Afro-Alpine Plant Diversity in the Tropical Mountains of Africa

Abstract

The Afro-alpine Zone is a fragmented vegetation type that occurs above 3200m elevation on 14 scattered mountains and covers some 4525km2 in tropical Africa. Defined by the strong diurnal climate of “summer every day and winter every night,” the Afro-alpine Zone is typified by a unique flora characterized by Giant Groundsel and Giant Lobelia species. The Afro-alpine Zone is mostly concentrated in the eastern region of the continent, with a single western occurrence on Mount Cameroon. It is estimated that the Afro-alpine region harbors between 515 and 521 species of flowering plants, 52 fern species, and >277 moss species, with endemism levels around 35% for flowering plants and 30% for mosses. This represents moderate diversity and richness compared to other tropical alpine areas such as the Páramos of the South American Andes and the highlands of New Guinea. Typical plant communities in the Afro-alpine are tussock- and shrub-dominated grasslands and alpine bogs or fens, in which are embedded communities of Giant Lobelias and particularly Giant Groundsels. Biogeographically, the evolution of Afro-alpine diversity appears to be driven by age, size, and the geographical proximity of the mountains to each other, similar to the processes described by the General Dynamic Model for oceanic islands but overall much more complex. Due to the difficulty of exploration in some of these mountains and the limitation and biases of the available literature, there is work to be done in terms of finalizing data on the Afro-alpine biotic composition and determining its underlying biogeographic history. Understanding these processes may provide important insights on the conservation of these unique habitats, which are especially threatened by immediate human activities (e.g., overuse of fire) and anthropogenic-driven climatic change.