The Bordas Escarpment transects this ecoregion, running from near the southern limit northwest to the vicinity of Rio Grande City, Texas, arching back northeast to the vicinity of Choke Canyon Reservoir in Texas. The region east of the Bordas Escarpment is flat with deep, sandy soils, of which vast areas both north and south of the border have been converted to agricultural use. West of the Bordas Escarpment the topography changes to gently rolling hills with a thin layer of high calcium soil over a thick layer of caliche. Some large portions of the west are poorly suited for cultivation but good for ranching and excellent wildlife habitat.[3]
A series of Cenozoicstrata of limestone, sandstone, siltstone, and claystone occur throughout most of the region. These strata are slightly tilted, gently slanting seaward, with increasingly recent exposures to the east, including some Quaternary bodies at the coast transitioning into the sea, and a few older Cretaceous exposures and outcrops appearing in some far western interior areas. Elevations generally range from near sea level to 300 meters, transitioning at ca. 300–500 meters into the Sierra Madres, Edwards Plateau, and Chihuahua Desert in western areas. A series of small mountain ranges occur in the region, isolated on the coastal plain between the Sierra Madre Oriental and the Gulf of Mexico. These ranges are not part of the strata of the Gulf Coast Plain or the complexly folded and faulted Jurassic and Cretaceous formations of the Sierra Madre Oriental. The Sierra de San Carlos, (and Sierra de Tamaulipas just beyond the southern limit of this ecoregion) are plutons, igneous rock intrusions of nepheline syenite to gabbroic composition, emplaced during the Mid-Tertiary with a few minor sierras of alkaline basalt flows occurring locally (e.g. in the vicinity of Llera, Tamaulipas).[4]: 42–47 pp.
The Coastal Sand Plain, sometimes referred to as the "Wild Horse Desert", is a region of Quaternary sand deposits extending about 60 miles inland from the Laguna Madre. It is bordered by Baffin Bay to the north and the Lower Rio Grande Valley to the south. Quaternary to Tertiary marine sedimentary strata, which may be exposed in western areas, underlie the sand sheet. The sand sheet is six feet deep in many places with maximum dune elevations reaching 30 feet. Although the area is generally flat, the unstable sands often form a dune and swale topography where vegetated dunes are interspersed with active, unstable, wind-blow dunes. The active dunes attain areas as large as 250 acres, predominantly in the eastern third. Grasslands cover much of the sand plain where seacoast bluestem (Schizachyrium littorale) is dominant in all but the wettest areas. These grasslands are banded with live oak (Quercus virginiana) groves, forming dense forest in spots, and smaller honey mesquite (Prosopis glandulosa) mottes in discontinuous belts which are sometimes connected with one another and collectively cover at least a quarter of the sand sheet. Numerous ephemeral, internally drained ponds form where subsidence and blow-outs occur.[5]
Hydrology:
The region is generally semi-arid however, various wetlands are present. The Laguna Madre is one of only five hypersaline coastal lagoons (or negative estuaries) in the world and a significant ecosystem in itself, laying between the Gulf of Mexico and the Tamaulipan mezquital ecoregion.[6] As one moves inland from the hypersaline lagoon, a relatively narrow band of freshwater marshlands are encountered running north to south, albeit occurring fragmented and irregularly. These marshes are dynamic, fluctuating with rainfall and tropical storm activity, and alternating with wet and dry periods. When and where present, these marshlands can be locally, surprisingly extensive with deep marshes and both permanent and ephemeral freshwater ponds that support populations of salamanders (Siren intermedia), turtles (Trachemys), and millions of migrating waterfowl, such as redheads (Aythya americana) in the winter.[7][8]
