The Ten Ecological Regions of Texas

Map — Texas Parks & Wildlife ecological regions

Most states can be described in a sentence or two of geography. Texas cannot. It is large enough — roughly 268,600 square miles, about 7 percent of the United States — that it crosses several of the continent's major biomes at once: eastern hardwood forest, southern coastal marsh, central grassland, southwestern desert and the southern Great Plains. Where those biomes meet, Texas holds an unusual concentration of plant and animal life, more species of birds than any other state among them.

To make sense of that variety, scientists and land managers divide the state into ecological regions — areas that share a broadly similar climate, geology, soils and natural vegetation. Texas Parks & Wildlife recognizes ten. They are the practical unit for almost everything that follows on this site: where water comes from, which crops grow, what pollutes the air, and which species are in trouble all depend on which region you are standing in.

What defines an ecological region

An ecological region is shorthand for a recurring combination of conditions. Four factors do most of the work:

• Geology and soils. The deep black clays of central Texas, the sandy loams of the east, the caliche and limestone of the Hill Country, and the windblown sands of the Panhandle each support a different natural community.
• Climate. Rainfall falls steeply from east to west — more than 55 inches a year in the far east, less than 10 in the far west. That single gradient explains much of the state's ecological map.
• Native vegetation. Pine forest, tallgrass prairie, oak savannah, thornscrub and desert shrubland mark the regions even where farming and cities have replaced most of the original cover.
• Land use. How people have worked the land — timber, row crops, cattle, irrigation, oil and gas, or urban growth — both reflects the underlying region and reshapes it.

The ten regions at a glance

The table below sketches each region by its rough size, the rainfall it receives, and the natural vegetation that defines it. Areas are approximate; regions overlap and sources vary.

Texas ecological regions — comparative summary

Region	Approx. area	Annual rainfall	Defining cover
Piney Woods	East Texas	40–55 in	Pine & hardwood forest
Gulf Prairies & Marshes	Coastal belt	30–50 in	Coastal prairie & marsh
Post Oak Savannah	East-central	28–40 in	Oak savannah
Blackland Prairies	Central corridor	30–45 in	Tallgrass prairie
Cross Timbers & Prairies	North-central	25–40 in	Oak woodland & prairie
South Texas Plains	Far south	20–32 in	Thornscrub & brush
Edwards Plateau	Hill Country	15–34 in	Live oak & juniper
Rolling Plains	Northwest-central	22–30 in	Mixed & short grass
High Plains	Panhandle	15–21 in	Shortgrass plain
Trans-Pecos	Far west	8–12 in	Chihuahuan desert

1 · Piney Woods

The state's eastern edge is a southern extension of the great pine-hardwood forest that runs across the American Southeast. Loblolly and shortleaf pine mix with oak, hickory, sweetgum and — in the bottomlands — bald cypress draped over slow blackwater bayous. This is the wettest part of Texas, and the most heavily forested.

It is also the heart of the state's timber economy: most of Texas's commercial forestland and nearly all of its pulp and paper capacity sit here. The pressures are those of any working forest — conversion of natural stands to pine plantation, fragmentation, and the loss of bottomland hardwood to reservoirs and clearing.

For a closer look at the region's bottomland forests, see our profile of the East Texas hardwood forests.

2 · Gulf Prairies and Marshes

A band of nearly level land follows the coast from the Louisiana line to the Rio Grande — coastal prairie inland, salt and brackish marsh at the water's edge, and barrier islands beyond. The marshes are among the most productive habitats in North America, nurseries for shrimp, crab and finfish and wintering ground for vast numbers of waterfowl and shorebirds, including the endangered whooping crane at Aransas.

It is also the most industrialized stretch of the Texas coast. The Houston Ship Channel and the petrochemical complexes of the upper coast sit on former prairie and wetland; subsidence, navigation channels and freshwater diversion all reshape the marshes that remain.

3 · Post Oak Savannah

Between the eastern forest and the central prairies lies a transitional belt of scattered post oak and blackjack oak over grassland — a true savannah where trees and open prairie meet. Sandy, often acidic soils set it apart from the black clays to its west. Much of it is now improved pasture and hay meadow, grazed by beef cattle.

4 · Blackland Prairies

A narrow corridor of deep, dark, fertile clay runs from the Red River south through Dallas and Waco toward San Antonio. In its natural state it was tallgrass prairie — little bluestem, big bluestem and Indiangrass shoulder-high in a good year. That fertility was its undoing as wild land: the Blackland is one of the most thoroughly converted prairies on the continent, with well under one percent of the original grassland remaining intact.

