This research project will examine the general hypothesis that desertification has altered a previous, relatively uniform distribution of water and nitrogen by increasing their spatial and temporal heterogeneity, leading to changes in community composition and biogeochemical processes in Chihuahuan Desert ecosystems. The Jornada Experimental Ranch (southern New Mexico), with a 75-year history of rangeland research, has documented extensive changes in vegetation cover - from perennial grassland to several kinds of shrublands - which are one result of desertification. The work will include measurements of net primary production, root growth, decomposition, soil water dynamics, surface hydrology, dynamics of animal populations, animal-produced soil disturbance, nitrogen cycling processes, and stable isotope distributions of nitrogen and carbon in widespread ecosystems, ranging from black grama (Bouteloua eriopoda) grassland, to desertified, persistent shrublands of creosotebush (Larrea tridentata), tarbush (Flourencia cernua) and mesquite (Prosopis gladulosa). A conceptual model of desertification will be tested by long-term water augmentation and mechanical homogenization of water and nutrients. Data from these studies will be used to parameterize process models. Measurements of water, wind, and gaseous transport and run-on diversion experiments will provide data for a desert landscape model. Data derived from satellite remote sensing of vegetation and soils will be incorporated into a dynamic geographic information system model of the Jornada Basin. Institutional support remains excellent for the continuation of this project. Facilities are very good. The three-institution collaborative arrangement involving several investigators has been well thought out and should prove to be highly beneficial and productive. Results from this research project should yield major findings that are fundamental to the broad field of ecology. Additionally, results should be important to the future, better enlightened management of arid land resources.
