Sierra de la Laguna dry forests
Located at the southern end of the Baja California Peninsula in Mexico, the Sierra de la Laguna dry forests ecoregion was once an isolated island, containing a large number of endemic species. After sufficient mountain uplift and the joining the Baja Peninsula mainland, this ecoregion underwent significant speciation, and is thus today high in species diversity; this portion of the peninsula contains the majority of the species found in the southern part of the Baja Peninsula. The Sierra de la Laguna dry forest is a subtropical dry forest classified within the Tropical and Subtropical Broadleaf Forests biome; the ecoregion is threatened by overgrazing from domestic cattle and the hunting by humans. Designated as a Protected Natural Area (PNA), this important ecoregion is at risk from habitat fragmentation.
Location and general depiction
ecoregion is contained in a larger geographic unit known as the Cape Region, and constitutes the southernmost part of the Baja California peninsula. The area is considered an island of vegetation due to its particular origin as an isolated land area, ten million years ago (during the Miocene), which later rejoined the more desert-like peninsula. The region is shaped by a vast complex of granitic mountains, running southward from the Gulf of California to the Pacific. These mountains are dissected by valleys and canyons, and surrounded by vast plateaus. The topographical features and geological events that gave rise to The Cape Region are responsible for the diversity of climates and of vegetation in this area.This
Subtropical dry forests, with less than 500 millimeters of precipitation per year, dominate lower portions of the mountains (300 to 800 meters in elevation). The trees in this region endure a long dry season during which, the majority of them lose leaves. The forest is transitional both with the pine oak forests at higher elevations, and with the xeric scrub at lower portions. The dry forest of Sierra de la Laguna is characterized by abundance of low trees and scrubs, and poor vertical stratification. The dominant tree species in the subtropical forest are Mauto (Lysiloma divaricatum), Palo Blanco (L. candida), Elephant Tree (Bursera microphylla) and Palo Zorrillo (Hesperalbizia occidentalis). Herbaceous elements are poorly developed, but their representatives are Caribe (Cnidoscolus angustidens), Spiny Aster (Chloracantha spinosa var. strictospinosa), Solanum spp., and cacti such as Biznaga (Ferocactus spp). Given its biological and climate, the Sierra de la Laguna dry forest is not analogous to the more continental dry forests located in Sonora and other parts of Mexico.
The prehistoric and present isolation of Sierra de la Laguna from the rest of the Baja Peninsula has played a major role in producing an extraordinary array of flora and fauna species. Isolation and their alleged history of contractions and expansion, has promoted high levels of speciation in dry forests of many tropical regions. There are 224 species of vascular plants inhabiting Sierra de la Laguna dry forests. Of 138 species of spiders and collembola present in the Sierra de la Laguna, 38 taxa (27 percent) are found in the dry forest. There are a total of 287 vertebrates recorded in the ecoregion. Half the reptile and amphibian species of Sierra de la Laguna inhabit the dry forest habitat within this ecoregion: more than 29 of 194 species of birds, and 29 of 40 species of mammals.There are a number of special status taxa that are found in the San Lucan xeric scrub, denoted variously as Lower Risk/Least Concern (LR/LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
The degree of endemism is high, and this is well demonstrated by the proportion of endemic species with respect to total recorded species: over ten percent of animal and plant species found at Sierra de la Laguna are endemic. This fact corresponds well with the data that endemism in tropical dry forests is generally higher than in moist forests. The isolation of this region has contributed to a scarcity of natural predators, and the poor competitive ability of some animals. Rodents and lagomorphs are almost absent from the region, favoring the abundance of species that would otherwise be abated by direct competition (such is the case with the Acorn Woodpecker, Melanerpes formicivorus. Large areas of habitat still remain intact, as the topographical features renders this ecoregion challenging to explore and exploit.
The amphibians present in the Sierra de la Laguna dry forests are represented by the Red-spotted Toad (Anaxyrus punctatus). Previously the Pacific Chorus Frog (Pseudacris regilla) was designated to occur here, but new DNA data render this taxon of unclear occurrence and range for this area.
