Apachian/Madrean Region of South-Western North America, Mexico and U.S.A

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  • Location: Largely in north-west Mexico from Sinaloa border with Sonora and Chihuahua, centred on continental divide northward to south-east Arizona and south-west New Mexico in U.S.A.; about latitudes 26°-32°N and longitudes 111°-107°W
  • Area: Approximately 180,000 km², 600 km long and 300 km west to east.
  • Altitude: 500-3500 m; highest are Sierra Mohinora in south, several peaks c. 3000 m in north.
  • Vegetation: Nine physiognomic vegetation types: Madrean montane coniferous forest; oak-coniferous woodland; barrancan oak woodland; oak savanna; Madrean chaparral; short-grass prairie; tropical deciduous forest; subtropical thorn scrub; and subtropical desert fringe.
  • Flora: Northern portion of Sierra Madre Occidental phytogeographic province, where Apachian and Madrean floristic districts interdigitate. Approximately 4000 species of vascular plants; many endemics; a large number of species at northern limits, many at eastern or western limits.
  • Useful plants: At least 700-1000 wild plants useful; at least 250 estimated wild congeners of major crops; highest diversity of crop land-races of 18 pre-Columbian cultivated species north of neotropics. One endangered domesticate - Panicum sonorum; threatened medicinal plants.
  • Other values: Watershed protection; remote homeland of some of Mexico's least industrialized Amerindians; source of new industrial and medicinal crops; refuge for bats, Mexican wolf, thick-billed parrot, numerous threatened fishes and other vertebrates; ecotourism.
  • Threats: Pulping and lumber development (US$400-600 million funded) concomitant with North American Free Trade Agreement (NAFTA); species-selective over-harvesting of trees; erosion from agriculture, overgrazing and forest replacement with pastures of exotic grasses; extensive open-pit mining; increasing illicit drug traffic, associated violence and subjugation of native peoples to produce contraband.
  • Conservation: Much of region in U.S.A. variously protected - U.S. Forest Service for most montane habitats; also several National Monuments, private foundation for Animas Mountains. Less than 10% of area in Mexico protected - one National Park (40 km²), some mountains under SEMARNAP, several mountainous and other regions protected by private owners. Several areas designated for protection by State of Sonora. Informal conservation of less than 1% of region by Amerindian communities.

Geography

The region represents two floristic districts of the Madrean province centred on the Sierra Madre Occidental of northern Mexico (Map 22). Within or associated with this region are myriad individual ranges forming the Sierra Madre in north-western Mexico and more than two dozen major mountain ranges in south-eastern Arizona and far south-western New Mexico.

The Apachian district (picture) extends northward to the Mogollon Rim in south-western U.S.A. This district is represented by a northern archipelago of biological "sky-island" mountain ranges, including the Pinaleño, Galiuro, Santa Catalina, Santa Rita, Baboquivari, Patagonia, Huachuca, Chiricahua, Animas and smaller ranges. Also included is the "Deming Bridge" surrounding the Chiricahua and Animas mountains - it is the lowest place on the continental divide between Mexico and Canada. The adjacent mid-elevations and sky-island peaks in northern Mexico form the southern portion of the Apachian district, which merges with the northern reaches of the Madrean district. The Madrean district is characterized by the cordilleran flora between the Sierra Mohinora in the State of Chihuahua near the Sinaloa-Durango border and the northernmost edge of the Sierra Madre Occidental proper, c. 150 km south of the U.S. border.

Volcanic tuff and Laramide limestones dominate the surface geology. The region is drained to the west primarily by the Río Yaqui, Río Mayo and Río Fuerte watersheds, and to the east by the Río Bravo (Rio Grande) and Río Conchos. The northern outlier archipelago in south-eastern Arizona falls largely within the Gila River drainage. Precipitation ranges from 300 mm per year to more than 1200 mm, with summer monsoons predominating among the seasonal contributions. At the highest elevations most of the region experiences severe winter freezes, especially in the northern mountains. The lower elevations and even some areas at intermediate elevations toward the southern end of the region are essentially frost-free. Numerous frost-sensitive tropical plant species reach their northernmost limits in the region, especially in protected microenvironments. Near the northern end of the region many species reach their eastern or western limits on the Deming Bridge, the spill-over point on the continental divide (R.D. Worthington, pers. comm.).

