Environmental policies in African rangelands affect development and welfare as well as environmental measures. Biodiversity is widely perceived as declining, and environments as undergoing degradation, through rural population growth and resource use. These assumptions are often underpinned by environmental discourses contesting control of natural resources, rather than by objectively measured trends and causalities. Orthodox biodiversity conservation policy advocates fortress conservation. Savanna species do better where they can disperse across wider landscapes with conservation-compatible rural land uses, rather than isolated in protected areas, but community-based conservation initiatives have been disappointing. Policies addressing land degradation, and their underlying assumptions, are subject to similar challenges. The paper outlines a natural experiment investigating biodiversity and land cover changes 1975–1995 for 100,000 km 2 cross-border rangeland including the Serengeti–Mara conservation areas and their buffer zones. Ecological, ethnic and micro-economic continuities make it possible to control for confounding factors and identify main drivers of change. Privatisation of formerly communal rangeland, and its conversion to commercial monoculture, have driven drastic land cover and wildlife declines in Kenya. Population growth and agropastoral land use were not significant factors. The gap between natural and social science, and western versus local understandings, needs bridging to achieve more effective environmental policy.