South Texas Brushlands
(Area - 8,515,100 ha)
Description - The South Texas Brushlands physiographic area,
entirely in southern Texas, is part of the Tamaulipan biotic province that extends into
Mexico at least as far as the Rio Soto la Marina in Tamaulipas and the Monterrey region of
eastern Nuevo Leon. These parts of Mexico should be added to the Partners in Flight
planning unit as soon as possible. The area is dominated by chaparral, or brushland
habitat, and fairly recent agricultural fields. However, the region also includes fairly
extensive grasslands, oak forests, and some tall riparian forests. In the brushlands, much
of the area was originally covered by mesquite-acacia savanna, and areas of semi-open
thorn scrub generally less than 3 meters tall alternating with grassy areas. The relative
coverage of grassy areas is questionable, and may have varied during wet-dry cycles.
Forested areas included live oak mottes and taller riparian zone forests along the Rio
Grande, Nueces and other rivers. Cenizo, or purple sage, covered some of the area as well,
mainly on caliche capped ridges along the Rio Grande and Bordas escarpment. Coastal
acreage, relatively small in this physiographic area, were once dominated by a complex of
coastal marsh, upland grasslands, and floodplain forest.
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Conservation recommendations and needs - Currently, the South Texas brushlands is a mosaic of fairly natural habitats, with extensive agricultural fields, root-plowed pastures, with scattered farm and ranch houses and cities of less than 100,000 people. The most densely populated sections are San Antonio and the Lower Rio Grande Valley, which has an extensive amount of irrigated farmland. However, the biggest factors have been direct loss of habitat because of land clearing, and degradation of existing habitats, often because of overgrazing or changes in hydrology. Human population growth and economic forces favoring increased agricultural efficiency appear to be the main issues affecting birds and their habitats in the South Texas brushlands physiographic area. In general, birds that have probably declined most severely in the 20th Century are those that inhabit riparian forests, tall thorn-forest, and native grasslands. Subtle changes such as introduced plant species that may have affected bird populations have largely been unstudied.
Throughout the South Texas brushlands, little quantitative bird and habitat information exists, and as a result, no specific acreage figures can be recommended to conserve or restore. However, the following guidelines have been developed for the area. All existing riparian forest, both open canopy and closed canopy, should be maintained and additional areas restored between existing large tracts. Continued implementation and expansion of the Lower Rio Grande Valley Wildlife Corridor (US Fish and Wildlife Service and others) offers the best opportunity to protect and restore quality riparian habitats. In thorn-forest, all existing mature thorn-forest should be protected because of its scarcity and the dependence upon it by birds such as the Elf Owl. Priority restoration of thorn-forest is suggested for old fields adjacent to existing riparian forest to provide additional foraging habitat for Gray Hawk, Hook-billed Kite, Northern Beardless-Tyrannulet, and Altamira Oriole. Sabal palm forest acreage should be maintained and increased as opportunity arises. Maintenance and enhancement of adequate water supplies to resacas is crucial to maintain adjacent wetlands and sabal palm forests.
The three types of upland thorn-scrub should be preserved as much as possible. Ramaderos have more potential to be preserved in large tracts, and those actions could provide benefits to Audubon’s Oriole and Varied Bunting. Barretal is so fragmented and limited in size that all remaining habitat should probably be conserved. Upland thorn-scrub forest as a whole probably needs little conservation emphasis at this point, especially since several other habitats are under much greater threat.
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