Herbaceous vegetation of seasonally wet habitats on inselbergs and lateritic crusts in West and Central Africa

Inselbergs, mountain ridges and lateritic crusts are characteristic landscape elements in many tropical regions. They are of great interest from a botanical point of view. Their vegetation is relatively uniform and differs from the surrounding vegetation. The first synopsis of herbaceous vegetation of seasonally wet or inundated habitats on rocks, inselbergs, mountain ridges and lateritic crusts in several bioclimatic zones of tropical West Africa and Atlantic Central Africa is presented. A classification of 43 partial data sets, based on 378 relevés, resulted in four associations and several rankless communities, grouped into four different classes (Drosero-Xyridetea, Afrotrilepidetea pilosae, Lycopodietea cernui andMicrochloetea indicae). Plant communities from Atlantic Central Africa and West Africa are very distinct from a floristic point of view; in an ordination, they are clearly separated. TheDrosero indicae-Utricularietalia subulatae (Drosero-Xyridetea) comprises ephemeral vegetation in rock pools and depressions over lateritic crusts. It contains theEriocaulo pumili-Ophioglossion gomezianum, which combines communities with short-lived plant species in small pools on rock outcrops and in shallow depressions over laterite, and theGenliseo africanae-Sporobolion pauciflori, which colonizes similar habitats but is geographically restricted to few mountains in Guinea, Sierra Leone and Liberia. Mats of monocytyledonous plants (Afrotrilepidetea pilosae, Afrotrilepidetalia pilosae) are very widespread in humid parts of tropical West Africa. They colonize gentle slopes and are often close to communities of theDrosero-Utricularietalia subulatae. Three alliances can be distinguished: West African alliancesCyanotido lanatae-Afrotrilepidion pilosae andSpermacoco hepperanae-Afrotrilepidion pilosae, and an Atlantic Central AfricanOreonesiono testui-Afrotrilepidion pilosae. Small-sacle alterations of the ecological situation often result in a mosaic-like pattern of the plant communities. Especially small inselberg and rock outcrop habitats are often affected by heavy fluctuations of their environmental and climatic conditions. Besides regular short-term dynamics, there are also long-term vegetation dynamics with cycles spanning several years.