Guinean montane forests

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Southern Guinea Photograph by Rebecca Ham

The Guinean Montane Forest consists of high altitude peaks and plateaus that spread across four countries in the Upper Guinean region of West Africa. One of the peaks, Bintumani (on the Loma Mountains of Sierra Leone), is the highest peak west of Mount Cameroon. The broad range of elevation, coupled with the underlying geology and anthropogenic activities, have given rise to different plant associations on several of the mountains. Although details of the number of endemic plants are not fully compiled, 35 plant species are known to be strictly endemic, with several mountains containing their own unique plant species, such as the orchid Rhipidoglossum paucifolium, known only from Mount Nimba. The fauna is also diverse with close to 15 strictly endemic vertebrate species, including species found on single mountains, such as the Mount Nimba endemic toad, Nimbaphrynoides occidentalis. Mining on Mount Nimba, slash and burn farming, and human-made fires were the major threats prior to a decade of civil conflicts in Sierra Leone and Liberia. The current status of this ecoregion is poorly known because of continuing civil war in the region. A conservation assessment should be done immediately following cessation of fighting, and efforts made to declare the Loma Mountains and Tingi Hills as national parks.

Location and General Description

The Guinean Montane Forest ecoregion consists of scattered mountains and high plateau areas that rise out of a gently undulating landscape. Parts of the ecoregion are found in four West African countries, from Guinea in the west to Côte d’Ivoire in the east. Some landscapes rise precipitously (e.g., Loma Mountains and Tingi Hills in Sierra Leone, and Mount Nimba on the border between Liberia, Guinea, and Côte d’Ivoire) while others are more gentle such as the Fouta Djallon in Guinea, a heavily eroded plateau with an elevation of 1,100 meters (m). Bintumani Peak on Loma Mountain (1,947 m) is the highest peak west in West Africa, west of Mount Cameroon. Tingi Hills, just south of the Loma Mountains, and Sankabiaiwa (Sankan Biriwa), both attain a height of 1,860 m, making them the second highest peaks after Bintumani. Other notable mountains in this ecoregion are Mount Nimba (elevation of 1,752 m), the Simandou Massif in Guinea (1,650 m), the Ziama Massif (1,387 m) in Guinea, Mount Dutova in Liberia, and the Man Massif and Mont Peko in Côte d’Ivoire. With the exception of the Fouta Djallon, all of these peaks are rounded, as a result of millions of years of erosion and weathering.

The mountains in this ecoregion are formed of Precambrian basement rocks, with the predominant granitic rock also containing dolerite, gneiss, schist, and quartzite. Lithosols are the most common soil type on many of the mountains, although soil type may vary by aspect and degree of weathering. These soils are generally infertile, and some are rich in mineral deposits such as iron ore on Mount Nimba and the Fouta Djalon Plateau. On the Loma Mountains in Sierra Leone, Jaeger and Lamottee indicated that the height of the herbaceous plant, Hyparrhenia diplandra, is dependent on soil depth and altitude.

caption Fougoumba, Fouta Djallon, Guinea. (Source: Photograph by WWF/ Rebecca Ham)

Average rainfall is between 1,600-2,400 millimeters (mm) per year, and most major rivers in West Africa have their origins within the peaks of the Guinean Montane Forest ecoregion. For example, the most westerly tributary of the Niger River originates in the Loma Mountains of Sierra Leone, while the Senegal and Gambia Rivers originate in the Fouta Djallon of Guinea. The Sewa River in Sierra Leone has many of its tributaries arising from the Loma Mountains and Tingi Hills, making it the most important watershed in the country. There is considerable variation in the rainfall on different sides of the mountains. Most rain falls on the southern side of the mountains as it passes inland from the Atlantic Ocean. On the northern slopes there is little rainfall from the Atlantic due to rain-shadow effects. In addition these leeward slopes are also subject to the dry Harmattan winds blowing from the Sahara Desert, giving rise to xeric conditions. Temperatures are also quite extreme on these mountain slopes, with maximum temperatures ranging between 24°C and 33°C while minimum temperatures can fall below 10°C.

