Tamaulipan Matorral

Category: Desert Biomes.

Geographic Location: North America.

Summary: On the border between the United States and Mexico, the Tamaulipan matorral is a diversity hot spot for cacti and succulents, but it has been considerably diminished by human activities.

The Tamaulipan Matorral ecoregion occurs at the lower elevations of the eastern slopes of the Sierra Madre Oriental mountain range. It is found in Mexico in the northeastern states of Nuevo León, Coahuila, and Tamaulipas, and in the United States in the southern part of Texas. This ecoregion is characterized by desert scrub vegetation; it is rich in thorny shrubs, cacti, and succulents. The Tamaulipan matorral is an important habitat for mammals and reptiles as well as resident and migratory birds. The area of intact Tamaulipan matorral is much reduced from its original distribution, and human activities are likely to result in further losses.

The Sierra Madre Oriental was formed by uplift, faulting, and erosion that began approximately 23 million years ago. The coastal plain along the Gulf of Mexico lies to the east of the range, and the Mexican plateau lies to the west of the Sierra Madre Oriental. The Sierra Madre Oriental extends 621 miles (1,000 kilometers) from the Mexican state of Coahuila south through Nuevo León, Tamaulipas, south to where it joins the volcanic belt that crosses central Mexico. Abrupt mountains are present in one part of the ecoregion, but most of the landscape is made up of undulating mountains, hills, valleys, and plateaus. Sedimentary rocks of marine origin characterize the ecoregion.

This ecoregion is located where the nearctic and neotropical ecozones meet. The Tamaulipan Matorral biome experiences desert-like conditions. Annual precipitation levels are below 39 inches (99 centimeters) per year, and the geology of the region further compounds these xeric (dry) conditions in that the small quantities of rain that do fall are quickly soaked up by the limestone substrate. The lowest temperatures are generally in December, and severe frosts can occur. In contrast to the climate of this ecoregion, the forests farther south along Sierra Madre Oriental on the coastal plain of Veracruz have a tropical, moist climate.

Vegetation

The vegetation of the Tamaulipan matorral is predominately made up of woody shrubs, small trees, cacti, and succulents that are adapted to withstand the ecoregion’s xeric environment and temperature extremes. Plant species that are common in this ecoregion include cacti such as living rock cactus (Ariocarpus spp.), star cactus (Astrophytum asterias), Christmas cactus (Cylindropuntia leptocaulis), pincushion cactus (Mammillaria spp.), and paddle cactus (Opuntia spp.), as well as spiny shrubs including acacia, mountain mahogany (Cercocarpus spp.), leadtree (Leucaena spp.), catclaw mimosa (Mimosa aculeaticarpa var. biuncifera), and mesquite (Prosopis spp.).

Other xerophytic plants are Salvia ballotaeflora, leatherstem (Jatropha dioica), cenizo (Leucophyllum texanum), and Spanish dagger (Yucca spp.). The composition of the plant communities along the slopes of the Sierra Madre Oriental changes with elevation. Higher up the slopes, the matorral vegetation gives way to pine forests. A total 165 plant species have been reported for the ecoregion. This ecoregion is a center of diversity for cacti and succulents. Species endemic here (not found elsewhere) include Agave victoria-reginae and Astrophytum caput-medusae.

Fauna

The Tamaulipan Matorral biome is home to mammal species such as the Mexican prairie dog (Cynomys mexicanus), Saussure’s shrew (Sorex saussurei), yellow-faced pocket gopher (Pappogeomys castanops), Allen’s squirrel (Sciurus alleni), Mexican ground squirrel (Spermophilus mexicanus), collared peccary (Pecari tajacu), and coyote (Canis latrans). As of 2022, the Mexican prairie dog is considered to be highly endangered as its population has been reduced to about 4 percent of its natural habit because of poisoning by ranchers.

The matorral is an important biological corridor, refuge, nesting, and feeding ground for birds. More than 170 avian species belonging to 42 families have been observed in this ecoregion, about half of which are residents; the other half consist of migratory species. Resident species include the burrow owl (Athene cunicularia), hooded oriole (Icterus cucullates), eastern meadowlark (Sturnella magna), long-billed thrasher (Toxostoma longirostre), hooded yellowthroat (Geothlypis nelsoni), blue bunting (Cyanocompsa parellina), and olive sparrow (Arremonops rufivirgatus).

Threats and Conservation

Land clearing for agriculture, cattle grazing, logging, and human settlement have resulted in significant habitat losses. Irrigation associated with intensive farming has led to the buildup of salts in the soil. The development of the manufacturing zone along the United States-Mexico border has attracted more people to the region, thereby escalating the rate of habitat destruction.

Both deliberate and accidental fires have destroyed wide swaths of matorral. All in all, 90 percent of the Tamaulipan matorral has been lost in Texas, and only 30 percent of this ecoregion remains intact in Mexico. Only 6 percent of the region in Mexico falls under protected status. Global warming is a likely culprit for disruption of some habitat here, as mounting changes in temperature and elevation zones exert pressure on species to move, adapt, or die.

Around 60 of the plant and vertebrate species that live in the Tamaulipan matorral are threatened, endangered, or vulnerable to extinction. Illegal collection of rare endemic cacti such as star cacti and living rock cacti is a major issue for many species. Introduced diseases such as blight (Phytophtora infestans) and insect pests including Cerambycid beetles have been observed to cause mortality to some rare cacti, such as the star cactus.

Given that this ecoregion is a hot spot for biodiversity and an important habitat for birds, preserving the little remaining Tamaulipan matorral is a conservation priority. Protected areas include the El Cielo Biosphere Reserve in Tamaulipas, Cumbres de Monterrey National Park in Nuevo Leon, the Bajo Río San Juan and Las Lajas national irrigation districts in Nuevo Leon, and the Laguna Madre and Río Bravo delta protected areas for flora and fauna in Tamaulipas.

Bibliography

Goldman, E. A. and R. T. Moore. “The Biotic Provinces of Mexico.” Journal of Mammalogy 26, no. 4 (1946).

Miller, B., G. Ceballos, and R. Reading. “Prairie Dog and Biotic Diversity.” Conservation Biology 3 (1994).

Noss, Reed. “Tamaulipan Matorral.” One Earth, 2022, www.oneearth.org/ecoregions/tamaulipan-matorral/. Accessed 31 Aug. 2022.

Oldfield, S. Cactus and Succulent Plants—Status Survey and Conservation Action Plan. Cambridge, United Kingdom: International Union for Conservation of Nature, 1997.