The Western Gulf coastal grasslands (Spanish: Pastizales costeros del Golfo Occidental) are a subtropical grasslandecoregion of the southern United States and northeastern Mexico. It is known in Louisiana as the "Cajun Prairie", Texas as "Coastal Prairie," and as the Tamaulipan pastizal (Spanish: Pastizal Tamaulipeco) in Mexico.
Williams Prairie, a 10-acre (40,000 m2) remnant prairie preserve west of Houston in Waller County, Texas, USA
The ecoregion covers an area of 77,425km2 (29,894sqmi), extending along the shore of the Gulf of Mexico from southeastern Louisiana (west of the Mississippi Delta) through Texas and into the Mexican state of Tamaulipas as far as the Laguna Madre. Specific areas include a number of barrier islands, and the resacas or natural levees of the Laguna Madre.[2] The coast is vulnerable to tropical storms that can seriously damage habitats.[3]
This ecosystem, in part, has edaphic origins: the soils of this ecoregion are largely dominated by vertisolclays, the mechanical properties of which make it difficult for many tree species to grow and establish. As a result, extensive forest cover is precluded, allowing grasses and other herbaceous species to dominate.[4] However, there are interspersed areas of higher sand and silt content that break up the otherwise heavy clay environment: these areas typically correspond to floodplain/riparian zones, and are more permissive of tree-growth, featuring galleries or even closed-canopy bottomland expanses.[5]
Climate
From Southwest Louisiana west to the Upper Texas coast, the climate is wet humid subtropical, featuring significal annual precipitation. The climate becomes more arid farther south along the Texas coast into northeastern Mexico, though precipitation totals still remain high enough for the humid subtropical classification.
This coast is rich in wildlife, and 700 species of birds, animals and reptiles have been counted here, although many are now threatened or endangered. This coast is a critical habitat for the Attwater's prairie chickens (Tympanuchus cupido attwateri), over one million of which inhabited the prairie in Texas and Louisiana in the 19th century, but extreme reduction of their habitat put them on the U.S. endangered species list in 1967. Another endangered bird of the coast is the whooping crane (Grus americana). Many species of wading birds, shorebirds, and other waterbirds are abundant. Birds in the Mexican part of the region include Morelet’s seedeater (Sporophila morelleti), red-billed pigeon (Columba flavirostris), brown jay (Cyanocorax morio), Neotropic cormorant, white-winged dove (Leptotila verrequxi) and Audubon's oriole (Icterus graduacauda).
Less than 1% of the ecoregion remains in pristine condition, almost entirely in Texas, while most of the coast has been converted to farmland, including rice paddies, grazing land, or urban areas including Houston, Texas. Estuaries and other coastal wetlands are better preserved than the prairie and indeed the protected areas of the coast are mainly sanctuaries for waterbirds.
Human use
Largely because of the region's flatness and grassland potential, a higher percentage of the land is in cropland than in bordering ecological regions. Rice, grain sorghum, cotton, and soybeans are the principal crops. Urban and industrial land uses have expanded greatly in recent decades, and oil and gas production is common.[6]
EPA Level IV ecoregions
The Western Gulf Coastal Plain is a Level III ecoregion in the US Environmental Protection Agency's scheme of US ecoregions. It is roughly coextensive with the Western Gulf coastal grasslands, with the important exception that the EPA-defined area terminates at the national boundary, while the natural ecoregion extends into northeastern Mexico. In the EPA's definition, the principal distinguishing characteristics of the Western Gulf Coastal Plain are its relatively flat topography and mainly grassland potential natural vegetation. Inland from this region the plains are older, more irregular, and have mostly forest or savanna-type vegetation potentials.[6] The EPA identifies ten Level IV ecoregions: Northern Humid Gulf Coastal Prairies; Southern Subhumid Gulf Coastal Prairies; Floodplains and Low Terraces; Coastal Sand Plain; Lower Rio Grande Valley; Lower Rio Grande Alluvial Floodplain; Texas–Louisiana Coastal Marshes; Mid-Coast Barrier Islands and Coastal Marshes; Laguna Madre Barrier Islands and Coastal Marshes; and Lafayette Loess Plains.
