Beginning in the late 1960s, the West African Sahel zone repeatedly made headlines because of a number of environmental and economic problems that manifest themselves in changes in land cover. While these changes often were referred to as "desertification," scientists did not develop consensus regarding the exact meaning of this notion, the mechanisms governing it, and the extent of the problem in the Sahel. Recent remote sensing-based studies have shown an overall greening trend in parts of the Sahel, which might indicate that positive developments have been going on. The meaning of "greening" is as vague as that of "desertification," however, and its implications on the ground are far from clear and unambiguous. This research project will develop empirical evidence that will inform basic understanding of the interactions among land use, land cover, and people's livelihoods in the face of variable and unpredictable rainfall in contrasting study sites in two Sahelian countries, Mauritania and Senegal. The investigators will adopt a cross-disciplinary perspective and borrow methods from the natural and social sciences in order to approach this complex research problem. They will use remote sensing techniques to measure and map current and past land-cover changes, relate them to rainfall data, conduct a variety of focus group discussions to reconstruct current and past land-use and management practices, georeference different land-use units in the study sites, and investigate how decision making on land use and management by different resource user groups takes into account environmental constraints and opportunities. They also will assess how land use and management affects land cover measured by remote sensing. Defining a range of resource user groups and teasing out and quantifying linkages between them and their biophysical environment will lay the ground work for future integration of land-use decision making with spatially explicit models of environmental change. This project will help enhance basic understanding of human and natural systems in dryland environments, particularly the relative contributions of human behavior and climate variability to land- use and land-cover change. The project results may help break the gridlock in the desertification debate by deepening understanding of the driving forces influencing desertification and greening. Moreover, identifying economically viable and environmentally sustainable land-use strategies under climate variability might be used to help communities and aid agencies to make more informed resource management decisions.