Vegetation

The evergreen woodlands and savannas of this region evolved out of more generalized Madro-Tertiary vegetation before the end of the Pleistocene (Axelrod 1979). Despite the commonality of species in genera such as Pinus, Juniperus and Quercus, there are at least two distinct floristic assemblages of woodland species in the mid- to upper elevations (McLaughlin 1986). These allied but readily distinguishable floristic elements are the Apachian - in the northern horseshoe-shaped district rimming the northern Sierra Madre Occidental and extending as far north as the Mogollon Rim; and the Madrean - the more seminal flora characteristic of the Mexican mountains between the Sierra Mohinora and approaching the U.S. border (McLaughlin 1986, 1989).

Within these two districts, eight main physiognomic vegetation types can be found: montane evergreen forest, oak-coniferous (evergreen) woodland, oak savanna (the oaks mostly drought-deciduous), chaparral, short-grass prairie, tropical deciduous forest, subtropical thorn scrub and subtropical desert fringe (Marshall 1957; Rzedowski 1978; Brown 1982; Búrquez, Martínez-Yrizar and Felger, in press). A ninth type (which may be the counterpart of the oak savanna) is barrancan oak woodland, which forms a distinctive narrow belt on the western slopes of the Sierra Madre (Gentry 1942). Three of these types - montane evergreen forest, mixed evergreen woodland and chaparral - are strongly associated with the Madro-Tertiary flora (Axelrod 1979). The Sonoran Desert reaches its north-eastern limit at the lower flanks of the western sky islands, and the Chihuahuan Desert reaches its north-western limit at the lower flanks of the eastern sky islands. The Pinaleño and Chiricahua mountains and a few north-facing peaks in south-western Chihuahua support spruce-fir forest at their highest elevations.

Flora

An estimated 4000 vascular plant species are found within this region (Felger and Wilson 1995). McLaughlin (1995) provides an excellent overview of the flora of the sky islands of the Apachian district. The Chiricahua Mountains (c. 1840 km²) support a flora of c. 1200 species (Reeves 1976; Bennett, Johnson and Kunzmann, in prep.); the Animas Mountains, c. one-fifth the size of the Chiricahuas, have a flora of c. 638 species (Wagner 1977). The Rincon and Huachuca mountains, with respectively 959 and 907 species, are rather rich whereas the Pinaleño Mountains, with 786 species, are comparatively depauperate (Bowers and McLaughlin 1987; McLaughlin and Bowers 1990; McLaughlin 1993, 1995).

The species-richness of the mountain floras increases farther to the south in Sonora and Chihuahua. The flora of the Sierra de los Ajos is estimated at 1000 species (Fishbein, Felger and Garza 1995), and White (1949) documented 1200 species and infraspecific taxa for the Sierra del Tigre and Río Bavispe region in north-eastern Sonora. The Río Mayo and surrounding areas in south-eastern Sonora and south-western Chihuahua include at least 2100 vascular plant species (Gentry 1942; Martin, in prep.), with many endemic species and a large number of "tropical" taxa at their northern limits. The rugged terrain and diverse habitats of the Parque Nacional de la Cascada de Basaseachic in south-western Chihuahua support c. 750 species in only c. 40 km² (Spellenberg, Lebgue and Corral-Diaz, in prep.). Nearby at Nabogame (18 km north-west of Yepachic) in an area of similar size but more arid and with less habitat diversity, Laferrière (1995) documented 601 species. The expansive central Sierra Tarahumara has c. 1900 species (Bye, unpublished).