Several rivers cross the region, all flowing eastward to the Gulf of Mexico. Many of these river have created innumerable oxbow lakes, resacas, and abandoned channels with associated marshes and swamps as they meander across the flat coastal plain east of the Bordas Escarpment. The few remaining riparian zones in this region that have not been cleared for agriculture, housing, and industry, can support unexpectedly lush tropical jungle vegetation, particularly in the south.[2] The San Antonio River (a major tributary of the Guadalupe River) runs at the approximate northeastern border of this region. Other major rivers (north to south) include: the Nueces River and its tributary the Frio River; Rio Grande (referred to as Rio Bravo in Mexico) and its tributaries Rio Salado, Rio San Juan; the Rio San Fernando (sometimes called the Rio Conchos and not to be confused with the major drainage Rio Conchos of Chihuahua); the Rio Soto La Marina and its tributaries Rio San Carlos, Rio Pilón, San Antonio, Rio Purificacion, Rio Corona, Rio Santa Ana, form the approximate southern border.[9][10]
A number of large lakes occur in the region, but they were all constructed in the decades fallowing the Second World War in the 20th century. These include: Choke Canyon Reservoir and Lake Corpus Christi in the Nueces River drainage in the USA; Amistad International Reservoir and Falcon International Reservoir on the Rio Grande; Presa Venustiano Carranza in Coahuila on the Rio Salado, Presa El Cuchillo in Nuevo Leon and Presa Marte R. Gómez in Tamaulipas on the Rio San Juan, and Presa Vicente Guerrero in Tamaulipas on the Rio Soto La Marina drainage in Mexico.[9][10]
Road in thornscrub vegetation, Yturria Brush National Wildlife Refuge, Hidalgo County, Texas (15 April 2016)
Rio Grande southeast of Falcon Reservoir, Municipality of Mier, Tamaulipas, Mexico (12 August 2007)
Thornscrub south of Reynosa, Municipality of Reynosa, Tamaulipas, Mexico (13 August 2007)
Sierra San Carlos, Municipality of San Carlos, Tamaulipas, Mexico (14 July 2007)
Sierra San Carlos, with a pine tree (Pinus teocote) on left, Municipality of San Carlos, Tamaulipas, Mexico (12 July 2007)
Thornscrub ranchland west of Tepehuajes, Municipio Soto La Marina, Tamaulipas, Mexico (20 May 2002)
Flora
This semi-arid region is dominated by Mezquital (Spanish for a mesquite grove[11]), thorny brush, and chaparral vegetation referred to as Tamaulipan thornscrub. In this subtropical environment some plant growth continues through most of the year, particularly in the south. Years with droughts or tropical storms and hurricanes can dramatically affect vegetation at any given locality, particularly the herbaceous ground layer, which may be sparse with patches of bare earth in a dry year, or thick and verdant in a wet year.[3] Thornscrub vegetation tends to grow taller and thicker in the east, benefited by coastal moisture where it can be impenetrable in places, and it is often shorter and more open in interior areas of the region, although soils also influence this throughout the region.[12][13] Mixtures of sand and clay make up much of the soils with pockets of near pure sand and near pure clay occurring locally.[14] Sandy soils in this region tend to support more open vegetation with widely spaced trees and shrubs in grasslands, while clay soils tend to support a greater diversity and denser, sometimes even canopied areas of trees and shrubs.[12] Past land usage can also have a significant influence, where recently cleared areas may have a near monoculture of honey mesquite (Prosopis glandulosa), with pricklypear (Opuntia engelmannii var. lindheimeri), and non-native grasses in the understory.[15] Some species of are nearly ubiquitous, occurring in most of the soils and vegetation communities, although varying in levels of dominance, some of these include honey mesquite, spiny hackberry (Celtis ehrenbergiana), desert Christmas cholla (Cylindropuntia leptocaulis), Texas persimmon (Diospyros texana), Texas prickly pear (Opuntia engelmannii var. lindheimeri), and black brush (Vachellia rigidula).[12][15] Other common trees and shrubs more often found on clay soils include white bush (Aloysia gratissima), goat bush (Castela erecta), brasil (Condalia hookeri), knackaway (Ehretia anacua). Texas lignum-vitae (Guaiacum angustifolium), Texas purple sage (Leucophyllum frutescens), retama (Parkinsonia aculeata), Berlandier acacia (Senegalia berlandieri), and huisache (Vachellia farnesiana var. farnesiana).[2][12][16]
