Henrickson and Johnston • CHIHUAHUAN DESERT VEGETATION 21 Chihuahuan Desert-U.S. and Mexico, II. 1986, pp. 20-39 tains (2190 m) as well as a series of smaller ranges. The region has some VEGETATION AND COMMUNITY TYPES OF THE internal drainage but mostly drains through the Rio Grande and Peco1 CHIHUAHUAN DESERT rivers. The Mapimian Region extends through eastern Chihuahua and Coa ]AMES HENRICKSON1 AND MARSHALL C. ]OHNSTON2 huila from the Rio Grande to the transverse extension ofthe Sierra Mader; Oriental in southern Coahuila. The region has a range and basin topog 1Department of Biology, California State University, Los Angeles, California 90032 USA; raphy with basins 700-1200(-1400) min elevation, many with interna and 2Department ofBotany, The University of Texas, Austin, Texas 7 8712 USA drainage with small to large ephemeral lakes, some receiving rivers orig inating in the adjacent Sierra Madre Occidental. Most of the ranges ar ABSTRACT limestone and extend only 700-1200 m above the plains but some higl A classification of plant communities ofthe Chihuahuan Desert Region, inclusive of all ranges occur including the limestone Sierra de la Madera (3023 m), Sierr montane habitats is presented. A total of 16 intergrading communities is recognized including de la Menchaca (2818 m), Sierra del Carmen (2731 m), Sierra San Marco eight Desert Scrub and Woodland communities: Chihuahuan Desert Scrub (with 5 facies), del Pino (2645 m), Sierra Mojada (2380 m), Sierra de Paila (2370 m· Lechuguilla Scrub, Yucca Woodland, Prosopis-Atrip/ex Scrub, Alkali Scrub, Gypsophilous Scrub, Arborescent Cactus Scrub, and Riparian Woodland; three Grassland communities: and Sierra Jimulco (3135 m). Grama Grassland, Sacaton G~ssland, and Tobosa Grassland; a Chaparral community: South of this region is the high plateau, the Altiplano Mexicano, whic Montane Chaparral; and four Montane Woodland communities: Juniper-Pinyon Woodland; forms the Saladan Region. This region extends through parts ofZacatee2 Oak Woodland, Pine Woodland, and Mixed Fir Forest. Representative species in each are and San Luis Potosi and is a large, mostly igneous-rock, partly limeston listed. area of moderate relief with internally draining basins from 15 50-210 m elevation with scattered, often small, dry lakes, no rivers, and only RESUMEN few high ranges as the igneous-rock Sierra Astillero (3195 m) in norther Se Presenta una clasificacion de comunidades de plantas de la region del Desierto de Zacatecas and the Sierra de Catorce (3060 m) in northern San Luis Potos Chihuahua, incluyendo todos los habitats montaiiosos. Un total de 16 comunidades son This physical setting provides topographic diversity with an elevation: reconocidas, incluyendo ocho comunidades de bosque y matorral: Matorral del Desierto de range from about 500-3195 m, with igneous-rock, limestone, gypsm Chihuahua (con cinco facies), Matorral de Lechuguilla, Bosque de Yucca, Matorral de parental materials that provide a variety of substrates varying from mom Prosopis-Atrip/ex, Matorral Halofilo, Matorral Y esofilo, Matorral de Cacto Arborescente, y Bosque Ribereiio; tres comunidades de pastizal: Pastizal de Tobosa, Pastizal de Grama, y tain ridges, slopes, canyons to alluvial fans, fine-textured basins, salir Pastiza1 de Sacaton; una comunidad de chaparral: Chaparral Montes; y cuatro comunidades playas, gypsum fiats, silaceous and gypsum dunes as well as freshwat< de Bosque Montes: Bosque de Junipero-Piiion, Bosque de Encino, Bosque de Pino, y Bosque springs, seeps, and rivers covering some 13° (ca 1500 km) oflatitudin de Coniferas Mixtas. Se enumeran especies representativas de cada comunidad. range that provides for a wide diversity of habitats. This is presented • a climate characterized by warm summers, cool winters, with associat( periods of freezing and occasional snows during the winter months, wi· Vegetation in the Chihuahuan Desert Region, which we outline in the about 69 to 90% of the rainfall coming during the hottest summer montl maps (Garcia 1976) accompanying the Gazetteer ofthe Chihuahuan Des­ between May and October, with measured average rainfalls of 156-3< ert Region by Henrickson and Straw (1976), varies from a Desert Scrub mm in the bolsons, recorded to 425 mm at higher elevations and in the Chihuahuan Desert proper to diverse non-desert vegetation types unknown amount on the higher mountains and with rainfall also varyiJ including Chaparral,· Pinyon-Oak, and Oak, Pine and Fir woodlands or greatly from year to year. forests at progressively higher elevations in montane areas. We divide the We here present a brief deScription of 'the vegetative cover over th Chihuahuan Desert Region into three regions following Morafka (1977). diverse region (Table 1). We recognize a series of often