of the Chihuahuan Desert has some form of conservation management
mostly US, UIUCN categories I-IV
The effort to protect freshwater rivers, streams, pozas (small ponds), or basins, must intensify, however, since the Chihuahuan may be the most globally distinct arid ecoregion in terms of freshwater biodiversity (Olson and Dinerstein 1998).
75% of the ecoregion is in Mexico
Meseta Central subregion, home to some of the world's rarest cacti, is completely without rigorous biodiversity protection
Chapter 8 Threat Analysis
Overgrazing of livestock or diversion of water is a problem across all subregions and at many priority sites within them
local, such as the introduction of exotic fish species in native freshwater communities,
the effects of degradation and fragmentation of terrestrial habitats may be less apparent to non-scientists than to biologists because the effects are often only apparent on longer time scales.
importance of the fish species endemic to rather ordinary looking desert pools
water mismanagement and growing human populations
Table 8-1. Overarching threats to biodiversity in the Chihuahuan Desert
Whereas a particular threat may operate over many sites, the cumulative effect of several threats at a single site can place the biodiversity it contains in grave danger
Chapter 9 Towards generating a biodiversity vision for the Chihuahuan Desert
nothing short of the return of the full complement of large mammals
likelihood that remote areas will become increasingly depopulated over coming decades as people relocate closer to cities and towns may reduce pressures
resiliency of some of these habitats particularly in the face of overgrazing by livestock-suggests that better stewardship could lead to rapid positive changes in habitat quality
areas of high endemism for cacti and other endemic plants,
globally rare assemblages of freshwater fish species, and
representation of all major plant communities in the four biogeographic subregions of the desert
restoration of flora and fauna associated with prairie dog colonies,
restoration of desert springs altered by the presence of exotic species,
restoration of riparian corridors along desert rivers that suffer from altered water flow,
restoration of desert plant communities affected by overgrazing and overbrowsing, and
restoration of gypsophyllous habitats that have been degraded.
restoration of populations of:
Cacti. Adequate reserves may have to encompass whole basins or ranges for area endemics or complexes of local endemics. At other sites, very local endemics are restricted to single valleys, dunes, or hillsides. Hernandez and Barcenas (1995) have identified two highest priority areas for endemic cacti, Huizache and Tolimán in the Meseta Central, containing 13 and 14 endemic species, respectively. Four high priority areas were also identified-Cuatrociénegas, Matehuala, Doctor Arroyo, and Mier y Noriega-holding 10-12 species each
Gypsum dunes, high endemic, cessation of mining, major gypsophyllous communities
The globally rare assemblages of freshwater fish and snail species inhabiting the Cuatrociénegas basin are a critical priority. No other freshwater system, particularly one found in deserts, displays the extraordinary local endemism, adaptations, and radiations seen in the basin's fauna. The Chihuahuan Desert's freshwater biota as a whole is also unusual in that it has many localized faunas restricted to individual springs, streams, and rivers spread throughout the region. The great age of the area and isolation of basins has contributed to this pattern. A majority of the region's desert springs and streams suffer from a host of threats including water extraction and the invasion of exotic species
prairie dog colonies and their associated flora and fauna (e.g., burrowing owls, pronghorn, ferruginous hawks, falcons, etc.)