Map of the Western Gulf Coastal Plain USEPA ecoregion
Quaternary-age deltaic sands, silts, and clays underlie much of the Northern Humid Gulf Coastal Prairies on this gently sloping coastal plain. The original vegetation was mostly grasslands with a few clusters of oaks, known as oak mottes or maritime woodlands. Little bluestem, Indiangrass, brownseed paspalum, gulf muhly, and switchgrass were the dominant grassland species, with some similarities to the grasslands of the Texas Blackland Prairies (ecoregion 32). Almost all of the coastal prairies have been converted to cropland, rangeland, pasture, or urban land uses. The exotic Chinese tallow tree and Chinese privet have invaded large areas in this region. Some loblolly pine occurs in the northern part of the region in the transition to the South Central Plains (ecoregion 35). Soils are mostly fine-textured: clay, clay loam, or sandy clay loam. Within the region, there are some differences from the higher Lissie Formation to the lower Beaumont Formation, both of Pleistocene age. The Lissie Formation has lighter colored soils, mostly Alfisols with sandy clay loam surface texture, while darker, clayey soils associated with Vertisols are more typical of the Beaumont Formation. Annual precipitation varies from 37 inches (94cm) in the southwest portion to 58 inches (150cm) in the northeast, with a summer maximum.[6]
The Southern Subhumid Gulf Coastal Prairies ecoregion is drier than Ecoregion 34a to the north, not only receiving less annual precipitation, but also typically experiencing summer drought. Annual precipitation ranges from 26 inches (66cm) in the southwest to 37 inches (94cm) in the northeast, with May and September peaks. Soils are hyperthermic compared to thermic in most of Ecoregion 34a. Little bluestem, yellow Indiangrass, and tall dropseed were once dominant grasses. Eragrostoid grasses, including the genera Bouteloua, Buchloe, Eragrostis, Hilaria, and Setaria increase in importance in Ecoregion 34b compared to 34a. Invasive species such as honey mesquite and huisache are a concern. Almost all of the coastal prairies have been converted to other land uses: cropland, pasture, or urban and industrial.[6]
Covering primarily the Holocene floodplain and low terrace deposits, the Floodplains and Low Terraces ecoregion, especially to the southwest, has a different bottomland forest than the floodplains of the South Central Plains (ecoregion 35). Bottomland forests of pecan, water oak, southern live oak, and elm, are typical, with some bald cypress on larger streams. The Brazos and Colorado River floodplains are a broad expanse of alluvial sediments, while floodplains to the south are more narrow. Soils include Vertisols, Mollisols, and Entisols. Large portions of floodplain forest have been removed and land cover is now a mix of forest, cropland, and pasture.[6]
The Coastal Sand Plain ecoregion provides a distinct break in both vegetation and surficial materials from the fine-textured soil grasslands of the Southern Subhumid Gulf Coastal Prairies (34b) to the north. This sand sheet landscape consists of active and (mostly) stabilized sand dune deposits with lesser amounts of silt sheet deposits (silt and fine sand) to the north. This depositional plain is characterized by a closed internal drainage system with only occasional discontinuous drainage remnants due to sand movement. Closed depressions pond water in response to seasonal and tropical storm precipitation. Soils developed on these parent sediments are Entisols and Alfisols with thick sand surfaces. The dominant grasses on the coastal sand ridges and islands extend inland covering parts of the sand plain. Vegetation is mostly mid and tall grasses such as seacoast bluestem (Schizachyrium littorale), switchgrass, gulfdune paspalum (Paspalum monostachyum), fringeleaf paspalum, sandbur, purple threeawn, pricklypear, and catclaw with an overstory of southern live oak and honey mesquite trees. The potholes have a variety of bulrush es and sedges. Most of the Coastal Sand Plain has been moderately to heavily grazed, and large areas have been converted to non-native range or pasture grasses. The region has little cropland compared to the Southern Subhumid Gulf Coastal Prairies (34b).[6]
