A brief biogeographical journey of the Green Heart of Africa
Birth of a forest
Alternately reduced, fragmented or expanded, the forests of the Congo River Basin have been constantly adapting to the constraints brought by climatic changes over a million years. Here is a snapshot in time of a surprisingly young forest.
Back then, a savanna-forest mosaicThere is strong evidence that forest cover was reduced during the last Ice Age, lasting from 1.6 million to 10,000 years ago. While forested areas in the Congo River Basin are known to have persisted in some areas called refugia, such as in present-day Cameroon, they were much reduced elsewhere.1 At that time, most forests consisted of savanna-forest mosaic - patchwork pieces of land where savannas and forests meet.
Only in several places could one find closed-canopy forest, such as in river galleries (forested areas along the river banks), along the hills of the western coastal part of the Congo Basin forests and in the mountains to the east of the Congo River Basin. Today, these closed-canopy areas persist, and contain a greater richness of species than other parts of the basin.2
The rainforests returnAbout 10,000 years ago, as the last Ice Age ended, glaciers receded and rainfall increased. The changing climate allowed savannas to be reclaimed by trees, and the forest grew to reach its current size.
Because the forests of the region were only formed recently – that is, in geological terms – they are referred to as being “young”.3
Natural forest destructionThe Ice Age was not the only factor that influenced the change in expanse of forests. The most recent natural destruction of forest is attributed to an extended period of dryness some 2,000-2,500 years ago, while the mosaic aspect of the forests in several areas is probably the result of climatic changes that have affected forests over the last 3,000 years.
Today, the natural ‘reconstruction’ of forest continues, although it is slowed down by human deforestation.4
The human factorTo what extent did our ancestors contribute to the size and composition of today’s forests? We know that modern-day humans have been present longer in Africa than anywhere else, but it is difficult to see what impacts they had on forests before the spread of agriculture to the region, some 3,000 years ago.
The savanna-forest mosaic to the south of the Congo Basin forests, extending north almost to the equator in west Congo-Brazzaville, has been historically attributed to denser agricultural populations of humans burning the savanna, which has prevented the growth of the rainforest.
Is there such a thing as a native forest?With the advent of agriculture, shifting cultivation (a form of subsistence farming) has grown to such intensity that it has led many authors to wonder if there is any area in Africa that hasn’t been affected by humans at one point or another.
Studies in apparently pristine rainforests have often found ancient traces of cultivation and habitation, such as charcoal, pottery fragments and evidence of settlements.5
If this were true, then a more appropriate term for the dense, ‘unexplored’ deep jungle would be “old regrowth forest”.6
1 Adams, J. 1994. The Distribution and Variety of Equatorial Rainforests. Encyclopaedia 'Biosphere' (Biosfera)
2 CARPE. 2005. The Forests of the Congo River Basin: A preliminary assessment. Balmar. Washington DC
3 CARPE. 2005. The Forests of the Congo River Basin: A preliminary assessment. Balmar. Washington DC
4 Maley J. 2001. Si la Fôret tropicale m’était contée. Canopée No19
5 Adams J. 1994. The Distribution and Variety of the Equatorial Rainforests. Encyclopaedia 'Biosphere' (Biosfera)
6 CARPE. 2001. If the Forest Disappeared What Would We Lose and What Might We Gain? Congo River Basin Information Series. Issue Brief #8