Effect of Mesquite Trees on Vegetation and Soils in the Desert Grassland

Studies were conducted in the mesquite-desert grassland to assess effects of shade, roots, and litter of mesquite trees on understory vegetation and microenvironmental factors. Elimination of mesquite shade and root action increased foliar cover of understory vegetation in the canopy zone from 19% with intact mesquite to 24%. Replacement of mesquite shade with artificial shade screens further increased understory vegetative cover to 32%. Only forbs responded to elimination of mesquite roots in open areas. Vegetation responses indicated improved soil moisture in the canopy zone with both treatments, but there were no detectable soil moisture differences among treatments during the major part of the growing season. Greater vegetal cover with no-shade and artificial shade treatments was apparently associated with differential utilization of moisture compared with the mesquite shade treatment. Increased soil moisture made available by mesquite removal and in excess of that lost by evaporation was reflected in greater vegetative cover. With artificial shade, potential evaporation was similar to that for natural shade-thus increased moisture was utilized for growth of understory vegetation.