Forests - Congo
The human impact on the Congo basin has definitely had many negative effects in more recent times, but it is important to note that natural evolution has had a far greater effect.
Around 130,000 years ago, Africa experienced colder and more arid conditions than it does at present. At about this time a warmer and moister climate phase began with greater extents of rainforests: deserts were almost totally covered in vegetation. This lasted until around 115,000 years ago. This cooling and drying trend reached its maximum about 70,000 years ago. This was followed firstly by a period of slight warming and moistening in the climate, then by another period of high aridity. Conditions then became warmer and moister again, followed by another period of dryness which lasted until the end of the last Ice Age. During these changes the forests would have expanded and contracted accordingly.
Ten thousand years ago, during the last ice age, there were fewer and smaller forests of the tropical montane type (i.e. in mountainous or upland areas) and there was significantly less biodiversity. Later, as the climate became more like todays, these areas were able to spread. Today, the Congo is considered to be one of the most biologically rich areas in Africa.