Southern North America: Southern Mexico

Situated on the southeastern slopes of the Sierra Madre del Sur Mountains, this ecoregion is an important center of endemism for butterflies, and has the greatest diversity of scorpions and spiders in all of Mexico. However, little of the original habitat remains because of agriculture development for fruit and coffee plantations. Also, overgrazing by sheep has also severely damaged vegetation and led to erosion problems.

  • Scientific Code
  • Ecoregion Category
  • Size
    16,400 square miles
  • Status
  • Habitats

Location and General Description
The Southern Pacific dry forests ecoregion is located on the southeastern slopes of the Sierra Madre del Sur Mountains, which give way to a narrow fringe of coastal plains on which the dry forests of this ecoregion occur. The elevation ranges from sea-level to 1400 m. The climate is tropical dry, with precipitation levels of 800 mm/year. There is a lengthy dry season, which is responsible for the deciduous nature of the vegetation. The forests grow mostly on shallow, well-drained soils derived from limestone. Closer to the base of the Sierra Madre del Sur Mountains, the soils become more rocky, and are derived of igneous rocks. The dominant species include Lysiloma divaricatum, Bursera excelsa and Bursera fagaroides, which can be found in association with Ceiba aesculifolia, Comocladia enleriana, and Trichilia americana. In the state of Michoacán, the species more commonly present are Ficus mexicana, F. padifolia, Brosimum alicastrum, Licania arborea, Sideroxylon capiri and Enterolobium cyclocarpum. In the states of Guerrero and Oaxaca, the composition of the forests transforms and the more abundant species are Brosimum alicastrum, Bumelia persimilis, Godmania aesculifolia, Manilkara zapota, Pterocarpus acapulcensis, Licania arborea, Tabebuia palmeri, Bombax palmeri, Bombax ellipticum and Plumeria rubra. Herbaceous taxa and epiphytes are rather scarce. In the area of the border between the states of Chiapas and Oaxaca, the climate is tropical subhumid (the precipitation is 1040-1600 mm/year) and is dominated by plumajillo (Alvaradoa amorphoides), cacho de toro (Bucida macrostachya), brasil (Haematoxylon brasiletto), carnero (Coccoloba floribunda), mulato (Bursera simaruba), copalillo (Bursera bipinnata) and mezquite (Prosopis juliflora) (SAG 1968).

Biodiversity Features
The dry forests of southern Pacific Mexico constitute a narrow belt of vegetation along the coast, and have a unique assemblage of species, including many endemic. The genera Acacia, Ipomoea and Euphorbia have more endemic species in these forests than anywhere else in Mexico (Rzedowki 1991, Torres-Colín 1988). A high number of endemic plants are found in the portions of this ecoregion which occur in Oaxaca (Torres-Colín 1988). Butterflies of the Papilionidae family also have an important center of endemism in this region, with 11 endemic species (Llorente-Bousquets & Luis-Martínez 1993). This region also has the greatest diversity of scorpions in Mexico, including the large Centruroides centruroides. 311 species of spiders have been recorded here, constituting the richest site in Mexico (Robles-Gil et al. 1993). The region the second for endemic reptiles, after the trans-volcanic belt region (Flores-Villela 1988). It is also one of the few areas of Mexico where one can find Mexican beaded lizard (Heloderma horridum), one of only two venomous reptiles in the world (Challenger 1998).

Characteristic fauna includes the Lesser long-nosed bat (Leptonycteris curasoae yerbabuenae), greater fishing bat (Noctilio leporinus) , coati (Nasua narica), Buller’s pocket gopher (Pappogeomys bulleri), javelina (Tayassu tajacu) , red-crowned ant-tanager (Habia rubica), elegant quail (Callipepla douglasii), green iguana (Iguana iguana), and black iguana (Ctenosaura similis).

Current Status
Over several centuries, the deciduous forests of the Mexican Pacific have been severely exploited and disturbed. Agricultural expansion, primarily for fruit and coffee plantations have replaced vast expanses of forest (Challenger 1998). This impacts native biodiversity, directly through habitat loss, and indirectly through erosion and soil loss.