Grasslands with sparsely scattered trees and shrubs occur on level to gently rolling sites with sandy soils. These are dominated by dense graminoids such as Texas grama (Bouteloua rigidiseta), little bluestem (Schizachyrium scoparium), sand dropseed (Sporobolus cryptandrus), and many others. Wildflowers include bull-nettle (Cnidoscolus texanus), shrubby blue sage (Salvia ballotiflora), hairy tubetongue (Justicia pilosella), Texas palafoxia (Palafoxia texana), and hairy zexmania (Wedelia texana). Shrub-dominated patches may develop within these grassy sites where tighter, clay soils occur, reaching six meters or higher, often dominated by several of the ubiquitous species noted above.[2][12][15]
Saline lakes and saline thornscrub occur in some interior, low-lying areas with interior draining basins, created by runoff and evaporation. Lakebeds (often dry) may lack vegetation or have sparse halophytic grasses and forbs like alkali sacaton (Sporobolus airoides), sea ox-eye daisy (Borrichia frutescens), and saltwort (Batis maritima). Surrounding saline thornscrub is semi-open with ubiquitous shrubs under 5 m., growing with species like saladillo (Varilla texana), knifeleaf condalia (Condalia spathulata), Johnston's seaheath (Frankenia johnstonii), and screw bean mesquite (Prosopis reptans) among others. Soils may have a thin layer of gravel over clay with patchy grasses and cacti such as Fitch's hedgehog cactus (Echinocereus reichenbachii var. fitchii) and horse crippler (Echinocactus texensis).[18][19][20] Internally drained basins with non-salin, or freshwater also occur on clay lined or clay loam soils that hinder drainage. Sometimes called potholes, lagunas, lagunitas, ponds, or copitas, these are ephemeral wetlands but may remain moist over extended periods of time.[21]
Riparian zones and floodplains can support luxuriant forest on the alluvial soils of the major rivers. These can sometimes have a dense canopy up to 15 meters high. Dominant canopy species may include many of the ubiquitous and common species noted above, as well as granjeno (Celtis ehrenbergiana), sugar hackberry (Celtis laevigata), Texas ebony (Ebenopsis ebano), anacua (Ehretia anacua), Mexican ash (Fraxinus berlandierana), tepeguaje (Leucaena pulverulenta), and cedar elm (Ulmus crassifolia). Riverbanks may have a reduced over-story with black mimosa (Mimosa asperata), black willow (Salix nigra), and giant reed (Arundo donax) an invasive species. Numerous species of vines and epiphytes like Spanish moss (Tillandsia usneoides) are frequently encountered as well as rarer Bailey's ballmoss (Tillandsia baileyi). The herbaceous layer is often not well developed. In the Nueces River drainage and northward, pecan (Carya illinoinensis) and plateau live oak (Quercus fusiformis) may be common. Diversity increases southward and the Rio Grande Delta has a denser understory with a sub-canopy layer at 4 to 5 meters including Sierra Madre torchwood (Amyris madrensis), Texas torchwood (Amyris texana), Barbados cherry (Malpighia glabra), catclaw acacia (Senegalia wrightii), brushholly (Xylosma flexuosa), and others. Monumental Montezuma cypresses (Taxodium mucronatum) once lined portions of the Rio Grande and other southern rivers, but few remain today. Parque Nacional El Sabinal in the town of Ciudad Cerraivo, Nuevo Leon preserves some fine examples of old Montezuma cypress in an urban environment.[22] Only a few, small groves of Mexican sabal palm (Sabal mexicana) remain on the Rio Grande Delta, but it is believed they once occurred as far as 120 km. inland. Palms may dominate the canopy or share dominance with other floodplain species reaching 15 meters. The herbaceous layer may include bunch cutgrass (Leersia monandra),
