Shrubby and forest fringe communities of the inselberg - rainforest ecotone in Atlantic Central Africa

Abstract

Background and aims -Inselbergs are rock outcrops standing out from the surrounding plains. In the rainforest landscape they can be considered as forming "xeric islands". Plants on inselbergs endure very harsh edaphic and microclimatic conditions. The inselberg -rainforest ecotone is characterized by the spatial transition from monocotyledonous mats and grasslands to an herbaceous fringe, a shrubby fringe, a forest fringe and a saxicolous forest. We describe here the plant communities of the shrubby and forest fringes of 25 sites in Southern Cameroon, Equatorial Guinea and Gabon. We identify their affinities with other inselberg plants communities described in West and Central Africa and evaluate their conservation value. Methods -We used cluster analysis and ordination to classify 191 phytosociological relevés into plant communities, as well as the IndVal method to highlight the character species of each plant community. Key results -A total of 709 vascular plant species and 394 morpho-species were recognized within the 191 plots. The four plant communities recognized correspond to three groups of inselbergs distinct by their geographical location, mean annual rainfall, altitude, rock substrate and the presence of buffaloes. They differ from plant communities described in other habitats in Central Africa and from the rock outcrop and inselberg plant communities described in West Africa. A limited number of species are restricted to the inselberg habitat or endemic to the study area. Conclusions -Inselbergs contribute to the regional biodiversity through (i) the presence of some endemic species restricted to the inselberg habitat and to Atlantic Central Africa, (ii) the presence of species that inside the rainforest zone, can only be found on inselbergs, their main distribution being in the savannas or on mountains at higher elevations and (iii) their unique species assemblages. To preserve the inselberg flora and plant communities in Atlantic Central Africa, several sites and the surrounding rainforest should be protected within each of the three ecogeographical groups identified.

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