The plant families with the largest numbers of species in the region are Asteraceae, Fabaceae, Poaceae and Euphorbiaceae. The Sierra Madre Occidental is a major centre of oak diversity - there are at least two dozen species of Quercus in the region.

The rugged Apachian/Madrean region is a zone of mass meeting and geographic termini of species and floras from the north and the south. At least 17 plant families reach their northern limits - at least within western North America: Begoniaceae, Bombacaceae, Bromeliaceae, Caricaceae, Clethraceae, Cochlospermaceae, Eriocaulaceae, Erythroxylaceae, Gesneriaceae, Magnoliaceae, Melastomataceae, Meliaceae, Myrtaceae, Olacaceae, Opiliaceae, Piperaceae and Zamiaceae. Seventy-two percent of the tree flora, 164 species of southern or tropical origin, reach their northern limits in the region. Examples of prominent genera of tropical trees at their northern limits in western North America include Trophis, Chlorophora and six species of Ficus (Moraceae), Tabebuia (Bignoniaceae), Drypetes (Euphorbiaceae), Platymiscium (Fabaceae), Cinnamomum and Persea (Lauraceae) and Aphananthe (Ulmaceae) (Felger and Johnston 1995). Also at their northern limits are the pseudobulb-forming orchids, represented by ten genera, many of which are epiphytic.

The importance of the floristic contribution of the two major vegetation types of this region to the overall diversity of the Mexican flora has been described by Rzedowski (1991, 1993). Even though conifer-oak forest and tropical deciduous forest/thorn scrub account for respectively 21% and 17% of the Mexican territory, they contribute the largest number of vascular plant species to the flora. Of Mexico's estimated 22,000 vascular plant species, c. 7000 (24%) are in conifer-oak forests whereas c. 6000 species (20%) occur in tropical dry forests. These figures are higher than those for tropical humid forests and deserts of Mexico. The conifer and oak forest of Mexico, to which the Apachian/Madrean region generally belongs, has the highest endemism of all the major vegetation types in Mexico - 70% of the flora is endemic. If the conifer and oak forest is analysed in relation to "Mega-Mexico 3" of Rzedowski (1993), which encompasses the western U.S. borderlands (including those in our region) and also Central America into northern Nicaragua, 85% of the species are endemic. Hence, the flora of the Apachian/Madrean region is the north-western backbone of the two richest floras of Mexico - a country that ranks as one of the three top mega-diversity centres of the world.

Useful plants

The ethnobotanies of the Tarahumara, Guarijio, Mayo, Mountain Pima and Sonoran mestizos have been studied by Gentry (1942, 1963); Pennington (1963); Bye (1976); Laferrière (1991); Reina-Guerrero (1993); Yetman, Van Devender and López Estudillo (in press); and others. More than 300 food plants and 450 medicinal plants from this region have been documented ethnographically. These include large ethnofloral representations of Agavaceae, Cactaceae, Fabaceae and Solanaceae. Relatively unique phytochemical properties have been identified from analyses adjunct to these ethnobotanies, for instance the high papain content of Jarilla chocola (Tookey and Gentry 1969) and the high soluble-fibre content of Hyptis, Plantago and Salvia seed mucilages (Brand et al. 1990). Other utilitarian categories have generated considerable interest, such as fish poisons used by the Tarahumara (Pennington 1963). The "toloache" (Datura lanosa) of the western barrancas of Chihuahua has the highest content of hyoscine (scopolamine) of any Mexican species studied; this alkaloid is in great demand by the pharmaceutical industry (Bye, Mata and Pimentel-Vázquez 1991).

