Madrean Semidesert
Covering south Texas and a substantial part of northern Mexico, the Madrean Semidesert is a landscape of hot, dry scrublands where sparse grasses, cacti, and thorny shrubs such as mesquite are the dominant vegetation. The desert is home to many birds, reptiles, and amphibians rarely seen in the U.S., but common in Mexico and Central America. Even in this lightly populated region, small farms and development along the Rio Grande have left little habitat truly intact.
Location – Following the Rio Grande south to the very southern-most tip of Texas into adjacent Mexico.
Climate
Average readings from Brownsville, Texas indicate mean annual temperatures of 22.9ºC (73ºF) and annual precipitation of only 112mm (4 inches).
Features
Rolling to flat plains with extensive river floodplain and desert wash (arroyos). The native vegetation type covering much of northeastern Mexico and parts of southern Texas is mesquite-grassland, spiny shrubs and trees dominate, but grasses, forbs, and succulents are also prominent. The slightly higher, drier, and rockier sites originally had vegetation of chaparral and cacti, whereas the flat, deep soils supported mesquite as well as taller brush and a few drought-resistant trees, often rather openly spaced and savanna-like in a grassland matrix. Leguminous shrubs and trees constitute one-third of the diverse woody flora, which the rural population uses for extensive grazing of livestock, fuel, and timber for fencing and construction.
History and Trends
Clearing and conversion of shrubland for agriculture has had the greatest impact on altering the patterns and processes of the landscape of south Texas and northeastern Mexico. Both banks of the Rio Grande are now crowded with homes, businesses, and farms. The only remaining natural areas south of the river are the salt marshes and mud flats east of the city of Matamoros. The Rio Corona floodplain was relatively intact until recently, but since the clearing of some lands for agriculture there has been increased erosion, pollution from agro-chemicals, invasion of exotic species, and general loss of native wildlife.