Introduction

Near Todos Santos, Baja California Sur, Mexico (Photograph by David Olson)

Located at the southern most part of the Baja Peninsula, this diverse landscape of mountains, valleys, and plateaus is covered with a variety of xeric vegetation. Plants and animals of this region evolved independently before joining the Baja Peninsula. A dry, arid climate supports a number fauna and species of, about ten percent which are endemic. This region supports a number of endemic birds and is listed as an Endemic Bird Area (EBA). Established as a Protected Natural Area (PNA), much of the ecoregion remains intact.

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 originated in the Miocene as an isolated portion of land prior to joining the peninsula in its present position, and thus is considered an "island" of vegetation. The region is composed of a vast complex of granitic mountains, valleys, canyons, and plateaus. The ecoregion occupies the plateaus between the coast and the lower limits of the dry forests, which begin around 250 meters (m). Precipitation is about 400 millimeters (mm) annually. Some elements of the dry forest are present in this community, but xeric elements are dominant and include Opuntia cholla, Bursera microphylla, Lysiloma divaricata, Stenocereus thuberii, Cnidoscolus angustidens, Yucca sp., and Ferocactus spp. Herbaceous elements are present and include Plantago linearis, Bouteloua hirsuta, and Commelina coelestis.

Biodiversity Features

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. Although the ecoregion has not been studied intensively, it is widely recognized that it houses 31 of 48 of the reptile species for the Cape Region. Almost a third of the region’s recorded species of collembola and spiders (30 of 138 species) have been found in this ecoregion. In general, more than ten percent of animal and plant species found at Sierra de la Laguna are endemic. All of the ecoregion is contained within the extensive Baja California Endemic Bird Area. The isolation of this region has also contributed to the scarcity of predators, and to the poor competitive ability of some animals. Rodents and lagomorphs are virtually absent in this region, favoring certain species of animals that would otherwise be subject to competition. This is the case with Melanerpes formicivorus, for example. The Cape Region has also served as a natural refuge for species migrating from neighboring regions undergoing long-term geological change.

Current Status

The Mexican state of Baja California Sur, which includes this ecoregion, contains the highest proportion of intact xeric scrub of any Mexican state. Large areas of habitat remain intact, as the topography makes this ecoregion difficult to exploit. 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 killed wild species (mostly predators) that are considered as threats to their domestic animals. If this continues, it could alter the natural processes maintaining biodiversity in the area. Although human disturbance in the 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

This xeric scrub ecoregion is limited to the southern tip of the Baja Peninsula in Mexico, and is thus isolated from other similar habitats. Delineation’s for this ecoregion follow INEGI, from which we lumped the following vegetation classifications: "sarcocaulous matorral", "crasicaulous matorral", and portions of "agricultural landuse". Reference was also made to Rzedowski, and reviews and revisions to the linework were done by expert opinion at several ecoregional priority setting workshops.

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