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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

513: Mount Nimba

Major Habitat Type:

montane freshwaters

Author:

Michele Thieme, WWF-US, Conservation Science Program, Washington, DC, USA

Reviewers:

Christian Lévêque, Centre National de la Recherche Scientifique (CNRS), Paris, France

Countries:

Guinea; Ivory Coast

Boundaries:

Mount Nimba forms part of the southern extent of the “Guinean Backbone” that stretches from northern Guinea to northern Côte d’Ivoire and rises 1,000 m above the surrounding lowland plains. This mountainous region is located at the intersection of Guinea, Ivory Coast and Liberia.

Main rivers or other water bodies:

The Cavally and Ya rivers, as well as tributaries of the Sassandra and Cess Rivers, originate on Mount Nimba.

Topography:

Mount Nimba is part of an ancient mountain range, the Guinean range, which was upthrust between the end of the Jurassic and the end of the Eocene (Lévêque 1997). Since then, erosion has worn away the softer schists and granito-gneiss, exposing the underlying ore-containing quartzite (Lamotte 1983). This large ridge is about 40 km long and 8-12 km wide. Steep cliffs and quartzite peaks are prominent features of the landscape, along with deep valleys, high plateaus, rounded hilltops, and granite blocks. The highest peak in the ecoregion is Mont Richard Molard at 1,752 m (WWF and IUCN 1994).

Climate:

Rainfall varies markedly with elevation and season. About 3,000 mm of rain falls at the highest altitudes, but much less, between 700-1,200 mm, falls at the edges of the ridge (WWF and IUCN 1994). The vast majority of rainfall occurs between May and October.

Freshwater habitats:

Rivers descending the steep slopes of Mount Nimba run swiftly, often experiencing torrential floods during the rainy season. Rheophytes, plants that can live in running water, dominate the riparian vegetation (Hughes & Hughes 1992). 

Terrestrial Habitats:

Vegetation of the Mount Nimba ecoregion changes with elevation. Grasslands cover the summits, dominated by Loudetia kagerensis and Protea occidentalis on the slopes. The plum tree (Parinari excelsa) dominates mid-altitude (above 1,000 m) forests. A cloud or “mist” hangs over the mountain for months at a time at elevations over 850 m, promoting a lush growth of epiphytes in these forests (WWF and IUCN 1994). The forests give way to plains savanna that covers the piedmont below altitudes of about 500 m      (Lamotte 1983).

Fish Fauna:

Moderate richness and high endemism of aquatic species, particularly among fish and amphibians; characterize the highland Mount Nimba ecoregion. 

Other noteworthy aquatic biotic elements:

The endemic aquatic fauna of Mount Nimba includes frogs, fish, a freshwater crab, and the endangered Mount Nimba otter shrew (Micropotamogale lamottei). Of the frogs, the endemic Nectophrynoides occidentalis, which occurs in montane grasslands, and N. liberiensis, also found on Mount Nimba, are totally viviparous. Species richness is high among aquatic invertebrates. For example, 81 species of dragonflies (Odonata) have been identified from the Nimba region (Legrand 1985). The Cape clawless otter (Aonyx capensis) also lives in the mountain streams.

Justification for delineation:

This ecoregion is defined by the high elevation Mount Nimba and distinguished by an endemic aquatic fauna. The Guinean Highlands, of which Mount Nimba forms a part, separate the coastal rivers and streams to the west from the northwards-flowing Niger River to the east. The highlands have effectively formed a barrier to movement of aquatic species between these systems (Hugueny 1989). The fish fauna of the highlands has affinities with the Upper Guinea bioregion (Daget 1963). Within the highlands, Mount Nimba’s relative high elevation, the presence of rapids and waterfalls that has led to isolation, and the stability of the aquatic environment over time have promoted speciation.

Level of taxonomic exploration:

Poor. Although a biological research station exists on Mount Nimba, only a few studies have been completed on aquatic species.

References/sources:

Daget, J. (1963). "La réserve intégrale du Mont Nimba. Poissons. (2ème note)" Mém. IFAN 66 573-600.

Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.

Hugueny, B. (1989). "West African rivers as biogeographic islands: Species richness of fish communities" Oecologia 79 236-243.

IUCN, W. W. F. and (1994). "Centres of plant diversity: A guide and strategy for their conservation. 3 Volumes" Cambridge, UK: IUCN Publications Unit.

Lamotte, M. (1983). "The undermining of Mt. Nimba" Ambio 12(3-4) 174-179.

Legrand, J. (1985). "Additions to the Odonata fauna from Mount Nimba [Ivory Coast]" Revue Francaise d'Entomologie (Nouvelle Serie) 7(1) 37-38.

Lévêque, C. (1997) Biodiversity dynamics and conservation: The freshwater fish of tropical Africa. Cambridge, UK: Cambridge University Press.

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