Jalisco dry forests
The Jalisco dry forests on the Pacific coast of Mexico is characterized by low lying mountains and a relatively high diversity of floral and faunal species. Among the richest tropical dry forests, not only is species richness high, but endemism is high, also. About sixteen percent of flora and twenty nine percent of vertebrates are endemic. This region also serves as an important stop for migrating birds from North America on their route towards South America. The two major reserves within this ecoregion are not sufficient to protect this species-rich habitat from logging and agricultural development pressures.
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 sea level to 2000 meters (m) along the coast, and up to 4000 m 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 to 1200 millimeters (mm) of rainfall each year. There is also a distinct dry season during which most trees lose their leaves. Soils are shallow, and are derived from metamorphic and volcanic rocks. Historic lava flows and volcanic formations are abundant in Colima, nearer the volcano.
A considerable diversity of plants dominate and characterize the dry forests of Jalisco including: Glassywood (Astronium graveolens), Amapola Blanca (Bernoullia flammea), Sideroxylon cartilagineum, Bursera arborea, West Indian Laurel (Calophyllum brasiliense), Angelica Tree (Dendropanax arboreus), Ficus lapathifolia and Mexican Mahogany (Swietenia humilis), these trees forming a middle forest layer with trees of fifteen to twenty metres in height.
Spanish Elm (Cordia alliodora), Croton pseudoniveus, Vara Blanca (Lonchocarpus lanceolatus), Trichilia trifolia, Casa Iguana (Caesalpinia eriostachys) form the upper forest layer with trees of twenty to thirty metres for the top canopy height. Herbaceous plants and epiphytes are scarce, except for some species of Tillandsia. There are however abundant columnar and arborescent cacti including Opuntia excelsa, Pachycereus spp., Stenocereus spp. and Cephalocereus spp. Also found in this ecoregion are stands of coastal palm forest of Cohune Palm (Orbignya guacuyule) near the coastal zone.
These forests are among the biologically 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. Of the 724 species of vertebrates that inhabit the dry forests of Mexico, 233 (29 percent) are endemic. 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, of which sixteen percent are endemic.
Approximately 20 percent of the ecoregion's mammals are endemic and 27 percent are endangered. There are also ten endemic mammalian genera, including five monotypic genera: Giant Mexican Shrew (Megasorex gigas), Banana Bat (Musonycteris harrisoni), Michoacan Deer Mouse (Osgoodomys banderanus), Allen's Woodrat (Hodomys alleni) and Magdalena Rat (Xenomys nelsoni).
Reptiles and amphibians
Reptiles and amphibian species are endemic to the Jalisco dry forests at a rate of 51 percent and 58 percent respectively. Special status amphibians in the ecoregion include: the Endangered Jeweled Toad (Incilius gemmifer), which is a stream-breeding anuran; the Vulnerable Blint-toed Chirping Frog (Eleutherodactylus modestus), found in the leaf litter of the forest; Other anuran species occurring in the Jalisco dry forests are the Central American Rainfrog (Craugastor rugulosus); the Pale Chirping Frog (Eleutherodactylus pallidus), a narrow range endemic to the Mexican state of Nayarit and the Marias Islands; Forrer's Grass Frog (Lithobates forreri); Sinaloa Toad (Incilius mazatlanensis); Shovel-nosed Treefrog (Diaglena spatulata), a frog found in lowland xeric and thorn-scrub forest and tropical deciduous forest; and Shiny Peeping Frog (Eleutherodactylus nitidus). There is a single caecilian present in the ecoregion, the Oaxacan Caecilian (Dermophis oaxacae), a Mexican endemic associated with areas of xerophyllic vegetation.
The avifauna is comprised of about 300 bird species, with several endemics. Some notable avian species found in this ecoregion are the Mexican Parrotlet (Forpus cyanopygius), Rufous-bellied Chachalaca (Ortalis wagleri) and San Blas Jay (Cyanocorax sanblasianus). Two Endemic Bird Areas cover the majority of the ecoregion; however, they do not currently offer the ecoregion any official protection.
The forests of this ecoregion are also critical for migratory birds coming from Canada and the U.S. with 45 percent of the species, and 55 percent 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. Furthermore, many species of climber plants produce 17 percent of the biomass of dry leaves covering the forest floor, contributing to nutrient cycling. 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 faunal organisms.
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. Coastal development to support the burgeoning local population is creating considerable land conversion for urbanization and agricultural uses.
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, but this latter number could rise quickly if current practises 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. This reserve/refuge, unfortunately, does not protect the coastlines or Chamela Bay Islands.
Types and Severity of Threats
Habitat destruction and over-exploitation of wildlife are the chief threats endangering the survival of many species of plants and animals that are found in the Jalisco dry forests. 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 considerable areas for their survival, while others are dependent on very specific habitats.
There are only two protected areas covering less than ten percent of the original extent of the ecoregion. The remainder 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. In addition to progressive destruction of their habitat, many wildlife species face extinction due to hunting and collection. In other cases, native villagers have intentionally reduced the populations of some species, particularly carnivores, in order to reduce competition between livestock and wildlife. 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 Southwest Mexico were originally derived from current land cover maps and by consulting Rzedowski. 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.
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
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