It has been estimated that among the regional floras in arid and semi-arid south-western North America, 18% of the species have been utilized by people for food and 20% for medicinal purposes (Felger and Nabhan 1978; Felger and Wilson 1995). About 10% of the edible species, or 1.8% of the flora, served as major food resources (Felger 1979). These estimates, based on compilation of known data, are verified by individual ethnobotanical studies (e.g. Gentry 1942, 1963; Bye 1976, 1985; Felger and Moser 1985; Laferrière 1991; Rea, in press). For example, the Tarahumara utilized at least 220 species of plants for food. Their pharmacopoeia includes c. 300 plant species (Bye 1985), 47 of which are collected and sold in urban markets of northern Mexico (Bye 1986).

The region is the richest in wild congeners of domesticated crops of any New World area north of the Tropic of Cancer (Nabhan and Felger 1985; Nabhan 1991). The wild relatives of domesticated crop plants include more than 250 species (Felger and Wilson 1995). Eighteen crop species are well represented in the region, including domesticates of Agave, Cucurbita, Lepidium, Hyptis, Panicum, Phaseolus, Prunus and Solanum, and many of these are found exclusively in the region. The land-race diversity of the native crops is richer than in any other American region north of the tropics.

At Nabogame (near Sierra Mohinora) in Chihuahua, the northernmost population of "teosinte" is disjunct by several hundred km from the tropical range of these wild and weedy maize relatives, where they sometimes introgress with cultivated maize (Doebley and Nabhan 1989). Native Seed/SEARCH, a Tucson-based organization devoted to the preservation and dissemination of indigenous crop plants, has made the seed of the Nabogame teosinte available to plant breeders. The mosaic of wild montane vegetation and Amerindian fields has provided ideal settings for studying introgression between wild and domesticated Capsicum, Cucurbita, Phaseolus and Zea.

Nabhan (1990b) identified the geographic patterns of 18 wild Phaseolus species in the Sierra Madre Occidental - a richer assemblage than found anywhere else north of the Tropic of Cancer. The 13 species at the south-western edge of the region (southern Sonora and northern Sinaloa west of the divide) are far more than predicted by species richness/latitudinal distribution regressions. Several of these bean species are endemic to the sierras, yet the region's germplasm resources remain under-collected. Preliminary results from pollination, DNA and isozyme studies by R. Bye suggest reciprocal gene flow between wild Phaseolus coccineus subsp. formosus and the special domesticate "tekómari", the P. coccineus subsp. coccineus of the Tarahumara. Gene flow between the wild and cultivated forms is aided by Tarahumara agro-ecological practices (which include the management of nearby forests) and may be responsible for the maintenance of this productive scarlet runner bean, which is adapted to high mountain areas with short growing seasons.

Social and environmental values

Mt Graham, the summit of the massive Pinaleño Mountains, is a sacred site of religious and cultural importance to the San Carlos Apache (McCarthy 1991). Portions of the Apachian/Madrean region have been inhabited for centuries by some of the least industrialized indigenous peoples in North America. The Tarahumara are one of the largest groups of native peoples in Mexico; their detailed folk science of plants has been acclaimed since the studies of Lumholtz (1902). The Guarijio, Mountain Pima, Opata, Mayo and Apache inhabitants of the region also merit special interest for their knowledge and uses of botanical resources.

The Apachian-Madrean forest is the largest oxygen- and biomass-producing terrestrial ecosystem in south-western North America. Watersheds of the Sierra Madre Occidental provide water to the densely populated areas on the coastal plain, where much of Mexican commercial food production takes place. The northern Sinaloa - southern Sonora irrigated districts draw on the Yaqui, Mayo and Fuerte rivers and are major producers of wheat as well as winter vegetables for export. The Río Bravo (Grande) provides irrigation water for southern Texas and adjacent Tamaulipas, where citrus, melons, chilies and tomatoes are important crops. Protection of headwaters from logging and overgrazing can help to stabilize hydrological resources required by agriculture and urban populations.

This is a region of tremendous habitat diversity and species-richness. Over half the bird species north of Mexico in North America (including Greenland) occur in the Chiricahua Mountains (Kunzmann, Johnson and Bennett, in prep.). The sky islands of southern Arizona, New Mexico and northern Mexico provide forested places for recreation, environmental education and the spiritual solitude of urban inhabitants living in the nearby desert lowlands.

