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Ecoregions of Texas

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Average Annual Temperatures of Texas for January

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Average Annual Temperatures of Texas for July

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Average Annual Precipitation of Texas (1961–1990)

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Dominant Soils of Texas

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Oak Wood and Prairies/Post Oak Savannah

This ecosystem is part of a historic oak belt, which travels south from Canada towards Central America. Few true examples of old-growth Post Oak

Savannah in Texas still exist today.

The Post Oak Savannah is dominated by native bunch grasses scattered post

oaks and some plateau live oak, black hickory, and blackjack oak. In recent times this historical vegetation has been replaced by species such as yaupon

holly, cedar elm, sugarberry, and eastern red cedar. Upland areas are typically where bunch grasses are concentrated.

Cattle ranching and hay production are the primary uses for this area along with development for residential property. These land uses along with

degradation from the absence of historical land management and fire patterns have caused the reduction in the number of acres of representative

Post Oak Savannah that exist today. The endangered Houston toad occurs in the eastern portion of this eco-region where deep sands resides.

Blackland Prairies

Prior to human settlement, fire and grazing by bison were probably the two most important factors in the overall maintenance of the Blacklands area. Fires were typically very large and would burn until conditions or landforms would contain them

The east-central portion of the Blackland prairie was once part of a vast tall grass prairie made up of big bluestem, little bluestem, switchgrass and sideoats and other flora.

Of the original 12 million acres, less than one percent remains after more than 150 years of agriculture and improper grazing,

Coastal Sand Plain

The Coastal Sand Plains occupies more than two million acres at the southern tip of the state, just north of the Lower Rio Grande Valley

The Coastal Sand Plains are composed of grasslands and coastal oak motts intermixed with mesquite, granjeno and salt marshes. Unstable, windblown sand produces the characteristic dunes of this ecoregion. Numerous herds of wild horses roamed the Coastal Sand Plains during the 19th century, and the area was appropriately labeled Los Llanos Mesteños (The Wild Horse Plains).

South Texas Brush Country

Topography is considered almost flat to gently rolling. A few

major rivers run through the north and northeastern portion of

this region forming bottomland ecosystems

Soils are primarily acidic sands. Flats with poor drainage often

contain huisache and some mesquite trees. Droughty flats and

ridges with gravelly or rocky soils that have better drainage

contain shorter mesquite, blackbrush, cenizo, etc.

Fire historically played a role in shaping the South Texas Plains. Grasses were thought to be a major component of the region

prior to settlement. As grasses were grazed by livestock, the fragile soil structure eroded away leaving mostly rocky, dry soils which are now able to support mostly woody species. Now that much of the grass layer is gone, fire is not able to play much of a role except in extreme drought situations or when the land is managed for grass and fire re-establishment.

Rolling Plains

Part of the Great Plains of the central United States, the topography is

characterized as being rough terrain.

This region was historically comprised of numerous large ranch holdings,

although that number is dwindling as a number of the large landholdings are being sub-divided into smaller plots.

The income producing opportunities supported by this eco-region include ranching (cattle), cotton, wheat, sorghum, rangeland, oil, and game hunting.

Even though there are no tree ring studies to document fire frequency, historically this area is assumed to have had a fire occurrence every 5 to 10

years. This frequency created the low populations of woody species observed by early explorers to the region. Following settlement, fires were suppressed

and improper grazing occurred. Overgrazing by livestock weakened the native grasses, removed fuel needed for a burn and set the stage for

aggressive woody plant species to increase. Droughts accelerated the process. Some of the woody plants were natives that increased while others

were not native to the sites. Cattle and wildlife helped to spread some of these plants as most of the seeds pass undigested in droppings. Mesquite

beans, which are high in protein, are relished by cattle, especially during

drought.

