Location and General Description
This ecoregion is contained in a larger area known as the Cape Region, and constitutes the southernmost part of the Baja California Peninsula. The area is considered an island of vegetation (Arriaga & Ortega 1988, Challenger 1998) due to its origin as an isolated land area, ten million years ago (during the Miocene), which later joined the more desert like peninsula. A vast complex of granitic mountains, running southward from the Gulf of California to the Pacific shapes the region. These mountains are intersected by valleys and canyons, and surrounded by vast plateaus.
The topographical features and geological events that gave rise to this particular region are responsible for the diversity of climates and vegetation in the same area. The highest strata of mountains (1600 – 2000 m) are composed of pine-oak forests that transform into oak-pine forests (1200 m) and oak forests (800m) as elevation decreases (Morelos-Ochoa 1988). The climate is temperate subhumid with summer rains and occasional winter rains. These pine-oak forests constitute the wettest portions in the state of Baja California Sur (760 mm annually). Slight variations in climatic conditions make up three different vegetation assemblages in the temperate forest. Pine forests at the highest elevations are dominated by Pinus lagunae, and shrubs such as Muhlenbergia spp. and Festuca spp. Pine-oak forests dominated by associations of Pinus lagunae with Quercus devia, Arbutus peninsularis, and Quercus tuberculata, and a variety of lower trees like Calliandra peninsularis and Mimosa xantii, as well as shrubs complement the landscape. Oak forests are closer to the subtropical forest, and they are inhabited by species such as Quercus arizonica, with virtually no pine trees. Some shrubs and lower trees are unique to this community including Dodonea viscosa, Bumelia peninsularis, and Buddleia crotonoides. Rzedowski (1988) observed there are no epiphytes in this region, giving way to an extraordinary abundance of mosses and lichens (Challenger 1998).
The past and present isolation of Sierra de la Laguna from the rest of the peninsula has played a major role in producing an extraordinary array of unique species including the pine (Pinus lagunae) and the black oak (Quercus velutina). Pine-oak forests are the only temperate forests in the state of Baja California Sur, which makes them particularly significant in terms of the biological diversity that still survives there. Pine-oak forests in general present high numbers of vertebrate species with species of restricted distribution (Flores-Villela & Gerez 1994). The ecoregion holds approximately 694 species of plants, 85 of which are endemic to the Sierra de la Laguna. Three of the plant species that represent the main elements of the vegetative associations include Pinus lagunae, Arbutus peninsularis and Bumelia peninsularis.
According to CONABIO there are 108 species of arthropods, 2 amphibian, 27 reptile, 74 birds and 30 mammal species. The herpetofauna adapted to this habitat includes 20% of the 48 recorded species that are endemic to the Cape Region (Alvarez-Cárdenas et al. 1988). Some of the endemic reptiles are the southern alligator lizard (Elgaria multicarinata) and the yucca night lizard (Xantusia vigilis). The avifauna inhabiting pine-oak forests is important because half of the bird species breeding at Sierra de la Laguna do so only in pine-oak forests (Rodríguez-Estrella 1988). The cape pygmy-owl (Glaucidium hoskinsii), white-winged dove (Zenaida asiatica) and golden eagle (Aquila chrysaetos) are only a few of the species found in this ecoregion. The endemic birds in this and the Gulf of California xeric scrub ecoregion include the Xantus’s hummingbird (Hylocharis xantusii) and the threatened Beldinng’s yellowthroat (Geothlypis beldingi) (Stattersfield et al. 1998). Of the 30 or so species of mammals present, one of them (an endemic bat) lives only in pine-oak forests (Gallina-Tessaro et al. 1988). The degree of endemism is high (Arriaga & Ortega 1988), and this is well demonstrated by the proportion of endemic species with respect to total recorded species. More than ten percent of the animal and plant species found at Sierra de la Laguna are endemic such as the ornate shrew (Sorex ornatus). The isolation of this region has contributed to the scarcity of predators, and to the poor competitive ability of some animals (Arriaga & Ortega 1988). Rodents and lagomorphs are virtually absent from the region, this fact favors the abundance of animals that would otherwise be abated by direct competition (as is the case of the acorn woodpecker, Melanerpes formicivorus) (Rodríguez-Estrella 1988).
