Plant diversity and composition of peatlands adjacent to the white- and blackwater rivers in the central Congo Basin

The central Congo Basin is home to the world's largest tropical peatland complex. This region, dominated by swamp forests, is poorly understood. In other flooded tropical forest systems, there is a well-documented influence of nutrient inputs from nearby black (lower nutrient) and white (higher nutrient) water rivers on plant species composition and community structure (e.g. Amazon igapó vs várzea forests). Here, we test whether swamp forest communities in the central Congo Basin, located close to either the whitewater Congo River (three communities) or the blackwater Ruki River (three communities), also differ (n = 52 vegetation plots in total, 41 peat-forming swamp forest, 10 swamp forest on mineral soil, 1 savannah). Overall, tree species richness (stems ≥10 cm diameter) of the peat-forming communities adjacent to black- versus whitewater rivers did not differ. However, the swamp forest on mineral soil adjacent to the blackwater river was found to have significantly lower richness than that adjacent to the whitewater river (consistent with Amazon patterns). Non-metric multidimensional scaling shows differing community composition in the peat-forming swamp forests adjacent to the white- and blackwater rivers. Overall, we find that the peat-forming communities have half the species richness (29 species/300 stems) of the African terra firme forest (65 species/300 stems), with composition modestly influenced by differing nearby water sources. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.