Marine Environment

The habitats of the Gulf of Mexico are very diverse. Texas has seagrasses, oyster

reefs, salt marshes, barrier islands, coastal wetlands, muddy estaurine bottoms,

reefs - natural and artificial- and open water. These areas provide plants and

animals with their basic needs and support hundreds of species that call the Gulf

of Mexico home.

With its wide range of habitats, the Gulf of Mexico supports a variety of

invertebrate species, including oysters, crabs, shrimp, and snails. There are 29

species of marine mammals in the Gulf of Mexico. The ecoregion also supports a

variety of invertebrate species, including oysters, crabs, shrimp, and snails.

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The Piney Woods

Many parts of this ecoregion are characterized by longleaf pine forests on rolling sandy uplands. A variety of broad-leaved plants, shrubs, and grasses grow in this ecoregion of Texas. Photos: National Park Service

The Big Thicket national preserve is part of the Piney Woods. There are over 85 species of trees, 1,000 flowering plants, and over 180 kinds of birds in the Big Thicket. Photos: National Park Service

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Big Thicket Pine

Bald Cypress Marsh

Palmetto Leaf

Neches River

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Texas, Our TexasRM 7 continuedGulf Coast Plains and Marshes

Barrier islands, peninsulas, marshes, and flat plains characterize this ecoregion. Sixty percent of the Texas Gulf Coast shoreline erodes from 30 cm to 15 m per year. Photo: U.S. Army Corps of Engineers

The western part of the Gulf Coast Plain is one of the most biologically diverse regions of Texas. Nearly 500 species of resident and migratory birds have been recorded in the Texas coastal region. Photo: U.S. Army Corps of Engineers

Barrier Island

Rosette Spoonbills Whooping Cranes

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Texas, Our TexasRM 7 continuedEdwards Plateau/Llano Uplift

The Llano Uplift is located within the Edwards Plateau ecoregion. It is sometimes referred to as the Hill Country. Domelike rock formations of exposed pink granite are located in this region. Unique plant communities are often found on these domes. An example of this type of rock formation is the Enchanted Rock.The southeast portion of the Edwards Plateau is an area of canyonlands. A diversity of plants can be observed in this area, including deciduous forests, grasses, mesquite trees, and wildflowers. Photos: Texas Parks and Wildlife

Mexican free-tailed bats, the Texas blind salamander, and the golden-cheeked warbler are just a few of the unique animals that can be observed in the region. Cool, clear springs and streams provide water for the vegetation and wildlife. Photos: Texas Parks and Wildlife

Enchanted Rock

Mexican Free-Tailed Bats

Canyonlands

Texas Blind Salamander

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Texas, Our TexasRM 7 continuedHigh Plains

This ecoregion usually receives less than 20 inches of precipitation per year. Seasonal lakes called playas are found in this ecoregion. These lakes are filled with salts due to the erosion of nearby hills by rainwater. Playas are key sites of biodiversity. They provide important habitats for ducks, geese, sand hill cranes, shorebirds, amphibians, and small mammals. Photo: Loren M. Smith, Texas Tech University

The Palo Duro Canyon is the second largest canyon in the United States. It was formed by water erosion of the Prairie Dog Town Fork of the Red River.

Playa

Palo Duro Canyon

Prairie Dog

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Texas, Our TexasRM 7 continuedTrans Pecos/Chihuahuan Desert

The area generally west of the Pecos River in Texas is often called the Trans-Pecos. It occupies the northern part of the Chihuahuan Desert, which extends south nearly 500 miles into Mexico. Shown here is Croton Peak in the northern part of Big Bend National Park. Roadrunners are well-adapted to desert habitats of the Southwest. They eat insects, spiders, snails, lizards, and some fruits and seeds.