The Lower Rio Grande Valley ecoregion once supported dense, diverse grassland and shrub communities and low woodlands. However, mesquite, granjeno (spiny hackberry), and a variety of brush and shrub species invaded the landscape. Now, it is almost all in cropland, pasture, and urban land cover. The region is underlain by a mix of Quaternary clays and sands with some Miocene-age sediments of the Goliad Formation at the western edge. Mollisols are extensive, and the soils are deep, mostly clay loams and sandy clay loams. The freeze-free growing season is often over 320 days compared to 250–260 days along the northern Texas coastal area of the Northern Humid Gulf Coastal Prairies (34a). Along with the Lower Rio Grande Alluvial Floodplain (34f), the Lower Rio Grande Valley contains important nesting grounds for the white-winged dove, a favored hunting species in southern Texas.[6]
The Lower Rio Grande Alluvial Floodplain ecoregion includes the Holocene-age alluvial sands and clays of the Rio Grande floodplain that are now almost completely in cropland or urban land cover. The soils, mostly Vertisols and Mollisols, are deep, loamy and clayey, and tend to be finer-textured than in the Lower Rio Grande Valley (34e) to the north. Some Entisols and Inceptisols occur near the river. The floodplain ridges once had abundant palm trees, and early Spanish explorers called the river "Rio de las Palmas." Most large palm trees and floodplain forests had been cleared by the early 1900s. A few small pieces of unique floodplain forests remain, including Texas ebony, Texas palmetto, and sugar hackberry–cedar elm floodplain forests. It is the most subtropical climate of Texas, but hard freezes occasionally occur, affecting plants and animals that are at the northern limit of their range. Crops include cotton, citrus, grain sorghum, sugar cane, vegetables, and melons. The Rio Grande’s water is mostly diverted from its channel for irrigation and urban use, and little or no flow reaches the Gulf of Mexico. Both the Central and Mississippi flyways funnel through the southern tip of Texas and many species of birds reach their extreme northernmost range in this region. In addition, subtropical, temperate, coastal, and desert influences converge here, allowing for great species diversity. Nearly 500 bird species, including neotropical migratory birds, shorebirds, raptors, and waterfowl, can be found here.[6]
The Texas–Louisiana Coastal Marshes region is distinguished from ecoregions 34h and 34i by its extensive freshwater and saltwater coastal marshes, lack of barrier islands and fewer bays, and its wetter, more humid climate. Annual precipitation is 48 to 54 inches (120 to 140cm) in Texas and up to 60 inches (150cm) in Louisiana. There are many rivers, lakes, bayous, tidal channels, and canals. The streams and rivers that supply nutrients and sediments to this region are primarily from the humid pine belt of the South Central Plains (ecoregion 35). Extensive cordgrass marshes occur. The estuarine and marsh complex supports marine life, supplies wintering grounds for ducks and geese, and provides habitat for small mammals and American alligators. Brown shrimp, the most commercially important marine species in Texas, is common along the whole coast, but in this northern coastal zone white shrimp are also commercially important. Eastern oysters and blue crabs are also common and commercially important in the region. Sport fishery species such as red drum, black drum, southern flounder, and spotted seatrout occur throughout the coastal bays of this region and ecoregion 34h.[6]
Mid-Coast Barrier Islands and Coastal Marshes (34h)
The Mid-Coast Barrier Islands and Coastal Marshes portion of the Texas coast is subhumid compared to the humid climate of Ecoregion 34g to the northeast and to the semiarid climate of ecoregion 34i to the south. Annual precipitation within ecoregion 34h increases to the northeast, ranging from 34 to 46 inches (86 to 117cm). The region encompasses primarily Holocene deposits with saline, brackish, and freshwater marshes, barrier islands with minor washover fans, and tidal flat sands and clays. In the inland section from Matagorda Bay to Corpus Christi Bay, Pleistocene barrier island deposits occur. Typical soils on the coastal marshes are Entisols, with a minor extent of Histosols. Mollisols occur on tidal flats and coastal marshes, and Entisols form in sandy barrier islands and dunes. Smooth cordgrass, marsh hay cordgrass, and gulf saltgrass dominate in more saline zones. Other native vegetation is mainly grassland composed of seacoast bluestem, sea-oats, common reed, gulfdune paspalum, and soilbind morning-glory. Some areas have clumps of sweetbay, redbay, and dwarf southern live oak trees. In the Coastal Bend area, the barrier islands support extensive foredunes and