A photograph taken by NASA of the Edwards Plateau and Balcones Escarpment
|Biome||Temperate grasslands, savannas, and shrublands|
The Edwards Plateau is a geographic region at the crossroads of Central, South and West Texas. It is bounded by the Balcones Fault to the south and east, the Llano Uplift and the Llano Estacado to the north, and the Pecos River and Chihuahuan Desert to the west.San Angelo, Austin, San Antonio and Del Rio roughly outline the area. The southeast portion of the plateau is known as the Texas Hill Country.
The bedrock consists primarily of limestone, with elevations ranging between 100 and 3000 ft. Caves are numerous.
The landscape of the plateau is mostly savanna scattered with trees. It mostly lacks deep soil suitable for farming, though the soil is fertile mollisols and some cotton, grain sorghum, and oats are grown. For the most part, though, the thin soil and rough terrain areas are primarily grazing regions, with cattle, sheep, and Angora goats predominant. Several rivers cross the region, which generally flow to the south and east through the Texas Hill Country toward the Gulf of Mexico; springs occur (in wet years), but permanent surface water supplies are sparse throughout the area, except for man-made reservoirs. The area is well drained; rainwater flows into the Edwards Aquifer recharge zone at the south of the plateau to feed rivers to the south. Rainfall varies from 15 to 33 inches per year, on average, from northwest to southeast, and the area has a moderate temperature and a reasonably long growing season.
Trees of the savanna include juniper and oak species scattered over grasses, a vegetation type historically shaped by droughts and regular fires. Some pecan trees are found near the springs and rivers. The Balcones Fault is associated with the Edwards Plateau formation. This fault line is an ecological demarcation for the range definition of a number of species.
Caves of the Edwards Plateau are important habitats for a great deal of wildlife. The area is home to some of the largest colonies of bats in the world, including millions of Mexican free-tailed bats. The largest colony of these inhabits Bracken Cave near San Antonio, while the Congress Avenue Bridge in Austin is the summer home for over half a million (they winter in Mexico) and is the largest bat colony anywhere in an urban area. The Edwards Plateau is home to at least 14 endemic freshwater fishes, including two subterranean species of catfish and 13 fish species considered to be spring-associated. Mechanisms for spring association of fishes is not fully understood, but thought to mediated by water temperature. The large numbers of reptiles and birds also include breeding populations of the Texan endemic golden-cheeked warbler (Dendroica chrysoparia).
Nearly all the natural habitat of the plateau has been converted to ranchland, farmland, or urban areas, such as Austin and San Antonio, with only about 2% remaining in scattered fragments, especially to the east of the plateau. Further alteration to the savanna has incurred though the encroachment of shrubs now that grassland fires are carefully controlled. Small areas of intact habitat remain, particularly around Austin, where areas are protected, such as the Balcones Canyonlands National Wildlife Refuge. Another important area for wildlife is Fort Hood military base.
Earliest human settlement of this area was by Native Americans. First it was used and wandered about by Jumano and Coahuiltecan groups, then the Apacheria extended into the Southern Plains by the forerunners of the Lipan and Mescalero Apaches. After the expulsion of the Apachean groups from the Plains by the Comanche, this area was dominated by the Penateka band of the Southern Comanche.