Examples of these communities in protected areas are likely insufficient to provide a refuge for associated

Chapter 12: West TexasWest Texas is the most diverse physiographic area of Texas, containingthe greatest relief (from just over 1,000 feet to 8,751-foot Guadalupe Peak) andthe most abrupt climatic gradients. Larger mountain ranges may receive morethan 20 inches of rain annually, while lowland sites less than 30 miles distantreceive less than 10 inches (Cottle 1931, Plumb 1988). Most of the regionreceives very little rainfall and potential evaporation greatly exceeds rainfallthroughout the year (MacMahon 1988). Westernmost Texas (El Paso andHudspeth counties) is most arid, with less than 8 inches of rainfall and -83 inchesannual evaporation (Correll and Johnston 1970). West Texas is sparsely132populated (80 percent of the region's 900,000 residents live in one city, El Paso)and only one human activity, ranching, has greatly altered the landscape.The term “Trans-Pecos” refers to the part of Texas west of the PecosRiver, an unsatisfactory entity for ecological analysis as it excludes floristicallysimilar semi-desert areas east of the Pecos. This thesis treats the Trans-Pecoswith adjacent Loving, Winkler, Ward, and Crane counties as a single ecologicalregion, with all parts receiving less than 15 inches of annual rainfall. Thus defined,the region also includes the Stockton Plateau, a limestone area geologicallycoterminous with the Edwards Plateau, but more arid (Bray 1905, Webster 1950).The vegetation of West Texas is varied and diverse, due to ...