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.
Since the late 1960s, the West African Sahel zone has repeatedly made headlines for a number of – potentially related – environmental and economic problems, which manifest themselves in changes in land cover. While these changes are generally referred to as ‘desertification’, there has been a lack of consensus among scientists over the exact meaning of this notion, the mechanisms governing it, and the spatial extent of the problem. Despite its obvious imperfection and inadequacies, the term failed to fade away among scientists and practitioners and its evolving understanding has had important implications for management policies and the international aid industry in drylands. This project was motivated by recent remote sensing-based studies, which have shown an overall greening trend in parts of the Sahel, seemingly contradicting the prevailing paradigm of widespread desertification. Although this greening trend might indicate that positive developments have been going on, the meaning of 'greening' has been as vague as that of 'desertification'. Ground studies to investigate the realities of the greening trend on the ground, and its implications for environment and livelihoods, were largely missing. This NSF-funded research project addressed that gap by developing approaches of integrating field data of vegetation cover, the perceptions of local land users of their changing environment and trends in remotely sensed NDVI, while focusing mostly on the country of Senegal. We began by investigating a small number of field sites in great depth, and progressively expanded to including a much larger sample of sites while reducing the thematic depth of the assessment. The latter approach turned out to provide a better match to the coarse resolution of the remote sensing observations and allowed us to obtain data and observations over a more extensive area. Our findings showed that the satellite-observed greening trend corresponded with increasing vegetation cover in at least a part of the greening area. However, even in the sites where vegetation cover has increased based on a comparison of historical and current vegetation surveys, there has been an impoverishment of the woody vegetation, as evidenced by a loss of large trees and a loss in species diversity. In addition to the loss of species diversity, a shift towards more arid-tolerant species could be documented. The perceptions of local land users, in particular transhumant pastoralists who are intimately familiar with the vegetation and routinely cover large areas with their livestock, also confirm an increase in green vegetation in some places. However, instances of vegetation degradation dominate their perception of vegetation change, which is not reflected in the mostly positive remote sensing-derived greenness trends. This perception of degradation is explained by a loss of palatable pasture species and of woody species of high use value, whereas the satellite-derived greenness reflects overall biomass production and obscures any changes in species composition. Despite a prevailing consensus among our informations about deteriorating environmental conditions in the past couple of decades, in particular with respect to the timing of rainfall and the quality of vegetation resources, the majority of our informants observed increasing wealth in their communities, indicated by larger livestock herds, improved housing, and more monetary wealth than in the past. However, the distribution of wealth appears to be increasingly unequal, leaving sections of the population faced with devastating poverty. These observations did not differ significantly between the sites that have seen a greening according to satellite data and those that have not. Our findings thus challenge the prevailing chain of assumptions of (1) the satellite-observed greening trend indicating an improvement of environmental conditions in the sense of a rehabilitation of the vegetation cover after the great droughts of the 1970s and 80s, and (2) the improvement of environmental conditions possibly translating into more stable livelihoods and greater well-being of the populations. Instead, they point to a number of different pathways of greening, not all of which are unanimously positive. Our project provided training for one undergraduate student in Geography, who as a NASA Space Grant Intern participated in the satellite image analysis and modeling of woody vegetation cover for part of the study area, and two PhD students, one in Anthropology and one in Arid Lands Resource Sciences, who both participated in different sections of the field work. The students were involved in all aspects of the research, from the preparation of the field work to analyzing data and contributing to journal publications. The project also reinforced institutional ties of the University of Arizona with the Senegalese Centre de Suivi Ecologique, which was established in the aftermath of the great droughts and whose mission is the monitoring of environmental conditions and the facilitation natural resource management in Senegal. Last Modified: 02/10/2014 Submitted by: Stefanie M Herrmann Herrmann S. M.,Sall I. and Sy O. 2014. People and pixels in the Sahel: a study linking coarse-resolution remote sensing observations to land users' perceptions of their changing environment in Senegal. Ecology and Society 19: 29. www.ecologyandsociety.org/vol19/iss3/art29/
