The Jornada LTER is a program of long-term ecological research to investigate the processes leading to the desertification of semiarid grasslands in southern New Mexico and the changes in ecosystem properties that accompany this desertification. The central hypothesis is that during desertification the distribution of soil resources changes from spatially homogeneous, as seen in semiarid grasslands, to heterogeneous, as seen in shrublands (Schlesinger et al. 1990) and that these changes in soils act as a positive feedback to further the invasion and persistence of shrubs. For the continuation of LTER activities, we propose a variety of studies to address this hypothesis, including investigations of the magnitude and spatial distribution of plant production, animal populations, soil resources and movements of water and soil nutrients in comparative grassland and shrubland communities. We also propose a major, new long-term experiment to investigate the effects of cattle grazing, as a long-term disturbance to semiarid grassland ecosystems. The results of these various field studies will be synthesized and extended to larger regions by developing models that simulate ecosystem function at the patch, patch-mosaic and landscape level. The proposed continuation of the LTER effort includes the archiving and maintenance of long-term data sets that can be used to further LTER network comparisons and contribute to the U.S. Global Change Research Program.