Eastern Guinean forests

Published: May 5, 2014, 7:56 pm

Topics:

Conservation Biology (main) Biodiversity (main) Ecology (main)

Krokosua Hills Rainforest, Ghana Photograph by Claude Martin

WWF Terrestrial Ecoregions Collection

The Eastern Guinean Forest comprises a broad swath of land extending from western Côte d’Ivoire to eastern Ghana and extending into the Togo Hills. There is a high diversity of non-human primates here, including western chimpanzee (Pan troglodytes verus). Thirteen amphibians are strictly endemic to the ecoregion and, together with plants and butterflies, these groups illustrate the clearest difference from the contiguous lowland forests further west.

The threats facing this ecoregion are numerous and diverse. Considerable areas of forestland have been converted to farmlands, often using a rotation ‘farmbush’ farming system. The total area under protection is relatively small, and pressure to extract forest resources, especially timber, fuel wood, and charcoal remains high due to a ready timber export market and increasing urban population centers such as Abidjan and Accra. Habitat loss and hunting for bushmeat has recently caused the extinction of one non-human primate subspecies, Miss Waldron’s colobus (Piliocolobus badius waldroni), and the endemic Togo mouse (Leimacomys buettneri) may also be extinct.

Location and General Description

The Eastern Guinean Lowland Forest extends from the east banks of the Sassandra River in western Côte d’Ivoire (06° 05’ W) to the edge of Lake Volta (01° 50’ W) in Ghana. There is a small extension of this ecoregion east of Lake Volta into the Togo Hills, which lie mostly in Togo but extend across the border to easternmost Ghana, with one outlier in Benin. The Togo Hills are unusual because they support forest vegetation within an area that is otherwise savanna-woodland. The dry lowland area on the eastern edge of the ecoregion is termed the Dahomey Gap and is a major biogeographical barrier. In the border areas between Ghana and Côte d’Ivoire, the ecoregion extends to 8° N and gradually fades into a mosaic of forest patches and tall grasslands of the Guinea Forest-Savanna Mosaic.

Topography undulates between 50 and 300 meters (m) above sea level, with many small projecting inselbergs, some over 400 m high. Within the Togo Hills (Chaine de Togo), the topography shows much altitudinal variation and the maximum elevation reaches 1,000 m. The Akatora range in northwestern Benin has a maximum height of 650 m. The parent rock in this region is mostly Precambrian basement material of the African Shield. Pre-Cretaceous basinal rocks also occur on the northern margins. In the regions marked by lower rainfall, the soils are mostly acrisols, while the high rainfall zones contain red ferrasols. Soil fertility is generally low in this region, although a few areas have more fertile soils. In Ghana for example, the soils in the moist semi-deciduous forest zone are rich, while bauxitic soils are common in the upland evergreen forest region. A temperature gradient occurs from the coastal zones and moving northwards. Temperatures in the forested south range between 22°C and 34°C, whereas in the north temperatures are more extreme and can reach a maximum of 43°C and fall to 10°C on cold nights. The rainfall pattern in this ecoregion is complex, but can be generally divided into distinct wet and dry seasons, with the latter lasting longer here than in the neighboring Western Guinean Lowland Forests. In Benin and Togo, rainfall seldom exceeds 1,500 millimeters (mm). In the southwestern zone of Ghana, there is an average rainfall of 1,000 mm to 2,100 mm per year. Only in Côte d’Ivoire is the rainfall greater, averaging between 1,400 mm and 2,500 mm per year. Rainfall also declines inland, and as four to five months of the year are virtually without rain in some of these countries. Forest composition changes along this gradient, from the coastal zone to the inland areas.

In the phytogeographical classification of White, this ecoregion falls within the Upper Guinea Forest block of the Guineo-Congolian regional center of endemism. The Sassandra River in southwestern Côte d’Ivoire serves as its western limit and the ecoregion is separated from the Niger Delta and forests further east by the Dahomey Gap. Moist and wet evergreen forest in the extreme south grades into moist semi-evergreen forest inland, which in turn becomes dry semi-evergreen forest in the northern parts of the ecoregion. This dry forest represents the fringe of the forest belt. The width of the rainforest belt in West Africa has varied over millions of years during periods of wetter and drier weather, most recently associated with Ice Age events.