Economic assessment

Although only a few non-timber resources have been quantified in terms of their economic potential, there is potential for cottage industries based on the sustainable harvest of wild plants. For example, during a "dry" year roughly 20 tons of dry fruits of wild "chiltepines" (Capsicum annuum var. aviculare) are harvested in the State of Sonora; as much as 50 tons might be harvested during a "wet" year (De Witt 1991). The total export to U.S.A. is c. 6 tons, where the retail price in 1990 was US$72 per pound (Nabhan 1990a).

One of the best-known medicinal plants of this region is a lovage known as "chuchupate" (Ligusticum porteri, = L. madrensis). The Tarahumara value its aromatic roots for medicinal and ritual purposes. A local business is based upon the medicinal preparation "COPANGEL", two-fifths of which is the ground roots of this perennial herb. Clinical studies by the Mexican national health programme have determined that it is effective in the treatment of peptic ulcers (Mundo, Aizpuru and Lozoya, in press). The roots also are exported to the U.S.A., Japan and Germany. The species' popularity in medicinal herb markets has increased to the point that over-collection has diminished many local populations. This moisture- and shade-loving species also is declining as the forests are cleared and arroyo heads erode. Based upon the retail value of COPANGEL, one ha of chuchupate is worth c. US$75,000.

Acorns ("bellotas") of Emory oak (Quercus emoryi) are wild-harvested each summer in north-eastern Sonora and south-eastern Arizona. A favourite of Sonorans and many Arizonans, the seeds are eaten fresh. They are sold locally, and in Sonoran markets and Tucson they can be purchased for c. US$3.50 per kg. Unlike the acorns of many other oak species, they are palatable with no preparation due to their relatively low tannin content. These acorns have an extremely high glycemic index value (Brand et al. 1990). Various other Madrean oaks likewise have "sweet" acorns and represent a potentially significant resource. The current price of acorn meal can be as high as US$22 per kg in Korea, and the supply falls far short of demand.

Several species of columnar cacti in the lowland subtropical zones in Sonora and Chihuahua yield highly desirable fruits which can be eaten directly, dried or prepared as juice, condiments or wine. They are harvested for local consumption and occasionally reach marketplaces in nearby cities (such as Hermosillo, Sonora). The demand is high and vendors usually sell out very early when the fruit is available. Desirable species include mountain organpipe or "saguira" (Stenocereus montanus) and organpipe or "pitaya dulce" (S. thurberi). Organpipe jam sells retail for US$15 per kg; 10 kg of fresh fruits yield 1 kg of jam. In some regions of northern Sonora, the local Amerindian people annually harvest 45 kg of fruit per person. The harvest of fruits from wild populations of columnar cacti by native peoples seems to have virtually no effect on the populations, at least in a subsistence economy (Hastings and Turner 1965; Felger and Moser 1985).

In recent years ecotourism has provided a major economic resource for the region. This usually non-destructive industry is growing and expanding rapidly. The Chiricahua Mountains in Arizona and the Tarahumara region in south-western Chihuahua are especially popular, as is the Alamos region in south-eastern Sonora.

Threats

The remoteness of the rugged sierras in Mexico and their relatively small human populations and cultural conservatism have allowed the region to retain much of its ecosystems in a rather natural state until recently. However, in the Sierra Madre Occidental an ever-increasing human population is placing more demands on the environment. Whereas the New Mexico mountains and many areas in Arizona are well protected for the foreseeable future, certain Arizona mountains and many of the areas in northern Mexico are in a precarious situation. Funding of large-scale development by non-local national and multinational private and corporate sources poses threats to local cultures and environments.