White classified the forests here as part of an Afromontane archipelago-like regional center of endemism. Lowland forest, part of the greater Guinea-Congolian forest complex, occurs on the lower reaches of the mountains closer to the coast. On northern slopes, forest-savanna mosaic becomes montane forest with increasing elevation and precipitation. At mid-altitudes (above 1,000 meters), the forest is often shrouded in clouds, resulting in verdant growth of epiphytes. With increasing altitude on the highest mountains, forests give way to grassland intermixed with bamboo, wetlands, and gallery forests. The vegetation of the northern leeward slopes is significantly more adapted to desiccation than the vegetation of the southern slopes due to reduced rainfall and the drying effects of the Harmattan winds. At 1,100 m, the Fouta Djallon is not high enough to develop true montane vegetation although it is found on some isolated peaks. Remnant forests here are dominated by Parinari excelsa. Grassland wildfires are largely human caused, but natural fires due to lightning strikes also occur. Human-made fires in the montane forest of Mount Nimba are believed to have assisted in the process of forest conversion to grassland during recent millennia.

The broad range of elevation, coupled with underlying geology and human influences, have given rise to different plant associations on several of the mountains in this ecoregion. On the Fouta Djalon Plateau (which is surrounded by the Guinean Forest-Savanna Mosaic ecoregion), agricultural development and periodic burning have transformed the once dominant Parinari excelsa forest into a grassland. The dominant flora of the grassland includes the genera Anadelphia, Loudetia, and Tristachya. Grassland also occurs on the ridges and peaks of Mount Nimba and is generally dominated by Andropogon and Loudettia, while the sedge, Hypolytrum cacuminum, occurs on some wetter slopes. The Mount Nimba grassland vegetation has been interpreted as ancient and natural, rather than produced by fires set by humans. Because of its location within the forest zone (Western Guinean lowland forests), the vegetation on the lower slopes of Mount Nimba is tropical forest, reaching elevations of 700 m. Above the 800-m contour line, Parinari excelsa, Gaertnera paniculata, Garcinia polyantha, and Syzygium staudtii dominate the forests, together with a rich array of epiphytes. Dense mats of Afrotrilepis pilosa occur on rocky outcrops providing suitable habitat for the growth of a microflora composed of Disa welwitschii, Osbeckia porteresii, Polystachya microbambusa, and Swertia mannii.

Both the Loma Mountains and Tingi Hills of Sierra Leone lie at the northern margin of the Western Guinean lowland forest ecoregion. According to Cole, four plant communities have been recognized on these massifs, including closed forests and Guinea savanna (460 - 915 m), sub-montane shrub savanna (915 - 1,700 m), montane grassland (prairie d’altitude) (1,700 m), and sub-montane gallery forests (1,700 m).

For the closed forest and Guinea savanna, the common plant associations in the humid valleys include Uapaca togoensis, Cola lateritia var. maclaudii, Parinari excelsa, Piptadeniastrum africanum, and Canarium schweinfurthii. Certain tree species (e.g., Guarea cedrata, Heritiera utilis, and Triplochiton scleroxylon) that occur here are considered to be growing out of their normal range. The understory vegetation is dominated by three species, Ochna membranacea, Caloncoba echinata, and Morus mesozygia, together with a limited herbaceous layer. The rare herb, Ramusatia vivipara, is limited to specialized habitats. In the savannas where fire is frequent, Lophira lanceolata, Parkia biglobosa, and Pterocarpus erinaceus are the dominant trees, while Anadelphia leptocoma, Andropogon tectorum, and Hyparrhenia diplandra are the dominant grasses.