The high forest here shares some traits with the lowland forests to the west, including a canopy at least 30 meters (m) tall. Some individuals in the mixed moist semi-evergreen rainforest in Ghana tower 55 m to 60 m. The Mimosaceae and Caesalpiniaceae families dominate the moist evergreen forests. The semi-evergreen forest is relatively rich floristically, including representatives from the Meliaceae, Chrysobalanaceae, and Rubiaceae. The dry peripheral forest contains several species that periodically shed their leaves.

In Ghana, seven vegetation types with unique plant associations have been identified in the forest zone. The wet evergreen forest, which occurs entirely in the southwest, is dominated by trees that also occur in the Western Guinean Lowland Forest, including representatives of the genera Lophira, Heritiera, and Cynometra. The moist evergreen forest is made up of two types (northwest and southeast), and includes trees such as Entandrophragma utile, Khaya ivorensis, and Triplochiton scleroxylum. The wetter subtype of the dry semi-deciduous forest is dominated by Hymenostegia afzelii, with the drier subtype of the semi-deciduous forest dominated by Diospyros mespiliformis and Anogeissus leiocarpus. The southeast outliers, a much drier forest type on the Accra plains, are made up of low canopy trees such as Millettia thonningii, Tlbotiella gentii, and Drypetes parvifolia.

In Cote d’Ivoire, semi-deciduous and moist evergreen forests are the dominant forest types. The semi-deciduous forest is dominated by four families (Malvaceae, Sterculiaceae, Ulmaceae and Moraceae), with Celtis spp., Mansonia altissima, Pterygota macrocarpa, Nesogordonia papaverifera, Sterculia rhinopetala, and Milicia excelsa comprising the dominant plant associations. Mimosaceae and Caesalpiniaceae are the dominant families in the moist evergreen forest type, with Piptadeniastrum africanum, Parkia bicolor, Erythrophleum ivorense, Anthonotha spp., Parinari excelsa, and Klainedoxa gabonensis being common plant associations. Both the moist evergreen forest and semi-deciduous forests in Cote d’Ivoire also contain Entandrophragma spp. and Khaya spp.

The extent of forests in Togo and Benin is now greatly reduced relative to what existed at the turn of the century, with existing small fragments made up of semi-evergreen or deciduous forest. The Lama forest in south-central Benin is dominated by plant associations that include Milicia excelsa, Triplochiton scleroxylon, Antiaris africana, Diospyros mespiliformis, Afzelia africana, and Ceiba pentandra. Other trees common in these regions include Cola grandifolia, Vitex spp., Celtis spp., Khaya grandifolia, and Holoptelea spp.

Biodiversity Features

The Eastern Guinean Forest is rich in animal and plant life. The flora and fauna have strong similarities to the adjacent Western Guinean Lowland Forests, but there are also significant differences that allow their separation. The two [[ecoregion]s] are separated by the Sassandra River, a barrier which has influenced species distribution and evolution. For example, the western and eastern subspecies of sooty mangabey (Cercocebus torquatus atys, C.t. lunulatus) and of diana monkey (Cercopithecus diana diana, C. d. roloway) are separated by the Sassandra River. Moreover, a subspecies of the king colobus, Colobus polykomos vellerosus (listed as C. vellerosus on the IUCN 2000 Red List and considered vulnerable) and Lowe’s subspecies of mona monkey, Cercopithecus mona lowei are only found east of the Sassandra River.

This area has a rich non-human primate fauna but recently, one of these primates, Miss Waldron’s red colobus (Procolobus badius waldroni), was reported to have become extinct, although the species’ critical status had been known for some time. Its range included only the forests of Côte d’Ivoire and Ghana, where hunting for bushmeat has been a threat for some time. Some remaining primates are also threatened as a result of habitat loss and the rising demand for bushmeat. The western sooty mangabey (Cercocebus torquatus lunulatus), the western subspecies of chimpanzee (Pan troglodytes verus EN), and the diana monkey (EN) are all in need of protection from this threat.