tropical sage (Salvia coccinea), and blue boneset (Tamaulipa azurea), or dead palm fronds may restrict the development of the ground layer.[2][23][24][25]
Mammals: This region once hosted an impressive number of carnivores but, most were very rare, or entirely extirpated by the early to mid 20th century. The gray wolf (Canis lupus) is extirpated and black bears (Ursus americanus) are now largely restricted to the Sierra de Picachos in Nuevo Leon, Mexico.[28] The most recent records of the jaguar (Panthera onca) in Texas, USA are from the early 1950s, but the species still lingers, although at risk of extinction in Mexico. Similarly, jaguarondi (Herpailurus yaguarondi), ocelot (Leopardus pardalis), and margay (Leopardus wiedii) are all threatened or endangered in the US and Mexico. Some puma or mountain lion (Puma concolor), White-nosed coati (Nasua narica), and American Badger (Taxidea taxus) populations still persist, apparently in stable numbers in some remote areas, although the latter is considered a threatened species in Mexico. A few other species such as the Northern Raccoon (Procyon lotor), Coyote (Canis latrans), and to a lesser extent Bobcats (Lynx rufus) have adapted to human encroachment and development.[29][30]
In Tamaulipas, Mexico protected areas include western portions of the Laguna Madre y Delta del Rio Bravo and Parras de la Fuente, Reserva de la Paloma de Ala Blanca (ca. 23.8888°N, 98.5000°W), and in Coahuila, Mexico the Parque Nacional Los Novillos. Many of the protected lands in Mexico are actually "paper parks" owned and administer by local ejidos and municipalities, with few resources devoted to their management, no accommodations, no facilities or trails for visitors, and little management or enforcement of wildlife regulations. Nonetheless, such parks do limit land usage and development, and thus provide a significant degree of protection for habitat and the flora and fauna within.[41][42][43]
^ abFulbright, Timothy E., and Fred C. Bryant (2004).The Last Great Habitat. A Special Publication of the Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville. Special Publication No. 1, 1-32 pp.
^Ferrusquía-Villafranca, Ismael. 1993. Geology of Mexico: A Synopsis, pages 3-107. In. T. P. Ramamoorthy, Robert Bye, Antonio Lot, and John Fa (Eds.). Biological Diversity of Mexico: Origins and Distribution. Oxford University Press, Inc. New York. ISBN0-19-506674-X
^Fuibright, Timothy E., David D. Diamond, John Rappoie, and Jim Norwine. 1990. Coastal Sand Plain of Southern Texas. Rangelands 12(6): 337-340.
^Tunnell, Jr. John W. and Frank W. Judd. editors. (2002). The Laguna Madre of Texas and Tamaulipas. Texas A&M University Press, College Station, Texas. xxi, 346 pp. ISBN1-58544-133-3
^Smith, Elizabeth H. (2002). Redheads and Other Wintering Waterfowl. 169-181 pp. In Tunnell, Jr. John W. and Frank W. Judd. (editors). The Laguna Madre of Texas and Tamaulipas. Texas A&M University Press, College Station, Texas. xxi, 346 pp. ISBN1-58544-133-3
^Farr, William L. (2015). Herpetofauna of Tamaulipas. 101-121 pp. In. Lemos Espinal, J. A. (Editor). Amphibians and Reptiles of the US-Border States. Texas A&M University Press. College Station, Texas. x, 614 pp. ISBN978-1-62349-306-6
^ abAgustin Palacios Roji Grcía and Joaquin Palacios Roji Grcía. (2007). Por Las Carreteras de México. Guia Roji, S.A. de C. V. México, D. F., Mexico. 151 pp. ISBN970-621-492-5
^Gooch, Anthony, and Angel García de Paredes. 1978. Cassell's Spanish-English Dictionary. Cassell Ltd. London and Macmillan Publishing Co. Inc. New York. xxv, 1109 pp. ISBN0-02-522910-9
^ abcdeBlair, W. Frank. (1950). The Biotic Provinces of Texas. Texas Journal of Science. 2(1): 93-117.
^Martin, Paul S., C. Richard Robins, and William B. Heed. 1954. Birds and Biogeography of the Sierra de Tamaulipas, an Isolated Pine-Oak Habitat.The Wilson Bulletin.Vol. 66, No. 1: 38-57.
