Isla del Carmen (Photograph by David Olson)

The Gulf of California xeric scrub is located on the eastern coast of the Baja Peninsula is defined by the Sierra of La Giganta Mountains. Both species richness and endemism are high in this arid habitat, which receives some of the lowest precipitation in all of Mexico. Twenty genera of plants, nine species of the herpetofauna, twelve species of mammal, and two species of avifauna are endemic to this region. Although much of this region remains intact, cattle overgrazing and urban development have destroyed vast tracks of habitat.

Location and General Description

This region is delineated by its most prominent feature, the mountain range of Sierra of La Giganta. La Giganta runs north south on the eastern portion of the Baja California peninsula. Igneous (piroclastic, basaltic, and andesitic lava) and sedimentary rocks from the tertiary make up the region. Its altitudes vary between 200 to 1000 meters (m), and in some localized portions they reach more than 1000 m. The climate is dry hot in the narrow coastal plains on the east of the peninsula, but it becomes dry semi-hot as the distance from the coast increases. Precipitation reaches some of the lowest levels of all Mexico (<100 millimeters (mm) per year). Temperature oscilations are extreme.

Piebald chuckwalla (Sauromalus varius), San Esteban Island, Baja California, Mexico. (Photograph by John Kipping, California Academy of Sciences & CalPhotos)

Dominant flora species are creosote (Larrea tridentata) and desert burr sage (Ambrosia dumosa), but other species also found are: Jatropha cinerea, palo fierro (Olneya tesota), Acacia brandegeana, Cercidium floridum, and Pithecellobium undulatum. Species of more mesic habitats occur on the many oases that are present in the peninsula: palma de taco (Washingtonia robusta), Typha domingensis, Phragmites communis and Phoenix dactylifera. The oases are remnants of mesic environments that existed in the peninsula in past times; they consist of regular-sized bodies of water dispersed throughout the peninsula, and are surrounded by vegetation that belongs to wetlands interspersed with common elements of the xeric scrub.

Biodiversity Features

Rattleless rattlesnake (Crotalus catalinensis), Santa Catalina Island, Baja California, Mexico. (Photograph by Dr. Robert Thomas and Margaret Orr, California Academy of Sciences & CalPhotos)

The Gulf of California xeric scrub represents one of the largest well-preserved extensions of arid lands in Mexico. It is home to many endemic and endangered species. The isolation of the Baja California Peninsula from other deserts and from the continent is in part responsible for the high levels of endemism and diversity of organisms in this region: 238 species of plants, 32 reptiles and amphibians, 199 birds (2 endemic), and 64 mammals (12 endemic). There are 20 endemic genera of plants, and 20-25% of the plant species are endemic; 9 species of the herpetofauna are endemic and 10 are exclusive to oases; 37 of the birds are migrants that come from the U.S. and Canada. The xeric scrubs of Baja California house the oldest tree of any desert: the palo fierro or ironwood (Olneya tesota). More than 160 plant species, depend upon legumes such as ironwood and mesquite (Prosopis pubescens) for their regeneration in arid lands, as well as endangered wildlife species like the desert bighorn (Ovis canadensis) and masked bobwhite quail (Colinus virginianus ridewayi), that use ironwood both as shelter and as a forage resource. Ironwood nursing relationships promote diversification and increase richness of other plants in arid ecosystems. Unlike its continental counterpart -the Sonoran desert- biodiversity in the Gulf of California xeric scrub occurs mostly in various oases that remain in this arid region. Oases represent a relict of the ancestral vegetation that once dominated Baja California; they serve as refuges for endangered and endemic species or for those species that were extirpated from less dry environments in the peninsula. They also serve as "stopovers" for migrant birds that resume migration after foraging on the rich sources of food that oases provide. Arid lands are characterized by high number of endemic taxa; despite their apparent "aridity", these ecosystems are highly valuable for conservation in terms of the biological uniqueness of biotas they support.

Current Status

The Gulf of California xeric scrub remains partially intact, despite intensive human activity in and around the area. Large portions of habitat are well preserved, but the system is considered fragile and in high danger of perturbation due to cattle grazing, agricultural fires, and extraction of water from the oases.

Types and Severity of Threats

Bahia de los Angeles, Baja California, Mexico. (Photograph by Timothy Green)

Cattle has effectively displaced populations of pronghorn, mule deer, and mountain sheep, and hunting of the puma (Felis concolor) has been a common practice among villagers; both phenomena have reduced the populations of the aforementioned mammals. Habitat destruction for agriculture and human settlement threatens the xeric scrub and its many endemic cacti; as a consequence, the introduction of animal and plant species could displace native fauna and flora through direct competition. Tourism activities in the region have become extensive, enhancing the dangers of pollution and other disturbing effects on the flora. The introduction of buffel grass (Cechrus ciliaris) to feed cattle has been especially harmful, because it accumulates combustible litter that causes the complete burning of ironwood and other native plants. As arid grasslands replace the xeric scrub, the recruitment of perennials may be lower or completely non-existent; if this practice remains uncontrolled, the landscape of the region could change dramatically. Populations of the peninsular yellowthroat (Geothlypis beldingii) have already disappeared from some of the oases due to human pressure on the habitat. A reserve has been proposed to protect the region. Management plans for the area are needed, as fires and logging threaten the habitat and human exploitation of resources and irregular settlements are growing at a quick pace.

Additional information on this ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
• World Wildlife Fund Homepage

Further Reading

• Alvarez, S., P. Galina, y L. Grismer. 1997. Anfibios y reptiles. Pages 125-142 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR. ISBN: 8449414180
• Arriaga, L., S. Díaz, R. Domínguez, y J. L. León. 1997. Composición florística y vegetación. Pages 69-106 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
• Búrquez, A., y M. A. Quintana. 1994. Islands of diversity: Ironwood ecology and the richness of perennials in a Sonoran Desert biological reserve.
• 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.
• Ferrusquía-Villafranca, I. 1993. Geología de México: Una Sinopsis. Mexico: Instituto de Biología, UNAM.
• Jiménez, M.L., C. Palacios, y A. Tejas. 1997. Los Macroartrópodos. Pages 107-124 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
• Maya, Y., R. Coria, y R. Domínguez. 1997. Caracterización de los Oasis. Pages 5-26 in L. Arriaga and R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. Mexico: CIBNOR.
• Rodríguez-Estrella, R., L. Rubio, y E. Pineda. 1997. Los oasis como parches atractivos para las aves terrestres residentes e invernantes. Pages 157-196 in L. Arriaga, y R. Rodríguez-Estrella (editors). Los Oasis de la Península de Baja California. México: CIBNOR.
• Rzedowski, J. 1978. Vegetación de Mexico. Editorial Limusa. Mexico, D.F., Mexico. ISBN: 9681800028
• SEMARNAP. 1996. Programa de áreas naturales protegidas de México, 1995-2000.
• Tewksbury, J. J., y C. A. Petrovich. 1994. The influences of ironwood as a habitat modifier species: A case study on the Sonoran Desert coast of the Sea of Cortez.