back-island dune fields. Scarps can characterize bay margins due to beach erosion. Salt marsh and wind-tidal flats are mostly confined to the back side of the barrier islands with fresh or brackish marshes associated with river-mouth delta areas. Marsh hay cordgrass becomes less important to the south in this region. Black mangrove begins to appear from Port O'Connor south. This area of the coast has all three commercially important species of shrimp as well as important oyster and blue crab fisheries. Convergence of longshore currents from north and south occurs south of the Corpus Christi area near Padre Island National Seashore. Corpus Christi Bay serves as the ecozone or boundary between two distinct estuarine ecosystems. Copano and Mesquite Bays to the north are low to moderate-salinity bays and attract whooping cranes and other birdlife. To the south in 34i, hypersaline Laguna Madre forms a unique ecosystem and supports greater expanses of seagrasses.[6]
Laguna Madre Barrier Islands and Coastal Marshes (34i)
The Laguna Madre Barrier Islands and Coastal Marshes ecoregion is distinguished by its hypersaline lagoon system, vast seagrass meadows, wide tidal mud flats, large overwintering redhead duck population, numerous protected species, great fishery productivity, and a narrow barrier island with a number of washover fans. The lower coastal zone in Texas has a more semi-arid climate and has less precipitation, 27–29 inches (69–74cm), compared to 34g and 34h. There is extreme variability in annual rainfall, and evapotranspiration is generally two to three times greater than precipitation. As no rivers drain into the Texas Laguna Madre, the lagoon water can be hypersaline. Combined with the Laguna Madre of Tamaulipas, it is the largest hypersaline system in the world. The shallow depth, clear water, and warm climate of this lagoon are conducive to seagrass production. Nearly 80% of all seagrass beds in Texas are now found in the Laguna Madre. The food web of the Laguna Madre is predominantly based on this submerged aquatic vegetation (seagrass and algae), rather than free-floating phytoplankton. Because of the hypersalinity, oysters are not commercially harvested to a large extent, although the region does contain the only strain of high-salinity adapted oysters in North America. The blue crab harvest is also smaller than the other two coastal regions to the north. Pink shrimp make up an important part of the commercial harvest while white shrimp are more abundant to the north in 34g. The historically highly productive commercial fisheries have now given way to an important sport fishery for species such as red drum, black drum, and spotted sea trout. Marshes are less extensive on the southern coast. A few stands of black mangrove tidal shrub occur in this region.[6]
The Lafayette Loess Plains had coastal prairie natural vegetation similar to the Northern Humid Gulf Coastal Prairies (34a), but are capped with a loess veneer associated with the Mississippi Valley. Well to poorly drained Alfisols and Mollisols with silt loam surface textures developed on the late Pleistocene-age terraces. The historical vegetation dominated by big bluestem, little bluestem, yellow Indiangrass, switchgrass, and other herbaceous species has been replaced by crops of rice, soybeans, cotton, sugarcane, sweet potatoes, and wheat, along with crawfish aquaculture. Urban expansion in the area has been substantial. There is more pasture compared to the large extent of small grains production in ecoregion 34a to the west. Narrow hardwood forests occur along some streams and lowlands.[7]
The Chihuahuan Desert is a desert ecoregion designation covering parts of northern Mexico and the southwestern United States. It occupies much of far West Texas, the middle to lower Rio Grande Valley and the lower Pecos Valley in New Mexico, and a portion of southeastern Arizona, as well as the central and northern portions of the Mexican Plateau. It is bordered on the west by the Sonoran Desert, the Colorado Plateau, and the extensive Sierra Madre Occidental range, along with northwestern lowlands of the Sierra Madre Oriental range. Its largest, continual expanse is located in Mexico, covering a large portion of the state of Chihuahua, along with portions of Coahuila, north-eastern Durango, the extreme northern part of Zacatecas, and small western portions of Nuevo León. With an area of about 501,896 km2 (193,783 sq mi), it is the largest hot desert in North America. The desert is fairly young, existing for only 8000 years.
