Zacatonal
Introduction
This ecoregion is known as the Islas Revillagigedo dry forests montane (Zacatonal) grassland, and is located it the mountains of central Mexico. Grasses and shrubs make up most of the vegetation, of which many of species are to this region. An area of endemism for avifauna also, twenty-three species are not found anywhere else. Two parks provide minimal protection for this ecoregion, while hunting, fires, agricultural activities, and cattle farming make up the main threats to the region.
Location and General Description
The mountain range of the Trans-volcanic Mexican belt is home to this ecoregion, which occurs within mountain slopes or valley depressions in the vicinity of the pine-oak forests of central Mexico. The soils are derived of volcanic rocks, are fairly deep, and have high contents of organic matter.
The climate is temperate subhumid at low elevations, but becomes cold subhumid in areas closer to the mountain tops. Located at altitudes between 1100-2500 meters (m) above sea level, the region is composed primarily of grasses that do not reach large heights (20-70 centimeters (cm)).
Scattered trees form part of the community, but this is uncommon common. Pine-oak forests, however, are sometimes interspersed with this type of vegetation along the ecoregion transitional zone. In the Mexican state of Morelos, the dominant species are Hilaria cenchroides, Abildgaardia mexicana, Bouteloua radicosa, and B. hirsuta. In the Mexican state of Hidalgo the composition of the vegetation is somewhat different, with Muhlenbergia spp., Potentilla candicans, P. ranunculoides, Agrostis perennans, Deschampia elongata, Trisetum virletti, and Poa annua as the dominant species. In the state of Mexico, the dominant elements belong to the genera Poa, Festuca, Muhlenbergia, Sporobolus and Calamagrostis. Epiphytes do not form part of these vegetation associations, but fungi are very well represented as well as bryophytes and other herbaceous elements.
Biodiversity Features
Compared to other similar associations in the Valley of Mexico, this ecoregion is outstanding for its unique composition of its vegetation. The region is also important in terms of its diversity of vertebrates: 10 species of amphibians, 42 reptiles, 204 birds and 48 mammals are found in this area. Of the 204 species of birds, seven are threatened, 23 are endemic and 85 are migrant.
A rich mixture of neotropical and nearctic reptiles indicate this ecoregion is a center of diversity. The zacatonal itself constitutes small islands of vegetation in the middle of a vast area of pine-oak forests, thus the relationships that take place between the biotas of either area are important for the maintenance of overall biodiversity of this region.
Approximately 75% of the plants in this habitat type, found throughout Mexico, are endemic, which places them among the most diverse in terms of the number of endemic species per area. This ecoregion is considered as a fragile ecosystem that does not tolerate continuous perturbation; they constitute a relict flora of ancient times (during the Pleistocene) when climatic conditions allowed them to cover a great area of Mexico, but are now reduced to certain areas within temperate forests.
Distinctive vertebrate species include: eastern cottontail (Sylvilagus floridanus), common opossum (Didelphis virginiana), striped skunk (Mephitis mephitis), Chihuahuan desert horned lizard (Phrynosoma orbiculare), and Sierra Madre sparrow (Xenospiza baileyi).
Current Status
Large areas of zacatonal in central Mexico are still intact. This ecoregion is offered minimal protection in two national parks, however conservation efforts in this region should be oriented toward a regulation of tourism, as well as a revision of the laws for logging and illegal trade of exotic species. McDonald suggests that the zacatonal habitat in Mexico should be recognized as a threatened habitat and categorized as "untouchable" since the strict preservation of only a few square kilometers of this vegetation could save at least 100 species of plants from extinction.
Types and Severity of Threats
Hunting, occasional fires, agricultural activities, and cattle farming are the main threats that endanger the biota of this region. Illegal trade of exotic birds like hummingbirds and owls is extensive and may soon lead to a drastic reduction of these birds populations. Habitat destruction in the form of logging could be especially noticeable because of erosion and loss of soil which it produces. This is of special importance given that the area constitutes one of the main sources for aquifer re-fill, and it also supplies water for the nearby villages. The area in general is important in terms of its ability to retain water, which contributes to climate regulation and the maintenance of hydric cycles that are crucial to the organisms that depend on the surrounding forest. Fires also represent a major threat to the region, and have been increasing gradually.
Justification of Ecoregion Delineation
These small patches of montane grasslands occur across the Trans-Volcanic belt of Mexico. Initial linework follows the classification of "zacatonal" by Mata et al. Linework was later reviewed at several ecoregional priority setting workshops and from expert opinion. Reference was also made to Rzedowski.
References
- Barrios-Rodríguez, M. A. and J. M. Medina-Cota, 1996. Estudio florístico de la Sierra de Pachuca, estado de Hidalgo. México: CONABIO-IPN.
- 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, Mexico, D.F., November 1997. Ecological and Biogeographical Regionalization of Mexico.
- CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.
- Contreras-MacBeath, T. and F. Urbina-Torres. 1995. Historia natural del área de protección de flora y fauna silvestre Corredor Biológico Chichinautzin. México: SEP/FOMES, Centro de Investigaciones Biológicas UAEM.
- Delgadillo, C. 1993. Diversidad de la brioflora mexicana. Pages 355-368 in T. P. Ramamoorthy, R. Bye, A. Lot, y J.Fa, (Editors). Diversidad Biológica de México. Mexico: Orígenes y Distribución. Instituto de Biología, UNAM.
- López-Paniagua, J., J. Arévalo, J. M. Chávez, y F. J. Romero 1990. La diversidad biótica del corredor biológico Chichinautzin. II Simposio Internacionatl sobre áreas naturales protegidas en México. 22-26 octubre 1990. Memorias.
- Maas, J., R. Patrón, A. Suárez, S. Blanco, G. Ceballos, C. Galindo, and A. Pescador. 1981. Ecología de la Estación Experimental Zoquiapan. México: Universidad Autónoma de Chapingo.
- Mata, G., J. Lopez, X. Sanchez, F. Ruiz, and F. Takaki. 1971. Mapa de tipos de vegetación de la Republica Méxicana. Secretaria de Rucursos Hidraulicos. Mapa at a scale of 1:2,000,000.
- McDonald, J. A. 1993. Fitogeografía e historia de la flora alpina-subalpina del noreste de México. Pages 665-688 in T. P. Ramamoorthy, R. Bye, A. Lot, y J.Fa, (Editors). Diversidad Biológica de México. Mexico: Orígenes y Distribución. Instituto de Biología, UNAM.
- 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. 1978. Vegetación de Mexico. Editorial Limusa. Mexico, D.F., Mexico.
- Urbina-Torres, F. 1990. Avifauna del corredor biológico Ajusco-Chichinautzin, Morelos, México. II Simposio Internacionatl sobre áreas naturales protegidas en México. 22-26 octubre 1990. Memorias.
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