Types and Severity of Threats
Sheep farming is a major threat (Toledo et al. 1989). Furthermore, tourism is increasingly popular in the coastal areas of the ecoregion, leading to considerable development pressure. The only remaining intact dry forest occurs along the coast of the state of Michoacán, an area of very difficult access. Illegal hunting is an additional threat, and has severely reduced the populations of green iguana (Iguana iguana) and black iguana (Ctenosaura similis). Despite the biological importance of this region and the outstanding threats that it faces, only two protected areas have been established, one along the coast of the state of Oaxaca and the other in Guerrero. Another eight areas have been proposed for protection. Recently, a number of terrestrial priority areas were nominated, a number of which overlap with this ecoregion, including Sierra Sur y Costa de Oaxaca, El Triunfo-La Encrucijada-Palo Blanco, and Bajo Rio Verde-Chacahua (Arriaga et al. 2000). Several Important Bird Areas have also been identified here, including Sierra Norte, Sireea de Miahuatlan, and La Sepultura (Benitez et al. 1999).

Justification of Ecoregion Delineation
These dry forests flank the southern valleys and foothills of the Sierra Madre de Sur, across much of southern Pacific Mexico. Initial linework follows the current landcover classifications of INEGI (1996). From this map we lumped the following classifications: "subevergreen lowland forest", subevergreen middle elevation forest", "evergreen lowland forest", "evergreen middle elevation forest", patches of "savanna", and all subsequent agricultural activity. Later modification occurred from expert opinions, following suggestions from Rzedowski (pers. comm.) at a regional ecoregion delineation workshop (CONABIO 1996 and 1997).

Arriaga, L., J. M. Espinoza, C. Aguilar, E. Martínez, L. Gómez, y E. Loa (coordinadores). 2000. Regiones terrestres prioritarias de México. Escala de trabajo 1:1 000 000. Comisión Nacional para el Conocimiento y uso de la Biodiversidad. México.

Benitez, H., C. Arizmendi, y L. Marquez. 1999. Base de datos de las AICAS. CIPAMEX, CONABIO, FMCN y CCA, Mexico.

Challenger, A. 1998. Utilización y conservación de los ecosistemas terrestres de México. Pasado, presente y futuro. Conabio, IBUNAM y Agrupación Sierra Madre, México

CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.

CONABIO Workshop, Mexico, D.F., November 1997. Ecological and Biogeographical Regionalization of Mexico.

Flores-Villela, O. 1988. Riqueza de la Herpetofauna de México. Simposio sobre Diversidad Biológica de México, Oaxtepec, Morelos del 3 al 7 de octubre 1988. Instituto de Biología, UNAM. México.

INEGI Map (1996) Comision Nacional Para el Conocimiento y Uso de la Biodiversidad (CONABIO) habitat and land use classification database derived from ground truthed remote sensing data Insitituto Nacional de Estastica, Geografia, e Informática (INEGI). Map at a scale of 1:1,000,000.

Llorente-Busquets, J., y A. Luis-Martínez 1993. Análisis conservacionista de las mariposas mexicanas: Papilionidae (Lepidoptera, Papilionoidea). Pages 149-178 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Diversidad Biológica de México. Orígenes y Distribución. Instituto de Biología, UNAM, Mexico

Robles-Gil, P., G. Ceballos, y F. Eccardi. 1993. Mexican diversity of fauna. Cemex & Sierra Madre, México.

Rzedowski, J. 1991. Diversidad y orígenes de la flora fanerogámica de México. Acta Botánica Mexicana14: 3-21.

Rzedowski, J. 1978. Vegetación de Mexico. Editorial Limusa. Mexico, D.F., Mexico.

Rzedowski, J. pers.comm. at CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México..

SAG. 1968. Región de la Costa del Pacífico del estado de Chiapas y parte de la misma costa del estado de Oaxaca. Secretaría de Agricultura y Ganadería, México.

Toledo V.M., J. Carabias, C. Toledo, y C. González-Pacheco. 1989. La producción rural en México: alternativas ecológicas. Coleccion Medio Ambiente, núm. 6. Fundación Universo Veintiuno, México.

Torres-Colín, L. 1988. Composición florística y vegetal del cerro Guiengola (cartel). Simposio sobre Diversidad Biológica en México, del 3 al 7 de octubre de 1988, Oaxtepec, Morelos. Resúmenes. Instituto de Biología, UNAM, México.

Prepared by: Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: In process