Only four small mammals are strict endemics to this ecoregion, a species of Dephua mouse (Dephomys eburnea), a rodent, Malacomys cansdalei, a white-throated shrew, Crocidura wimmeri (EN), and the Togo mouse (Leimacomys buettneri CR). Although Kingdon reports that the Togo mouse is little known and probably extinct, the World Conservation Union (IUCN) ranks it as critically endangered and a specialist group will need to meet and decide if it is in fact, extinct. Other endemic and near-endemic mammals are Lowe’s subspecies of mona monkey (Cercopithecus mona lowei), the lesser spot-nosed monkey (Cercopithecus petaurista petaurista), olive colobus (Procolobus verus), and royal antelope (Neotragus pygmaeus). The remaining near-endemics are small rodents and shrews, including Kitamps rope squirrel (Funisciurus substriatus), Western palm squirrel (Epixerus ebi), Gambian sun squirrel (Heliosciurus punctatus), Oenomys ornatus, and Crocidura muricauda. Most of these near-endemic species are found only in the eastern and western portions of the Upper Guinea forest. The rare pygmy hippopotamus (Hexaprotodon liberiensis EN) also occurs marginally in the western part of this ecoregion. This species is regarded as a "living fossil" because very similar species occurred in India, Madagascar, southern Europe and East Africa in geologically recent times. The top carnivores in this ecoregion are leopard (Panthera pardus EN), golden cat (Profelis aurata), and African civet (Civettictis civetta). These are all rare, largely as a result of habitat modification and overhunting of their prey animals.

Small populations of forest elephant are found in this ecoregion, often isolated in unconnected forest patches. Forest elephants may play a significant role in influencing forest composition and structure, and their possible extinction in this ecoregion would effect the woody forest species that are dependent on them for seed dispersal and regeneration. The role of elephants as seed dispersers was examined in the forests of Ghana, where there is no immediate evidence of population collapse, but Balanites wilsoniana is cited as one species that is likely to suffer should elephants go extinct. Tieghemella heckelii has been cited as another species that appears to be dependent on forest elephants for regeneration.

The species richness of birds in this ecoregion is high, but there are no strict endemics and all the endemic species are shared with the western portion of the Upper Guinea forest. These two forest ecoregions together are regarded as an Endemic Bird Area, which contains 15 unique bird species. The Western Guinean Forest ecoregion is richer in these endemic species than the Eastern Guinean Forest ecoregion. Near-endemic species found in the Eastern Guinean Forest ecoregion include white-breasted guineafowl (Agelastes meleagrides VU), Ghana cuckoo-shrike (Campephaga lobata VU), brown-cheeked hornbill (Ceratogymna cylindricus), African barred owlet (Glaucidium castaneum), rufous-winged illadopsis (Illadopsis rufescens), and Sierra Leone prinia (Prinia leontica), emerald starling (Lamprotornis cupreocauda), Sharpe’s apalis (Apalis sharpei), black-throated rufous warbler (Bathmocercus cerviniventris), yellow-headed rockfowl (Picathartes gymnocephalus VU), Ladgen’s bushshrike (Malaconotus lagdeni), and rufous fishing owl (Scotopelia ussheri EN) .

While the herpetofauna is poorly known, there are high rates of endemism in the amphibians, with 13 strictly endemic species, mainly treefrogs. The reptile fauna is less rich in endemics, with only one species regarded as strictly endemic to the ecoregion and more than 10 species nearly endemic and mainly shared with the Western Guinean Forest ecoregion. Larsen has recorded 120 species of butterfly endemic to the West African forest ecoregions. He also documented a number of butterflies that are narrowly endemic only to the Togo Mountains portion of the ecoregion, and that this is an area of complex biogeography.

