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The Trans Pecos region of extreme western Texas and the Stockton Plateau and the Sand Hills near the southeast comer of New Mexico is perhaps the most complex of all the regions. Elevations range from 2,500 to more than 8,500 feet. This is a region of strongly diverse habitats and vegetation, varying from desert valleys and plateaus to wooded mountain slopes. Even the mountains vary, with some composed of volcanic rocks, and others of limestone.
Over most of the area average annual rainfall is less than 12 inches. Precipitation may be as high as 20 inches at higher elevations. July and August are usually the high rainfall months.
The soils of the Trans Pecos are based on Mountain outwash materials. They are generally alkaline and have poor drainage in some areas.
The most important plant communities are creosote-tarbush desert shrub, grama grassland, yucca and juniper savannahs, pinon pine and oak forests, and a limited amount of ponderosa pine forests. Saline sites support salt brush (Atriplex spp.), alkali sacaton (Sporobolous airoides) and other salt tolerant plants.
Some of the important climax forage plants are Bothriochloa spp., sideoats grama, green sprangletop (Leptochloa dubia), Arizona cottontop, bush muhly (Muhlenbergia Porteri), plains bristlegrass (Setaria macrostachya), Indian grass, alkali sacaton, vine-mesquite (Panicum obtusum), dropseeds, blue grama, black grama, chinograss (Bouteloua ramosa) and other species of grama, tobosa, sacaton and three awns. Common invader grasses are burro grass (Scleropogon brevifolius), fluffgrass ( Erioneuron pulchellum ), Erioneuron pilosum, ear muhly (Muhlenbergia arenacea), and sand muhly (M. arenicola). Other commonly invading plants are Croton dioicus, snakeweeds (Xanthocephalum spp.) and Cactaceae.
About one out of twelve species of the Texas flora occurs in the Trans-Pecos and nowhere else in Texas (Correll and Johnson). On the eastern edge along the Pecos River is a region of low rainfall and high evaporation where the principal growth consists of such shrubs as lechuguilla (Agave lecheguilla), ocotillo (Fouquieria splendens), several species of Yucca, cenizo and other arid-land plants. In the more arid areas, chino and tobosa grasses prevail. In places creosote bush ( Larrea tridentata ) and tarbush ( Flourensia cernua) grow with tussocks of burro and salt grasses (Correll and Johnson).
The High Plains region of Texas, together with the Rolling Plains region, comprise the southern end of the Great Plains. The High Plains consist of about 20 million acres of a relatively level high plateau separated from the Rolling Plains by the Caprock Escarpment. The Canadian River Breaks divide this region into southern and northern sections. Elevation ranges from 3,000 to 4,500 feet, sloping gently toward the southeast. “Playa lakes” are shallow, round depressions which spot the surface, sometimes covering more than forty acres.
The southern edge adjoins the Edwards Plateau and Trans Pecos regions. A transition from productive grazing land to sand hills marks the boundary between the High Plains and the Trans Pecos.
Average annual rainfall is 15 to 21 inches. Extended droughts have occurred here several times during this century. Rainfall is lowest in winter and mid-summer and highest in April or May and September or October. Surface texture of soils on the High Plains ranges from clays on hardland sites in the north to medium textures on mixed land sites and sands in the southern portion of the region. Caliche generally underlies these surface soils at depths of two to five feet.
Irrigation farming is supported with underground water, but large areas of cattle range land remain on the High Plains. The principal large wildlife species is antelope. The vegetation on the High Plains is variously classified as mixed-prairie, short-grass prairie and in some locations as tall-grass prairie. There are distinct differences among the plant communities found on the hardlands, mixed lands, sandy lands, draws and caliche breaks. Successional patterns usually are different and relatively uncomplicated compared with other areas of Texas.
A short-grass association dominated by buffalo grass is the most important plant association on the High Plains. However, distinctly different plant communities exist on the hardlands, mixed lands, sandy lands, and draws. The region characteristically is free from brush, but mesquite and yucca have invaded parts of the area. Sandy lands support shinnery oak, and sand sage and junipers have spread out of some of the breaks onto the Plains proper.
The High Plains region is generally treeless, but mesquite and yucca have invaded. Forbs are common, but not in the abundance found in other regions of Texas. Some of the more interesting species found in the Plains Country are smooth cliff brake (Pellaea glabella), gay feather (Liatris lancifolia), Crepis runcinata, Townsendia texensis, and numerous Eriogonums, including the rare E. Correllii (Correll and Johnson).
