Toggle Nav

Southern North America: Southern Mexico

Situated along the Balsas River Valley this dry forest ecoregion has a tropical subhumid climate. A center of endemism for a number of genus of plants, the region is also know for its mammalian diversity, which includes such interesting mammals as jaguarundi, coati, ocelot, and collared peccary. There are a number of terrestrial priority sites within this ecoregion, as well as Important Bird Areas. Only ten percent of the original forest remain; agriculture, cattle farming, and illegal trade of exotic species are the main threats to this ecoregion.

  • Scientific Code
    (NT0205)
  • Ecoregion Category
    Neotropical
  • Size
    24,100 square miles
  • Status
    Critical/Endangered
  • Habitats

Description 
 Location and General Description
The region is located in southern Mexico, south of the mountainous Trans-volcanic belt. It runs west to east over a vast portion of relatively flat terrain, and occurs mostly below 1000m (except on isolated peaks). The Balsas River and its drainage basin delineate the regions eastern boundary, while the mountains of Sierra Madre del Sur mark the western boundary along the Pacific coast. The Trans-volcanic belt presents the limit in the north, and the Sierra Norte mountains of the state of Oaxaca constitutes its easternmost limit. The Balsas basin has been also termed the "Balsas Depression" (because it forms a valley descending down to 200 m) in the west. The northern side of the depression is a plateau (containing the highest elevations) that reaches 1000 m above sea level, with few, scattered peaks at 2000 m. The soil is mostly derived of sedimentary rocks, although igneous rocks are also abundant, especially in areas where the volcanic activity of the Trans-volcanic belt was highest. The climate is tropical subhumid, with a severe dry season that can last up to eight months. The precipitation levels are always below 1200 mm/year. Dominant species are Bursera longipes, B. morelensis, B.odorata, B. fagaroides and chupandra (Cyrtocarpa procera). Other species of trees that can be found are pochote (Ceiba parvifolia), brasil (Haematoxylon brasiletto), cazahuate (Ipomoea spp.), Lysiloma microphylla, and Ipomoea murucoides. Cacti are also common elements of this community (e.g. Lemairocereus and Cephalocereus). The herbaceous stratum is poorly developed, but species such as Bouteloua curtipendula, B. rothrockii and Hilaria semplei can be found.

Biodiversity Features
The isolation of the Balsas dry forests from other forests of its kind has promoted the diversification of many taxa, resulting in a high number of endemic species. For this reason, this is one of the most studied and most appreciated regions in terms of its value for biological conservation. It is regarded as the main speciation zone for the genus Bursera (24 species of the 60 known worldwide; Rzedowski 1993). It is also a center for diversification and endemism of Leucaena (Zárate-Pedroche 1994). In the Balsas dry forests, the family Commelinaceae has what has been called as a modern center for diversification; in this region the Commelinaceae is indeed a family with high numbers of endemic species (Hunt 1993). The region is also the center of diversification of the family Fabaceae. Many species of the genus Lonchocarpus are endemic to the Balsas region, and the largest of the guaje rojo trees (Leucaena esculenta) is found only in this habitat, as well as the endemic fabaceae Macroptilium pedatum (Sousa & Delgado 1993). Other genera rich in endemic species are Acacia, Ipomoea, and Euphorbia (Rzedowski 1991; Torres-Colín 1988). At least 15 species of Mammillaria occur in this region (Martínez-Alvarado & Flores-Castorena 1995). In terms of the fauna, the Balsas dry forest is considered as a zone with high mammalian diversity (Gaona-Ramírez et al. 1990) and includes the Jaguarundi (Herpailurus yagouaroundi), coati (Nasua narica), ocelot (Leopardus pardalis), collared peccary (Tayassu tajacu), jaguar (Pantera onca), coyote (Canis latrans), grey fox (Urocyn cinereoargenteus), and silky pocket mouse (Perognathus flavus). It is also diverse in papilionid butterflies, of which 11 are endemic species (Llorente-Busquets & Luis-Martínez 1993). This region is also considered outstanding in terms of the richness and endemism of the herpetofauna (Challenger 1998). Many species of mammals have their distribution limits in this area (e.g. Perognathus flavus), or have been recorded only in this region (bats such as Myotis californica, Myotis volans and Lasiurus xanthinus) (Romero-Almaraz 1996). The only survivor of the amphibian family Rhinophrynidae, the toad "sapo gota" (Rhinophrynus dorsalis), lives in the southern estuaries of the Balsas dry forest. CONABIO has identified a number of terrestrial priority sites within this ecoregion, including: Manantlán-Volcán de Colima, Cerro Ancho-lago de Cuitzeo, Hoya Rincón de Parangueo, Cerro Viejo-sierras de Chapala, and Tancítaro (Arriaga et al., 2000). A number of important areas for bird conservation have also been identified in this ecoregion, including: Tumbiscatío, Tancítaro, Cuitzeo, Pátzcuaro, Cuenca Baja del Balsas, Sierra Chincua, Tacámbaro, and Sierra de Taxco-Nevado de Toluca (Benitez et al., 1999). The strict endemic Balsas Screech Owl (Otus seductus) is found here along with the green parakeet (Aratinga holochlora), banded quail (Philortx fasciatus), greater roadrunner (Geococcyx californianus), crested guan (Penelope p. purpurascens), and orange-fronted parakeet (Aratinga caracularis).

