Grasslands are defined as areas dominated by grasses, with tree or shrub canopies covering less than 25 percent of the area. In Texas before European settlement they occupied about two-thirds of the landscape and ranged from desert and semidesert grasslands of the mountains and foothills of the Trans-Pecos to midgrass prairies of the Rolling Plains and Edwards Plateau to tallgrass or true prairies of the Blackland and Upper Coastal prairies. More than 470 native grass species live in Texas. With over 570 species, subspecies, and varieties of grasses, Texas leads the United States in numbers of grasses. The rich agricultural lands of Texas are so in large part due to the grasses that they once supported. The gentle topography and fertile soils of former grasslands today support most of the state's row crops, for most of the grasslands of the Coastal and Blackland prairies and High Plains have been converted to cropland. In fact, less than 1 percent of the original Blackland Prairie remains approximately as it once was. The fertile soils and mild climate of the Blacklands were responsible for the development of the cotton economy in Central Texas in the mid-1800s. More recent technological advances have allowed irrigation of the High Plains, and hence exploitation of the rich soils and gradual slopes of the region for cotton and small-grain production.
In general, grasslands of the Blackland Prairie and Coastal Prairie are southern extensions of the true prairie, the Rolling Plains and Edwards Plateau are southern extensions of midgrass Great Plains grassland, and the High Plains are a southern extension of the shortgrass prairie. The grasslands of Texas comprise seven geographic regions: (1) the Blackland Prairies (including the Grand, San Antonio, and Fayette), (2) the Coastal Prairie (including the Sand Plain), (3) the Rolling Plains (including the Rolling Red Prairie), (4) the Edwards Plateau, (5) the High Plains, (6) the South Texas Plains, and (7) the Trans-Pecos.
Blackland Prairie. As defined, the Blacklands consist of about 12.6 million acres. In Texas before European settlement, uplands were dominated by little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), Indian grass (Sorghastrum nutans), and tall dropseed (Sporobolus asper). The lowlands throughout and the typical clayey Vertisol soils in the northeast (where precipitation is highest) were dominated by eastern grama grass (Tripsacum dactyloides) and switch grass (Panicum virgatum). Also in the northeast, over loamy Alfisol, are unique communities dominated by Silvenus dropseed (Sporobolus silveanus), mead sedge (Carex meadii), and switch grass. Included within the Blacklands were expansive, virtually open grasslands along with areas of scattered trees and shrubs or mottes of woody vegetation. Numerous wooded stream bottoms crossed the prairies, and these were dominated by sugarberry, elm, cottonwood, pecan, and oak trees. The Lampasas Cut Plain, which separated the main belt of the Blacklands and the Grand Prairie, also supported junipers, oaks, and elms. Most of the main belt of the Blacklands has been converted to cropland or tame pasture. In addition, the cities of San Antonio, Austin, Temple, Waco, and Dallas have covered large areas of former grassland. Most of the areas that have not been plowed have been abusively grazed by domestic livestock. The largest areas of native sod are within the Grand Prairie, but overall the Blacklands represent the most completely altered of all Texas grasslands and their remnants are in need of conservation.
Coastal Prairie. The Coastal Prairie extends from Baffin Bay to the Louisiana border, forming a crescent that comprises about 6.35 million acres. Also included here are the 1.75-million-acre Coastal Sand Plain, which extends south from Baffin Bay to the subtropical zone, and the barrier-island grasslands. Grasslands of the Upper Coastal Prairie, north of San Antonio Bay, are dominated by little bluestem, brownseed paspalum (Paspalum plicatulum), Indian grass, and low panic (Dichanthelium species). The lower coastal prairie supports little bluestem, cane bluestem (Bothriochloa barbinodis), tall dropseed, and a variety of midgrasses. The Coastal Prairie was never a broad, expansive open grassland, but rather is dissected by numerous wooded stream bottoms. Furthermore, without periodic fire the Coastal Prairie is quickly invaded by woody species. The barrier-island grasslands were dominated by little bluestem, sea oats (Uniola paniculata), and fimbry (Fimbristylis species). Many fresh and brackish marshes are included within the barrier islands, and much variation exists with dune stability. The Coastal Sand Plains of South Texas were dominated by little bluestem, cane bluestem, Indian grass, Pan American balsamscale (Elyonurus barbiculmis), silveusgrass (Trichoneura elegans), and other grasses, along with live oak mottes and individual trees. Most of the Coastal Prairie has been plowed and converted to row crops or tame pasture, especially Bermuda grass (Cynodon dactylon) and King Ranch bluestem (Bothriochloa ischaemum). In addition, overgrazing and fire suppression have led to invasion or increase of the most diverse assemblage of native and introduced woody species of any Texas grassland. Included are Macartney rose (Rosa bracteata), Chinese tallow tree (Sapium sabiferum), mesquite (Prosopis glandulosa), and huisache (Acacia farnesiana). Overgrazing and fire suppression in the Sand Plain have led to an increase in mesquite, live oak, and shrubs more characteristic of the brush country to the northwest.