The most abundant native grasses are buffalo grass and blue grama (Bouteloua gracilis). Other important grasses are side-oats grama, black grama (Bouteloua eriopoda), little bluestem, western wheat-grass, Indian grass and switchgrass, with Sand dropseed and sandbur are common on the sandy lands to the south.
The Edwards Plateau region comprises an area of West Central Texas commonly known as the “hill country.” It is bounded on the east and south by the Balcones Fault. To the north it extends to the Western Cross Timbers of the Oak Woods and Prairies region and grades into the Plains regions. The Pecos River and eastern edge of the Stockton Plateau define the western extent of the Edwards Plateau region.
Elevations range from slightly less than 100 feet to over 3 ,000 feet. Several river systems dissect the surface, creating a rough and well-drained landscape. Average annual rainfall increases from west to east, ranging from 15 to 33 inches. Seasonal rainfall patterns peak in May/June and in September. Soils of the Edwards Plateau are usually shallow with a variety of surface textures. They are underlain by limestone.
Man-made lakes, ranches, and farms are scattered throughout the region.
Scrub forest is the most characteristic plant association of the area. Ash, juniper, Texas oak, and stunted live oak are dominant in the more dissected southern and eastern canyonlands of the region. Mesquite occurs throughout the Edwards Plateau; together with live oak, it dominates the wood vegetation in the west. Some savanna type vegetation also occurs and was formerly more widespread.
According to Correll and Johnon, the most important climax grasses of the Plateau include switchgrass, several species of bluestems and gramas, Indian grass, Canada wild-rye, curly mesquite and buffalo grass, with the rough, rocky areas typically supporting a tall or mid-grass understory and a brush overstory complex made up primarily of live oak, Texas oak, shinnery oak, junipers and mesquite.
The northwestern portion of the Edwards Plateau transitions into “mesquite-tobosa country” similar to that of the Rolling Plains, whereas the Stockton Plateau portion supports the shorter vegetation of semi-desert grassland (Correll and Johnson). Throughout the region, the brush species are generally considered as “invaders” with the climax largely grassland or open savannah, except on the steeper, rockier canyon slopes which have continually supported a dense cedar-oak- thicket.
The Plateau is a region of high endemism, such as netleaf forestiera (Forestiera reticulata), plateau milkvine (Matelea edwardsensis), basin bellflower (Campanula Reverchonii), Lindheimer crownbeard (Verbesina Lindheineri), Lythrum ovalifolium, Tridens Buckleyanus, twisted-leaf yucca (Yucca rupicola), sotol (Dasylirion heteracanthium ), bracted twist-flower (Streptanthus bracteatus ) and cliff bedstraw (Galium Correllii) (Correll and Johnson). In addition to endemism, the Plateau flora reveals a close relationship to that of Mexico (Correll and Johnson).
Included in the Edwards Plateau is the Llano Uplift area. Geologically the region is a large dome with rolling to hilly topography. Granite exfoliation domes, the largest of which is known as Enchanted Rock, are common. In contrast to the clays and clay loams of the Edwards Plateau, sandy soils predominate on the Llano Uplift. Rainfall averages about 30 inches, peaking in May or June and September. Oak and oak-hickory woodlands are common vegetational types, along with mesquite savanna and some grassland types that were once more widely distributed. The Savanna occurs on loamier soils underlain by caliche.
The South Texas Plains, also known as the Rio Grande Plains or Tamaulipan Brushlands, consists of about 20,000,000 acres. Topography is level to rolling. Elevations range from 1,000 feet to about sea level. Soils of the South Texas Brush Country are clays and clay loams. Soil reactions vary from alkaline to slightly acid. The average annual rainfall of 16 to 35 inches, increasing from west to east. Average monthly rainfall is lowest in January and February, and highest during May or June. After a midsummer depression, another peak is reached in September. Summer temperatures are high, with extremely high evaporation rates in the Laredo area.
Thorny brush is the predominant vegetation type in the region, including mesquite, acacia, prickly pear, and mimosa, among others. Areas of shallow soils and rapid drainage generally support this plant life. A grassland or savanna type vegetation which also occurs was somewhat more extensive in the 19th century and earlier, but long continued grazing and other factors have altered the plant communities to such a degree that ranches of the region now face a severe brush problem.
