Land Degradation on the South Side of Africa-LADESA 94

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The present project aims at investigating the detailed physical processes and spatial patterns of land degradation in Subsaharan Africa, the phenomenon collectively called by the term 'desertification', due to the combined effect of climate variations and human activities. Field works were carried out along the two transects in the West African Sudano-Sahelian Region. The main results obtained can be summarized as follows :(1)Throughout the areas surveyed, lateritic cuirass-capped plateau surface and glacis or pediments fringing scarp foot of hills and plateaux are the landform types which are most prone to degradation.(2)Both patterns and processes of progress of and recovery from land degradation, are more closely related with local edaphic conditions rather than regional precipitation pattern.(3)As long as viable seeds are preserved in the soils, rapid revegetation can be achieved over alluvial plains and sand dunes in response to the return of good rains.(4)Over the "fossil sand dunes and sheets", which are located to the for south of the desert boundary and receive an annual rainfall of 600-700mm sporadic and selective degradation has caused by shifting sands activated by the destruction of vegetavive cover due to overgrazing and excessive cultivation.(5)It must be emphasized that the land degradation due to moving sands is not caused by the southward march of the Sahara Desert but by the remobilisation of once fixed sand dunes or sheets owing to the coupled effect of human activities and persistent drought conditions.(6)In order to answer the questions related to the irreversibility and/or resilience in land and vegetation, long-term observations at a time-scale of 10-20 years in several fixed areas and transects are indispensable.