^Richardson, Alfred and Ken King. 2011. Plants of Deep South Texas, A Field Guide to the Woody and Flowering Species. Texas A&M University Press. College Station, Texas. xii, 457 pp.
^ abcdTexas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Savanna Grassland (Accessed: 18 August 2020).
^ abcTexas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Calcareous Thornscrub (Accessed: 18 August 2020).
^Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Mixed Deciduous Thornscrub (Accessed: 18 August 2020).
^Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Saline Lake (Accessed: 18 August 2020).
^Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Saline Thornscrub (Accessed: 18 August 2020).
^Cram, Silke, Irene Sommer, Luis-Miguel Morales, Oralia Oropeza, Estela Carmona, and Francisco Gonzalez-Medrano. 2006. Suitability of the vegetation types in Mexico's Tamaulipas state for the siting of hazardous waste treatment plants. Journal of Environmental Management. 80 (2006): 13-24.
^Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Closed Depression Wetland (Accessed: 18 August 2020).
^Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Palm Grove Riparian Forest (Accessed: 18 August 2020).
^Loflin, Brian and Shirley Loflin. (2009). Texas Cacti. Texas A&M University Press, College Station. xv, 291. ISBN978-1-60344-108-7
^Hernández, Héctor M. and Carlos Gómez-Hinostrosa. 2011. Mapping the Cacti of Mexico, Their geographical distribution and based on referenced records. DH Books, Milborne Port, England with CONABIO, Succulent Plant Research, Vol. 7: 128 pp. ISBN978-0-9538134-8-3
^World Wildlife Fund, ed. (2001). "Tamaulipan mezquital". WildWorld Ecoregion Profile. National Geographic Society. Archived from the original on 2010-03-08. Retrieved 2010-11-25.
^ abSchmidly, D. J. (2004). The Mammals of Texas. [Sixth Edition]. University of Texas Press, Austin, Texas. xviii, 501 pp. ISBN0-292-70241-8
^ abCeballos, G. Ed. (2014). Mammals of Mexico. Johns Hopkins University Press. Baltimore, Maryland. xiii, 957 pp. ISBN1-4214-0843-0
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^Howell, S. N. G. and S. Webb. (1995). A Guide to the Birds of Mexico and Northern Cantral America. Oxford University Press. Oxford. xvi, 851 pp. ISBN0-19-854012-4
^Terres, J. K. (1996). The Audubon Society Encyclopedia of North American Birds. Wings Books, a division of Random House Value Publishing, Inc.. New York. N. Y. 1109 pp. ISBN0-517-03288-0
^ abLemos Espinal, J. A., Editor. (2015). Amphibians and Reptiles of the US-Mexico Border States. Texas A&M University Press. College Station, Texas. x, 614 pp. ISBN978-1-62349-306-6
^Werler, J. E. and J. R. Dixon. (2000). Texas Snakes, Identification, Distribution, and Natural History. University of Texas Press, Austin, Texas. xv, 437 pp. ISBN0-292-79130-5
^García de León, Francisco J., Delladira Gutiérrez Tirado, Dean A. Hendrickson, and Héctor Espinosa Pérez (2005). Fishes of the Continental Waters of Tamaulipas: Diversity and Conservation Status. In Jean-Luc E. Cartron, Gerardo Ceballos, and Richard S. Felger (eds.). Biodiversity, Ecosystems, and Conservation in Northern Mexico. Oxford University Press, Inc. New York, N. Y. xvi, 496 pp. ISBN0-19-515672-2
^Miller, R. R., W. L. Minckley, and S. M. Norris. (2005). Freshwater Fishes of Mexico. University of Chicago Press. Chicago, Illinois. xxv, 490 pp. ISBN0-226-52604-6
^Thomas, Chad, Timothy H. Bonner, & Bobby G. Whiteside. (2007). Freshwater Fishes of Texas: A Field Guide. Texas A&M University Press. College Station, Texas. xiv, 202 pp. ISBN978-1-58544-570-7