According to Correll and Johnson, there are distinct differences in climax plant communities and successional patterns on the various range sites, with the characteristic grasses of the sandy loam soils being seacoast bluestem, species of Setaria, Paspalum, Chloris and Trichloris, silver bluestem and coast sandbur (Cenchrus incertus) and the dominants on the clay and clay loams are silver bluestem, Arizona cottontop (Trichachne californica), buffalo grass, curly mesquite (Hilaria Belangeri) and species of Setaria, Pappophorum and Bouteloua. He describes the low saline areas as characterized by gulf cordgrass ( Spartina spartinae ), seashore saltgrass and sacaton (Sporobolus Wrightii). whereas the grasses of the oak savannahs are mainly seacoast bluestem, Indian grass, switchgrass, crinkle-awn (Trachypogon secundus) and species of Paspalum. On the rolling open or brush-covered hills, the Malvaceae are also abundantly represented here as well as in the coastal area (Correll and Johnson).
The Brush Country has a greater diversity of animal life than any other in Texas. It is home for many near tropical species which abound in Mexico, many grassland species that range northward, and some desert species commonly found in the Trans Pecos.
Virtually all of this region has been moderately to severely grazed by domesticated cattle. Limited crop production occurs in the Sand Plains. In the past the region has been called the “Wild Horse Prairie” because of the large herds of feral horses roaming here in the 19th century.
The Gulf Prairies and Marshes Area occupies approximately 9,500,000 acres along the coast of Texas. The Gulf Prairies and Marshes region is a nearly level, slowly drained plain less than 150 feet in elevation, dissected by streams and rivers flowing into the Gulf of Mexico. The region includes the barrier islands lining the coast which protect the shoreline from the constant buffeting of harsher ocean waves, and the highly productive estuaries and marshes that support a thriving fishing economy.
Rainfall varies from 20 to 50 inches per year distributed fairly uniformly throughout the year. The growing season is usually more than 300 days, with high humidity and warm temperatures. Surficial and windblown sands and dunes characterize this region’s soils. Soils on the Gulf Prairies and Marshes are acid sands, sandy loams, and clays. Sandy loams predominate, with clays occurring in river bottoms.
Vegetation is primarily grassland types but with extensive oak mottes and salt marshes including sacaton and small areas of brush. The oak scrub has become much more extensive at the expense of grassland. Much of the area has been invaded by trees and brush such as mesquite, prickly pear, oaks, and acacias. Tall bunch grasses are the dominant climax species. At settlement certain areas of the gulf prairies contained extensive cane breaks, the cane being the native Arundinaria gigantea.
Most of the lower lands are in large cattle ranches. Uplands in the Gulf Prairies are ranching interspersed with farming.
The climax vegetation of the Gulf Prairies is mostly tall grass prairie, with some post oak savannah. Much of the area has been invaded by trees and brush. Examples of these are mesquite, live oaks, prickly pear and acacias. The principal prairie grasses are big bluestem, seacoast bluestem (Schizachyrium scoparium var. littoralis), Indiangrass, eastern gamagrass, gulf muhly (Muhlenbergia capillaris), species of Panictum and others. Introduced grasses, such as Bermuda and carpet grass, are common in pastures and have escaped into uncultivated areas. The families Amaranthaceae and Chenopodiaceae are well-represented in the Coastal Prairies and Marshes (Correll and Johnson). Carex, Cyperus, Eleocharis, Juncus, Scirpus, several cordgrasses (Spartina spp.) and seashore saltgrass (Distichlis spicata) are found in the salt marshes.
The Piney Woods topography is gently rolling to hilly forested land. It is part of a much larger region of pine-hardwood forest that extends into Louisiana, Arkansas, and Oklahoma. Elevation in Texas varies from 200 to 500 feet above sea level. Humidity and temperatures are typically high and the area is comparatively free from persistent winds. Soils are mostly pale to dark gray sands or sandy loams and are generally acidic.
The area is interspersed with native pine-hardwood vegetation, farm lands, and pasture. Deer are locally abundant throughout the Piney Woods. Ranches are varied in size; cattle are the primary livestock. Paper pulp production is an important economic pursuit within this
The southeastern part was once dominated by the Longleaf Pine Forest, while mixed pine/oak occurs west and north of the Piney Woods. Major trees species are loblolly and yellow pine, and blackjack and post oak. Hardwood forests of sweetgum, magnolia, tupelo, elm, and ash occur in the lowlands. Swamps are common and are most outstanding in the southern part of the Pine-Oak Forest.
Herbs and shrubs are plentiful in the Piney Woods, including predominant populations of Andropogon, Sporobolus, Panicum, Paspalum, Muhlenbergia, Eragrostis, Chasmanthium, Broomsedge (Andropogon virginicus), smutgrass (Sporobolus indicus), red lovegrass (Eragrostis oxylepis), and Indiangrass (Correll and Johnson).
