The Tamaulipan mezquital (), also known as the Brush Country, is a deserts and xeric shrublands ecoregion in the Southern United States and northeastern Mexico. It covers an area of , encompassing a portion of the Gulf Coastal Plain in southern Texas, northern Tamaulipas, northeastern Coahuila, and part of Nuevo León.
Distribution The Sierra Madre Oriental range to the west separates the Tamaulipan mezquital from the drier Chihuahuan Desert. The Tamaulipan matorral is a transitional ecoregion between the mezquital and the Sierra Madre Oriental pine-oak forests to the west and the Veracruz moist forests to the south. The Western Gulf coastal grasslands, known as the Tamaulipan pastizal south of the border, fringe the Gulf of Mexico. The Edwards Plateau savannas lie to the north, and the East Central Texas forests and Texas blackland prairies to the northeast.
Geography
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.Fulbright, 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.
A series of Cenozoic strata 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).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.
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.Fuibright, Timothy E., David D. Diamond, John Rappoie, and Jim Norwine. 1990. Coastal Sand Plain of Southern Texas. Rangelands 12(6): 337-340.
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.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. 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.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. 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.
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. 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.Texas Water Development Board, TWDB Maps: Major Surface Water Features.Agustin 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.
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.
Gallery
Flora This semi-arid region is dominated by Mezquital (Spanish for a mesquite groveGooch, 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. ), 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. Thornscrub vegetation tends to grow taller in the east, benefited by coastal moisture where it can be impenetrable in places, and it is often shorter and may be more open in interior areas of the region, although soils also influence this throughout the region.Blair, 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. Mixtures of sand and clay make up much of the soils with pockets of near pure sand and near pure clay occurring locally.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. 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. 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.Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Savanna Grassland (Accessed: 18 August 2020). 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, granjeno or spiny hackberry (Celtis ehrenbergiana), tasajillo or desert Christmas cholla (Cylindropuntia leptocaulis), Texas persimmon (Diospyros texana), Texas prickly pear (Opuntia engelmannii var. lindheimeri), and blackbrush (Vachellia rigidula). Other common trees and shrubs more often found on clay soils include whitebrush (Aloysia gratissima), goatbush or amargosa (Castela erecta), brasil (Condalia hookeri), colima (Xanthoxylum fagara), Texas ebony (Ebenopsis ebano), anacua (Ehretia anacua), guayacan (Guaiacum angustifolium), Texas purple sage or cenizo (Leucophyllum frutescens), retama (Parkinsonia aculeata), guajillo or Berlandier acacia (Senegalia berlandieri), and huisache (Vachellia farnesiana var. farnesiana).Texas Parks and Wildlife (& Nature Serve Explorer), Ecological Mapping Systems of Texas: Tamaulipan Calcareous Thornscrub (Accessed: 18 August 2020).
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.