Montane forests, riparian corridors, playas and lakes, and pine-oak woodlands, and desert scrub are among the communities hosting these transitory populations. [migratory]
conservation of keystone habitats (e.g., riparian habitats, springs)
Appendix Table A2.1 Terrestrial habitat types of the Chihuahuan Desert used in the representation analysis:
I. Desert Scrub and Woodlands
A. Larrea desert scrub (matorral desertico micrófilo)
B. Desert scrub (lechugillal, matorral desertico rosetófilo)
C. Yucca woodland (izotal, matorral desierto rosetófilo)
D. Izotal (Dasylirion-Yucca-Agave)
E. Prosopis scrub (matorral espinoso)
F. Alkali scrub (matorral halófito)
G. Gypsophilous scrub (matorral gipsofilo)
H. Arborescent Cactus Scrub (matorral sarcocrasicaule, garambullal)
I. Lowland riparian woodland (vegetacion riparia de tierra bajo: bosque)
A. Grama grassland (pastizal mediano abierto)
B. Sacaton grassland (zacatonal)
C. Tobosa grassland (pastizal de tobosa, baja con tobosal)
D. Yucca grassland (pastizal abierto)
E. Gypsum grassland
F. Lowland riparian marshlands (vegetacion subaquatica de tierra bajo)
III. Montane Chaparral and Montane Woodlands
A. Montane chaparral (chaparral)
B. Juniper-pinyon woodland (bosque de pino pinonero, bosque de esclero aciculifolio)
C. Pine-oak woodland (bosque de encino, bosque de pino-encino)
D. Mixed-conifer forest (bosque de Oyamel)
E. Montane deciduous woodland (bosque de galeria)
Appendix Table A2.2 Freshwater habitat types in the Chihuahuan Desert used in the representation analysis:
I. Warm springs
A. high salinity
B. low salinity
II. Cool springs
A. high salinity
B. low salinity
III. Large rivers & floodplain
IV. Perennial streams
A. high gradient
B. medium gradient
C. low gradient
V. Ephemeral streams
A. high gradient
B. medium gradient
C. low gradient
A. permanent terminal
VIII. Subterranean habitats
Rare or outstanding ecological and evolutionary phenomena: pronounced radiations, unusual adaptations, and highly local endemism of the biota of the Cuatrociénegas Valley, or the presence of relatively intact vertebrate faunas with top predators such as puma, jaguar, and a full range of prey species
(strict protection) versus areas of restricted resource use
replication of distinctive units. Conservation theory suggests that the probability of "global" persistence increases significantly when three or more examples of a "unit" (e.g., species populations, habitats) are effectively conserved.
highest priority areas identified (Chapter 6) are extremely large. Conservation at the scale of thousands and in some cases tens of thousands of km2 will likely be adequate to address minimum size requirements for some arealimited species and certain ecological processes.
Specific phenomena for the Chihuahuan desert ecoregion include: seasonal migrations of songbirds, shorebirds, raptors, and sparrows; migration corridors for monarch butterflies and sphingid moths; seasonal movements of bats tracking flowering cacti; altitudinal movements of birds and larger vertebrates between lowland and montane habitats; and dispersal corridors among mountain ranges for larger vertebrates
landscape features include: shape (configuration), degree of fragmentation, level of degradation and isolation, status of neighborhood patches of habitat, and adjacent or intervening land use (linkage analyses).
Intact habitat represents relatively undisturbed areas that maintain most original ecological processes and by communities supporting most of their original suite of native species. Altered habitat represents areas more substantially affected by human disturbance, but which still have the potential to sustain species and processes. Heavily altered habitat represents areas that have been degraded to the point of retaining little or no potential value for biodiversity conservation without longterm and extensive restoration. The experts discussed the definitions and made modifications appropriate to the Chihuahuan Desert. The definitions for intactness used as guidelines at the workshop are as follows:
Broadleaf and conifer forests
Intact: Canopy disturbance through human activities such as logging is restricted to less than 10% of defined habitat block. Understory largely undisturbed by timber extraction, intensive management, or grazing. Natural fire regimes still present. Although large mammals and birds may presently be absent from some blocks of habitat because of exploitation, insufficient area, or diminished resources, such blocks sustain many native communities and populations of plant, invertebrate, and vertebrate species and associated ecological processes. Altered: Canopy and understory significantly disturbed by human activities, but habitat remains suitable for some native species. Species composition and community structure are altered, and a large proportion of native species are absent but likely to return given sufficient time for recovery and adequate source pools. Examples include: large expanses of selectively logged forests; forests in which natural fires have been suppressed; areas where clearcuts cover are limited to between 10% and 25% of the landscape and patterned to facilitate natural ecological processes and recolonization; and 100 year old clearcuts that have been allowed to regenerate and contain adequate source pools for restoration. Heavily Altered: Habitat almost completely altered. Substrate alteration, exotic species introduction, and distance from source pools make recovery of original habitat unlikely without large and expensive restoration efforts. Examples include: urban and suburban development, forests converted to pasture or cropland, extensive clearcuts, and intensively managed plantation forests.