Introductions of grasses and legumes, mostly for complicated the plant successional patterns. Some of these plants have invaded or have been over seeded in native vegetation. The most important of these are Bermuda grass (Cynodon Dactylon), Dallis grass (Paspalum dilatatum), Vasey grass (Paspalum Urvillei), carpet grass (Axonopus affinis), Medicago spp., Lespedeza spp. and others.
In the extreme southeast around Jasper, there are broad, flat savannahs intergrading with shrub bogs within the pineywoods. These savannahs are underlain by a fluctuating water table, and support a rather distinctive and interesting flora including several species of orchids, as well as sundews-Drosera spp., pipeworts - Eriocaulon spp. and numerous sedges, grasses, and bulrushes (Correll and Johnson).
The Blackland Prairies consisted of about 11,500,000 acres, including the San Antonio and Fayette Prairies.
Topography of the Blackland Prairies region is gently rolling to nearly level and well dissected for rapid surface drainage. Elevation varies from 300 to 800 feet above sea level. Average annual rainfall ranges from 30 to 40 inches increasing from west to east. May is the peak rainfall month for the northern end of the region; however, the south-central part has a fairly uniform distribution throughout the year.
Fairly uniform dark-colored alkaline clays, often referred to as “black gumbo,” interspersed with some gray acid sandy loams, characterize the area.
The Blackland Prairies was true tallgrass prairie with little bluestem as a climax dominant. Other important grasses were big bluestem, Indiangrass, switchgrass, sideoats grama, hairy grama (Bouteloua hirsuta), tall dropseed (Sporobolus asper), silver bluestem and Texas winter-grass. Under heavy grazing, Texas wintergrass, buffalo grass, Texas grama (Bouteloua rigidiseta), and many annuals increase or invade. Mesquite also has invaded hardland sites of the southern portion of the Blackland Prairies. Post oak and blackjack oak have increased on the medium- to light -textured soils.
According to the Texas Parks and Wildlife Department, 99.9% of the Blackland Prairie is lost to other land uses. Only a few remnants are protected as hay meadows or conservancy land.
Isolates of the Blackland Prairies occur in the Oak Woods and Prairies region. These areas may be identified by their characteristically dark clay soils.
Source: Texas Parks & Wildlife
The original savannahs in the northern part of the Oak-Prairie region were characterized by native grasses such as little bluestem, silver bluestem, and brownseed paspalum with scattered clumps of trees. Post oak trees dominated, but other species included blackjack oak, water oak, winged elm, hackberry, and yaupon.
Fire working in concert with other factors such as drought, herbivory, and competition from grasses restricted shrub and tree growth and maintained the savannah. The natural fire frequency on level to rolling topography appears to have ranged from 5 to 10 years and on topography dissected with breaks and rivers the fire frequency may have been 20 to 30 years. Since the early 1800s, the suppression of fire, and soil disturbance and land clearing practices by farmers and ranchers have resulted in a higher density of smaller trees and more thick undergrowth of vegetation, especially yaupon.
Bottomlands in the early 1800s were typically composed of large hardwoods with very little understory vegetation. Many bottomlands have now been cut over and cleared. Others have thick understories resulting from timber cutting or various soil disturbances, or are relatively open due to continuous grazing. According to written accounts from early explorers and settlers in 1800s, white-tailed deer, wild turkey, bison, black bear, squirrel, mountain lion, and red wolf were once common in the Post Oak Savannah.
The most striking change to the savannah has been the degradation or loss of the native range grasses from overgrazing and the clearing of the native range to plant monocultures of improved grasses, such as coastal Bermudagrass, for cattle. The rich diversity of grasses and weeds in the native savannah provided food and cover for many wildlife species and the conversion to “improved pastures” is responsible for the decline and even disappearance of species such as the bobwhite quail in much of the area.
Prairie area also known as the Grand Prairie, consisting of the Fort Worth Prairie and the Lampasas Cut Plains.
There are about seventeen million acres in this region, with one million acres in the East Cross Timbers, about three million in the West Cross Timbers and about six and one-half million acres in the Grand Prairie. The Eastern Cross Timbers is best described as a mix of the Western Cross Timbers and the Oak Woodlands.
