Changes in land use and land cover result from a myriad of factors acting on the land surface. These factors fall into two large groups, those originating from human activity and those originating from natural forces. Among the human factors, the size and growth of the human population plays a large role, but it is not the only underlying human cause of land cover change. The impacts of population growth are amplified or attenuated by institutional factors and national and regional policies, as well as processes of globalization, all of which shape economic opportunities that the populations of West Africa respond to in complex and interrelated ways that ultimately affect land use and land cover patterns (Lambin and others, 2001). For example, the progressive integration of West Africa into a global market economy has led to expansion of foreign investment in the mining and timber industries of the Guinean forest countries, which increases the rate of forest loss. Structural adjustment programs have encouraged agricultural specialization toward a small number of cash crops, such as cotton and peanuts in the Sahelian countries, which replace a more diverse mix of local grains and tubers. Finally, increasing affluence of the growing population affects consumption patterns, such as the increased demand for processed food, meat, and dairy by the wealthy urban populations, with repercussions on natural resources and land use (Godfray and others, 2010).
In addition to human factors, natural factors have also contributed to changes on the land. With geology and landforms stable over long periods of time, climate is the most dynamic natural factor to affect land cover at annual to decadal time scales. Most importantly, the recurrence and persistence of drought conditions in the semiarid swaths of West Africa have directly changed the land cover by desiccating soils, shrinking water bodies, stressing the vegetation, and exposing bare soil and sandy substrate to erosion. Indirectly, it has affected people’s ability to use the land for crop cultivation and for foraging by livestock, forcing them to find other ways of securing their livelihoods, which in turn have altered the land use and land cover. For example, the threat of drought to agriculture in the Sahel pushed farmers and pastoralists to migrate from the arid frontier toward more humid stretches of land, or into the urban areas in search of jobs. In other instances, the combined pressures of drought and population increase have spurred investments in soil and water conservation, and in agricultural intensification in southern Niger and central Burkina Faso (Reij, Tappan, and Smale, 2009).
With the understanding that driving forces of land use and land cover change interact in complex ways, two key underlying drivers of change will be given particular attention: (1) population, which determines the demand and pressure on land resources, and (2) climate, which affects the supply or constraints of land resources.