Current Status

What remains of the Eastern Guinean Lowland Forest is highly fragmented, largely due to human activities over hundreds if not thousands of years. Most of the remaining large tracts of forest are gazetted as ‘protected areas’ under the control of national governments. Nearly all of these forest fragments are isolated from each other, and there are no efforts to develop and implement wildlife corridors in order to ameliorate the effects of isolation on fauna and flora. Protected sites represent barely 1 percent of the total ecoregion area, only 1,956 square kilometers (km²) out of a total area of 189,724 km². In Ghana, some of the most important protected areas include Kakum National Park, Bia National Park, Nini-Suhien National Park, Ankasa Game Production Area, and Agumatsa Wildlife Sanctuary. The latter (Agumatsa), is the only protected area in the biologically diverse Togo Hills. In the Togo Hills, some unprotected forest remains on the Danyi Plateau in Togo, as well as on the Togo Range and in an area to the East of Lake Volta in Ghana. Satellite imagery indicates that hundreds of square kilometers of forest might still survive in these areas, though it is believed that they are being rapidly cleared for agriculture. In Ghana, there are also a large number of forest reserves that are used for timber production. These forest reserves can contain significant levels of biodiversity even after they have been logged, and as high forest is generally absent outside these reserves (except for sacred forest patches) then their role in biodiversity conservation is very important. In Côte d’Ivoire, the largest remaining areas of forested [[habitat]s] are found in the southeastern region in the Marahoué National Park and along the Comoé River. In Benin, efforts at protecting some portion of the natural closed forest are underway in the Lama Forest.

Types and Severity of Threats

The reduced area of forests in this ecoregion today is the result of anthropogenic activities, primarily slash and burn agriculture, but also industrial logging and harvesting wood for fuel and charcoal in urban areas. Fire associated with traditional agricultural practices is the greatest threat to semi-deciduous forests in Ghana. In recent years, these fires have expanded southward, resulting in the ‘savannization’ of areas once forested. Declining fallow periods and rising human populations are expected to put additional pressures on the remaining protected forest reserves and national parks. Throughout the 1970s, agricultural policies promoting export production for coffee and cocoa led to widespread forest loss in Cote d’Ivoire and Ghana. Price declines in global markets for these products during the 1980s reduced the role of export commodity production as a cause of deforestation.

Logging of natural forest for valuable hardwoods such as iroko (Milicia excelsa) and mahogany (Khaya and Entandrophragma species) has also contributed to the decline in forest area in all four countries in this ecoregion. Domestic demand for timber is moderately high and the desire to generate foreign exchange has led to the development of large export markets in processed and unprocessed logs. Although very little timber is exported from Benin (and hardly any from Togo), Côte d’Ivoire, and Ghana are large exporters from this ecoregion. Where forestry management authorities are not strong enough to prevent it, roads cut to access commercial hardwoods allow shifting agriculturalists and smallholder cash cropper cultivators to penetrate into the forests. Commercial hunters also take advantage of the access provided by logging roads to travel further into the forest to harvest wildlife. The impact of bushmeat hunting to meet the growing demand in urban and rural areas has the potential to cause local as well as global extinctions, as has already been seen by the extinction of one primate subspecies in this ecoregion. No edible vertebrate species is safe from this activity, which is taking place without any form of control.

The heavily logged sites or previously burnt areas are at greatest risk of subsequent fires. Plantation forestry is now increasing but the area planted is small and insufficient to meet the growing demand from domestic markets. The demand for fuel wood, particularly from burgeoning urban centers such as Abidjan and Accra, will continue to gnaw away at the remaining unprotected forests. Between 75-84 percent of Ghanaian households are dependent on charcoal and firewood for cooking and heating. Fuel wood consumption is currently outpacing the growth of new wood, and various predictions have been made on the future lack of this essential commodity.

Justification of Ecoregion Delineation

This ecoregion comprises the Eastern portion of the Upper Guinea forest block, recognized as an Endemic Bird Area, Centre of Plant Diversity, and Hotspot. The boundaries follow the rainforest vegetation unit delineated by White. However, this ecoregion was divided from the Upper Guinea lowland forest ecoregion west of the Sassandra River, which forms a biogeograpic barrier for species and subspecies, including a large number of amphibians, as well as Colobus vellerosus, Cercopithecus (m.) lowei, and Cercocebus atys lunulatus. The eastern margin is separated from the Nigerian Lowland Forest by the dry [[habitat]s] of the Dahomey Gap, which has long been recognized as a significant natural break in the Guineo-Congolian rainforest block. The finger of rainforest that extends into Togo encompasses Monts Togo du Fazao, and de l’Atakora using the 600-meter elevation contour.

