Mangrove dynamics in the Rivières du Sud area, West Africa: an ecogeographic approach

Abstract

Because of the diversity of its mangrove environments, the extensive estuarine coast of West Africa, between Saloum (Senegal) and Sherbro (Sierra Leone) estuaries, provides the biogeographer with a highly favourable framework for the analysis of changes in mangrove communities. These changes can be studied at various organization levels of the mangrove ecosystem, emphasizing the multi-dimensional nature of successional processes. Although being denied elsewhere, the efficiency of biotic processes is demonstrated by numerous case studies relating changes in mangrove communities to simultaneaous edaphic modifications. More recently, disturbances in zonation patterns related to reduction of water discharges draws attention to the fact that varying longitudinal gradients, involving interaction between salt- and freshwater, may give rise to specific successional schemes. Last but not least, how mangroves develop to an equilibrium between deposition in swamp and erosion in the tidal creeks can be appreciated by recognition of a third volumetric dimension of successional processes. Since any successional pattern involves these three dimensional components, an attempt is made to recognize basic `multi-dimensional' sets of process variables, related to the characteristic depositional settings of the area. As a general rule, it can be stated that successional patterns are all the more dependant on varying environmental gradients since they occur in areas receiving large supplies of allochtonous sediments, either from landward (deltaic estuary) or seaward (tidal bay) origins.