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On the Jornada Experimental Range in southern New Mexico, 2 belt transects, 30.5 cm in width and totnling 2,188 m in length, were established in 1935 on 2 areas where honey mesquite (Prosopis ghzndulosa Torr.) was spreading into black grama [Boutelouu eriopoda (Torr.) Torr.] grassland. Maps were made of the transects which portrayed the vegetation occurring in each of the 7,180 contiguous, O.OPm2 plots along the transect. The vegetation on the transects in 1980 was compared to that portrayed by the transect maps made in 1935. One transect had been read in 1950 and 1955. During the 45-year period mesquite attained complete dominance and many new mesquite dunes formed. Black grama had a relatively high frequency in 1935 but bad completely disappeared by 1980, both on an area grazed by livestock and on an area protected from grazing. Mesa dropseed [Sporobolus fZexuosus (Thurb.) Rydb.], fluffgrass [Erloneuronpu&hellum (H.B.K.) Tateokalbnd broom snakeweed [Xmthocephuhm sarottVae (Pursh) Shinners] increased in abundance, even during the drought period between 1950 and 1955. Only 25% of the perennial forb species encountered in 1935-55 were found in 1980. The spread of honey mesquite (Prosopis glandulosa Torr.) and other shrubs in the Southwest has been well documented, with heavy grazing, seed dispersal by domestic animals and periodic droughts being advanced as causes contributing to the increase in shrubs (Buffington and Herbel 1965; York and Dick-Peddie 1969). Mesquite has many features which enable it to exploit altered ecosystems. These include rapidly developing, deep taproots and long lateral roots, long-lived seeds, high germination rates over a wide range of temperature and moisture conditions, ability to withstand high negative water potentials, high water use efficiency, and the ability to regenerate from underground dormant buds following injury (Glendening and Paulsen 1955, Mooney et al. 1977). Mesquite has increased in abundance on a wide range of soil types but in southern New Mexico its greatest increase has been on sandy soils (Buffington and Herbel 1965). In arid areas mesquite typically grows as a low multi-stemmed shrub. These multistemmed plants entrap drifting sand, forming what has been called “coppice dunes” (Melton 1940). Vast areas of former desert grassland have been transformed into hummocky landscapes dominated by mesquite dunes. Dunes large enough to class as pedons have developed soils which are distinct from those of the interdunal areas (Giles 1966). Mesquite dunelands have an appearance of stability but considerable soil movement was found over a 45-year period (Gibbens et al. 1983). The transformation of desert grasslands into dynamic dunelands has resulted in the complete loss of Authors are respectively,. former graduate student, Department of Animal and Range Science, New Mexico State Univ., Las Cruces 88003, now Range Science Officer, Gaburone, Botswanna. Africa; range scientist and hydrologist. USDA, Agricultural Research Service, Las Cruces, N. Mex. 88004; and associate professor, Department of Experimental Statistics, New Mexico State Univ., Las Cruces. This report is published as journal article 905. AgriCUhd Experiment StatiOn, New Mexico State Univ., Las Cruces. 370 some former dominant plants and in major shifts in abundance of other herbaceous plants. Early researchers at the Jornada Experimental Range in southcentral New Mexico witnessed the encroachment of mesquite into desert grasslands. They established belt transects across mesquitegrassland ecotones and made detailed records of the existing vegetation. During the ensuing years mesquite continued to increase in abundance. A comparison of present with past vegetation on the transects provides much insight on the reactions of grassland species to an increase of mesquite. This information is of value both in an ecological sense and in managing mesquite-dominated lands as a grazing resource.

Vegetation Changes from 1935 to 1980 in Mesquite Dunelands and Former Grasslands of Southern New Mexico