Biogeographical History
The forests of Congo have not always covered their current area, but have expanded and contracted over long periods of time, as climatic conditions changed. During the past two million years these forests have frequently been reduced and fragmented during dry periods. The last ice age-some 18,000 years ago- saw a significant reduction in rainfall over equatorial Africa, and most of the present-day forest was actually a forest-savanna mosaic. At the time, the closed canopy forest was mostly limited to refuge areas, especially along the hills of the western coastal portions of the forest and on the far eastern mountains.
Today these areas still maintain greater species richness and endemism than other parts of the Basin. However, climate fluctuations are not limited to ice ages, and the most recent natural destruction of the forest by a significant dry spell occurred only 2,000-2,500 years ago. Given this natural history combined with rapidly changing and sometimes significant impacts of human activity, the overall picture for the Congo Basin forest ecosystem is quite complex. Growth rates of plant and tree species, carbon accumulation, forest structure, biodiversity characteristics, and forest succession are all influenced by both human and natural changes, with significant implications for forest management and biodiversity conservation that are unfortunately only poorly understood.