The Piney Woods is a temperate coniferous forest terrestrial ecoregion in the Southern United States covering 54,400 square miles (141,000 km2) of East Texas, southern Arkansas, western Louisiana, and southeastern Oklahoma. These coniferous forests are dominated by several species of pine as well as hardwoods including hickory and oak. Historically the most dense part of this forest region was the Big Thicket though the lumber industry dramatically reduced the forest concentration in this area and throughout the Piney Woods during the 19th and 20th centuries. The World Wide Fund for Nature considers the Piney Woods to be one of the critically endangered ecoregions of the United States. The United States Environmental Protection Agency (EPA) defines most of this ecoregion as the South Central Plains.
South Texas is a region of the U.S. state of Texas that lies roughly south of San Antonio. The southern and western boundary is the Rio Grande, and to the east it is the Gulf of Mexico. The population of this region is about 4.96 million according to the 2017 census estimates. The southern portion of this region is often referred to as the Rio Grande Valley. The eastern portion along the Gulf of Mexico is also referred to as the Coastal Bend.
The Sierra Madre Oriental is a mountain range in northeastern Mexico. The Sierra Madre Oriental is part of the American Cordillera, a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America, and Antarctica.
The Gulf Coastal Plain extends around the Gulf of Mexico in the Southern United States and eastern Mexico.
Laguna Madre is a coastal lagoon in Northeastern Mexico. It extends along the coast of Tamaulipas for over 200 km, from the Río Bravo Delta on the north to the mouth of the Soto la Marina River near La Pesca in the south. Laguna Madre is separated from the Gulf of Mexico on the east by a number of barrier islands, including Barra Los Americanos, Barra Jesús María, and Barra Soto la Marina, and is bounded on the west by the Tamaulipan mainland. It is located in the municipalities of Matamoros, San Fernando, and Soto la Marina.
The geography of Texas is diverse and large. Occupying about 7% of the total water and land area of the U.S., it is the second largest state after Alaska, and is the southernmost part of the Great Plains, which end in the south against the folded Sierra Madre Oriental of Mexico. Texas is in the South Central United States of America, and is considered to form part of the U.S. South and also part of the U.S. Southwest.
The Atlantic Plain is one of eight distinct physiographic divisions of the contiguous United States. Using the USGS physiographic classification system, the Atlantic Plain division comprises two provinces and six sections. The Coastal Plain province is differentiated from the Continental Shelf province simply based on the portion of the land mass above and below sea level.
The Tamaulipan mezquital is a deserts and xeric shrublands ecoregion in the Southern United States and northeastern Mexico. It covers an area of 141,500 km2 (54,600 sq mi), encompassing a portion of the Gulf Coastal Plain in southern Texas, northern Tamaulipas, northeastern Coahuila, and part of Nuevo León.
South Bay is a bay in the Laguna Madre in Texas separated from the Gulf of Mexico by Brazos Island. It is the southernmost bay in Texas, about 1 mi (1.6 km) north of the Texas-Mexico Border.
