Location and General Description
The Jalisco dry forests are located along the Pacific coast of the Mexican states of Nayarit, Jalisco, and Colima. The forests lie on terrain dominated by small mountains, where elevations range from 0-2000 m along the coast, and up to 4000m near the Colima Volcano. This ecoregion is bound on the western margins by the Pacific, and grade to pine-oak influences and temperate floral associations at higher elevations. This habitat type extends into inter-montane valleys, and generally follows the elevational contours of the foothills of these mountains.
The climate is tropical subhumid, with rains during four or five months of the year. Mainly during the rainy season the ecoregion receives 730-1200 mm of rainfall each year. There is also a distinct dry season during which most trees lose their leaves (Rzedowski 1988). Soils are shallow, and are derived from metamorphic and volcanic rocks. Lava spills and volcanic formations are abundant in Colima, nearer the volcano.
A great diversity of plants dominate and characterize the dry forests of Jalisco including: Astronium graveolens, Bernoullia flammea, Sideroxylon cartilagineum, Bursera arborea, Calophyllum brasiliense, Dendropanax arboreus, Ficus cotinifolia and Swietenia humilis, forming a middle forest layer with trees of 15-20 m. Cordia alliodora, Croton pseudoniveus, Lonchocarpus lanceolatus, Trichilia trifolia, Caesalpinia eriostachys form the upper forest layer with trees of 20-30 m. Herbaceous plants and epiphytes are scarce, except for some species of Tillandsia (Pennington & Sarukhán 1998). There are however abundant columnar and arborescent cacti including Opuntia excelsa, Pachycereus spp., Stenocereus spp. and Cephalocereus spp. (Rzedowski 1988). Also found in this ecoregion are stands of coastal palm forest of Orbignya guacuyule near the coast (Davis et al. 1997).
These forests are among the richest tropical dry forests in the world. Mexican dry forests in general are considered richer in endemic species than dry forests elsewhere in the neotropics (Challenger 1998). Of the 724 species of vertebrates that inhabit the dry forests of Mexico, 233 (29%) are endemic (Flores-Villela & Gerez 1994). The convergence of the Sierra Madre Occidental and the Trans-volcanic belt physiographical provinces make this a particularly diverse dry forest. The Jalisco dry forests house almost 1200 species of plants (Lott et al. 1987), of which 16% are endemic.
Approximately 20% of mammals are endemic and 27% are endangered (Ceballos & Miranda 1986). There are also ten endemic mammalian genera (Ceballos & Miranda 1986), including Merriam’s desert shrew (Megasorex gigas), trumpet-nosed bat (Musonycteris harrisoni), Michoacan deer mouse (Osgoodomys banderanus), Chamela rat (Hodomys alleni) and Magdalena rat (Xenomys nelsoni) (Ceballos & Navarro-L. 1991, Hall 1981). Reptiles and amphibian species are endemic at a rate of 51% and 58% respectively (INE-SEMARNAP 1999). The avifauna is comprised of about 300 bird species, with several endemics (Arizmendi and Márquez-Valdelamar 2000). Some unique species found in this ecoregion are the Mexican parrotlet (Forpus cyanopygius), rufous-bellied chachalaca (Ortalis wagleri) and San Blas jay (Cyanocorax sanblasianus) (Stattersfield et al. 1998, Howell and Webb 1995). Two Endemic Bird Areas cover the majority of the ecoregion; however, they do not offer the ecoregion any official protection (Stattersfield et al. 1998). The forests of this ecoregion are also critical for migratory birds coming from Canada and the U.S. with 45% of the species, and 55% of the individuals present in the winter months in Jalisco listed as Nearctic migrants. Ecological phenomena also contribute to the maintenance of diversity in dry forests. Mammals, for example, play a crucial role in pollination and in plant dispersal due to a virtual lack of invertebrate pollinators (Ceballos & Miranda 1986). Furthermore, many species of climber plants produce 17% of the biomass of dry leaves covering the forest floor, contributing to nutrient cycling (Vizcaino-Cook 1983). In addition, the 27 species of termites in the ecoregion recycle nutrients after having consumed dead plant biomass, thus making them more readily available to other plants and organisms (Challenger 1998).
Despite their importance as a center of diversity and endemism, the Jalisco dry forests have been intensively exploited, particularly in the last 50 years. The region was recently made easily accessible to people when a coastal road was opened in 1972 (Davis et al. 1997).
