Sound interpretations of historical records and long-range projections based on contemporary observation and experiment in any ecosystem must consider the problem of weather and climate. In this regard, it is likely that the natural system, having evolved in the face of climatic fluctuation and change, will be capable of maintaining its integrity and production potential during and after the next episode of unfavorable climate. How the simplified system that humans are rapidly introducing to the region will respond should be a major concern.

Any long-term consideration of land use schemes in the Rio Grande Plain must take into account the certainty of major drought. As a boy, I had the opportunity to observe firsthand the severe drought of the 1950s (1951-1956) in Dimmit County. A cow with lips and tongue carpeted with prickly pear spines is an impressive and pathetic sight, but no more pathetic than the land itself. Then, at least, there were woody vegetation and cacti to offer some buffer against the combination of drought and overgrazing. The last stocks of perennial bunch grasses were to be found protected in clumps of spiny shrubs, and burning thorns off of Opuntia ("burning pear") has saved the breeding stock of more than one ranch in South Texas.

Since the 1950s drought there has been a rapid increase in the rate and efficiency of woody plant removal from the Rio Grande Plain. Although profitable in the short run, it remains to be seen how a shrub-bare South Texas will survive a major drought of 5 or even 10 years duration. Note that such droughts would be minor compared to prehistoric droughts known to last as long as 200 years in the central United States (Schneider, 1976). We must also consider the possibility that shrub removal itself may have an impact on the climate, as has been suggested for the Sahelian drought (reviewed by Schneider, 1976, pp. 141-145). Ironically, shrubs are being replanted in North Africa to counter desertification, while at the same time they are being rapidly removed from a similar ecosystem in South Texas.