Additional Information on this Ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
• World Wildlife Fund Homepage

Further Reading

• Allport, G. 1991. The status and conservation of threatened birds in the Upper Guinea Forest. Bird Conservation International 1:53-74.
• Aubreville, A. 1937. Les forêts du Dahomey et du Togo. Bulletin Comite d’Etude Historique et Scientifique Occidentale Francaise 20:1-112.
• Asibey, E. O. A. and J. G. K. Owusu. 1982. The case for high forest national parks in Ghana. Environmental Conservation 9:293-304.
• Eves, H. E. and M. I. Bakarr. 2001. Impacts of bushmeat hunting on wildlife populations in West Africa's Upper Guinea Forest Ecosystem. Pages 39–57 in M. I. Bakarr, G. A. B. da Fonseca, R. Mittermeier, A. B. Rylands, and K. W. Painemilla, editors. Hunting and Bushmeat utilization in the African rain forest: perspectives toward a blueprint for conservation action. Advances in Applied Biodiversity Science Number 2, Conservation International, Washington DC. ISBN: 1881173372
• Falconer, J. 1992. Non-timber forest products in southern Ghana. ODA Forestry Series no. 2. NRI, Chatham.
• FAO. 1988. An Interim Report on the State of Forest Resources in the Developing Countries. FAO, Rome, Italy. 18p.
• FAO/UNEP. 1981. Tropical Forest Resources Assessment Project. Forest Resources of Tropical Africa. Part II: Country Briefs. FAO, Rome, Italy.
• Frédoux, A. 1994. Pollen analysis of a deep-sea core in the Gulf of Guinea: vegetation and climatic changes during the last 225,000 years B.P. Palaeogeography, Palaeoclimatology, Palaeoecology 109:317-330.
• Gordon, D., W. Hawthorne, N. M. Bird, J. E. F. Falconer, N. O’Neill, E. O. A. Asibey, J. H. Francois, K. T. Boateng, K. Ghartey, K. Tufour, R. K. Bamfo, G. Pungese, K. Frimpong-Mensah, J. G. K. Owusu, S. J. Quashie-Sam and D. S. Amlalo. 1992. Ghana. Pages 183-192 in J. A. Sayer, C. S. Harcourt, and N. M. Collins, editors. The Conservation Atlas of Tropical Forests: Africa. IUCN and Simon & Schuster, Cambridge. ISBN: 0131753320
• Grubb, P. 1978. Patterns of speciation in African mammals: Bulletin of the Carnegie Museum of Natural Histroy 6:152-167.
• Hall, J. B. and Swaine, M. D. 1981. Distribution and ecology of vascular plants in a tropical rain forest. Forest vegetation in Ghana. Geobotany 1.
• Happold, D. C. D. 1996. Mammals of the Guinea-Congo rain forest. Proceedings of the Royal Society of Edinburgh 104B:243-284.
• Hawthorne, W.D. 1991. Fire damage forest regeneration in Ghana. Forest Inventory and Management Project. Forestry Department of Ghana, Kumasi.
• Hawthorne, W.D. 1993. Forest regeneration after logging. Findings of a study in the Bia South Game Production Forest Reserve. ODA Forestry Series no.3. NRI, Chatham.
• Hawthorne, W.D. and Abu-Juam, M. 1995. Forest protection in Ghana, with particular reference to vegetation and plant species. IUCN, Gland and Cambridge. ISBN: 2831702615
• Hawthorne, W.D. and M.P.E. Parren. 2000. How important are forest elephants to the survival of woody plant species in Upper Guinean Forests? Journal of Tropical Ecology 16:133-150.
• IUCN 1990. Biodiversity in Sub-Saharan Africa and its islands. Occasional Papers of the IUCN Species Survival Commission No. 6. IUCN Publications Unit, Gland, Switzerland. ISBN: 2831700213
• Kingdon, J. 1990. Island Africa. Princeton University Press, Princeton, NJ. ISBN: 0002194430
• Kingdon, J. 1997. The Kingdon Field Guide to African Mammals. Academic Press. 476p. ISBN: 069111692X