At higher altitudes, the shrub layer of the sub-montane shrub savanna of the Loma Mountains and Tingi Hills is comprised of Syzygium spp., Kotschya ochreata var ochreata, Monechma depauperatum, Dissotis elliotii, Dissotis fructicosa, and the tree ferns, Cyathea manniana and Cyathea dregei. Tree ferns are noted as common in the gallery forest. Herbaceous plants and grasses include Ctenium newtonii, Loudetia kagerensis, Wedelia africana, with pure stands of Hyparrhenia chrysargyra and Rhytachne rottboellioides noted. On the gentle slopes rising above 1,375 m, Syzygium guineense var macrocarpum, Tetracera alnifolia, Canthium henriquesianum, and Hibiscus noldeae comprise the shrub layer. Grasses and herbs include Samanea spp., Eupatorium africanum, Vernonia purpurea, and Hypolytrum cacuminum, while secondary forest species such as Harungana madagascariensis and Trema guineensis are present on the summit at Loma.

Bulbs, rhizomes, tubers, and succulent plants dominate the vegetation of the montane grassland (prairie l’altitude), with Gladiolus spp., Solenostemon monostachyus subspecies latericola, Cyanotis longiflora, Vernonia jaegeri, and Thesium tenuissimum being the most common species. Plants growing in thin soils above 1,650 meters (m) include Scirpus briziformis, Panicum lindleyanum, Swetia mannii, Neurotheca loeselioides, Bulbostylis spp., Polystachya bequaertii, and Vigna micrantha. Plants growing in the grass-herb savanna on the Sanka Biriwa summit include Tristachya fulva, Leocus pobeguinii, Solenostemon monostachyus, Dissotis erecta, and Kyllinga spp. On the 3- to 6-m-deep soils of Bintumani peak, tiny herbs and sedges such as Utricularia spp., Lobelia rubescens, Drosera pilosa, Neurophila gentianoides, Pycreus reductus, Erioculon spp., and Xyris spp. abound. The steep slopes of Loma and Tingi contain mosses and lichens known to colonize bare rock surfaces, with subsequent colonization by saxicoles and herbaceous plants. The endemic orophyte, Afrotrilepis jaegeri, is known to be adapted to such rocky habitats.

Parinari excelsa is reported to be the dominant tree species in the sub-montane gallery forests of both the Loma Mountains and Tingi Hills. Tree ferns, Cyathea camerooniana and Marattia fraxinea, and the bamboo, Oxythenanthera abyssinica, are also important here. Other trees include Anthonotha macrophylla, Pseudo spp. ondias microcarpa, Amphimas pterocarpoides, Daniella thurifera, Ficus congensis, Terminalia ivorensis, Allanblackia floribunda, and Musanga cecropioides. The ground flora of the gallery forest is made up of herbs, ferns, and climbers and includes Whitfieldia lateritia, Clematis grandiflora, Sopubia ramosa, Anisopappus africanum, Lonchitis currovi, and Ouratea squamosa.

Biodiversity Features

Information concerning the abundance and distribution of plants and animals in this ecoregion is fragmentary. In those areas that have been surveyed, checklists of flora and fauna exist, but many areas are essentially unstudied. These isolated mountains might have served as refugia during the cold periods of the recent Ice Ages, although it is believed that the fauna may have also arisen from ancestral forms due to isolation. The diversity and endemism on Mount Nimba is well documented, with over 2,000 species of vascular plants recorded. More than 500 new species were discovered there, including a number of strict endemics. All of the different component areas of this ecoregion boast several single-site endemics. However, little is known about the evolutionary history and ecological relationships of species on these mountains relative to other African montane forests.