There are two protected areas within this dry forest ecoregion. The Biosphere Reserve of Chamela-Cuitzmala houses 429 species of vertebrates, of which 81 are endemic and 72 are threatened (Ceballos et al. 1994), but this latter number could rise quickly if current practices persist and appropriate management measures are not implemented. The second protected areas is the Playa de Cuixmala, established as a reserved zone and wildlife refuge in 1986 (Davis et al. 1997). This reserve/ refuge, unfortunately, does not protect the coastlines or Chamela Bay Islands (Davis et al. 1997).
Types and Severity of Threats
Habitat destruction and over-exploitation of wildlife are the main threats endangering the survival of many species of plants and animals that live here. Vast areas formerly covered by original vegetation have been logged and converted to agricultural fields. Habitat destruction affects both the vegetation and the wildlife of the dry forest, because some species require vast areas for their survival, while others need very specific habitats (Ceballos & Miranda 1986). There are only two protected areas covering less than 10% of the original extent of the ecoregion. The rest is in danger of destruction from increasing human settlement, intensive logging, and agricultural pressure. The most significant effect of logging on the forests of Jalisco could be the loss of endemic species (Maas 1995). In addition to progressive destruction of their habitat, many wildlife species face extinction due to hunting and collection (INE-SEMARNAP 1999). In other cases, native villagers have intentionally reduced the populations of some species, particularly carnivores, in order to reduce competition between livestock and wildlife (Ceballos & Miranda 1986). Laws must be enforced to control illicit traffic of wildlife and exotic species. Game and hunting laws must also be revised and applied in all areas where wildlife species still survive.
Justification of Ecoregion Delineation
This ecoregion is distinguished from surrounding areas by high levels of endemism, particularly among mammals (20%) and birds (see description above for details). The delineation for these coastal and foothill dry forests of SW Mexico were originally derived from current land cover maps (INEGI 1996) and by consulting Rzedowski (1978). The linework follows INEGI and encompasses the "selva baja caducifolia", "selva baja subcaducifolia", and all human modified habitats that fall within the broader classification of these forest types. Linework was then reviewed and modified by expert opinion as several ecoregion workshops (CONABIO 1996 and 1997).
Arizmendi, M.C., and L. Márquez-Valdelamar, editors. 2000. Areas de Importancia para la Conservacion de las Aves en México. Fondo Mexicano para la Conservación de la Naturaleza, México.
Ceballos, G., and A. Miranda. 1986. Los Mamíferos de Chamela, Jalisco. Instituto de Biología, UNAM.
Ceballos, G., and D. Navarro-L. 1991. Diversity and conservation of Mexican mammals. Pages 167-198 in M.A. Mares and D.J. Schmidly, editors, American ammalogy: History, biodiversity, and conservation. Univ. Okla. Press, Norman, OK.
Ceballos, G., García, A. & Rodríguez, P. 1994. Plan de Manejo de la Reserva de la Biósfera de Chamela-Cuixmala. Fundación Ecológica de Cuixmala. UNAM, México.
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.
Davis, S.D., V.H. Heywood, O. Herrera-MacBryde, J. Villa-lobos and A.C. Hamilton. 1997. Centres of Plant Diversity: A Guide and Strategy for their Conservation: Volume 3, The Americas. IUCN Publications Unit, Cambridge, U.K.
Flores-Villela, O., and P. Gerez. 1994. Biodiversidad y conservación en México: Vertebrados, vegetación y uso de suelo. Conabio and UNAM, México.
Hall, E.R. 1981. The mammals of North America. John Wiley and Sons, Inc., NY.
Howell, S.N.G. and S. Webb. 1995. A guide to the birds of Mexico and Northern Central America. Oxford Univ. Press.
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.
INE-SEMARNAP. 1999. Programa de Manejo de la Reserva de la Biósfera Chamela-Cuixmala, México. SEMARNAP, México.
Lott, E.J., S. Bullock, and J.A. Solís. 1987. Floristic diversity and structure of plan and arroyo forests of coastal Jalisco. Biotropica 19:228-235
Maas, J.M. 1995. Tropical decidous forest conversion to pasture and agriculture. Pages 399-422 in S.H. Bullock, H.A. Mooney, and E. Medina, editors, Seasonally dry tropical forests. Cambridge University Press, Cambridge.
Pennington, T.D., and J. Sarukhán. 1998. Arboles Tropicales de México. UNAM, FCE, México.
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
Stattersfield, A.J., M.J. Crosby, A.J. Long, and D.C. Wege. 1998. Endemic bird areas of the World, priorities for biodiversity conservation. BirdLife International, Cambridge, UK.
Vizcaíno-Cook, M. R. 1983. Patrones espaciales y temporales de producción de hojarasca en una selva baja caducifolia en la costa de Jalisco, México. Tesis de maestría, Facultad de Ciencias, UNAM, México.
Prepared by: Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: Dr. Daniel Brooks