The forest type develops in all places where the plants reproductive cycle takes place on soaking wet soils or where the soil has at least a layer of water on its surface during the dry season. There can be periodic or occasional floods. These conditions are not very favourable for the decompositions of organic materials which therefore accumulate. Many species have developed still roots, others aerial roots. Light can filter through to favour the development of lower shrubs layers; this vegetation is very difficult to penetrate.