Location and General Description
The Western Gulf Coastal Grasslands ecoregion follows the coast of the Gulf of Mexico encompassing the wetlands of Louisiana and Texas, in the United States, west of the Mississippi Delta then south into Mexico to just past the Laguna Madre. Grasslands of the northern part of Tamaulipas State, in Mexico have developed on a portion of sandy plains that gently slope to the waters of the Laguna Madre, a sound off the Gulf Coast, which forms the most important hydrographic feature of the ecoregion.
The delta of the lagoon consists of an interlaced network of 'resacas'; each bordered by a loamy ridge or natural levee. In the past, the levees were covered by mesquite brush. Clay dunes near the coast were also covered with brush on their leeward sides, while the windward sides held a thick growth of zacatón grass (Sporolobus wrightii). Most of this Tamaulipas ecoregion was covered with mesquite brush, with some areas of prairie in the Loreto sand plain area (Johnston 1963). The soil is a reddish sandy loam that varies in depth from 1 foot to a fraction of an inch. It contains calcareous matter; the sandy soil grades down to a thick arenaceous "caliche" which is a layer of sand cemented into a limestone by interstitial deposition of calcium carbonate. The climate is semiarid with precipitation levels of less than 300mm/year (Rzedowski 1988).
The tall vegetation in this ecoregion (> 1 m) grows at sea level on top of reddish soils; Tridens texanus, Trichachne hitchcockii, Aristida roemeriana, Tridens muticus and Bouteloua radicosa are some of the most common species. Diamond (1993) described the little bluestem - brownseed paspalum (Schizachyrium scoparium - Paspalum plicatulum) series, the most representative classification on upland sites, as globally imperiled with only six to twenty occurrences recorded. Climax grasses include tall bunch grasses such as seacoast bluestem (Andropogon scoparuium var. littoralis), eastern gamagrass (Tripsacum dactyloides), gulf muhly (Mulenbergia capiallris var. filipes), and several species of panicum. Towards the Gulf Coast, the topography shifts to lower elevations and more saline soils. Concomitantly, the prairie becomes more intermixed with gulf cordgrass (Spartina spartinae), sedges (Carex spp., Cyperus spp.), rush (Junicus spp.), bulrush (Scirpus spp.), and saltgrass (Distichlis spicata). Occasional shrublands consisting of mesquite (Prosposis glandulosa), huisache (Acacia farnesiana), lime prickly ash (Zanthoxylum fagara), and Texas persimmon (Diospyros texana) may be found in the lower one third of the Texas coast and into Tamaulipas (Gould 1962, Johnston 1963). The vegetation in the southern edge of the Laguna Madre consists of scrubs of Prosopis, Acacia, Cordia, Neopringlea, Capparis, as well as perennial grasses and other herbaceous plants.
The tallgrass coastal prairie region of Texas is generally thought of as a continuum of the north-south range of tall grass communities in Texas (Diamond and Smeins 1984). In contrast, the coastal sand plain of Texas is distinct enough that it cannot be considered and extension of the true prairie continuum (Diamond and Fullbright 1990). In general, grasslands eventually meld into freshwater and intertidal marsh habitat at the interface with Gulf bays and estuaries.
About 700 species of vertebrates have been found in this ecoregion; approximately 145 of these require immediate protection, and some 86 are endangered or threatened (Jahrsdoerfer & Leslie 1988). There are 342 birds (3 near-endemics) and 86 mammals (2 endemics) recorded. Near-endemic birds include the green-cheeked amazon (Amazona viridigenalis), and the Tamaulipas crow (Corvus imparatus) (Stattersfield et al. 1998, Howell and Webb 1995). The Altimira yellowthroat (Geothlypis flavovelata) may be restricted to this ecoregion, but this is not confirmed (Stattersfield et al. 1998).
The nesting beach of the Kemp’s Ridley sea turtle (Lepidochelys kempii), the most endangered sea turtle, was unknown until its discovery about half a century ago at Rancho Nuevo in Tamaulipas where virtually the entire population nests. In 1942 there were 42,000 turtle nests, but fewer than 1,500 turtles were nesting by the mid 1990s (Márquez-M 1994).
Others characteristic and distinctive species include: Ocelot (Leopardus pardalis), jaguarundi (Herpailurus yaguarondi), lesser yellow bat (Scotophilus borbonicus), Mexican spiny pocket mouse (Liomys irroratus), Río Grande chirping frog (Syrrhophus cystignathoides), white-lipped frog (Leptodactylus fragilis), red-billed pigeon (Columba flavirostris), brown jay (Cyanocorax morio), Audubon’s oriole (Icterus graduacauda), white-tipped dove(Leptotila verrequxi), and white-collared seedeater (Sporophila morelleti).
Less than one percent of these grasslands remains in near pristine condition (Smeins et al. 1991). Conversion to agricultural production has caused the greatest loss. In addition, overgrazing, conversion to tame grasses, fragmentation, and woody encroachment have affected the area.
