Ecology, distribution, and classification of xeric monocotyledonous mats on inselbergs in West Africa and Atlantic central Africa
Parmentier, Ingrid; Oumorou, Madjidou; Porembski, Stefan; Lejoly, Jean; Decocq, Guillaume
This study describes xeric saxicolous plant communities of inselbergs embedded in a savannah matrix (in West Africa) and of inselbergs embedded in rainforest (in Atlantic central Africa). We looked at how the species' socio-ecology and distribution differ according to the different matrix vegetation. TWINSPAN-classification of 188 phytosociological relevés defined three plant communities all dominated by the poikilohydric mat-forming sedge Afrotrilepis pilosa. Besides this Cyperaceae, the communities in West Africa and Atlantic central Africa share only one species. Two new associations are described: Cyanotido lanatae-Afrotrilepidetum pilosae on West African inselbergs and Oreonesiono testui-Afrotrilepidetum pilosae on inselbergs from Atlantic central Africa. Each of them typifies a new alliance included in a new order. This new order typifies a new class: Afrotrilepidetea pilosae. Therophytes occurs with many species in Cyanotido lanatae-Afrotrilepidetum pilosae while chamaephytes are most abundant in Oreonesiono testui-Afrotrilepidetum pilosae. The flora of inselbergs surrounded by savannah is characterized by species largely distributed in tropical Africa (60%). Most species occur also in the matrix surrounding the inselbergs, only one being strictly confined to the inselberg habitat. On inselbergs embedded in rainforest 40 % of the species originate from the Lower Guinea sub-center of endemism. Nine species are only known to grow in the inselberg habitat. Mantel tests of correlation between floristic, climatic and spatial distances were computed in the two contrasted situations (savannah and rainforest matrix). For rainforest inselbergs the floristic dissimilarity is positively correlated to the spatial and climatic distances, while there was no significant correlation for savannah inselbergs. In our data set, the flora of inselbergs embedded in a savannah matrix was thus more uniform than that of inselbergs surrounded by rainforest.