Mesquite encroachment impact on southern New Mexico rangelands: remote sensing and geographic information systems approach

Honey mesquite (Prosopis glandulosa Torr.) invasion can negatively impact grazing capacity, spatial livestock distribution, and forage production in Chihuahuan Desert rangelands. High spatial resolution remote sensing data can be used to develop maps of shrub encroachment for arid rangelands. The objective of this study was to map changes in honey mesquite abundance and to evaluate honey mesquite impacts on perennial grass production at the Chihuahuan Desert Rangeland Research Center in south-central New Mexico using high resolution satellite imagery. The project employed QuickBird ortho-ready satellite imagery with spatial resolution of 2.4 m in multispectral bands and panchromatic resolution of 0.6 m for the study area on May 19, 2009. We used a maximum likelihood supervised classification algorithm to distinguish honey mesquite from other land cover categories. We then measured grass production (kg/ha) in May, 2009 on 10 permanent, evenly spaced key areas in each pasture. We identified 12×60 m plots from the classified map and used these to calculate honey mesquite canopy cover on the 40 transects across the study area. Areas classified as dominated by honey mesquite estimated from image analyses encompassed 143, 50, 92, and 136 hectares in pastures 1, 4, 14, and 15, respectively. Regression analyses showed that increasing levels of honey mesquite canopy cover corresponded to lower perennial grass forage production (r2 = 0.73, n = 40). Our findings indicate that classification of high-resolution satellite imagery is a very useful tool for mapping invasive shrubs and determining their influence on forage production in desert landscapes.