The Trans Pecos ecoregion has diverse topography. It includes desert flats and valleys, plateaus, sand hills, and mountain ranges. Grasslands, shrub lands, cactus savannas, and mountain woodlands also occur. Photo: Michel Farhi

Croton Peak

Blooming Cactus

Roadrunner

Grasslands

More Information On the Ecoregions of Texas Edwards Plateau/Llano Uplift The Edwards Plateau/Llano Uplift ecoregion is located in central Texas. An unusual landform in this ecoregion is a dome of granite called Enchanted Rock. The Enchanted Rock experiences a type of physical weathering called exfoliation. Exfoliation is a process in which the surface of rock weathers by peeling into sheets instead of breaking down into small sediments. Edwards Plateau The Edwards Plateau region comprises an area of central Texas commonly known as the Texas Hill Country. It is a land of many springs, stony hills, and steep canyons. The region is home to a whole host of rare plants and animals found nowhere else on earth. Average annual rainfall ranges from 15 to 34 inches. Rainfall is highest in May or June and September. Soils of the Edwards Plateau are usually shallow with a variety of surface textures. They are underlain by limestone. Elevations range from slightly less than 100 feet to over 3,000 feet above sea level. Several river systems dissect the surface, creating a rough and well-drained landscape. The limestone of the Edward's Plateau is honeycombed with thousands of caves. Beneath the eastern edge of the Plateau lies a hidden world of underground lakes known as the Edwards Aquifer. Today, the Edwards Plateau is characterized by grasslands, juniper/oak woodlands, and plateau live oak or mesquite savannah. Open grasslands and savannahs were more common in presettlement times than they are today. Llano Uplift The Llano Uplift is also known as the central mineral region. Although surrounded by the Edwards Plateau region, the Llano Uplift is distinguished by its unique geology. Home to some of the oldest rocks in Texas, the central mineral region contains unique minerals and rock formations. The region is characterized by large granite domes, such as Enchanted Rock near Fredericksburg. Rainfall averages about 24 to 32 inches per year, peaking in May or June and September. The landscape is rolling to hilly and elevation range from 825 to 2,250 feet above sea level. Soils are predominantly coarse textured sands, produced from weathered granite over thousands of years. Native vegetation consists of oak-hickory or oak-juniper woodlands, mesquite-mixed brush savannah, and grasslands. Open grassland and savannah were once more common than they are today. The Piney Woods Rolling terrain covered with pines and oaks, and rich bottomlands with tall hardwoods, characterize the forests of the east Texas Pineywoods. This region is part of a much larger area of pine-hardwood forest that extends into Louisiana, Arkansas, and Oklahoma. The average annual rainfall of 36 to 50 inches is fairly uniformly distributed throughout the year, and humidity and temperatures are typically high. The soils of the region are generally acidic and mostly pale to dark gray sands or sandy loams. Elevations range from 200 to 500 feet above sea level. Because the Piney Woods ecoregion receives ample precipitation it has abundant vegetation. Vegetation such as pine forests and grasses holds soil in place. Very little erosion takes place in these areas. Seasonal flooding occurs along riverbanks. Sediments are carried and deposited in different locations along the river route. The thick areas of vegetation help to inhibit river erosion. These characteristics of the Piney Woods ecoregion provide stable environments for wildlife to thrive.

