Cross-Niger transition forests

The Albertine Rift montane forests cloak the mountains of the western branch of the East African Rift, spanning five countries: the Democratic Republic of the Congo, Uganda, Rwanda, Burundi, and Tanzania, and taking in ranges such as the Virunga and Rwenzori mountains and isolated massifs near Lake Tanganyika. These tropical moist broadleaf forests are rich in the plant families Euphorbiaceae, Rubiaceae, and Meliaceae, with vegetation shifting by elevation from dense lowland forest through moss- and fern-draped montane forest into giant bamboo and high moorland. Although it sits in the heart of tropical Africa, the high terrain gives the region an essentially temperate climate, with annual rainfall generally between 1,200 and 2,200 millimeters and reaching about 3,000 millimeters on the western slopes of the Rwenzori. The ecoregion holds the highest faunal endemism in Africa and is the only home of the mountain gorilla, earning it a place on the Global 200 list of priority conservation areas, with strongholds protected in parks including Virunga, Volcanoes, Bwindi Impenetrable, Nyungwe, and Kahuzi-Biega. Gardeners may recognize the giant montane bamboo that forms a distinct belt across these slopes.

The Cameroon Highlands forests cloak the chain of mountains that runs inland from the Gulf of Guinea and forms much of the border between Cameroon and Nigeria, rising to Mount Oku at 3,011 meters. Above roughly 900 meters the slopes carry a mosaic of submontane and montane forest, montane grassland, and bamboo, with characteristic trees such as Podocarpus latifolius, Prunus africana, Syzygium guineense, Nuxia congesta, and Rapanea (Myrsine) melanophloeos. Although it sits in tropical Africa, the altitude keeps mean maximum temperatures below 20 degrees Celsius, while rainfall ranges from around 4,000 mm a year near the coast to 1,800 mm or less further inland. The forests are exceptionally rich in endemic life, including the endangered Cross River gorilla, the flagship Bamenda apalis, and a large suite of amphibians found nowhere else, though forest cover has declined by more than half since the 1960s through farming, logging, and fire.

The Central Congolian lowland forests occupy the heart of the Congo Basin within the Democratic Republic of the Congo, filling the Cuvette Centrale south of the great arc of the Congo River, which acts as a natural barrier isolating the basin along its northern, eastern, and western edges. The terrain is largely flat lowland, and its vegetation forms a mosaic: seasonally inundated and permanent swamp forests in the north give way to drier semi-evergreen rainforest and patches of grassland in the south, with dominant canopy trees including Gilbertiodendron dewevrei and Staudtia stipitata. The climate is hot and humid with little seasonal variation, mean maximum temperatures near 30 degrees Celsius in the central portion easing toward the southeast margins. This remote region holds the world's largest populations of the bonobo, which is endemic to the DRC, alongside African forest elephants, the strictly endemic Dryas monkey, and the near-endemic Congo peafowl. Much of it lies within Salonga National Park, one of the largest tropical-forest national parks in the world.

The Comoros forests ecoregion covers the volcanic islands of the Comoros archipelago in the Mozambique Channel between Madagascar and East Africa, including Grande Comore (Ngazidja), Anjouan (Nzwani) and Mohéli (Mwali) of the Union of the Comoros along with Mayotte, a region of France. Its natural cover is tropical moist broadleaf forest, ranging from semi-deciduous and evergreen lowland forest up to montane forest near the peaks, with characteristic canopy trees such as Ocotea comorensis, Khaya, Olea capensis and Prunus africana, and giant heath (Erica comorensis) at the highest elevations. The climate is wet and tropical, with a hot rainy season and a cooler drier season; rainfall is highly uneven, exceeding 5,000 mm a year on some uplands while the driest coasts receive around 1,000 mm. The islands hold roughly 1,000 native plant species, about 30 percent of them endemic, and shelter the Livingstone's fruit bat (Pteropus livingstonii) as a flagship species, though little intact forest remains and the ecoregion is rated critically endangered. For gardeners in warm, humid climates, native ornamentals from here include tree ferns (Alsophila) and the endemic palm Ravenea hildebrandtii.

The Congolian Coastal Forests (also called the Atlantic Equatorial coastal forests) stretch along Central Africa's Atlantic seaboard from the Sanaga River in Cameroon south through Equatorial Guinea, Gabon, the Republic of the Congo, and Cabinda in Angola to the mouth of the Congo River in the Democratic Republic of the Congo. The dominant cover is coastal evergreen moist broadleaf forest, grading into mixed semi-evergreen forest in the drier south, with coastal grassland and montane forest above 1,000 meters on ranges such as Monte Alen and the Monts de Cristal. The climate is wet tropical with little seasonal variation, rainfall declining from about 2,000 mm a year in the north to 1,200 mm in the south. The ecoregion is a botanical stronghold, holding over 200 strictly endemic plants and three plant families largely confined to tropical Africa, the Huaceae, Medusandraceae, and Scytopetalaceae, while serving as a refuge for the African forest elephant, western lowland gorilla, chimpanzee, and mandrill. Conservation pressure is high, with logging concessions covering nearly the entire region.

The Cross-Sanaga-Bioko coastal forests are a tropical moist broadleaf forest ecoregion of west-central Africa, spanning southeastern Nigeria, southwestern Cameroon, and the lowlands of the island of Bioko in Equatorial Guinea, running from the Cross River south to the Sanaga River and reaching up to 300 km inland from the Atlantic coast. The dominant habitat is coastal evergreen rainforest, grading into mixed moist semi-evergreen forest further inland, with plant families such as Annonaceae, Leguminosae, Euphorbiaceae, Rubiaceae, and Sterculiaceae well represented. This is one of the wettest parts of tropical Africa, with heavy rainfall throughout the year, humidity that rarely drops below 90 percent, and rainfall exceeding 10,000 mm per year in the southwestern foothills of Mount Cameroon while averaging around 3,000 mm along the coast and roughly 2,000 mm inland. The ecoregion is exceptionally rich in endemic plants and supports some of the highest numbers of forest-restricted birds and mammals in Africa, including the Cross River gorilla and Preuss's red colobus, with a 2017 assessment finding that about 26 percent of the region lies within protected areas such as Korup and Cross River National Parks. For gardeners, it is a useful reminder that its native flora is adapted to constant warmth, very high humidity, and abundant year-round rainfall rather than seasonal drought.