• Larsen, T.B. 1994. The butterflies of Ghana - their implications for conservation and sustainable use. Unpublished report, London.
• Lawson, G.W. editor. 1986. Plant ecology in West Africa: systems and process. John Wiley and Son, Chichester. ISBN: 0471903647
• Leach, G. and R. Mearns. 1988. Beyond the Fuelwood Crisis. Earthscan Publications Ltd., London, United Kingdom. ISBN: 1853830313
• Lieberman, D., M. Lieberman and C. Martin. 1987. Notes on seeds in elephant dung from Bia National Park, Ghana. Biotropica 19:365-369.
• Martin, C. 1991. The rainforests of West Africa: ecology-threats-conservation. Birhauser-Verlad, Basel, Switzerland.
• Mensah-Ntiamoa, A. Y. 1981. 1989. Pre-feasibility study on wildlife potentials in the Kakum and Assin-Attandanso Forest Reserves – Central Region – Ghana. Unpublished. Department of Game and Wildife, Accra, Ghana.
• McGraw, W. S. 1998. Three monkeys nearing extinction in the forest reserves of eastern Côte d'Ivoire. Oryx 32:233-236.
• Merz, G. 1986. Movement patterns and group size of the African forest elephant Loxodonta africana cyclotis in the Taï National Park, Ivory Coast. African Journal of Ecology 24:133-136.
• Munslow, B., Y. Katerere, A. Ferf, and P. O'Keefe. 1988. The Fuelwood Trap: a Study of the SADCC Region. Earthscan, London, United Kingdom.
• Nketiah, K. S., E. B. Hagan and S. T. Addo. 1988. The Charcoal Cycle in Ghana – A Baseline Study. Report Prepared for UNDP, Accra, Ghana.
• Oates, J. F., M. Abedi-Lartey, W. S. McGraw, T. T. Struhsaker and G. H. Whitesides. 2000. Extinction of a West African Red Colobus monkey. Conservation Biology 14:1526-1532.
• Owusu, J. G. K., C. K. Manu, G. K. Ofosu and Y. Ntiamoa-Baidu. 1989. Report of the Working Group on Forestry and Wildlife (Revised version). A Report Prepared for the Environmental Protection Council, Accra, Ghana.
• Robinson, J. G. and E. L. Bennett, editors. 2000. Hunting for Sustainability in Tropical Forests. Columbia University Press, New York. ISBN: 0231109776
• Sayer et al 1992a. Rainforest atlas
• Sayer, J. A., A. Green and D. Bourque. 1992b. Benin and Togo. Pages 97-101 in J. A. Sayer, C. S. Harcourt, and N. M. Collins, editors. The Conservation Atlas of Tropical Forests: Africa. IUCN and Simon & Schuster, Cambridge. ISBN: 0131753320
• Schiøtz, A. 1999. Treefrogs of Africa. Edition Chimaira, Meckenheim, Germany. ISBN: 3930612240
• Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wege, D. C. 1998. Endemic Bird Areas of the World. Priorities for Biodiversity Conservation. BirdLife International. Cambridge, United Kingdom. ISBN: 1560985747
• Vooren, F. and J. Sayer. 1992. Cote d’Ivoire. Pages 133-142 in J. A. Sayer, C. S. Harcourt and N. M. Collins, editors. The Conservation Atlas of Tropical Forests: Africa. IUCN and Macmillan Publishers, United Kingdom. ISBN: 0131753320
• Voorhoeve, A. G. 1965. Liberian High Forest Trees. Centre for Agricultural Publications and Documentation, Wageningen, The Netherlands.
• Waitkuwait, W. E. 1992. Restauration d’un ecosysteme forestier: contribution de l’amenagement de la faune. Pages 203-214 in A. P. Vooren, W. Schork, W. A. Blokhuis and A. J. C. Spijkerman, editors. Compte rendu seminaire sur l’amaenagement integre des forets denses humides et des zones africoles peripheriques, Tropenbos Series 1. Pays-Bas, La Fondation Tropenbos, Wageningen.
• WCMC 2000. Protected areas database.
• 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). Eastern Guinean forests. Retrieved from http://editors.eol.org/eoearth/wiki/Eastern_Guinean_forests