Boundaries

The Sangha ecoregion spans the borders of three central African countries — Cameroon, Central African Republic (CAR), and Republic of Congo (ROC). It encompasses the Sangha River basin, extending from the headwaters of the Mambéré River in the north on the Cameroon-CAR border, almost down to Malebo Pool in southern ROC. The watershed for the Congo basin, roughly following the Congo-Gabon border, defines the western boundary of the ecoregion, with the Massif du Chaillu marking the southwestern edge and the headwaters of the Boumba River marking the northwestern extent (Hughes & Hughes 1992; Sayer et al. 1992). The rivers and streams of the Sangha ecoregion run through some of the densest forests in the Afrotropical realm and support an impressive array of aquatic species.

Freshwater habitats

Permanent swamps increasingly dominate the landscape in the central and southern portions of the ecoregion. Raphia swamps proliferate along the main course of the Sangha as it passes south through the Cuvette Centrale and meets the Congo River. The shallow water of these swamps is deep brown to black, deoxygenated and highly acidic (pH 3.5-5.2) (Hughes & Hughes 1992; Laraque et al. 1998). The Likouala and Kouyou Rivers south of the mainstem Sangha also course through extensive swamp forest. Large areas of floating grasses often occur within the rivers. Further south, a mosaic of marshy savanna, boggy steppe, and temporarily inundated swamp forest exist along the Alima, Nkeni, and Lefini rivers (Hughes & Hughes 1992; Sayer et al. 1992; Wetlands International 2002).

Terrestrial habitats

Periodically inundated swamp forest, large expanses of dense evergreen and deciduous rainforest and savannas characterize the terrestrial landscape of the ecoregion. Extensive closed canopy forests and large areas of natural savanna woodland occur in the north and central portion of the ecoregion  Savanna occurs primarily in the north of the ecoregion where the headwaters of the Sangha River begin. Evergreen rainforest grades into swamp forests as the eastward-flowing rivers of this ecoregion descend in elevation. This landscape grades into the inundated floodplains, permanent swamp forests, and swamps of the Cuvette Centrale in the south (Hughes & Hughes 1992; Sayer et al. 1992).The riparian swamp forests of the upper Sangha and its tributaries range in width from a few meters up to 7 km (Hughes & Hughes 1992).

Justification for delineation

This ecoregion largely follows the watershed of the Sangha River basin. The river systems of the Sangha ecoregion are permanent and have existed since before the major earth movements of the Miocene. The flat central part of the ecoregion, the Cuvette Centrale, is part of the ancient continental Congo basin, invaded by the sea during the Mesozoic. Following this invasion by the sea, the peripheral land surrounding the Cuvette Centrale experienced massive uplift, accentuating the basin (Beadle 1981). The Dja, an upper tributary of the Sangha, is completely isolated from the Ngoko/Sangha by a large waterfall, the Nki Falls in Cameroon. The fauna upstream of Nki Falls is completely different (more like that of the Nyong and other basins in the Southern Gulf of Guinea Drainages [533] from that of the downstream portion of the river (pure Congo-fauna). Thus, the upper Dja is included in the Southern Gulf of Guinea Drainages [533] ecoregion instead of the Sangha.

Level of taxonomic exploration

Fair