Floristic diversity results from a combination of geographic isolation, varied topography and soils, migration, speciation, climatic factors and anthropogenic activities. Studies of the Loma Mountains have produced considerable information about the flora, with records for 1,576 species distributed in 757 genera and 135 families. Nine species are endemic, and include Afrotrilepis jaegeri, Digitaria phaeotricha var. patens, Dissotis sessilis, Gladiolus leonensis, Ledermanniella jaegeri, Loudetia jaegeriana, Loxodera strigosa, Schizachyrium minutum (S. brevifolium), and Scleria monticola. The four endemic plant families found in tropical Africa are also represented in the Loma Mountains by Triphyophyllum peltatum (Dioncophyllaceae), Octoknema borealis (Octoknemataceae), Bersama abyssinica (Melianthaceae), and Napoleona leonensis, and Napoleona vogelii (Lecythidaceae). For the entire Guinean Montane Forest (including the following mountains: Fouta Djalon, Loma, Tingi, Nimba, and Man), 35 endemic plants including 11 palaeo-endemics have been recorded. The 11 palaeo-endemics are Borreria macrantha, Cyanotis lourensis, Droogmansia scaettaiana, Eriosema parviflorum, Eugenia pobeguinii, Hypolytrum cacuminum, Kotschya lutea, Mesanthemum aurantum, Rhytachne glabra, Vernonia nimbaensis, and Xyris festucifolia.

The vascular epiphytes of the Loma Mountains and Mount Nimba have been the subject of extensive studies. A total of 101 species in the Orchidaceae have been recorded for Mount Nimba, including one endemic species Rhipidoglossum paucifolium. Phorophytes like Heritiera utilis, Lophira alata, and Parinari excelsa were also reported to carry an abundance of epiphytes. The epiphytic communities of the Loma Mountain and Tingi Hills of Sierra Leone are much better developed in the gallery forests than other vegetation types. On the north-facing slopes of these mountains, the fern, Platycerium spp., is reported to produce fronds that are 1 meter across.

The faunal diversity is also rich and contains a number of endemic species. In the mammals, four species are either strictly endemic, or narrowly shared with the surrounding lowland habitats. These are Mount Nimba otter shrew (Micropotamogale lamottei, EN), two species of white-toothed shrew (Crocidura obscurior and C. nimbae) and a species of leaf-nosed bat (Hipposideros marisae VU). A number of other rare forest mammals may also occur marginally in the mountains of this ecoregion, including Johnson’s genet (Genetta johnstoni, DD) and a murid rat (Praomys rostratus). The western chimpanzee (Pan troglodytes verus, EN) also occurs in this ecoregion, with high densities reported from Mt Loma. The largest predator in the ecoregion is the leopard (Panthera pardus, EN). Ecological studies of some of the mammals on Mount Nimba were completed in the early 1970s.

Avifaunal diversity is also high, and a number of rare species occur, including two near-endemic species, the Sierra Leone prinia (Prinia leontica, VU) and the iris glossy-starling (Coccycolius iris). The avifauna of Mount Nimba has been well described and includes the near-endemic Sierra Leone prinia, the grey-winged robin-chat (Cossypha polioptera), and lemon dove (Columba larvata), and Sharp’s apalis (Apalis sharpii). The white-eyed prinia (Prinia leontica) is found only in the gallery forests of the Guinea Highlands at 500 m to 1,550 m. The presence of the rare yellow-headed rockfowl (Picathartes gymnocephalus, VU) has also been confirmed in the Loma Mountains.

The ecoregion is also of importance for endemic amphibians. More than 10 species are believed to be strictly endemic, including Nimbaphrynoides occidentalis, an endemic toad occurring in savannas on Mount Nimba. Because of the xeric conditions in the savanna of Mount Nimba, this toad has evolved a reproductive adaptation that does not involve a larval stage. Instead the female gives birth to fully developed young toads after a gestation period lasting more than eight months. In terms of reptiles, the area is of lower importance, with less than five species of near-endemic reptile being recorded.

Several new species of insects in the family Coleoptera have been reported for both the Loma and the Nimba Mountains. For the Loma Mountains, these include Promecolanguria lomensis, Barbaropus bintumanensis, and Barbaropus explanatus. The species recorded on Mount Nimba include Promecolanguria dimidiata, Promecolanguria pseudosulcicollis, Promecolanguria mimbana, Promecolanguria armata, and Barbaropus nigritus. It is very likely that all the mountains of this ecoregion contain single-site endemic invertebrates, although the data are not compiled to prove this.