Grasslands, xeric shrublands/deserts
Intact: Habitat remains unplowed or unaltered by major changes in hydrologic patterns. The full suite of native plant species is still present, each in abundances within its natural range of variation. Successional patterns follow natural cycles (e.g., grazing by domestic livestock has not had a major effect on species composition or seral stages). Natural fire regimes are still present. Although large mammals and birds may presently be absent from some blocks of habitat due to exploitation, insufficient area, or diminished resources, such blocks still sustain many native communities and populations of plant, invertebrate, and vertebrate species and associated ecological processes.
Altered: Heavy grazing has altered dominance patterns of plant species. Some exotic species are present and surface water patterns may be altered, but the substrate has not been disturbed or plowed. Natural fire regimes have been largely suppressed. Original habitat is likely to return with time, moderate restoration, and adequate source pools.
Heavily Altered: Habitat is almost entirely altered, such as by human development, plowing, or crop cultivation. Native species are almost entirely replaced by exotics and crops. Surface water patterns have been extensively altered. Natural fire regimes have been completely suppressed.
Intact: Upstream land uses such as grazing, logging, urbanization, or agriculture are limited or well-managed. Habitats are largely undisturbed by altered hydrographic integrity, pollution, fragmentation, or other forces. Few exotic species are established, and native species face little or no exploitation pressures. Although large fish or aquatic reptiles may presently be absent from some habitat where they originally occurred due to exploitation, insufficient area, or diminished resources, such areas sustain many native communities and populations of plant, invertebrate, and vertebrate species and their associated ecological processes.
Altered: Human disturbance has extirpated many sensitive species, but habitat remains suitable for some native species. Species composition and community structure are altered, but native species are likely to return given sufficient time for recovery and adequate source pools. Examples are freshwater systems receiving point-source pollution, stream reaches isolated by lowhead dams, and areas where riparian cover has been removed.
Heavily Altered: Many species are already extirpated or extinct. Habitat is almost completely altered. Surrounding land development, the presence of large permanent structures altering hydrographic integrity, established exotic species, and consistently poor water quality make recovery of original habitat unlikely without large and expensive restoration efforts. Examples are dewatered or heavily channelized streams in areas of agricultural development, or highly polluted lakes in industrial or urban areas.
Type of threats
intensive logging & associated road building
intensive burning or grazing leading to habitat loss (particularly in riparian areas)
agricultural expansion & clearing for development
permanent alteration from burning
pollution, e.g., oil, pesticides, herbicides, mercury, heavy metals, defoliants
burning frequencies and intensities outside of the natural range of variation
loss of habitat, resources, or individual organisms from introduced species
unsustainable extraction of non-timber products
grazing patterns, frequencies, and intensities outside the natural range of variation
road building & associated erosion and landslide damage
off-road vehicle damage
excessive recreational impacts
Threats to freshwater habitats are generally similar, but with some important differences:
degraded water quality (e.g. point or nonpoint source pollution; changes in temperature, pH, DO, other physical parameters; sedimentation and/or siltation)
altered hydrographic integrity (flow regimes, water levels), resulting from dams, withdrawals, channelization, etc.
habitat fragmentation, from dams or other barriers to dispersal and general movement
reduced organic matter input
additional habitat losses, such as siltation of spawning grounds
excessive recreational impacts
unsustainable fishing or hunting
unsustainable extraction of wildlife as commercial products
competition, predation, and infection by established exotic species
APP F - site descriptions
APP G - species list
APP H -
What are the most spatially intensive processes?
Species that require large areas to maintain viable populations
Large-scale disturbance regimes
What are the most critically sensitive areas?
Critical areas at "down-times" - key watering areas, dry season water areas, areas that are important during unusual weather extremes for shelter or other resources
Local sites (e.g., caves, springs, etc.) of high biodiversity or endemism, and centers of endemism, in general
Source-sink relationships - areas that are likely sinks for a number of species
-Although this issue was not directly addressed in our approach, the identification of effective linkage areas in following analyses should consider sink habitats and landscapes for sensitive species. Moreover, by estimating minimum habitat sizes for viable populations of target species in the persistence analyses, one can eliminate certain habitat blocks (priority or not) as sinks for certain species.
Locations of watersheds - which ones are and are not entirely within the ecoregion?
The freshwater analysis identified a series of priority sites and watersheds independent from the terrestrial analysis. Some of the priority watersheds extend beyond the terrestrial boundaries of the Chihuahuan Desert ecoregion complex