The South Texas plains and brush country stretches from the edges of the Hill Country into the subtropical regions of the Lower Rio Grande valley. Much of the area is dry and covered with grasses and thorny brush such as mesquite and prickly pear cacti.
There are some lakes dotting the region, as well as short-lived "resacas." A resaca is a former channel of the Rio Grande River that has been cut off, like an oxbow. (Floods along the Rio Grande River can change the way the river flows so that some of those twists and turns are cut off from the rest of the river, forming an "oxbow.") Resacas will occasionally fill with silt and water, creating marshes and ponds. The plants and wildlife around the resacas vary seasonally depending on the quantity and quality of the available water.
The Rio Grande is a very long river. Where it flows through South Texas is called the lower Rio Grande valley. The Rio Grande Valley is an ecosystem found nowhere else in the United States. It is a subtropical environment, which lies further south than any other part of the United States except Hawaii and part of Florida. It is very humid. Many tropical birds from South America can be found here. Palms, subtropical woodlands and even citrus trees grow here. The Rio Grande delta (the land at the mouth of the river, where it flows into the ocean) once had an extensive palm forest. The Spanish explorer Alonso Alvarez de Pineda first named the river the Rio de las Palmas, "River of Palms," in 1519. The fertile land along the Rio Grande River has given rise to many farms. Presently, there are only 37 acres of protected palm forest compared to approximately 40,000 acres that once covered the delta region.
Birdwatchers from across the world come to South Texas to view the many birds along the border and coastal areas. The World Birding Center is found here. Hunters also seek special hunts on private ranches here.
Major Rivers: Guadalupe, San Antonio, Nueces, Lavaca, Rio
Major Aquifer: Edwards, Trinity, Carrizo-Wilcox, Gulf Coast
Size: 28,000 square miles
The South Texas Brush Country is characterized by plains of thorny shrubs and trees and scattered patches of palms and subtropical woodlands in the Rio Grande Valley. The plains were once covered with open grasslands and a scattering of trees, and the valley woodlands once covered large areas. Today, the primary vegetation consists of thorny brush such as mesquite, acacia, and prickly pear mixed with areas of grassland.
Soils of the region are alkaline to slightly acidic clays and clay loams. The deeper soils support tall brush, such as mesquite and spiny hackberry, whereas short, dense brush grows in the shallow, caliche soils.
Regional Average Rainfall: 20-32 inches per year
Regional Average Net Evaporation rate: 16-28 inches
The average annual rainfall is 20 to 32 inches with higher average rainfall as you go west to east. The average monthly rainfall is lowest during winter, and highest during spring (May or June) and fall (September). Summer temperatures are high, with very high evaporation rates. Data source: National Climate Datat Center, U.S. Dept of Commerce.
Southern live oak
Texas wild olive
Ashy dogweed: Mesquite grassland openings of thorny shrublands
on deep, sandy soils
Black lace cactus: Grassy openings on rangeland
Runyon's cory cactus
Johnston's frankenia: Rocky hillsides or saline clay loam flats within openings of thorny shrublands
Star cactus: Openings of thorny shrublands on rocky clay loam soils
Texas ayenia: Subtropical woodlands on alluvial deposits on flood plains and terraces of the Rio Grande
Walkers manioc: Openings of thorny shrublands on sandy loam soils
Texas longnose snake
Mexican Burrowing toad
Jaguarundi, Ocelot: Dense, thorny, low brush