Savannization Processes in Tropical Africa (TAGELAQP/SAPITA 91-92)

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The field data obtained from the 1989-90 season research in the African savannas were analyzed and were featured into a publication that includes following results :1. Northern Africa (Cameroon)1) East Cameroon forest/savanna contact : A model for explaining savannization processes was constructed on the basis of the relationship between the structure and composition of semideciduous and gallery forests and soil profiles.2) West Cameroon Highlands : Pollen analysis and radiocarbon datings of cores indicate that forest degradation followed by savannization began at 3, 000-2, 500 yr BP and intensified since 2, 000-1, 500 yr BP. Spreading of Podocarpus, a montane forest element, during the LGM to the lower elevations was also confirmed.3) West Cameroon Highlands : A model showing patterns and processes of land and vegetation degradation over cattle-grazed grassy slope was constructed.4) Sudano-Sahelian savanna zone : An attempt was made to formulate progressive land degradation under cond … More itions of increased human impact and persistent drought.5) Recently, deforestation of humid forests has been greatly accelerated due to shortened fallow period of slash-and-burn cultivation and to illegal exploitation of reserved forests.2. Sothern Africa (Zambia, Zimbabwe and Malawi)6) West Zambia : Geoecological analysis of soil profiles and radiocarbon dates of buried soils suggest that human impact creating "miombo" woodland over the Kalahari Sands dates back to to 2, 500 yr BP, widespread from 1, 000 yr BP and intensified from 400 yr BP.7) Nyika Plateau : Widespread grasslands over the plateau have been derived from clearing of evergreen montane forests some 500 years ago for fuelwood by iron-smelting peoples, resulting in widespread soil degradation.3. Throughout equatorial Africa, hitherto available data indicate that the degradation of forest vegetation and savannization have proceeded by the coupled effects of human activities and climatic aridification since 3, 000-2, 500 yr BP. Reconstruction, however, of more detailed history, call for more well-dated data.4. Recent Subsaharan drought seems to be caused by decreased convective activities and may relate with a global-scale anomaly of Walker Circulation.5. Landsurface-atmosphere interaction changes induced by "desertification" and savannization and their climatic and ecological implications remain unanswered. Less