Large areas of habitat still remain intact, as the topographical features make this ecoregion difficult to explore and exploit (Arriaga 1988). Portions of the Sierra de Laguna dry forest ecoregion still remain intact however; accessible areas are being converted for cattle grazing. There is still no recognizable fragmentation of the habitat, mostly due to the reduced exploitation of forest resources (Ortega & Arriaga 1988). In June 1994, the region was established as a Protected Natural Area (PNA) with pine-oak forests and subtropical dry forest as the key areas for protection. The fragile nature of this region requires legal protection over a long period, in order to prevent it from disturbances caused by human overpopulation and exploitation of forest resources for livestock.
Types and Severity of Threats
Native villagers often kill wildlife (mostly predators) that is considered as a threat to their domestic animals (Ortega & Arriaga 1988). If this continues, it could alter the natural processes maintaining biodiversity in the area. Although human disturbance in Sierra de la Laguna has been kept to a minimum, any uncontrolled perturbation to this fragile ecosystem could create an imbalance. This would ultimately cause the disappearance of an extraordinary array of evolutionary phenomena that has produced such a unique vegetation assemblage in the middle of an enormous desert.
Justification of Ecoregion Delineation
These montane pine-oak forests of the southern Baja Peninsula of Mexico are isolated from all other similar habitats and are host to a number of endemic species. Linework for this ecoregion follows the INEGI (1996) current landcover maps, encompassing all "oak and pine forest" classification within the Sierra de la Laguna region, as well as portions of "low deciduous forest", "matorral", and agricultural activities which fall within these parameters. Classification and justification follow Rzedowski (19789). Linework was reviewed by experts during ecoregional priority setting workshops (CONABIO 1996 and 1997) in Mexico.
Alvarez-Cárdenas, S., P. Gallina-Tessaro, and A. González. 1988. Herpetofauna. Pages 167-184 in La Sierra de la Laguna de Baja California Sur L. Arriaga, and A. Ortega, editors, Centro de Investigaciones Biológicas de Baja California Sur, México.
Arriaga, L. 1988. Importancia ecológica de las perturbaciones exógenas en un bosque de pino-encino. Pages 115-132 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Su. Centro de Investigaciones Biológicas de Baja California Sur, México.
Arriaga, L., and A. Ortega. 1988. Características generales. Pages 15-26 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur . Centro de Investigaciones Biológicas de Baja California Sur, 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..
CONABIO 2000. Listado de Regiones Terrestres Prioritarias, Sierra de la Laguna. Retrieved (2001) from http://www.conabio.gob.mx/rtp/fichas/rtp_001.pdf
Flores-Villela, O., and P. Gerez. 1994. Biodiversidad y conservación en México: Vertebrados, vegetación y uso de suelo. Conabio and UNAM, México.
Gallina-Tessaro, P., González, A. 1988. Mastofauna. Pages 209-228 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. Centro de Investigaciones Biológicas de Baja California Sur, México.
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.
Morelos-Ochoa, S. 1988. La vegetación: una aproximación a través de la fotointerpretación. Pages 69-82 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur . Centro de Investigaciones Biológicas de Baja California Sur, México.
Ortega, A., and L. Arriaga. 1988. Consideraciones finales. Pages 229-237 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. Centro de Investigaciones Biológicas de Baja California Sur, México.
Rodríguez-Estrella, R. 1988. Avifauna. Pages 185-208 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. Centro de Investigaciones Biológicas de Baja California Sur, 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., Crosby, M.J., Long, A.J., and Wege, D.C. 1998. Endemic bird areas of the World, priorities for biodiversity conservation. BirdLife International, Cambridge, UK.
Prepared by: Alejandra Valero, Jan Schipper, Tom Allnutt, and Christine Burdette
Reviewed by: In process