Vegetational Areas
Biologically, the South Central Texas Regional Planning Area is a region of transition from the lowland forests of the southeastern United States to the arid grasslands of the western uplands and tropical thorn scrub to the south. The essence of this landscape consists of dendritic networks of wooded stream corridors populated by typically eastern species that dissect upland grasslands and savannahs that harbor western species. The vegatational areas containing portions of the South Central Texas Regional Planning Area are the Edwards Plateau, South Texas Plains, Blackland Prairies, Gulf Prairies and Marshes, and the Post Oak Savannah. Each area is shown and described below.
Edwards Plateau
In the South Central Texas Region, the Edwards Plateau vegetational area includes all of Kendall County, and the northern portions of Uvalde, Medina, Bexar, and Comal Counties, and that portion of Hays County located within the planning area. This limestone-based area is characterized by springfed, perennially flowing streams which originate in its interior and flow across the Balcones Escarpment, which bounds it on the south and east. The soils are shallow, ranging from sands to clays and are calcareous in reaction. This area is predominantly rangeland, with cultivation confined to the deeper soils.
Noteworthy is the growth of Bald cypress (Taxodium distichum) along the perennially flowing streams. Separated by many miles from cypress growth of the moist Southern Forest Belt, they constitute one of Texasê several "islands" of vegetation. The principal grasses of the clay soils are several species of bluestem (Schizachyrium and Andropogon spp.), gramas (Bouteloua spp.), Indiangrass (Sorghastrum nutans), common curlymesquite (Hiaria belangeri), buffalograss (Buchloe dactyloides) and Canadian wild rye (Elymus canadensis).
The rocky areas support tall or mid-grasses with an overstory of live oak (Quercus virginiana) and other oaks (Q. fusiformis, Q. buckleyi, Q. sinuata var. breviloba), cedar elm (Ulmus crassifolia) and mesquite (Prosopis glandulosa). The heavy clay soils have a mixture of buffalograss (Buchloe dactyloides), sideoats grama (Bouteloua curtipendula) and mesquite (Prosopis glandulosa).
South Texas Brush Country
South of San Antonio, including all or parts of Uvalde, Zavala, Dimmit, Medina, Frio, LaSalle, Bexar, Atascosa, Wilson, Karnes, DeWitt, and Goliad Counties lies the South Texas Plains vegetational area, which is characterized by subtropical dryland vegetation, consisting of small trees, shrubs, cactus, weeds and grasses. Principal plants are honey mesquite (Prosopis glandulosa), live oak (Quercus virginiana), post oak, several members of the cactus family (Cactaceae), blackbrush acacia (Acacia rigidula), guajillo (Acacia berlandieri), huisache (Acacia smallii) and others that often grow very densely.
The original vegetation was mainly perennial warm-season bunchgrass in post oak, live oak and mesquite savannahs. Other brush species form dense thickets on the ridges and along streams. Long-continued grazing has contributed to the dense cover of brush. Most of the desirable grasses have persisted under the protection of brush and cacti.
There are distinct differences in the original plant communities on various soils. Dominant grasses on the sandy loam soils are seacoast bluestem (Schizachyrium scoparium var. litoralis), bristlegrasses (Setaria spp.) and silver bluestem (Bothriochloa saccharoides). Dominant grasses on the clay and clay loams are silver bluestem, Arizona cottontop (Trichachne californica), buffalograss (Buchloe dactyloides), common curlymesquite (Hilaria belangeri), bristlegrasses (Setaria spp.), gramas (Bouteloua spp.) and Texas wintergrass (Stipa leucotricha). Gulf cordgrass (Spartina spp.) and seashore saltgrass (Distichlis spicata) characterize low saline areas. In the post oak and live oak savannahs, the grasses are mainly seacoast bluestem (S. scoparium var. litoralis), Indiangrass (Sorghastrum nutans) and switchgrass (Panicum virgatum).
Blackland Prairies
This area, including parts of Bexar, Comal, Guadalupe, Hays, Caldwell, Gonzales, and DeWitt Counties, while called a "prairie," has timber along the streams, including a variety of oaks (Quercus spp.), pecan (Carya illinoiensis), cedar elm (Ulmus crassifolia) and mesquite (Prosopis sp.). In its native state it was largely a grassy plain. Most of this fertile area has been cultivated, and only small acreages of meadowland remain in original vegetation. In heavily grazed pastures, buffalograss (Buchloe dactyloides), Texas grama (Bouteloua rigidiseta) and other less productive grasses have replaced the tall bunchgrass. Mesquite and other woody plants have invaded the grasslands.
The original grass vegetation included big bluestem (Andropogon gerardi) and little bluestem (Schizachyrium scoparium), Indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), sideoats grama (Bouteloua curtipendula), hairy grama (Bouteloua hirsuta), tall dropseed (Sporobolus asper), Texas wintergrass (Stipa leucotricha) and buffalograss. Non-grass vegetation is largely legumes and composites.
Gulf Prairies and Marshes
The Gulf Prairies and Marshes vegetational area includes all or parts of Victoria, Refugio, and Calhoun Counties. There are two subunits: (1) the marsh and salt grasses immediately at tidewater, and (2) a little farther inland, a strip of bluestems and tall grasses, with some gramas in the western part. Many of these grasses make excellent grazing. Oaks (Quercus spp.), elm and other hardwoods grow to some extent, especially along streams, and the area has some post oak and brushy extensions along its borders. Much of the Gulf Prairies is fertile farmland.
Principal grasses of the Gulf Prairies are tall bunchgrasses, including big bluestem (Andropogon gerardi), little bluestem (Schizachyrium scoparium), seacoast bluestem (S. scoparium var. litoralis), Indiangrass (Sorghastrum nutans), eastern gamagrass (Tripsacum dactyloides), Texas wintergrass (Stipa leucotricha), switchgrass (Panicum virgatum) and gulf cordgrass (Spartina spp.). Seashore saltgrass (Distichlis spicata) occurs on most saline sites. Heavy grazing has changed the range vegetation in many cases so that the predominant grasses are less desirable broomsedge (Andropogon virginicus), smutgrass (Sporobolus indicus), threeawns (Aristida spp.) and many other inferior grasses. The other plants that have invaded the productive grasslands include oak underbrush, huisache (Acacia smallii), mesquite (Prosopis glandulosa), prickly pear (Opuntia spp.), ragweed (Ambrosia psilostachya), broomweed (Xanthocephalum spp.) and others.
Post Oak Savannah
This secondary forest region, also called the Post Oak Belt, includes all or parts of Guadalupe, Caldwell, Wilson, Gonzales, DeWitt, Goliad, and Victoria Counties. It is immediately west of the primary forest region, with less annual rainfall and a little higher elevation. Principal trees are post oak (Quercus stellata), blackjack oak (Quercus marilandica) and cedar elm (Ulmus crassifolia). Pecans (Carya illinoiensis), walnuts (Juglans spp.) and other kinds of water-demanding trees grow along streams.
The southwestern extension of this belt is often poorly defined, with large areas of prairie. The original vegetation consisted mainly of little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardi), Indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), silver bluestem (Bothriochloa saccharoides), Texas wintergrass (Stipa leucotricha), post oak and blackjack oak. The area is still largely native or improved grasslands, with farms located throughout. Intensive grazing has contributed to dense stands of a woody understory of yaupon (Ilex vomitoria) and oak brush and mesquite has become a serious problem. Such plants as broomsedge (Andropogon virginicus), broomweed (Xanthocephalum spp.) and ragweed (Ambrosia psilostachya) have replaced good forage plants.
