Tamaulipan mezquital
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.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, 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.
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 is dominant in all but the wettest areas. These grasslands are banded with live oak groves, forming dense forest in spots, and smaller honey mesquite 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.
Hydrology:
The region is generally semi-arid however, various wetlands are present. The Laguna Madre is one of only five hypersaline coastal lagoons in the world and a significant ecosystem in itself, laying between the Gulf of Mexico and the Tamaulipan mezquital ecoregion. 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, turtles, and millions of migrating waterfowl, such as redheads in the winter.
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 runs at the approximate northeastern border of this region. Other major rivers include: the Nueces River and its tributary the Frio River; Rio Grande and its tributaries Rio Salado, Rio San Juan; the Rio San Fernando ; 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.
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.
Flora
This semi-arid region is dominated by Mezquital, 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 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. Mixtures of sand and clay make up much of the soils with pockets of near pure sand and near pure clay occurring locally. 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, with pricklypear, and non-native grasses in the understory. 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, desert Christmas cholla, Texas persimmon, Texas prickly pear, and black brush. Other common trees and shrubs more often found on clay soils include white bush, goat bush, brasil, knackaway. Texas lignum-vitae, Texas purple sage, retama, Berlandier acacia, and huisache.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, little bluestem, sand dropseed, and many others. Wildflowers include bull-nettle, shrubby blue sage, hairy tubetongue, Texas palafoxia, and hairy zexmania. 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.
Woodlands occur in places with a well-developed canopy over an understory of grasses. The grasses in these communities contain a layer of taller species such as hooded windmill grass and four-flower trichloris, and a layer of shorter species such as grama and curly mesquite grass. In some places dense stands of Texas prickly pear occur instead of shrubs and grasses. Canopy species include many ubiquitous trees along with huisache, desert hackberry, brasil, Texas hogplum, colima, and others. Other shrubs include desert yaupon, desert olive, and lotebush.
Xeric rocky uplands with shallow calcareous soils on caliche and gravel substrates support shrublands one half to two meters high. Species such as cenizo, guajillo, Texas kidneywood, twisted acacia, Spanish dagger, and baretta and others grow with ubiquitous trees and shrubs. The creosote bush grows in western areas. The herbaceous layer may be sparse in places where rocky exposures occur. Forbs and wildflowers can be conspicuous in rocky areas, including narrowleaf thryallis, peonia, Gregg's senna, plateau rocktrumpet, and hairy zexmania.
Saline lakes and saline thornscrub occur in some interior, low-lying areas with interior draining basins, created by runoff and evaporation. Lakebeds may lack vegetation or have sparse halophytic grasses and forbs like alkali sacaton, sea ox-eye daisy, and saltwort. Surrounding saline thornscrub is semi-open with ubiquitous shrubs under 5 m., growing with species like saladillo, knifeleaf condalia, Johnston's seaheath, and screw bean mesquite among others. Soils may have a thin layer of gravel over clay with patchy grasses and cacti such as Fitch's hedgehog cactus and horse crippler. 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.
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, sugar hackberry, Texas ebony, anacua, Mexican ash, tepeguaje, and cedar elm. Riverbanks may have a reduced over-story with black mimosa, black willow, and giant reed an invasive species. Numerous species of vines and epiphytes like Spanish moss are frequently encountered as well as rarer Bailey's ballmoss. The herbaceous layer is often not well developed. In the Nueces River drainage and northward, pecan and plateau live oak 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, Texas torchwood, Barbados cherry, catclaw acacia, brushholly, and others. Monumental Montezuma cypresses 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. Only a few, small groves of Mexican sabal palm 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,
tropical sage, and blue boneset, or dead palm fronds may restrict the development of the ground layer.
Cacti: This region is rich in cacti diversity. In addition to wide-ranging species like lace cactus, and horse-crippler cactus, other species found in the province include: root cactus, triangle or barbed wire cactus, star cactus, Runyon's beehive cactus, Berlandier's hedgehog, pitaya, Allicoche hedgehog cactus, ladyfinger hedgehog, Dahlia cactus, Junior Tom Thumb cactus, Turk's head barrel cactus, peyote, Heyder's pincushion cactus, hair-covered cactus or Texas pincushion, pale mammillaria, twisted rib cactus and several others. Some of these species have very limited distributions and are endemic to the region such as Astrophytum caput-medusae from Nuevo Leon, Mexico.
Fauna
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 is extirpated and black bears are now largely restricted to the Sierra de Picachos in Nuevo Leon, Mexico. The most recent records of the jaguar in Texas, USA are from the early 1950s, but the species still lingers, although at risk of extinction in Mexico. Similarly, jaguarondi, ocelot, and margay are all threatened or endangered in the US and Mexico. Some puma or mountain lion, White-nosed coati, and American Badger 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, Coyote, and to a lesser extent Bobcats have adapted to human encroachment and development.Other mammals found in the region include the collared peccary, white-tailed deer, black-tailed jackrabbit, nine-banded armadillo, Mexican long-tongued bat, and the southern yellow bat. Rodents include the predatory northern grasshopper mouse, the Mexican prairie dog, Rio Grande ground squirrel and others such as Coue's rice rat, southern plains woodrat, Mexican spiny pocket mouse, and Merriam's pocket mouse.
