Location and General Description
The region is situated on the northwestern portion of the Yucatán Peninsula. The forests grow on a vast portion of flat terrain (<400 m above sea level), composed of limestone of coraline origin. Soils are generally young and of calcareous origin; and drainage is extensive, thus the soils hardly ever flood (CICY 1993). The climate is tropical subhumid but becomes drier in the central portion of this region. As in other subtropical forests, there is a long dry season that is responsible for the deciduous nature of the forests. Precipitation levels do not reach above 1200 mm/year, although the northern portions receive slightly less. Dominant vegetative species in the central portion of the region are: tsalam (Lysiloma bahamensis) and jabín (Piscidia piscipula), and can be accompanied by Alvaradoa amorphoides, Bursera simaruba, Cedrela mexicana, Chlorophora tinctoria, Cordia gerascanthus and Lonchocarpus rugosus in other areas. The accompanying species are Vitex gaumeri, Brosimum alicastrum, Caesalpinia gaumeri, Cedrela odorata, Ceiba pentandra and Sideroxylon fuetidissimum. In the northern part of the ecoregion, near the coast, cacti become more abundant. Common cactus species include: Cephalocereus gaumeri, Pterocereus gaumeri and Lemaireocereus griseus. Herbaceous plants, epiphytes and fungi are rather scarce, but bromeliads like Tillandsia do grow on some trees.
The dry forests of Yucatán constitute a unique island of vegetation in the Gulf of Mexico region. They are isolated from other dry forests by the sea and by a vast extension of humid forests in the Maya region. Some researchers hypothesize that the isolation of the dry forests has been responsible for the unique composition of the region’s flora and fauna, as well as for the specific processes governing animal and plant dispersion. Many animals and plants cannot survive or readily disperse into the surrounding ecoregions, a fact that has accounted for the local distributions, and thus, high numbers of endemic species of this region. Plant endemism has been estimated to reach nearly 10% of the total vegetation (Estrada-Loera 1991). The northern portion of the region, where cacti are abundant, contains 10 of the 14 endemic cacti of the Yucatán peninsula (CICY 1993). The region is considered among the Mexico’s richest regions in terms of its herpetofauna (Challenger 1998), because it houses many endemic amphibians and reptiles (Flores-Villela 1993). The Yucatán dry forests are one of the very few places in Mexico where the black-beaded lizard (Heloderma horridum), one of only two venomous lizards which exist, lives (Challenger 1998). This ecoregion is home to over 290 bird species (2 endemic) and approximately 96 mammals.
Mammals include the White-nosed coatí (Nasua narica), jaguar (Pantera onca), spider monkey (Ateles geoffroyi), and southern opossum (Didelphis marsupialis). Avifauna species include Swainson’s warbler (Limnothlypis swainsonii), yellow-lored (Yucatán) parrot (Amazona albifrons), lesser yellow-headed vulture (Cathartes burrovianus), and hooded warbler (Wilsenia citriha).
The Yucatán dry forests have been extensively cleared for agricultural and cattle farming pressures. Many square kilometers of dry forest have been substituted either by henequén plantations, or by secondary communities that arise from intense cattle grazing (CICY 1993). The northern portion of Yucatan contains a unique community of dry forests with abundant columnar cacti. However, this is one of the most damaged areas of dry forests, and is considered as an endangered community of plants that should be protected and saved from extinction (CICY 1993). Of 14 species of cacti that live in the peninsula, only 10 are common in this region. The endangered Yucatán cacti is becoming increasingly rare due to the increasing illegal extraction of these plants from their native habitats for trade in national and international markets.
Types and Severity of Threats
In the state of Yucatán, at least one species of cacti, Pereskipsis scandens, is now considered extinct. Another species, Pterocereus gaumeri, is considered a relic species and is highly endangered (CICY 1993). As with the cacti, many species of animals and plants are also facing extinction due to the accelerated loss of habitat in this region. Federal protection should focus on the enforcement of laws against the trade of exotic wildlife species and on regulating soil use. In general, protected areas in the Yucatán region are oriented to the preservation of wetlands, rather than to the dry forests. However, some areas of dry forest have been proposed for protected status. This could be the last opportunity to save many endemic species from extinction in the dry forests of Yucatán.
Justification of Ecoregion Delineation
These dry forests occupy a large portion of the Yucatan Peninsula, and the southeastern boundary with the moist forest denotes a gradual climatic and subsequent vegetation transition. The linework for the ecoregion follows INEGI (1996) vegetation cover maps, from which we lumped the following classifications: "low deciduous forest", "medium deciduous forest", "microphyll desert matorral", "grasslands", and all subsequent agriculture within this broader classification. These dry forest are isolated from similar habitat types, and bound along the northern and eastern portion by the Gulf of Mexico. Several endemic species are known to occur here. Linework was reviewed at ecoregional workshops (CONABIO 1996 and 1997).
Challenger, A. 1998. Utilización y conservación de los ecosistemas terrestres de México. Pasado, presente y futuro. Conabio, IBUNAM y Agrupación Sierra Madre, México.
CICY. 1993. Jardín Botánico Regional. Guía General. Yucatán, México: Centro de Investigaciones Científicas de Yucatán, A.C.
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..
Estrada-Loera, E. 1991. Phytogeographic relationships of the Yucatán Peninsula. Journal of Biogeography 18: 687-697.
Flores-Villela, O. 1993. Herpetofauna de México: distribución y endemismo. Pages 251-279 in T. P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Diversidad Biológica de México. Orígenes y Distribución. Instituto de Biología, UNAM, Mexico.
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.
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.
Prepared by: Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: In process