Introduction

The African climate has been far from stable. Equatorial rainfall is created by oceanic solar heating generating the intertropical convergence zone (ITCZ), so rainfall and hence forest growth is in part dependent on the relative position of the solar equator. The continent was south of its present position at the end of the Cretaceous with the equator running through the present-day Sahara, suggesting that the rainfall was high in what is today a desert. The amount of rain carried inland by the ITCZ is dependent on oceanic currents which are in turn modified by positions of continents; for example, Antarctica creates the cold Benguela current which brings aridity to southwestern Africa, and Madagascar casts a monsoonal rainshadow on southeast Africa. Ocean currents are also affected by periodic variations in the Earth's orbit, the Milankovitch cycle, which is thought to be responsible for repeated Pleistocene global cooling and warming (Imbrie & Imbrie, 1980). Finally, rainfall on the continent is affected by positions of mountains and lakes which create their own weather systems within the overall ITCZ and oceanic current climates.

Climatic fluctuations are partly responsible for eastern African moist forest biota distribution patterns. The three main patterns to elucidate are: apparently ancient links to the Guineo–Congolian forests of western and central Africa; apparently recent links to the western Guineo–Congolian forests; and high degree of endemism within the eastern African forests.