Cultivation of opium poppies and marijuana, usually considered a legal problem, now poses major ecological, social and economic threats. The presence of armed drug-plant cultivators, buyers and distributors is a danger to the local inhabitants, tourists and scientists. Native peoples in the Sierra Madre Occidental have been forced by criminals from outside the mountain communities to cultivate and harvest drug crops (R. Gingrich, Forest Guardians, pers. comm.). Failure to cooperate with drug lords and their underlings has resulted in injury and death (Weisman 1994). Aerial spraying of herbicides by law enforcement agencies has caused extensive but undocumented and unstudied damage to the native vegetation and flora, and poses possible human health hazards. The spraying of illegal fields on Sierra de Alamos and elsewhere threatens unique relict populations of tropical species. Massive sprayings of the herbicide paraquat may be responsible for reduction in populations of Rothschildia cincta, the larvae of which feed on Jatropha. The cocoons of this large saturnid moth are much used by the Yaqui Amerindians of Sonora for ceremonial purposes (Peigler 1994).

Open-pit mining for copper, gold and other metals in many parts of this highly mineralized region poses a continuing major threat. Air pollution from smelters (such as at Cananea and Nacozari in north-eastern Sonora) is likewise threatening and has been linked to the serious decline of the Tarahumara frog (Hale et al. 1995). The ever-present demand for and shortage of fresh water in nearby desert communities puts a serious strain on the water resources of the region. Every river system has been dammed and all river-delta areas have been seriously damaged. Construction of an enormous dam on the Río Fuerte near Huites in Sinaloa portends disastrous environmental problems and will lead to massive loss of tropical deciduous forest and riparian habitats. Many of the large deep canyons and barrancas could be destroyed by dams, which would cause a tragic loss of biological diversity.

Soil erosion due to over-intensive agriculture and grazing is an accelerating problem. In subtropical southern parts of the region there is a long history of slash-and-burn agriculture for "rozas" (maize fields, e.g. the "milpas" of Gentry 1942). Expansion in area and decrease in regeneration cycles of the rozas along with other agricultural practises, especially wood-cutting and livestock-grazing, contribute to the ongoing problems of erosion.

The most serious cause of desertification (defined as the reduction in species richness or diversity) in desert and subtropical regions in north-western Mexico is replacement of the native vegetation with buffel grass (Pennisetum ciliare) for cattle-grazing. In Sonora, more than 5000 km² have been cleared and a government goal calls for as much as 60,000 additional km² to be cleared and planted with this species (Búrquez, in press).

Local environmental degradation has resulted from the cutting of hardwood legumes and other trees and shrubs for cooking fuel and to a lesser extent for home-heating. Extensive over-exploitation in Sonora of mesquite (Prosopis velutina, P. glandulosa var. torreyana) and desert ironwood (Olneya tesota) for charcoal, exported primarily to U.S.A., threatens lowlands. Removal of these trees is often an integral part of the conversion to buffel grass (Nabhan and Carr 1994). Many of the subtropical hardwood trees such as "amapa" (Tabebuia impetiginosa, T. chrysantha) yield highly prized lumber for roof beams ("vigas") and fine cabinet-making. The great "sabinos" or bald cypresses (Taxodium mucronatum) yield a durable wood of high quality which commands a high price. These and many other species are legally protected by the Mexican forestry department, but enforcement is difficult. The selective cutting of the tree croton (Croton cf. niveus) of south-eastern Sonora and nearby northern Sinaloa for tomato stakes and fence posts has made this once common plant scarce (Bye 1995; Steinmann and Felger, in prep.).

The most dire threats to the sierras, however, are the logging and pulping industries. Almost all of the coniferous forests of northern Mexico have been cut one to four times. Large-scale financing is supporting clear-cutting, harvesting and destruction of understorey trees and plants and pulping of diverse species including oaks and other hardwoods. Fortunately, a massive forest-harvesting project in the region promulgated by the World Bank (Seedhead News 1991) has been abandoned, at least for the time being. A large pulp mill at Anahuac, Chihuahua has been expanded and renovated with a bank loan of US$350 million.

