Overview
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.
Topography and Characteristics
Major Rivers: Guadalupe, San Antonio, Nueces, Lavaca, Rio Grande.
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.
Major Cities / Rainfall / Elevation
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.
Alice - 27.52 in / 201 ft
Brownsville - 27.55 in / 19 ft
Crystal City - 20.70 in / 580 ft
Eagle Pass - 21.48 in / 808 ft
Falfurrias - 25.42 in / 120 ft
Goliad - 38.58 in / 142 ft
Laredo - 21.53 in / 430 ft
McAllen - 22.61 in / 100 ft
Pearsall - 25.73 in / 635 ft
Poteet - 29.00 in / 480 ft
Rio Grande City - 21.61 in/ 172 ft
San Antonio 32.92 in / 809 ft
Zapata - 19.72 in / 311 ft
Common Vegetation
Sugarberry
Brasil
Anaqua
Fresno
Great leadtree
Retama
Texas ebony
Southern live oak
Saffron plum
Texas kidneywood
Honey mesquite
Texas wild olive
Desert yaupon
Fiddlewood
Duckweed
Saltmarsh spikerush
Common cattail
Smartweed
Live oak
Wax myrtle
Plantain
Silverleaf sunflower
Panic grass
Rare Plants & Habitats
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
Common Wildlife
Crested Caracara
Chachalaca
Caracara
Road runner
Ferruginous pygmy-owl
Green jay
Elf owl
Texas tortoise
Indigo snake
Texas longnose snake
Mexican Burrowing toad
Grooved-billed Anis
Redwing blackbird
Swallowtail butterfly
Leopard frog
Indigo snake
Catfish
Sunfish
Rare Animals & Habitats
Jaguarundi, Ocelot: Dense, thorny, low brush
White-nosed coati: Woodlands
As an enthusiast deeply versed in the ecology of South Texas, particularly the expansive region spanning from the Hill Country to the Lower Rio Grande Valley, my passion converges with a wealth of firsthand knowledge and a nuanced understanding of the area's unique characteristics. This expertise extends beyond the mere surface, delving into the intricate dynamics of the South Texas plains and brush country, a terrain marked by aridity, grasses, and thorny brush, including mesquite and prickly pear cacti.
The region's topography is defined by major rivers such as the Guadalupe, San Antonio, Nueces, Lavaca, and the iconic Rio Grande. Noteworthy aquifers like Edwards, Trinity, Carrizo-Wilcox, and Gulf Coast contribute to the area's hydrological dynamics. Covering a substantial 28,000 square miles, this landscape is not just a canvas of dry expanses but a dynamic ecosystem with resacas, former channels of the Rio Grande, fostering marshes and ponds with seasonally varying flora and fauna.
A distinctive feature of the lower Rio Grande valley is its subtropical environment, a rarity in the United States, offering a habitat for tropical birds from South America. The once-extensive palm forest at the Rio Grande delta, reduced to a mere 37 acres from its historical 40,000 acres, serves as a poignant testament to the changing landscape shaped by both natural and anthropogenic factors.
Birdwatchers flock to this region, attracted by the diverse avian population along the border and coastal areas, with the World Birding Center standing as a testament to the area's ornithological significance. Furthermore, the fertile land along the Rio Grande River has fostered farms, contributing to the economic landscape of the region.
Delving into the topography and characteristics, the South Texas Brush Country unfolds with plains of thorny shrubs and trees, interspersed with patches of palms and subtropical woodlands in the Rio Grande Valley. The soil makeup, ranging from alkaline to slightly acidic clays and clay loams, influences the vegetation, dominated by thorny brush like mesquite, acacia, and prickly pear, alongside grassy expanses.
Meteorological data adds another layer to the narrative, with regional average rainfall varying between 20 to 32 inches annually and an average net evaporation rate ranging from 16 to 28 inches. The climate exhibits seasonal nuances, with summer temperatures soaring, evaporation rates peaking, and rainfall concentrated in spring and fall.
Cities like Alice, Brownsville, Crystal City, Eagle Pass, and others contribute to the mosaic of the region, each with its unique rainfall and elevation characteristics. For instance, the juxtaposition of data from Goliad, with an annual rainfall of 38.58 inches and an elevation of 142 feet, against Zapata, boasting 19.72 inches of rainfall and an elevation of 311 feet, highlights the climatic diversity within the South Texas expanse.
Venturing into the rich biodiversity, common vegetation like Sugarberry, Brasil, Anaqua, and others form a verdant backdrop to the region. Rare plants such as ashy dogweed and black lace cactus carve niches within the landscape, each tied to specific soil and habitat conditions.
The South Texas wildlife panorama unfolds with iconic species like the Crested Caracara, Chachalaca, Roadrunner, and Ferruginous Pygmy-Owl. Threatened and endangered species, including the Jaguarundi and Ocelot, find refuge in the dense, thorny low brush of this unique ecosystem.
In essence, South Texas is not just a geographical expanse; it's an intricate tapestry of ecosystems, shaped by climatic forces, hydrological dynamics, and human influences. The delicate balance between its flora and fauna, threatened species and expansive landscapes, showcases the need for conservation efforts to preserve this ecological treasure.
