Effect of honey mesquite (Prosopis glandulosa Torr) cover and soil depth on forage production in the Chihuahuan Deser

Honey mesquite (Prosopis glandulosa Torr) invasion of Chihuahuan Desert grasslands is an important concern for both ranchers and range managers. In the last 100 years, extensive areas of the Chihuahuan Desert have been invaded by mesquite. In New Mexico, Arizona and Texas, it is estimated that more than twenty million hectares are covered by this species. Since mesquite has low forage value for livestock, its control may be required to improve forage production on degraded rangelands. There are several factors involved in the proliferation of mesquite, among the most important are severe drought periods and the presence of deep sandy soils. To develop range management plans it is necessary to have ecological information about the factors that contribute to the proliferation of this species on desert rangelands, and the influence of mesquite on forage production. Thus, the objectives of this study were (1) To determine the possible relationships between forage production and three levels of mesquite (based on canopy cover), (2) To determine if soil depth (shallow 41 cm) and previous methods of shrub control (low and high levels) have influenced mesquite cover in the study area, and (3) To determine how climatic fluctuations influenced mesquite cover and forage production, and the direction and trend during the study period.;The results indicate that there was a main effect of soil depth on black grama production, with shallow soils being more productive than deep soils. Similarly, mesquite canopy cover was much higher in deep soils across the study area. The magnitude of mesquite canopy cover increase appeared to be more a function of soil depth, than past mesquite control with herbicides.;Data pooled across years showed that increases of total grasses and total standing crop production was primarily a function of the interaction soil depth with year. Generally forage production was most increased in wet years and least increased in dry years in shallow soils compared to deep soils. Moreover, soil depth had more influence on forage production than mesquite canopy cover at least at levels below 17%.;Total standing crop and snakeweed were higher on low than high mesquite kill areas in 1997. These data and that from previous studies on the Chihuahuan Desert Rangeland Research Center indicate that plant responses to long term (10 or more years) mesquite control are somewhat erratic and site dependent.