Analyse phytogéographique des forêts d’Afrique Centrale: le cas du massif de Ngovayang (Cameroun)

Abstract

Phytogeographical analysis of Central African forests: the Ngovayang massif (Cameroon) Background and aims – The Ngovayang massif, in southern Cameroon, is part of a group of small hills along the Atlantic coast of the Gulf of Guinea. This area is known for its floristic richness and its high level of endemism. We conducted a phytogeographical analysis of this massif and evaluated its floristic affinities with other forested sites in Central Africa. Methods – Phytogeographical analysis was based on a comparison of lists of tree species with dbh ≥ 10 cm, inventoried in 1-ha permanent plots, and established in old growth lowland forests of Central Africa. The floristic list for Ngovayang used for this analysis contained 201 species. Key results – The lowland forests of the Ngovayang massif are dominated by LeguminosaeCaesalpinioideae, followed by Olacaceae and Burseraceae, taxa characteristic of dense old-growth Atlantic moist forests. The Ngovayang flora includes a high proportion of Guineo-Congolean species (79%), particularly Lower Guinean species (30%). Phytogeographical analysis showed that forested sites of central Africa are clearly separated into continental sites and the more coastal sites of the Lower Guinean domain, including Ngovayang. Within the Lower Guinean domain, the main floristic discontinuity appears to be situated in southern Cameroon-northern Equatorial Guinea. Ngovayang and Takamanda, which are situated on opposite sides of the Cameroon volcanic line, show stronger floristic affinities with each other than either does with other Lower Guinean forest sites located to the south of the Ngovayang massif. Conclusions – Ngovayang may constitute a transition zone between Nigerian forests and those ranging from southern Cameroon to the Democratic Republic of the Congo. For tree species of the Lower Guinean domain, the climatic hinge separating boreal and austral climates appears to be a more important phytogeographic barrier than the Cameroon volcanic line or the Sanaga River.