Agroecological restoration of savanna ecosystems

As a result of deforestation, annual bush burning, overgrazing and intensive cultivation, most tropical forests have changed to derived savanna in many West African states. This change in vegetation has led to a decrease in rainfall and a change in many climatic conditions. Erosion problems have increased, soil fertility has declined in arable land and the soils have become compacted. Successive droughts and uncontrolled population growth have compounded the problem to the extent that traditional farming practices no longer ensure sustainability. Places where such deterioration of the environment has occurred in Nigeria and Ghana are highlighted Results of experiments which demonstrate that nutrient deficiency in the Sahel savanna is a more serious problem than low rainfall and that nitrogen and phosphorus are the limiting nutrients in many savanna ecosystems are reviewed. The roles played by trees in the savanna such as provision of shade, preservation of water, reduction of susceptibility to erosion and nutrient pump are highlighted and species whose cultivation must be intensified so as to promote sustainability in savanna ecosystems are listed. The principles of agroecological restoration of savanna ecosystems whose focus is on the restoration of ecological balance and which has been successfully practiced in Ghana are highlighted. (C) 1998 Published by Elsevier Science B.V. All rights reserved.