The National Wildlife Refuge System possesses several important sites within the US potion of this ecoregion, although the main emphasis of their acquisition was development of refuges specifically for waterfowl. Tallgrass prairie on these refuges were generally not considered key to acquisition priorities with few exceptions (e.g. Attwater’s Prairie Chicken National Wildlife Refuge). The refuges include: Delta National Wildlife Refuge, Lacassine National Wildlife Refuge, Cameron Prairie National Wildlife Refuge, Rockefeller National Wildlife Refuge, Sabine National Wildlife Refuge, Texas Point National Wildlife Refuge, McFaddin National Wildlife Refuge, Anahuac National Wildlife Refuge, Moody National Wildlife Refuge, Attwater’s Prairie Chicken National Wildlife Refuge, Brazoria National Wildlife Refuge, San Bernard National Wildlife Refuge, Big Boggy National Wildlife Refuge, Whitmire Division of Aransas National Wildlife Refuge, Aransas National Wildlife Refuge, Matagorda Island National Wildlife Refuge, Laguna Atascosa National Wildlife Refuge, Santa Ana National Wildlife Refuge, Padre Island National Seashore (National Park Service), and other significant areas owned or managed by state or NGOs.
Types and Severity of Threats
Fragmentation of remaining habitat via subdividing large tracts into more marketable "ranchettes" leads to other degrading factors such as overgrazing, exotic plant expansion, lack of fire as a natural or prescribed process, and modification of local hydrological features by means of land leveling. Urbanization around larger metropolitan areas such as Houston, Texas has been another direct cause of habitat loss. This will proceed with the continued proliferation of suburban development.
Coastal wetlands are less suited, in most cases, for high-density development and agricultural conversion. However, channelization projects with all the associated damage to overland sheet flow and hydrological function, continue to impact this portion of the grasslands. Subsidence, erosion, and loss of emergent wetlands are serious problems that will continue.
Justification of Ecoregion Delineation
Delineation’s for these grasslands follow Gould et al. (1960) classification of Gulf Coast Prairies and Marshes region for Texas, Bailey (1994) and The Nature Conservancy (1997). In Mexico, our linework follows INEGI (1996) classifications of "halophitic vegetation" and is bound by "matorral" and "agriculture". Linework was reviewed by experts during ecoregional priority setting workshops (CONABIO 1996 and 1997) in Mexico.
Bailey, R.G. 1994. Ecological classification for the United States. Washington, DC: USDA Forest Service.
CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.
CONABIO Workshop, Mexico, D.F., November 1997. Ecological and Biogeographical Regionalization of Mexico.
Diamond, D. D. 1993. Plant communities of Texas. Texas Natural Heritage Program, Texas Parks and Wildlife Department, Austin.
Diamond, D. D., and T. E. Fullbright. 1990. Contemporary plant communities of upland grasslands of the Coastal Plain. Southwestern Nature 35: 385-392.
Diamond, D. D., and F. E. Smeins. 1984. Remnant grassland vegetation and ecological affinities of the upper coastal prairie of Texas. Southwestern Nature 29:321-334.
Gould, F. W. 1962. Texas plants: A checklist and ecological summary. Texas Agriculture Experimental Station Leaflet 492. Texas A&M University, College Station.
Gould, F. W., G.O. Hoffman, and C.A. Rechenthin. 1960. Vegetational areas of Texas. Texas Agriculture Experimental Station Leaflet 492. College Station: Texas A&M University.
Howell, S.N.G. and S. Webb. 1995. A Guide to the Birds of Mexico and Northern Central America. Oxford Univ. Press, England.
INEGI Map (1996) Comision Nacional Para el Conocimiento y Uso de la Biodiversidad (CONABIO) habitat and land use classification database derived from ground truthed remote sensing data Insitituto Nacional de Estastica, Geografia, e Informática (INEGI). Map at a scale of 1:1,000,000.
Jahrsdoerfer, S.E. and D.M. Leslie. 1988. Tamaulipan Brushland of the Lower Rio Grande Valley of South Texas. Description, human impacts and management options U.S. Fish & Wildlife Service, Washington, D.C.
Johnston, M.C. 1963. Past and present grasslands of Southern Texas and Northeastern Mexico. Ecology 44: 456-466.
Knopf, F. L. 1994. Avian assemblages on altered grasslands. Studies in Avian Biology 15: 247-257.
Márquez-M., R. 1994. Synopsis of biological data on the Kemp´s ridley turtle , Lepidochelys kempi (Garman, 1880). NOAA Technical Memorandum, NMFS-SEFSC-343.
The Nature Conservancy. 1997. Designing a geography of hope: Guidelines for ecoregion-based conservation in The Nature Conservancy. Arlington, VA.
Rzedowsky, J. 1988. La Vegetación de México. Editorial Limusa, México.
Smeins, F. E., D. D. Diamond, and C. W. Hanselka. 1991. Coastal prairie. Pages 269-290 in R. T. Coupland (editor), Ecosystems of the world: Natural grasslands---introduction and western hemisphere. Elsevier, New York:
Stattersfield, A.J., M.J. Crosby, A.J. Long and D.C. Wege. 1998. Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. Birdlife Conservation Series No. 7, Cambridge, UK.
Prepared by: J. Bergan, Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: In process