Honey mesquite influences on Chihuahuan desert vegetation

Research has been lacking on the influence of honey mesquite (Prosopis glandulosa Torr.) on forage production in the Chihuahuan desert, In 1964 honey mesquite was controlled (65% kill) with the herbicide, Monuron, on portions of the New Mexico State University College Ranch. Both herbicide treated and nontreated areas occur within the same pasture on similar soils and have similar grazing histories (continuous grazing, conservative stocking rate), This has resulted in areas with moderate and low levels of mesquite (16% and 9% mesquite canopy cover, respectively), We evaluated relationships among forage standing crop, vegetation canopy cover, mesquite density, mesquite height, mesquite diameter, and mesquite volume on areas with low and moderate mesquite levels in fall 1992 and spring 1993, Regression analyses showed forage standing crop and canopy cover generally were not (P > 0.10) associated with mesquite height, mesquite diameter, canopy volume, and mesquite density on either low or moderate mesquite areas, Honey mesquite canopy cover on the non-treated area was nearly double that on the treated area, Data from long term permanent transects (1968-1992) showed no differences (P > 0.10) in total forage production between low and moderate mesquite areas in fall of 1992. On these transects mesquite increases in cover and density were over 3 times greater on the low compared to moderate mesquite areas in the 1982 to 1992 period, Our data indicate mesquite density and cover increase rapidly after herbicidal mesquite control even under conservative stocking, However at canopy cover levels below 17% honey mesquite appeared to have little effect on forage production, Potential maximum canopy cover of mesquite on these types of sites is about 37%, Our data show that under proper stocking both mesquite and perennial forages grasses can increase concurrently on desert grassland ranges, We recognize that the outcome of our study may have been modified with higher mesquite densities, different soil characteristics or a lack of desirable understory species.