Although precipitation is assumed to be the major control of the production of plants in arid and semiarid regions, annual precipitation explains only 20-40% of grass and shrub production variability among years. This failure suggests that researchers are not accounting for key mechanisms that control the ability of arid ecosystems to track fluctuations in precipitation. Yet increased fluctuations are a prominent feature of climate predictions in arid regions. This project puts forward four hypotheses to explain observed lags in ecosystem response to changing precipitation, and tests them by altering patterns of total precipitation and precipitation variability, with and without nitrogen manipulation. These manipulations, together with the model analysis, will help determine the cause and magnitude of lags in the ecosystem response to precipitation.

Results from this project will contribute to understanding the effect of climate change on carbon sequestration, forage production and the process of shrub encroachment, which are very important for stakeholders of the southwestern U.S., ranging from cattle ranchers to city authorities worrying about water supplies and ecosystem services. A demonstration project will be established in partnership with a nonprofit organization that provides award-winning science education to more than 12,000 children and 4,500 adults annually in southern New Mexico and western Texas. In addition, the project will develop web sites and outreach materials to transmit findings beyond the university.