Gulf Coast Plains/Prairies and Marshes The Gulf Coast 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 barrier islands along the coast, salt grass marshes surrounding bays and estuaries, remnant tallgrass prairies, oak parklands and oak mottes scattered along the coast, and tall woodlands in the river bottomlands. Average annual rainfall varies from 30 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. Although much of the native habitat has been lost to agriculture and urbanization, the region still provides important habitat for migratory birds and spawning areas for fish and shrimp. The Gulf Coast Plains and Marshes experience large amounts of weathering, erosion, and deposition. Wave action, a cause or agent of weathering, erosion, and deposition, is constant along the Texas coastline. The effects of wave action may happen slowly or very quickly. Sediments may be weathered and eroded along beaches and carried out into the ocean to form sand bars. Sediments may also be deposited along the coast, forming sand dunes and/or barrier islands over time. During catastrophic events such as hurricanes, wave erosion accelerates. Environments for wildlife such as shorebirds and turtles can be destroyed quickly. High Plains The High Plains ecoregion is one of the windiest regions in the United States. The climate is generally dry, and areas without vegetation experience wind erosion. The Palo Duro Canyon was formed by water erosion by a fork of the Red River. The canyon continues to become deeper as the water moves sediment downstream. Average annual rainfall is 15 to 22 inches. Rainfall is lowest in winter and mid-summer and highest in April or May and September or October. Extended droughts have occurred here several times this century. Native vegetation of the High Plains is shortgrass prairie dominated by buffalo grass.Today, the plains are mostly irrigated cropland and the native vegetation includes more mesquite and juniper. Although much of the shortgrass prairie and the vast prairie dog towns are gone, large flocks of wintering waterfowl still come to the playa lakes (shallow, round depressions which spot the surface, sometimes covering more than 40 acres). Trans Pecos/Chihuahuan Desert The Trans Pecos is perhaps the most complex of all the regions. It occupies the extreme western part of the state eastward generally to the Pecos River. This is a region of diverse habitats and vegetation, varying from the desert valleys and plateaus to wooded mountain slopes. Elevations range from 2,500 feet to more than 8,749 feet at Guadalupe Peak. Even the mountain ranges vary greatly in the environments they offer for plant and animal life. Some are characterized by volcanic rocks, others by limestone. Over most of the area average annual rainfall is less than 12 inches, but varies greatly from year to year and from lower to higher elevations. July and August are usually the higher rainfall months. The Trans Pecos ecoregion includes the Chihuahuan Desert. The Guadalupe Mountains and the Davis Mountains are located in this ecoregion, making it the most mountainous area of Texas. In general, soil in this region is eroded due to the decline of grasslands. Big Bend National Park is also located in this ecoregion. Flash-flooding and rapid runoff are agents of erosion in the park. Erosion of the limestone cliffs takes place because of acid rain.

Coastal Sand Plains The Coastal Sand Plains is fairly level with elevations less than 150 feet above sea level. Average annual rainfall is 24 to 28 inches per year and the soils are primarily windblown sands. The vegetation can be described as tallgrass prairie with live oak woodlands, mesquite savannah, and salt marshes. Oak Woods and Prairies Average annual rainfall averages 28 to 40 inches per year. May or June usually brings a peak in monthly rainfall. Upland soils are light colored, acidic sandy loam or sands. Bottomland soils may be light brown to dark gray and acidic with textures ranging from sandy loams to clays. The landscape of the region is gently rolling to hilly and elevations range from 300 to 800 feet above sea level. The region can be described as oak savannah, where patches of oak woodland are interspersed with grassland. Blackland Prairies The Blackland Prairies region is named for the deep, fertile black soils that characterize the area. Blackland Prairie soils once supported a tallgrass prairie dominated by tall-growing grasses. Because of the fertile soils, much of the original prairie has been plowed to produce food and forage crops. The average annual rainfall ranges from 28 to 40 inches. May is the peak rainfall month for the northern end of the region; however, the south-central part has a fairly uniform rainfall distribution throughout the year. The landscape is gently rolling to nearly level, and elevations range from 300 to 800 feet above sea level. South Texas Brush Country 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 average annual rainfall of 20 to 32 inches increases from west to east. 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. Although many land changes have occurred in this region, the Brush Country remains rich in wildlife and a haven for many rare species of plants and animals. Rolling Plains Several Texas rivers begin in the gently rolling hills and broad flats of the Rolling Plains. These are responsible for the rolling character of the land. The rivers have cut canyons that shelter some plants and animals typical of the Rocky Mountains. Average annual rainfall is 20 to 28 inches, with peaks in May and September. A summer dry period with high temperatures and high evaporation rates is typical. Elevations vary from 800 to 3,000 feet above sea level.