The Congo basin forms the core of humid forest in Central Africa. The Congo basin comprises five ecoregions of humid forest, and three additional ecoregions of forest – savannah mosaic on the edges of the basin in the north and south. The Congo basin contains about 1.8 million square kilometers of rainforest, or about 90% of all African rainforests; other regions are the Guinean lowlands of West Africa and the rainforests of Madagascar.
In the interior of the Congo basin, the Congolian lowland forests fall in elevation from approximately 1,000 meters the eastern edge of the Albertine Rift Mountains, into the Congo River basin towards the west. The largest ecoregion of the Congo Basin is the northeastern Congolian lowland forest, located in the eastern part of DRC and reaching into southern Central African Republic. This ecoregion includes the Ituri forest and several protected areas. Downstream to the west lay the Central Congolian lowland forests, a similar area of intact, dense, humid forest. Along the Congo River lie the Congolian swamp forests, home to habitats such as the Raphia palm. The Congo River forms a significant barrier for mammal species, and several species of monkeys and other primates are confined to one side of the river. Continuing downstream are the northwestern Congolian lowland forest and the Atlantic Equatorial coastal forests, reaching into Republic of Congo, Cameroon and Gabon. Parts of this region include the mono-dominant forests of Gilbertiodendron dewevrei. Closer to the Atlantic coast, these forests are slightly wetter than the interior Congo basin, and also contain some of the greatest plant and animal diversity of the entire basin. The interior humid forests of Guinea – Congo, the montane archipelago centered in Rwanda, and the highlands of east Africa are all regional centers of endemism, with an average 75% of all species endemic, meaning they are found in no other region of earth.
To the north and south, the Congo basin rainforests transition to drier forest savannah ecoregion, including the northern, western, and southern Congolian forest savannah ecoregions. Canopy trees often lose their leaves in the dry season, while understory herbs and shrubs often remain evergreen. Savannah woodlands in this region are typically located on plateaus 500-700 meters in elevation. Through millennia, human populations have farmed and raised animals on richer soils, often through the use of fire, while forests remain on areas of poor soils or along waterways, known as gallery forests.
Species common in the savannah woodlands include Afzelia africana, Aningeria altissima, Chrysophyllum perpulchrum, Cola gigantea, Morus mesozygia, and Khaya grandifoliola, a shade intolerant tree known as one of the African mahoganies. Transitioning further into grassland ecoregions, trees found in northern and southern grasslands include Isoberlinia spp, Burkea africana, Combretum collinum, Hymenocardia acida, Pariniari curatelifolia, Stereospernum kunthianum, Strychnos spp. and Vitex spp. In the southern Congolian savannah forests, common trees include Senegal date palms (Phoenix reclinata), wild custard apple trees (Annona senegalensis), and African breadfruit (Treculia africana). African woodland savannahs are usually home to diverse populations of large mammals such as elephant, rhino, lion, bongo, forest buffalo, and antelope. These areas are more accessible via road and have suffered greater conversion to agriculture. Savannah forests have also been home to millennia of shifting agriculture, but this has become unsustainable in many parts due to increased population and shorter fallow periods.
Precipitation averages 1,500-2,000 mm annually in most areas of humid forests. Forest savannah ecoregions are more dry, averaging 1,200-1,600 mm precipitation, with a distinct wet and dry season. Wet areas of the Atlantic equatorial coastal forests in Gabon can exceed 3,000 mm; rainfall generally decreases as the air moves from west to east towards the Albertine highlands. Interior Congo forests have relatively continuous precipitation throughout the year, whereas western regions have a dry season from January to March. Interior areas of the forest are situated upon highly weathered oxisol soil, but drier areas in the south and volcanic areas of the Albertine contain more nutrient rich soils. In the periphery of the Congo basin rainforest, precipitation drops to 1200-1600 mm and the landscape changes to deciduous forest and gradually woodland.
Plant diversity in the Congo basin is high, with approximately 10,000 plant species, but less diverse than the Amazon basin. Tree species are similarly diverse in African rainforest, but there are fewer understory plants and epiphytes. Possible reasons for this include the generally drier climate conditions in Africa, as well as the dry periods of climate history and lack of climate refugia for forest species during the ice ages. However, several plant taxa are found in both continents, resulting from the shared Gondwana region of the Pangea supercontinent: Annonaceae, Apocynaceae, Araceae, Araliaceae, Bombacaceae, Flacourtiaceae, Marantaceae, Myrtaceae, and Sapotaceae, as well as bamboos. Today, the most biodiverse regions of the Congo basin are the Atlantic equatorial forests of Gabon and Cameroon and the foothills of the Albertine Mountains along the border with Uganda, Rwanda, and Burundi. Other important biodiversity areas in Africa include the Guinean forests in West Africa, the Cape Floristic region of South Africa, and the island of Madagascar.
Ecoregion information largely derived from WWF and the Encyclopedia of Earth: Ecoregions of DRC.
Axelrod, D. I., & Raven, P. H. (1978). Late Cretaceous and Tertiary vegetation history of Africa. In Biogeography and ecology of southern Africa (pp. 77-130). Springer Netherlands.
Malhi, Y., Adu-Bredu, S., Asare, R. A., Lewis, S. L., & Mayaux, P. (2013). The past, present and future of Africa’s rainforests. Philosophical Transactions of the Royal Society B: Biological Sciences, 368(1625), 20120293.
Hamilton, A. A., & Taylor, D. (1992). History of climate and forests in tropical Africa during the last 8 million years. In Tropical forests and climate (pp. 65-78). Springer Netherlands.
Olson, D. M., Dinerstein, E., Wikramanayake, E. D., Burgess, N. D., Powell, G. V., Underwood, E. C., … & Kassem, K. R. (2001). Terrestrial Ecoregions of the World: A New Map of Life on Earth A new global map of terrestrial ecoregions provides an innovative tool for conserving biodiversity. BioScience, 51(11), 933-938.