BLOCKAGE OF VEGETATIONAL SUCCESSION OVER SEVERAL CENTURIES IN WETLANDS OF WESTERN FRANCE

A blockage of vegetational succession over several centuries is discus sed with different arguments. The initial observation is the similarit y between floristic composition of a recently established polder and p ermanent grassland reclaimed from the sea in the early middle ages. So il parameters showed that a desalinization has occurred at the time of the polder formation, but a residual salinity has remained in the soi l. A hydro-dynamic study has allowed understanding of the stabilizatio n of pedolagical processes. Hydrological state is closely dependent on the microtopographic level: directly descended from the original recl amations, but it is the permanent grazing management since the Xth cen tury which is the essential factor of blockage of vegetational success ion.