Current Status

Some of the mountain zones remain largely untouched, while others have been severely degraded and fragmented. Ecosystems on Mount Nimba have undergone marked fragmentation, as have those of the Fouta Djalon. By contrast, the Loma Mountains in Sierra Leone still have an unbroken sequence of intact habitats.

In general this ecoregion is not well protected in formal conservation areas. In total, there are two Biosphere Reserves (Monts Nimba in Liberia, Guinea, and Côte d’Ivoire and Massif du Ziama in Guinea) and two World Heritage Reserves (Mount Nimba in Côte d’Ivoire and Mount Nimba in Guinea). The Loma Mountains is a proposed National Park under the authority of the Wildlife Conservation Branch of the Sierra Leone government. Despite calls for it to be made into a National Park, a lack of financial and human resources has hindered progress towards the achievement of this conservation status. Recent civil unrest has set back efforts at protecting the Loma Mountains because the region is under the control of rebel forces; it is not known what impact the civil war might have had on the resources of this important area. The Tingi Hills in Sierra Leone is a Forest Reserve. There are also numerous small Forest Reserves in the highland areas of Guinea, and a large one at Ziama.

Despite the various designations of Mount Nimba as a Strict Nature Reserve, World Heritage Site, and Biosphere Reserve, mining for iron ore was still occurring prior to the Liberian civil war. Although the war has stopped mining operations, future mining is likely given the widespread destruction caused by war and the perceived need for generating income and employment for local people.

Types and Severity of Threats

Mining, fires, and deforestation are considered the principle threats in this ecoregion. Mount Nimba contains massive deposits of high-grade iron ore, making it the target of extensive mining operations in the past. In 1990 it was estimated that one proposed new area of mining activity could be worth $20 million (US) per year to Guinea. On the Liberian side of Mount Nimba, a multinational mining operation has done enormous damage to the forests and streams, but the recent Liberian civil war has put a ten-year halt to the destructive mining operations. A high population density, coupled with human-made fires, are credited with causing considerable deforestation in the Fouta Djalon. Current information on the Loma Mountains and Tingi Hills in Sierra Leone is virtually lacking owing to the decade-long civil war, although the Loma Mountains were in good condition in the early 1990s. There is no data available on the status and threats to the habitats of the other mountains in this ecoregion.

Justification of Ecoregion Delineation

White mapped montane areas in Sierra Leone, Liberia, and Ivory Coast as ‘undifferentiated montane vegetation’, and, in Guinea, as ‘mosaic of lowland rainforest, secondary grassland, and montane elements’. This ecoregion follows these vegetation divisions, but the lower boundary has been taken at the altitude of 600 meters (m). Although the habitats are not strictly montane at 600 m, the vegetation is regarded as distinct from the surrounding lowlands.