Extensive road building in montane zones as well as recent political changes and increasing interest in the natural resources of the region continue. Accessibility heralds important environmental, economic and social changes in formerly isolated montane areas. This accessibility is allowing scientists to inventory the rich natural resources. We hope that not all of the change will be destructive to local peoples and the environment.

Conservation

Throughout the Apachian/Madrean region there are countless peaks and great canyons rich in biological diversity. All are ecologically significant. In diverse parts of the region in situ conservation by indigenous and rural peoples has been informal but relatively effective.

Most of the south-eastern Arizona sky-island mountains are administered by the U.S. Forest Service - principally in the Coronado National Forest - which is often faced with conflicting goals of conservation, providing access for recreation, and responsibilities to alot timber sales, grazing leases and leases for various developments. Potential development of mountain areas for housing and resorts is of recurrent concern to environmentalists and scientists. In the Pinaleño Mountains, the development of a large astronomy centre on Mt Graham has led to the mobilization of conservationists and traditional Native Americans, pitting these groups against various U.S. federal agencies and a consortium of institutions including the University of Arizona and the Vatican. Construction of the telescopes, support facilities and roads has led to destruction of old growth spruce-fir forest; further development is planned.

Most of the larger mountain ranges in Arizona and New Mexico enjoy protection by various government agencies and private entities. For example, the Gray Ranch in south-western New Mexico, which includes the Animas Mountains, was purchased by The Nature Conservancy in 1990; protection continues under the Animas Foundation to which this large property has been transferred. The Huachuca Mountains are protected by having portions incorporated into Ft. Huachuca Military Reservation as well as a National Monument, and Ramsey Canyon managed by The Nature Conservancy. The Chiricahua Mountains of south-eastern Arizona are well protected, with a substantial designated wilderness area, a Research Natural Area at Cave Creek (set aside under the aegis of the Arizona-Nevada Academy of Sciences), a National Monument and the Southwest Research Station of the American Museum of Natural History.

Mexico has excellent environmental laws, and environmental awareness among the general population has grown substantially in recent years. Unfortunately, conservation efforts suffer from acute under-funding and resultant neglect. Although several areas in north-western Mexico have a special conservation status, enforcement of environmental policy and protection of natural areas has been lax or non-existent. The Zona Protectora Ciudad de Hermosillo and Arroyo los Nogales Preserve have been all but forgotten and are essentially buried under urban sprawl (Búrquez, in press). Governmental policy encourages the clearing of land in concert with introduction of exotic plants such as buffel grass. Many of the most damaging exotics were introduced into the south-western U.S.A. by the U.S. Soil Conservation Service, and later taken to Mexico.

Mexico does not lack for talented and educated individuals and has a bulwark of governmental agencies that could become far more effective in the conservation of natural areas - with increased support. Many of the Mexican mountainous areas are under control of the federal government, either the Secretaría de Agricultura y Recursos Hidráulicos (SARH) which manages forest refuges, or the Secretaría de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP) (formerly SEDESOL's Subsecretaría de Ecología), which manages the national system of protected natural areas. However, SARH functions more in a supervisory capacity than in a direct management role. "Ejidos" (community lands), private enterprise and para-state companies have more influence on the day-to-day administration of the forests.

In Chihuahua, nine Unidades de Administración Forestal (UAFs) of SARH have issued permits to ejidos, small property owners and large corporate logging operations (Resendiz-Vázquez 1984). The UAFs, more recently renamed Unidades de Conservación y Desarrollo Forestal, have become locally controlled (by state and municipality). At least two units are developing conservation programmes (in addition to their forest management, exploitation and product development) in collaboration with the U.S. Forest Service and the Canadian Model Forest Program. In all cases, the units must comply with federal law. On lands with indigenous peoples, another government programme is in effect - for example the Programa de Desarrollo Forestal Chihuahua-Durango (INI 1993) for the Tarahumara; there are similar programmes among the Guarijio and Pima.

