Nimba Mountains

A(i)Site contains one or more globally threatened species, A(iii)Site contains one or more highly restricted endemic species that are potentially threatened, B(i)Site contains a high number of species within defined habitat or vegetation types, C(iii)Site contains nationally threatened or restricted habitat or vegetation types, AND/OR habitats that have severely declined in extent nationally

The Nimba Mountain range is an area of exceptional biodiversity globally. It has over 1,400 plant species making it the richest documented botanical site in West Africa. It has plants globally endemic to the Nimba Mountains such as Osbeckia porteresii, Sporobolus pauciflorus, Impatiens nzoana, and Begonia quadrialata subsp. nimbaensis. At least 40 threatened species, and species with restricted disjunct distributions e.g. (Justicia jamisonii) also occur. Although it is recognised as a Biosphere Reserve and World Heritage Site, the rare plant species and habitats of the range are still threatened.

The Nimba Mountains are situated in the south-east of Guinea, in Lola Prefecture. The range extends into Liberia and Ivory Coast. The highest peak in Guinea is part of Nimba and reaches 1,752m above sea-level. The area of Nimba in Guinea covers 149.2km² and was protected in 1944. The majority (134.1km²) is recognised as a World Heritage Site and has been a core area of the Nimba Mountains Biosphere Reserve since 1980. Due to their height, age, and isolation, the Nimba Mountains are exceptionally rich in flora and fauna, with many rare and range-restricted species, including a few species endemic to the Nimba Mountains. The slopes of the mountains are forested and there is submontane grassland above this, on mainly ferralitic itabirites that have undergone various degrees of leaching of its alumina-silicate components. The high-altitude lateritic (ferralitic) bowal grasslands, and submontane forest are both recognised Threatened Habitats of Guinea.
The area is locally managed by the Centre for the Management of the Environment of the Nimba and Simandou Mountains (CEGENS).

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Due to the height and isolation of the Nimba Mountains, they are home to many rare and range-restricted species, including a few endemic to the mountain and others endemic to Guinea. Recent studies have resulted in over 1,400 plant species being recorded in the Guinean portion (pers. obs. Suter, 2018), making it the richest site in Guinea for plant species. At least 40 globally threatened species are known, though this is likely to increase as more IUCN assessments are made. The submontane forests have plants globally endemic to the Nimba Mountains, such as Osbeckia porteresii, Sporobolus pauciflorus, Impatiens nzoana, and Begonia quadrialata subsp. nimbaensis. The submontane grassland has threatened species found both at Nimba and in the Simandou mountains (e.g. Kotchya lutea, Rhytachne glabra, Bulbostylis guineensis, and Nemum bulbostyloides). There are also species found here that have disjunct distributions across Africa (e.g. Justicia jamisonii and Marsdenia exellii). Some species named ‘nimba’, while first collected at Nimba, have subsequently been found on other parts of the Guinean highlands (e.g. Ixora nimbana, Brachystephanus jaundensis subsp. nimbae, Dolichos nimbaensis, and Monanthotaxis nimbana).

The Nimba Mountains represent a rift area of the early Proterozoic era, similar in age and structure to the Simandou range intrusion. The range comprises itabirite, quartzite and other schists emplaced onto a terrain of tonalitic granite-gneiss, migmatite, and sedimentary gneisses. There is a significant iron ore deposit which is in the forms of haematites and goethites enriched from long-term leaching and weathering processes, including thrusting, faulting, folding and thermal processes.

The mountains are threatened by:
– Intense poaching, suffering from the ‘empty-forest’ syndrome.
– Agricultural encroachment, which has disturbed far more habitat, generally at low altitudes in forest, than any other form of disturbance.
– Regular, anthropogenic, and intense bushfires are a problem at the height of the dry season, when they do not occur naturally.
– Invasive species. In particular, Chromolaena odorata, which has invaded mid-altitude savannahs and forest-edges.
– Grazing of cattle at low elevations at the edge of forest.
– Isolation from neighbouring intact ecosystems due to agriculture, forestry, and roads in the surrounding lowlands.
– Mineral exploration in the mining enclave.
An area of 15.16km² was excised from the colonial Strict Nature Reserve of 1944 for mineral exploration, covering 10% of the Guinean Nimba Mountains, and 4.8% of the entire Nimba range. Within this enclave, an iron-ore mining concession of 6.25km² is currently in late-phase exploration. Mineral exploration has resulted in the construction of access roads and drill pads, affecting up to 0.5km². If a mine were developed, it would result in the disturbance of a several square kilometres of the enclave. For this reason, a detailed environmental impact assessment is underway to avoid and minimise negative impacts, particularly to the adjacent World Heritage Site, and to seek how best to close a future mine and rehabilitate the site for its long-term, subsequent conservation. Since the same habitat types are found within the mining enclave and the World Heritage site, this TIPA area will acknowledge the mining zone as an area of development, with the objective of minimising disturbance to the area as a whole.
Concerns have also been raised by the World Heritage Committee about a road upgrade running between Lola (Guinea) and Danané (Ivory Coast), in the Biosphere Reserve’s Buffer Zone. The World Heritage Committee has retained Nimba on the list of World Heritage Sites in Danger (2018).
Despite controls in place to manage these threats, continuing damage to the World Heritage Site is possible and will inevitably reduce the global populations of some species, and the extent of Threatened Habitats.

Charlotte Couch, Royal Botanic Gardens Kew

Martin Cheek, Royal Botanic Gardens Kew

Jamison Suter, Société des Mines de Fer Guinée

Carel Jongkind, Consultant Botanist