Birds: The southern part of the ecoregion is an Endemic Bird Area and is home to the red-crowned amazon, tawny-collared nightjar, Tamaulipas crow, long-billed thrasher, Altamira yellowthroat, and crimson-collared grosbeak. Other species occurring in this region include the white-tailed hawk, plain chachalaca, green parakeet, buff-bellied hummingbird, Couch's kingbird, and Audubon's oriole as well as wide-ranging tropical species such as the green jay, least grebe, Ferruginous pygmy owl, ringed kingfisher, and the great kiskadee.
Reptiles: The American alligator and the red-eared slider occur in the north of this region and the Morelet's crocodile and Mesoamerican slider in the south. Other turtles such as the Mexican box turtle, Rio Grande cooter, spiny softshell, and the yellow mud turtle occur there. The geographic distribution of the Texas tortoise nearly matches that of the Tamaulipan mezquital ecoregion. The Laredo striped whiptail is a species complex of all female lizards that reproduce by parthenogenesis that is endemic to this region. The reticulate collared lizard is also endemic. Other representative lizards include the Texas banded gecko, four-lined skink, common spotted whiptail, keeled earless lizard, Texas horned lizard, blue spiny lizard, and the northern rose-belly lizard, regarded by some as a full species. Some representative snakes of the Tamaulipan mezquital include the Tamaulipan hook-nose snake, Mexican milksnake, and Schott's whipsnake. More wide-ranging species include the Great Plains ratsnake, gopher snake, long-nose snake, and eastern patch-nose snake. Some tropical species reaching the northern margin of their ranges including the regal black-striped snake, Central American indigo snake, speckled racer, northern cat-eyed Snake. Venoumous snakes include the Texas coralsnake and western diamond-back rattlesnake, with the western massasauga rattlesnake occurring in the north and the Totonacan rattlesnake occurring in the south.
Amphibians: In spite of the semi-arid environment, enough wetlands are present to support salamanders such as the black-spotted newt and the lesser siren. A second species of siren is known to occur in the lower Rio Grande, thought to be a distant and isolated population of the greater siren by some, or an undescribed species by others. The Rio Grande leopard frog and western narrow-mouthed toad occur in the region along with several toads inhabiting the thorn scrub and grasslands including the green toad, Texas toad, Gulf Coast toad, and cane toad. Many tropical species reach the northern limits of their distributions there such as the Mexican treefrog, white-lipped frog, sheep frog, and the unusual burrowing toad, so unique it is classified in a family by itself.
Fishes: Two species, the San Ignacio pupfish from the upper Rio San Fernando basin near Linares and the swordtail platyfish occurring in the upper parts of the Rio Soto La Maria, in Tamaulipas are endemic to this region. The Amazon molly, is a unisexual species that reproduces through gynogenesis, a form of a form of parthenogenesis. Other fishes found in the area are alligator gar, longnose gar, Rio Grande cichlid, sailfin molly, Rio Grande silvery minnow, San Juan minnow, Tamaulipas shiner, Rio Grande shinner, Gulf killifish, and Rio Grande darter. Two endemic species from this region, the phantom shinner and the Salado shinner, are believed to be extinct.
Protected areas
Nature preserves are numerous in the region, however many are relatively small tracts of land concentrated on the north side of the Lower Rio Grande Valley. The state of Texas administers the following lands in the Lower Rio Grande Valley: Lake Casa Blanca International State Park ; Falcon State Park ; Bentsen-Rio Grande Valley State Park ; Estero Llano Grande State Park ; Resaca de la Palma State Park ; and the Las Palomas Wildlife Management Area comprised 18 units with tracts ranging from two to 604 acres. The U. S. Federal Government also administers lands in the Lower Rio Grande Valley including the Santa Ana National Wildlife Refuge and western and higher elevation areas of the Laguna Atascosa National Wildlife Refuge on the Gulf Coast. The multi-unit Lower Rio Grande Valley National Wildlife Refuge has nearly 40,000 acres open to the public and an additional 6,000 acres open to hunting . Also of note is the Sabal Palm Sanctuary, cooperatively manage by the Gorgas Science Foundation and the National Audubon Society, preserving some of the finest old growth riparian zones and sabal palm groves remaining.Beyond the Lower Rio Grande Valley of Texas protected lands include the Chaparral Wildlife Management Area, Lake Corpus Christi State Park, and Choke Canyon State Park: including the Calliham unit, the South Shore unit, and the adjoining James E. Daughtrey Wildlife Management Area.
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, 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.