Production of grasses and forbs was measured for 4 years beginning in 1976 and following aerial application of 2,4,5-T to 3,634 ha of mesquite (Prosopis glandulosa Torr.) dunelands on the Jornada Experimental Range in south-central New Mexico. Plant production was also measured on a 3,318-ha control area. The mesquite dunelands arc representative of large areas in the southwestern USA where mesquite has invaded former desert grasslands. Objectives of the study were to determine forage increases attributable to reduced mesquite competition and to evaluate the relationships between production and precipitation. Both sprayed and control areas were grazed by cattle. Temporary exclosures were used to exclude cattle from three sampling sites on the sprayed and control areas each year. The sampling sites were all on sandy ranges with relatively deep soils (>50 cm to caliche layer). A dune-centered sampling system permitted the determination of differences in production on dune and interdune areas. The mesquite dunes, occupying 28% of the land surface, produced more annual forbs and fewer perennial grasses than the interdune areas. Stem kill of mesquite averaged 56% at sampling sites on the sprayed area. End-of-season harvests were used to compare treatments.