Current Status
Most of the Balsas forests lying outside urban concentrations are very well preserved (Toledo & Ordoñez 1993). Dry forests once occupied 70% of the state of Morelos but now only 10% of the remaining vegetation is considered to have little perturbation (Jaramillo-Monroy et al. 1996).

Types and Severity of Threats
Agriculture and cattle farming are the main threats. Illegal extraction and illegal trade of exotic species are extensive and have reduced the populations of mammals like the white-tailed deer (Odocoileus virginianus), and the collared peccary (Tayassu tajacu). Native villagers hunt these species (González-Cota & Sánchez-Concha 1996) and later they sell them as meat. In the state of Michoacán, illegal trade of exotic species is also intense, and it has affected the populations of parakeets, macaws, song birds and other vertebrates that are useful as pets or food. The illegal trade of orchids and cacti is also detrimental in this region. It has been suggested that a more thorough knowledge of the region is needed. As well, a reinforcement of the laws that prohibit trade and extraction of exotic species, and a good management plan that is oriented to avoid excessive logging area necessary. Also needed is a revision of the system of protected areas, since most of them are very small for the habits and home-ranges of many of the vertebrates that they intend to protect. Another problem is that protected area’s zonification is not respected, therefore, even though core areas are preserved, there are no buffer zones to avoid edge-effects that impact the preservation of the a rich array of endemic species. Buffer zones in turn are disappearing due to the poor logging regulations that exist in protected areas. Road openings for highway construction have negatively affected these forests, because the plants become buried under the detritus that follows in their wake (Challenger 1998).

Justification of Ecoregion Delineation
The delineation’s for these dry forests in SW Mexico were derived from the current landcover maps of INEGI (date) and were modified by expert opinion at a number of ecoregional priority setting and delineating workshops (CONABIO 1996 and 1997)). Current landcover were not sufficient to complete the linework, as a majority of this ecoregion has been modified to an agricultural landscape. Much of the final linework was completed by expert opinion during the aforementioned ecoregional workshops (dates), and by consultation with CONABIO and Rzedowski (1978 and pers.comm.).

References
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. Mexico: Base de datos de las AICAS. CIPAMEX, CONABIO, FMCN y CCA.

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

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..

Gaona-Ramírez, S., G. López-Otega, yA. Castro-Campillo. 1990. Zonas de México con contenido mastozoológico notable. II Simposio Internacional sobre áreas naturales protegidas, 22 al 26 de octubre de 1990. Memorias. UNAM, México.

González-Cota, L., y R. Sánchez-Concha. 1996. Reserva de la Biósfera Sierra de Arteaga. Simposio sobre protección en áreas naturales protegidas. Valle de Bravo, Estado de México, del 18 al 20 de diciembre 1996. Memorias. AMIDES, UAEM, PROFEPA, México.

Hunt, D. R. 1993. Commelinaceae de México. Pages 409-426 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Diversidad Biológica de México. Orígenes y Distribución. Mexico: Instituto de Biología, UNAM.

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.

Jaramillo-Monroy, F., C. Ortiz-Narvaez, G. Torres-Gómez, y M.Recillas-Ocampo. 1996. Gestión para el establecimiento del área natural protegida Sierra Montenegro-Las Trincheras, Estado de Morelos. Simposio sobre protección en áreas naturales protegidas. Valle de Bravo, Estado de México, del 18 al 20 de diciembre 1996. Memorias. AMIDES, UAEM, PROFEPA, México.

Llorente-Busquets, J. & Luis-Martínez, A. 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. Mexico: Instituto de Biología, UNAM.

Martínez-Alvarado, D., y A. Flores-Castorena. 1995. El género Mammillaria en el Estado de Morelos. XIII Congreso Mexicano de Botánica, Cuernavaca, Morelos 5-11 de noviembre de 1995. Libro de resúmenes. UNAM, México.

Romero-Almaraz, M.L. 1996. Los mamíferos de las zonas sujetas a conservación en el estado de Morelos Simposio sobre protección en áreas naturales protegidas. Valle de Bravo, Estado de México, del 18 al 20 de diciembre 1996. Memorias. AMIDES, UAEM, PROFEPA, México.

Rzedowski, J. 1991. Diversidad y orígenes de la flora fanerogámica de México. Acta Botánica Mexicana 14:3-21.

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.

Rzedowski, J. 1993. Diversidad y orígenes de la flora fanerogámica de México. Pages 129-148 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Diversidad Biológica de México. Orígenes y Distribución. Mexico: Instituto de Biología, UNAM.

Sousa, M. & Delgado, A. 1993. Leguminosas mexicanas: fitogeografía, endemismo y orígenes. Pages 449-500 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Diversidad Biológica de México. Orígenes y Distribución. Mexico: Instituto de Biología, UNAM.

Toledo, V. M., y M. J. Ordoñez. 1993. El panorama de la biodiversidad de México: una revisión de los hábitats terrestres. Pages 739-758 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa , editors, Diversidad Biológica de México. Orígenes y Distribución. Mexico: Instituto de Biología, UNAM.

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.

Zárate-Pedroche, S. 1994. Revisión del género Leucaena en México. Anales del Instituto de Biología de la UNAM. Serie Botánica. 65(2): 83-162.

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

 

The Global 200

xHelp Improve this Site

Just 20 minutes of your time can help improve this site. By participating in a quick activity, you can help us make worldwildlife.org even better.

Start SurveyClose this box