Rolling Plains. The Rolling Plains extend westward from the Western Cross Timbers (see CROSS TIMBERS) to the Caprock at the edge of the High Plains and from the Edwards Plateau northward to the Texas-Oklahoma border. This diverse, thirty-million-acre area was historically midgrass prairie with scattered mesquite or, on rough, broken ground, grassland with numerous junipers and oaks. Important grasses include sideoats grama (Bouteloua curtipendula), little bluestem, Texas wintergrass (Stipa leucotricha), and common curly mesquite (Hilaria belangeri). On sandy soils, species such as sand bluestem (Andropogon gerardii var. hallii) and switch grass were also important, along with sand sagebrush (Artemisia filifolia). Many of the deeper, more fertile soils of the Rolling Plains have been converted to row crops, but the majority of the area consists of native sod that has a long history of overgrazing by domestic livestock. Native grasses such as hairy grama (Bouteloua hirsuta), three-awns (Aristida species), and sand dropseed (Sporobolus cryptandrus) have replaced climax native grasses, and woody species such as mesquite, lotebush, and red-berry juniper have increased in importance.
Edwards Plateau. The Edwards Plateau comprises about seventeen million acres in Central Texas. It is circumscribed by the Balcones Fault zone on the south and east, the Rolling Plains on the north, and the Pecos-Devils River divide on the west. The southern and western third is heavily dissected, with the slopes and canyons dominated by oak forests and Ashe juniper-live oak woodlands. The relatively flat, deep-soiled uplands were historically open woodlands or grasslands with scattered mottes or individuals of live oak and cedar elm. Grasslands were dominated by little bluestem, Texas cup grass (Eriochloa sericea), common curly mesquite, cane bluestem, and sideoats grama. Most of the Edwards Plateau still consists of native sod, though there has been a long and continuing history of heavy, abusive grazing by domestic livestock. Grasses such as three-awns, Texas grama, and hairy tridens (Erioneuron pulchellum) have replaced climax dominants. Ashe juniper, mesquite, agarita, lotebush, live oak, and other shrubs have increased due to suppression of fire and overgrazing.
High Plains. The High Plains include 19.4 million acres of west Texas, including most of the Panhandle. The area was primarily shortgrass prairie in pre-European settlement times, dominated by blue grama (Bouteloua gracilis) and buffalo grass (Buchloe dactyloides). Most of the flat landscape of the central and northern High Plains has been converted to irrigated cropland, which utilizes water from the Ogallala Aquifer. The sandier soils of the southern High Plains were historically dominated by sand dropseed, little bluestem, plains bristle grass, cane bluestem, and short grasses along with scattered mesquite and sand sage. This same midgrass sand-sage community also occurs in the northern Panhandle, north of the Canadian River. Also in this area there are deep, stabilized dunes that support an unusual tallgrass-Havard shin oak community. Dominant grasses include sand bluestem, little bluestem, switch grass, sand dropseed, and sand love grass. These sandier soils have generally not been plowed. However, overgrazing has caused an increase in annual three-awn, gramas, sand dropseed, tridens species, and sand sagebrush.
South Texas Plains. The South Texas Plains have such a long history of overgrazing by feral and, later, domestic, livestock that reconstruction of presettlement vegetation is nearly impossible. However, much of the northern and central part of the area was probably grassland with scattered mesquite and other shrubby species. Climax grasses included cane bluestem, Chloris species, and Bouteloua species, but no relicts of this type have been quantitatively sampled, and perhaps none remain. The current vegetation is characterized by mostly dense shrubland of mesquite, blackbrush, and spiney hackberry. Some areas have been mechanically cleared and planted with buffel grass (Cenchris ciliaris).
Trans-Pecos. In the Trans-Pecos, semidesert grassland generally occurs from about 3,500 to 4,500 feet elevation in the foothills of mountains, especially the Davis, Guadalupe, and Chisos mountains. These shortgrass communities grade into midgrass Piedmont grasslands at higher elevations, and tobosa (Hilaria mutica) occurs on run-on clay flats within a matrix of desert shrublands at lower elevations. Climax dominants of the semidesert and Piedmont grasslands include black grama (Bouteloua eriopoda), sideoats grama, chino grama (Bouteloua breviseta), California cottontop (Digitaria californica), and blue grama, plus, at higher elevations, Texas bluestem (Schizachyrium cirratum), cane bluestem, and bull muhly (Muhlenbergia emersleyi). Much of these grasslands has been severely overgrazed, especially near perennial springs or wherever water has been artificially made available to domestic livestock.
Two less extensive grassland areas occur in West Texas. Havard shin oak-tallgrass dunes occur in Ward, Crane, and Winkler counties. These are similar to dune areas in the Panhandle, but are more open and contain a greater variety of xeromorphic shrub species such as catclaw acacia, mesquite, and lotebush. Also, within the salt basin of Hudspeth and Culberson counties and scattered throughout west Texas are saline flats dominated by alkali sacaton (Sporobolus airoides). Such areas are often converted to four-wing saltbush shrubland by overgrazing.