strongly inte The northern Trans-Pecos Region, north of the Rio Grande consists of grading plant community-types. These are designated by a combinati< ~asins (800-)1100-1500 min elevation with scattered, igneous-rock and of physiognomically, floristically, and physiographically derived nam( limestone ranges including the igneous-rock Davis Mountains (2560 m), simply to provide for convenient communication. Many species occ Chisos Mountains (2390 m), Chinati Mountaii_ls (2360 m), Quitman throughout the Desert Scrub vegetation zone, varying in abundance ru Mountains (1980 m), the limestone Sierra Tierra Viejas (1860 m), and stature in different community-types. Other species range well outside Glass Mountains (1880 m), and the geologically mixed Franklin Moun- t 20 22 Chihuahuan Desert-U.S. and Mexico, II Henrickson and Johnston • CHIHUAHUAN DESERT VEGETATION 23 al. (1964) for the Mexican portion ofthe Desert, Rzedowski (1957, 1966) TABLE 1 for arid portions of San Luis Potosi and Zactaceas and for San Luis Potosi. OUTLINE OF PLANT COMMUNITIES OF THE CHIHUAHtlAN DESERT REGION Morafka (1977) and Medellin-Leal (1982) present brief discussions of vegetation throughout the Chihuahuan Desert Region and Brown et al. I. Desert scrub and woodlands (1979) and Brown (1982), present, in a digitized format, vegetation series A. Chihuahuan Desert Scrub (Matorral Desierto Micr6filo with 5 phases or facies). 1. Larrea Scrub (Gobernadoral, Larrea-Flourensia Scrub). and associations as part of their biotic communities of the American 2. Mixed Desert Scrub (Chaparrillo). Southwest. The Secretaria de Programaci6n y Presupuesto, Instituto Na­ 3. Sandy Arroyo Scrub (Matorral de Arroyos). cional de Estadistica, Geografia e Informatica is publishing comprehen­ 4. Canyon Scrub (Matorral de Caiion). sive geographical data for each state that includes discussions ofvegetation 5. Sand Dune Scrub (Matorral de Dunas or Medanos). and series of maps on vegetation, geology, climate, lJ.ydrology, soils, and B. Lechuguilla Scrub (Lechuguillal, Matorral Desierto Roset6filo con Agave lechu- potential land uses. These are :presently available for Coahuila, Nuevo guilla). C. Yucca Woodland, Dasylirion Scrub or Woodland (Izotal, Sotolal, Matorral Desierto Le6n, and Zacatecas. Roset6filo ). It is important to realize that man's activities have been strongly altering D. Prosopis-Atriplex Scrub (Mezquital). portions of the Chihuahuan Desert Region for years (York and Dick­ E. Alkali Scrub (Matorral Halofitico). Pettie 1969). Sheep, goat, and cattle grazing has occurred in some areas F. Gypsophilous Scrub (Matorral Gipsofilo). G. Cactus Scrub (Matorral Crassicaule, Matorral Cilindrico Crasicaule, Garambullal). for over four centuries. Grasslands have been overgrazed allowing shrub H. Riparian Woodland (Bosque Ripario). encroachment. Montane forests have been completely cleared away from some ranges (e.g., the Sierra Mojada in west-central Coahuila) to provide II. Grasslands beams for mines, vigas for houses, and charcoal for ore processing. In­ A. Grama Grasslands (Navajita or Pastizal de Grama). B. Sacaton Grassland (Zacatonal). digens have moved their camps from spring to spring undoubtedly dis­ C. Tobosa Grassland (Pastizal de Tobosa, Bajo con Tobosal). persing seeds. III. Chaparral RESULTS A. Montane Chaparral (Chaparral Montano). I. Chihuahuan Desert Scrub and Woodlands.-Much of the Chihua­ IV. Montane woodlands huan Desert is covered with a low scrub vegetation mostly 0.5-2 m tall A. Juniper-Pinyon Woodland (Bosque de Enebros y Piiiones). ranging from a relatively species-poor Larrea- or creosote bush-domi­ B. Oak Woodland (Bosque de Encinas). nated scrub on gently sloping plains to a more species-rich Mixed Desert C. Pine Woodland (Pinares). ,,- D. Mixed Fir Forest (Bosque Mixto de Abetos). Scrub on upland rocky bajadas: OtheF species are concentrated in relation to edaphic factors. Here we recognize a series of six often intergrading community-types, some with several distinct phases. A roughly estimated cover for each vegetation type is expressed as a percentage of the total Chihuahuan Desert Region. We support Gleason's (1926) individualistic Chihuahuan Desert Region area. concept of plant communities stressing that each species or genotypically A. Chihuahuan Desert Scrub: (Mattoral Desierto Micr6filo, with 5 phas­ distinct subgroup of a species has a certain range of habitat tolerances es or facies) ca 70%. and will be expected to occur wherever environmental extremes d~ ~ot Larrea tridentata, Flourensia cernua, Acacia neovernicosa, Parth,enium exceed these tolerances providing they can be dispersed to these localities. incanum, Jatropha dioica, Fouquieria splendens, Opuntia leptocaulis, 0. An outline of our system is presented in Table 1 showing