Today the region is row-crop farmland giving way, fast, to metropolitan growth. The Dallas–Fort Worth and Austin–San Antonio corridors both run through it, and the conversion of farmland to subdivision is among the clearest examples of the collision between agriculture and urban sprawl anywhere in Texas.

Less than one percent of the original Blackland tallgrass prairie survives — one of the rarest large ecosystems in North America.Native Prairies Association of Texas

5 · Cross Timbers and Prairies

North-central Texas alternates between belts of dense oak woodland — the "cross timbers" that early travelers found nearly impenetrable — and open prairie on the limestone and sandstone in between. It is classic ranching country, and increasingly a zone of energy development over the Barnett Shale beneath Fort Worth.

6 · South Texas Plains

South of San Antonio the land dries and the brush thickens into the Tamaulipan thornscrub — mesquite, acacia, granjeno and prickly pear over a hot, semi-arid plain reaching to the Rio Grande. Large private ranches dominate, and the dense brush shelters some of the state's most sought-after wildlife, from white-tailed deer to ocelots clinging on near the river. Where the river is tapped for irrigation, the Lower Rio Grande Valley turns to citrus and winter vegetables.

7 · Edwards Plateau

The Hill Country is a great uplifted block of limestone, deeply cut by clear spring-fed rivers — the Llano, the Guadalupe, the Frio, the Nueces. Its defining feature lies underground: the Edwards Aquifer, a karst limestone reservoir that supplies San Antonio and feeds Comal and San Marcos springs, home to a cluster of species found nowhere else on Earth.

Thin soils over rock make the plateau easy to overgraze and slow to recover. Ashe juniper ("cedar") has spread where fire was suppressed and grazing was heavy, and the rapid subdivision of Hill Country ranchland now competes with the aquifer's recharge zone for the same ground.

8 · Rolling Plains

West of the Cross Timbers and below the Panhandle's escarpment, the Rolling Plains roll out in mixed and short grass cut by the red, salty tributaries of the Brazos and Red rivers. Cotton and cattle share the land with oil. Mesquite and, increasingly, invasive saltcedar along the watercourses are the region's persistent brush problems.

9 · High Plains

The Llano Estacado — the "staked plain" — is a vast, flat, treeless tableland across the Panhandle and South Plains, so level that early Spanish explorers reportedly drove stakes to find their way back. Its agriculture is among the most productive in the nation: irrigated cotton, sorghum, corn and wheat, plus enormous cattle feedlots and dairies.

Nearly all of that water comes from a single source — the Ogallala Aquifer — and across much of the region it is being withdrawn far faster than nature replaces it. The slow drawdown of the Ogallala is one of the defining long-term resource questions in Texas, explored in our profile of regional water supply and demand.

10 · Trans-Pecos

West of the Pecos River, Texas becomes the Chihuahuan Desert — and, paradoxically, its most biologically diverse region. Desert basins of creosote and lechuguilla rise into "sky island" mountains: the Guadalupes (which hold the state's highest point), the Davis Mountains, and the Chisos within Big Bend. Each range is an island of cooler, wetter habitat marooned above the desert, with its own assemblage of plants and animals.

This is the emptiest quarter of Texas, with the darkest skies in the lower 48 and the least rainfall — under a foot a year in the basins. Its pressures are subtler than the east's: groundwater pumping for distant cities, springs going dry, and the fragmentation of the few large desert ranches.

Why ecological regions matter for policy

Dividing Texas into regions is more than a naturalist's convenience. It is the only honest way to talk about the state's environment, because nearly every issue plays out differently from one region to the next:

• Water. The Ogallala drawdown that dominates the High Plains has nothing in common with the marsh-and-bay freshwater questions of the Gulf coast, yet both are "Texas water policy."
• Working lands. What sustainable agriculture looks like on a Panhandle irrigation circle is not what it looks like on a Hill Country ranch or an East Texas tree farm.
• Growth. The fastest land-use change in the state — the spread of cities into the Blackland Prairie and Edwards Plateau — concentrates in just a few regions.
• Conservation. Rare-species protection, from the whooping crane to the Edwards Aquifer salamanders, is necessarily regional work.

Throughout this site, the regional profile is the backdrop against which the numbers make sense. Start with the region you live in, and the rest of Texas's environment becomes a great deal easier to read.

Sources & further reading

1. Texas Parks & Wildlife Department, Texas Ecological Regions and the Texas Conservation Action Plan.
2. Gould, F.W., Texas Plants — A Checklist and Ecological Summary (vegetational areas of Texas), Texas A&M.
3. U.S. Environmental Protection Agency, Level III and IV Ecoregions of Texas.
4. Texas Water Development Board, Texas Aquifers Study and regional water plans.
5. U.S. Census Bureau, state population and land-area statistics.