Additional Information on this Ecoregion

Further Reading

  • Adam, J. G. 1958. Elements pour l'etude de la vegetation des hauts plateaux du Fouta Djalon. Part 1. Bureau des sols, Direction des Services Economiques, Gouvernement General de l'Afrique Occidentale Francais, Dakar.
  • Allport, G. 1991. The status and conservation of threatened birds in the Upper Guinea Forest. Bird Conservation International 1:53-74.
  • Bourque, J.D. 1996. Inventaire preliminaire de la faune aviaire du Bassin de la riviere Kuundu et de la forest classee de Nialama, Republique de Guinée. Unpublished report.
  • Coe, M. 1975. Mammalian ecological studies on Mount Nimba, Liberia. Mammalia 39:523-587.
  • Coe, M., and K. Curry-Lindahl. 1965. Ecology of a mountain: first report on Liberian Nimba. Oryx 8:177-184.
  • Cole, N. H. A. 1967. Ecology of the montane community at the Tingi Hills in Sierra Leone. Bulletin de l'IFAN 29A:904-924.
  • Cole, N. H. A. 1968. The Vegetation of Sierra Leone. Njala University College Press. 198p.
  • Cole, N. H. A. 1974. Climate, life forms and species distribution on the Loma Montane grassland, Sierra Leone. Bot. J. Linn. Soc. 69:197-210.
  • Curry-Lindahl, K. 1966. Zoological aspects on the conservation of vegetation in tropical Africa. Acta Phytogeographica Suecia 54:25-32.
  • Collar, N.J. and S.N. Stuart. 1988. Key forests for threatened birds in Africa. ICBP, Cambridge, UK. ISBN: 0946888159
  • Colston, P. P. and K. Curry-Lindahl. 1986. The Birds of Mount Nimba, Liberia. British Museum of Natural History. # ISBN: 0565009826
  • Gatter, W. 1997. Birds of Liberia. Yale University Press. USA. ISBN: 0300075766
  • Hilton-Taylor, C. (Compiler) 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, UK. ISBN: 2831705657
  • Jaeger, P. 1965. Especes vegetales de l'etage altitudinal des monts Loma (Sierra Leone). Bulletin de l'IFAN 27A:34-120.
  • Jaeger, P. and M. Lamottee. 1966. Les richesses floristiques et faunistiques des monts Loma (Sierra Leone). Bulletin de l'IFAN 28A:1149-1190.
  • Jaeger, P., N. Halle and J. G. Adam. 1968. Contribution a l'etude des Orchidees des Monts Loma (Sierra Leone). Adansonia 8:265-310.
  • Jaeger, P. and J. G. Adam. 1975. Les forets de l'etage culminal du Nimba Liberien. Adansonia 15:177-188.
  • Jaeger, P. 1983. Le recesement des plantes vasculaires et les originalites du peuplement vegetal des monts Loma en Sierra Leone (Afrique Occidentale). Bothalia 14:539-542.
  • Johansson, D. 1974. Ecology of vascular epiphytes in West African rain forest. Acta Phytogeographica Suecica 59:1-129.
  • Morton, J. K. 1986. Montane Vegetation. In Plant Ecology in West Africa, G. W. Lawson (editor), 247-271. John Wiley and Sons Ltd., United Kingdom. ISBN: 0471903647
  • Morton, J. K. 1972. Phytogeography of the West African mountains. Pages 221-236 in D. H. Valentine, editor. Taxonomy, Phytogeography and Evolution. Academic Press, London, United Kingdom.
  • NIMCO. 1997. Project Minier des Monts Nimba: Environmental Impact Assessment. Man and the Biosphere, Paris.
  • Sayer, J.A., C.S. Harcourt, and N.M. Collins. 1992. The Conservation Atlas of Tropical Forests: Africa. IUCN and Simon & Schuster, Cambridge. ISBN: 0131753320
  • Schnell, R. 1952. Vegetation et flore de la region montagneuse du Nimba. Mem. l’IFAN 22:1-604.
  • Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wege. 1998. Endemic Bird Areas of the World. Priorities for Biodiversity Conservation. BirdLife International. Cambridge, United Kingdom. ISBN: 1560985747
  • Thompson, H. S. S. 1993. Status of white-necked picathartes - another reason for the conservation of the Peninsula Forest, Sierra Leone. Oryx 27:155-158.
  • Villiers, A. 1965. Coleopteres languriides des monts Loma (Sierra Leone). Bulletin de l'IFAN 27A:1015-1021
  • WWF and IUCN. 1994. Centers of plant diversity. A guide and strategy for their conservation. Volume 1. Europe, Africa, South West Asia and the Middle East. IUCN Publications Unit, Cambridge, U.K. ISBN: 283170197X
  • White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris. ISBN: 9231019554

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Citation

Fund, W. (2014). Guinean montane forests. Retrieved from http://www.eoearth.org/view/article/153185

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