The Great Texas Coastal Birding Trail is a state-designated system of trails, bird sanctuaries, and nature preserves along the entire length of the Texas Gulf Coast in the United States. As the state of Texas hosts more bird species than any other state in the U.S. the trail system offers some of the most unusual opportunities for bird-watching in the world. The "trail" is actually 43 separate hiking and driving trails that include 308 birding sites. The sites themselves feature a variety of viewing opportunities with boardwalks, observation decks, and other amenities. The trails boast more than 450 bird species. The trail system is managed by the Texas Parks and Wildlife Department as part of the Great Texas Wildlife Trails which also include the Heart of Texas Wildlife Trail, the Panhandle Plains Wildlife Trail, and the Prairies and Pineywoods Wildlife Trail.
The Laguna Madre is a long, shallow, hypersaline lagoon along the western coast of the Gulf of Mexico in Nueces, Kenedy, Kleberg, Willacy and Cameron Counties in Texas, United States. It is one of seven major estuaries along the Gulf Coast of Texas. The roughly 20-mile (32 km) long Saltillo Flats land bridge divides it into Upper and Lower lagoons joined by the Intracoastal Waterway, which has been dredged through the lagoon. Cumulatively, Laguna Madre is approximately 130 miles (210 km) long, the length of Padre Island in the US. The main extensions include Baffin Bay in Upper Laguna Madre, Red Fish Bay just below the Saltillo Flats, and South Bay near the Mexican border. As a natural ecological unit, the Laguna Madre of the United States is the northern half of the ecosystem as a whole, which extends into Tamaulipas, Mexico approximately 144 miles (232 km) south of the US border, to the vicinity of the Rio Soto La Marina and the town of La Pesca, extending approximately 275 miles (443 km) through USA and Mexico in total.
The East Central Texas forests or East Central Texas Plains (33) is a small temperate broadleaf and mixed forests ecoregion almost entirely within the state of Texas, United States. The northern forests perimeter is partially within the southeast Oklahoma border.
The Southeastern conifer forests are a temperate coniferous forest ecoregion of the southeastern United States. It is the largest conifer forest ecoregion east of the Mississippi River. It is also the southernmost instance of temperate coniferous forest within the Nearctic realm.
The Mississippi Alluvial Plain is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in seven U.S. states, though predominantly in Arkansas, Louisiana, and Mississippi. It parallels the Mississippi River from the Midwestern United States to the Gulf of Mexico.
Port Mansfield Channel or Mansfield Cut is an artificial waterway encompassing the Laguna Madre positioned at the 97th meridian west on the earth's longest barrier island known as Padre Island. During Post–World War II, the tidal inlet was dredged as a private channel differentiating North Padre Island better known as Padre Island National Seashore and South Padre Island. The navigable waterway was channeled during the late 1950s ceremoniously cresting the intertidal zone of the Gulf of Mexico by September 1957 on the Texas Gulf Coast.
The North American Southeastern Plains are a Level III ecoregion designated by the Environmental Protection Agency (EPA) in ten U.S. states. The region takes a U shape starting in western Tennessee, going south through eastern Mississippi, and forming most of Alabama. On the eastern side, the plains lie between the Appalachian Mountains and the coastal plains, forming central Georgia, South Carolina, and North Carolina. It forms part of eastern Virginia before terminating in Maryland.
The North American Mississippi Valley Loess Plains are a Level III ecoregion designated by the Environmental Protection Agency (EPA) in six U.S. states. The region lies primarily on the eastern border of the Mississippi Alluvial Plain, from the Ohio River in western Kentucky, through Tennessee and Mississippi, to Louisiana. A separate unit that includes Crowley's Ridge occurs west of the river in Arkansas and Missouri. It has been divided into four Level IV ecoregions.
The North American Southern Coastal Plain is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in six U.S. states. The region stretches across the Gulf coast from eastern Louisiana to Florida, forms the majority of Florida, and forms the coastlines of Georgia and much of South Carolina. It has been divided into twelve Level IV ecoregions.
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