Colonial science and ecological change - Tanzania's Mlalo basin, 1888-1946

East Africa's coastal mountains, island massifs jutting up out of the surrounding savannas, have a thirty-million-year natural history as biological refuges. Their slopes have been watered for millennia by the Indian Ocean monsoons and have fostered the evolution of a broad diversity of flora and fauna. African farmers have long sought out these climatic and botanical havens and developed around their water sources a sophisticated agricultural production system designed to mitigate the severe droughts which periodically plague eastern Africa. Although long-term settlement in the mountains caused environmental change, its character and scope has yet to be adequately explained. Nonetheless, over the past seventy years, colonial and postcolonial governments have moved to ameliorate what they have perceived as human-induced ecological stress. This article examines the early phase of the colonial debates over environmental degradation and its remedies in the Mlalo basin, an upland region in the West Usambara mountains of Tanzania. The policy discussions regarding Mlalo occurred in the context of a general crisis in colonial society between 1929 and 1940, during which colonial perceptions of agroecological decline and the economic pressures of depression challenged European colonial governments in Africa and Asia. In terms of ecological issues, worldwide concern over erosion in the American Dust Bowl resonated across East Africa, resulting in an official preoccupation with soil conservation. Tanganyika Territory's Mlalo basin came to be cited in the 1930s as one of several particularly striking manifestations of soil degradation and agroecological decline. When a food shortage known as njaa ya Chankola (Chankola's famine) struck between 1941 and 1946, the specter of human and environmental catastrophe justified colonial degradation scenarios, which in turn guided the colonial government's attempt between 1946 and 1949 to 'modernize' husbandry via the Mlalo Basin Rehabilitation Scheme.