illustrates the decline in the stocking rate on the Texas Agriculture Experiment Station at Sonora since
the site was obtained by the State in 1916. Throughout this period, managers of the ranch considered it to be
moderately stocked. Productivity has demonstrably declined to the point that it would now by physically
impossible to keep the same number of livestock alive (much less in productive condition) on the same
rangeland that once supported higher stocking rates for decades. Two factors have probably contributed to this
condition. One is an increase of low palatability woody shrubs which have a high water use potential (e.g.,
Juniperus pinchotti Sudw.) (Smeins et al. 1997). And another is erosion of the shallow (25 cm) silty-clay
(overlying a fractured limestock substrate) which has reduced the site's water-holding capacity. Indeed, it is a
common assertion in the region that frequency of drought is increasing and carrying capacity is decreasing,
even though no statistical difference in the monthly or annual precipitation or temperature has occurred. The
degree to which the decrease in stocking rate and perception of drought are attributable to reduced soil
moisture storage capability is complicated by the fact that erosion and infiltration are related to composition
shifts in vegetation cover which may be less palatable to livestock and/or increase the rate of
evapotranspiration loss from the site (Thurow et all 1986, Thurow and Hester 1997).