Effects of Drouth on Mesquite

Abstract

Comments from old time ranchers and historical documentation (Inglis, 1961) indicate a substantial increase of thorny type brush including mesquite (Prosopis glandulosa Torr.) in south and southwest Texas during the past hundred years. A fairly common expression among the older ranchers is, “We used to dig for firewood,” referring to the digging of mesquite roots in the then treeless grasslands. Likewise, “In those days we could see a cow for miles,” is often volunteered in commenting on the dense stands of mesquite now occupying the same land. The spread of mesquite has been attributed to many causes, with over-grazing, trailing, and associated soil and cover disturbances as the principal mechanisms. The effects of fire in both suppressing and opening the way to invasion of mesquite are also cited (Parker, 1952). A few authors refer to drouth, particularly in its adverse effects on grass competition (Young, 1948), as a major climatic hazard favoring spread of mesquite. There is little in the literature on the direct effects of drouth in eliminating or reducing invaded or residual stands of mesquite in south Texas. Droufh Kills Mature Mesquite During the period 1950 to 1963, observations were made of the effects of drouth on mesquite in an eleven county area of the westernmost South Texas Plains comprising 7,500,OOO acres of mesquite infested rangelands. The period of observation coincided with the most severe drouth on record from 1950 through 1956 (Waldrip, 1957). Rainfall durFIGURE 1. Overstory of drouth killed mes-