Various institutions such as the Centro Ecológico de Sonora in Hermosillo have been active in attempting to gain new or increase protection for nature preserves. There is an important undercurrent of conservation activity in governmental agencies and private organizations (e.g. Pronatura). Ultimately it will be through documentation of natural resources that protection will be achieved. Recent and increasing scientific interest in this region that, strangely, has been largely ignored, is encouraging. However, even during this enlightened time, the protection of many areas is tenuous. There will be great losses if timely action is not taken.

Many unique areas in north-western Mexico with important biological, anthropological, historical and social values are worthy of protection; a few are mentioned. During the early 1990s a number of significant areas, some of substantial size, were designated by the Centro Ecológico de Sonora for protection and conservation management under the Sistema de Areas Naturales Protegidas del Estado de Sonora (SANPES). Some of them in the Apachian/Madrean region include Mesa el Campañero and Arroyo el Reparo near Yécora, Sierra de Alamos with the Upper Río Cuchujaqui area south-east of Alamos, Sierra Mazatán, Cañón la Cruz del Diablo, Sierra la Mariquita and Sierra San Luis.

Río Bavispe, Sierra de los Ajos and nearby Sierra de la Purica and Sierra Buenos Aires were granted protection in the 1930s; however, these areas were not managed as preserves and they have not escaped logging or cattle-ranching. The Sierra del Tigre and Sierra de los Ajos in northern Sonora are included in forestry preserves administered by SARH. Other mountain areas such as the Sierra San Luis are privately owned and well managed.

Tropical deciduous forest, one of the world's important biomes, is threatened globally. In Mexico a single area has obtained protection - the Chamela-Cuixmala Biosphere Reserve in Jalisco (CPD Site MA7, see Data Sheet). Areas for potential protection that include samples of the northernmost tropical deciduous forests on the continent include the Sierra de Alamos (rising above the colonial town of Alamos), portions of the Río Cuchujaqui including the upper region (Van Devender et al., in press) and the lower elevations of the Arroyo el Reparo. The canyon of the Río Tepoca , c. 100 km west of Yécora (on Mexico Hwy 16), is likewise an important northern outlier of subtropical vegetation worthy of protection.

The spectacular deep and narrow Cañón la Cruz del Diablo just east of Guasabas is a unique scenic and biological region. Here flocks of military macaws fly over the northernmost Brahea nitida palms. The incomparable Barranca del Cobre and its associated canyons are to Mexico what the Grand Canyon is to U.S.A. The Río Conchos region is particularly deserving of greater protection. The incomparable 245-m high Basaseachic Waterfall and immediately surrounding area in south-western Chihuahua are in the Parque Nacional de la Cascada de Basaseachic (40 km²). Seriously under-funded and managed more to encourage tourism than for conservation, the vegetation has deteriorated (Sánchez-Vélez 1987). Funding of effective conservation which involves the indigenous people is essential. It is crucial to support local efforts to establish Biosphere Reserves in these and similar areas before it is too late.

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Authors

This Data Sheet was written by Dr Richard S. Felger (Drylands Institute, 2509 North Campbell Avenue #176, Tucson, Arizona 85719, U.S.A.), Dr Gary Paul Nabhan (Arizona-Sonora Desert Museum, 2021 North Kinney Road, Tucson, Arizona 85743, U.S.A.) and Dr Robert Bye [Universidad Nacional Autónoma de México (UNAM), Instituto de Biología, Jardín Botánico, Apartado Postal 70-614, 04510 Mexico, D.F., Mexico].

Acknowledgments

We thank Wallace Genetic Foundation, Pew Scolars on Conservation and Environmental Program, and the Biodiversity Support Program of the World Wide Fund for Nature for their support. We also thank Michael F. Wilson for generous assistance.

Map of the Apachian/Madrean Region of South-Western North America, Mexico and U.S.A