Gulf of California islands of Espiritu Santo, Gallo, Ballena and Partida Sur.A number of reptilian taxa are found in the ecoregion, including: the endemic Baja California Rat Snake (Bogertophis rosaliae); Hunsaker's Spiny Lizard (Sceloporus hunsakeri); Belding's Orange-throated Whiptail (Cnemidophorus hyperythrus); Spiny Chuckwalla (Sauromalus hispidus NT); San Lucan Leaf-tailed Gecko (Phyllodactylus unctus NT); Baja California Night Snake (Hypsiglena slevini), a Mexican endemic rangeing from Bahía San Juanico, in the east-central Baja California Peninsula, southward continuously Cabo San Lucas (as well as on the island of Santa Margarita and on Cerralvo and Danzante islands in the Gulf of California; and Hunsaker's Spiny Lizard (Sceloporus hunsakeri), endemic to the Cape Region of Baja California Sur and the
There are a number of mammalian species occurring in the Sierra de la Laguna dry forests. Among the mammals found here are: Eva's Desert Mouse (Peromyscus eva), endemic to Baja California Sur; Mexican Funnel-eared Bat (Natalus stramineus); the near-endemic Peninsular Bat (Myotis peninsularis EN), chiefly found in Baja California Sur; Dalquest's Pocket Mouse (Chaetodipus dalquesti VU), known only from the Cape Region of Baja California Sur.
Subtropical dry forests have been generally considered one of the most threatened of the tropical ecosystems, and in the state of Baja California Sur they hold the preponderance of the biodiversity for the state. 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. 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.
Ecological threat profile
The fragile nature of this region suggests the need for legal protection over a long period, in order to prevent disturbances caused by human overpopulation and exploitation of forest resources for livestock grazing. Native villagers often kill wild species (mostly predators) that they deem threats to their domestic animals. If this practice continues, the natural processes could be altered that maintain ecoregion biodiversity. Although human disturbance in Sierra de la Laguna has been minimal, any uncontrolled perturbation to this fragile ecosystem may create an imbalance. Such a change could ultimately cause the disappearance of a broad array of evolutionary phenomena that produce the unique vegetation assemblage here in the midst of an enormous arid landscape.
Justification of ecoregion delineation
The delineation for this ecoregion were derived according to the current land cover classifications of INEGI and compared with Rzedowski. Following this classification, we lumped oak pine forests, subtropical matorral ("crasicaule" and "sarcocaule"), and "selva baja cadulifolia" with all encompased human modified habitats to derive our initial linework. This was then reviewed and modified by expert opinion during several ecoregional workshops. This ecoregion is designated by the code NT0227 by the World Wildlife Fund.
- S. Alvarez-Cárdenas, P. Gallina-Tessaro, y A. González. 1988. Herpetofauna. Pages 167-184 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur (México: Centro de Investigaciones Biológicas de Baja California Sur.
- L. Arriaga. 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 Sur,México: Centro de Investigaciones Biológicas de Baja California Sur.
- L. Arriaga y J. L. León.1989. The Mexican tropical decidous forest of Baja California Sur: A floristic and structural approach. Vegetatio 84: 45-52.
- L. Arriaga y A. Ortega. 1988. Características generales. Pages 15-26 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur, México: Centro de Investigaciones Biológicas de Baja California Sur.
- G. Ceballos. 1995. Vertebrate diversity in Neotropical decidous forests. Pages 195-220 in S.H. Bullock, H.A. Mooney, y E. Medina, editors, Seasonally dry tropical forests. Cambridge, U.K.: Cambridge University Press.
- A. Challenger. 1998. Utilización y conservación de los ecosistemas terrestres de México. Pasado, presente y futuro. México: Conabio, IBUNAM y Agrupación Sierra Madre.
- 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.
- Gallina-Tessaro, P., y A.González. 1988. Mastofauna. Pages 209-228 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
- C. Michael Hogan. 2009. ''Elephant Tree: Bursera microphylla'', GlobalTwitcher.com, ed. N. Stromberg
- 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.
- Janzen, D. H. 1988. Tropical dry forests. The most endangered major tropical ecosystem. Pages 130-137 in E. O. Wilson, editor, Biodiversity. Washington: National Academy Press.
- Jiménez, M. L. 1988. Aspectos ecológicos de las arañas. Pages 149-166 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
- León de la Luz, J. L., R. Domínguez, y R. Coria. 1988. Aspectos florísticos. Pages 83-114 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
- Ortega, A., y L. Arriaga. 1988. Consideraciones finales. Pages 229-237 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
- Rodríguez-Estrella, R. 1988. Avifauna. Pages 185-208 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
- 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.
- Rzedowski, J. 1993. Diversity and origins of the fanerogamic flora of México. Pages 129-144 in T.P. Ramamoorthy, R. Bye, A. Lot, y J. Fa, editors, Biological diversity of Mexico: Origins and distribution. New York: Oxford University Press.
- Vázquez, M. M. 1988. Fauna colembológica de hojarasca y suelo. Pages 133-148 in L. Arriaga, and A. Ortega, editors, La Sierra de la Laguna de Baja California Sur. México: Centro de Investigaciones Biológicas de Baja California Sur.
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