The Oak Woods and Prairies region is gently rolling to hilly with elavation from 300 to 800 feet. Rainfall averages 35 to 45 inches per year with a peak in May or June. Upland soils are light colored, acid sandy loam or sands. Bottomland soils are acid with textures ranging from sandy loams to clays. The Oak Woods and Prairies support large cattle ranches. Oak-hickory forest interdigitates with tall-grass prairies in this region. The Western and Eastern Cross Timbers are major areas of oak-hickory, with open savannah as well as dense brush of post and blackjack oaks. Peat bogs and marshes are distributed along a line corresponding to surface exposures of the Carrizo Sands formations, running roughly southwest from northern Leon County to Palmetto State Park in Gonzales County. River valleys crossing the region support a forest of hackberries and pecans mixed with oaks on the alluvial soils.
The East Cross Timbers is a vaguely defined area along the Red River mainly between Grayson and Clay counties which ends to the south between the Blackland and Grand prairies (Correll and Johnson). The West Cross Timbers lie immediately west of the Grand Prairie.
According to Correll and Johnson, even with the wide variation in soils, the climax understory vegetation is rather uniform with the predominant grasses being little bluestem, big bluestem, Indian grass, switchgrass, Canada wild-rye, side-oats grama, hairy grama, tall dropseed and Texas wintergrass. Brush species also have invaded the prairie, and weedy annual and perennial grasses have increased in number, including hairy tridens (Erioneuron pilosum), Texas grama, red grama (Bouteloua trifida), tumble windmill grass (Chloris verticillata), tumblegrass, red lovegrass and some perennial weeds (Correll and Johnson).
The Rolling Plains region, together with the High Plains region, is the southern end of the Great Plains of the central United States. Topography is gently rolling to moderately rough and dissected by narrow intermittent stream valleys flowing east to southeast. Elevation is 800 to 3,000 feet. The eastern portion is sometimes known as the Reddish Prairies. Annual rainfall ranges from 22 inches in the west to nearly 30 inches in the eastern portion. May and September usually are high rainfall months. A summer dry period with high temperatures and high evaporation rates is typical. Soils vary from coarse sands along outwash terraces adjacent to streams, to tight clays or red-bed clays and shales. Soil reaction is neutral to slightly alkaline.
The region is bordered on the west by the Caprock Escarpment, on the south by the Edwards Plateau, and on the east by the Western Cross Timbers and Lampasas Cut Plain.
The original prairie vegetation included tall and midgrasses such as bluestems and gramas. Buffalo grass and species of three-awn, among others, tend to increase under grazing. Mesquite is a common invader on all soils. Shinnery oak and sand sage increase or invade on the sandy soils. Stream floodplains are dominated by various hardwood species. Juniper clings to the steep slopes along rivers.
The original prairie vegetation included tall and mid-grasses, such as little bluestem, big bluestem, sand bluestem (Andropogon Hallii,) side-oats grama, Indiangrass, switchgrass, hairy grama, blue grama, Canada wild-rye and western wheatgrass (Agropyron Smithii). Buffalograss, curlymesquite, tobosa (Hilaria mutica) species of three awn (Aristida spp.), sand dropseed, hooded windmill grass (Chloris cucullata) and Cenchrus species tend to increase under grazing. Mesquite is a common invader on all soils. Shinnery oak (Quercus Havardii ) and sand sage (Artemisia filifolia) increase or invade on the sandy lands. In addition to brush invaders, heavy grazing tends to increase sandburs (Cenchrus spp.), hairy tridens, red grama, Texas grama, tumblegrass, gummy lovegrass (Eragrostis curtipedicellata) Texas croton (Croton texensis), western ragweed and many other annuals and weedy perennials.
There are three subregions: the Mesquite Plains, Escarpment Breaks, and the Canadian Breaks. The Mesquite Plains subregion typifies the Rolling Plains Region. It is a gently rolling plain of mesquite-short grass savanna. Oak, cedar, acacia, and mimosa are important secondary elements of the brush portion on the savanna. Steep slopes, cliffs, and canyons occurring just below the edge of the High Plains Caprock comprise the Escarpment Breaks subregion. The Breaks are an ecotone or transition zone between the High Plains grasslands and the mesquite savanna of the Rolling Plains. Brush species including junipers, buffalo currant, and joint-fir dominate the vegetation of this subregion. The Canadian Breaks subregion is similar to the Escarpment Breaks, but also includes the floodplain and sandhills of the Canadian River in the northern Panhandle, bounded north and south by the edge of the Caprock. It is a mixed grass prairie with some low shrubs grading from succulents and dwarf shrubs in the east to shinnery, a savanna or groveland of scattered clusters of woody species, in the west.