Western Guinean lowland forests
The Western Guinean Lowland Forest contains the westernmost rainforest on the African continent.
The flora and fauna is distinctive, with larger numbers of narrowly endemic species than in the contiguous Eastern Guinean lowland forests ecoregion to the east. The two endemic duikers, Jentink’s duiker (Cephalophus jentinki) and zebra duiker (Cephalophus zebra), 13 strictly endemic amphibians, and three strictly endemic birds illustrate the distinctive species-composition of the ecoregion. Non-human primates are also diverse and include the Diana monkey (Cercopithecus diana diana), Campbell’s monkey (Cercopithecus mona campbelli) and western red colobus (Piliocolobus badius badius.
This ecoregion is not well protected and is endangered due to habitat loss to slash-and-burn farming, hunting for bushmeat, logging, civil conflict and mining activities. Increased conservation action is needed in this ecoregion when current conflicts in Sierra Leone and Liberia end.
Location and General Description
The Western Guinean Lowland forest stretches from eastern Guinea, across Sierra Leone and Liberia, to the Sassandra River in southwestern Côte d’Ivoire. It is the most westerly tropical rainforest block on the African continent. The topography is relatively flat to undulating with altitude ranges between 50 and 500 meters (m), although there are a few isolated mountains rising higher above the landscape. The ancient African shield formation on which the ecoregion sits has eroded over millions of years and is dissected by several major rivers including the Sewa, Mano, St. Paul, Cavally and Sassandra. Some of these might have served as physical barriers to the dispersal or migration of fauna. For example, the Sassandra River separates the western and eastern subspecies of Diana monkey (Cercopithecus diana diana and C. d. roloway). The soils are generally poor, lateritic and prone to heavy leaching. Some young alluvial deposits are found along river valleys and inland swamps are more fertile and are often converted to agriculture. Other unique soil formations exist throughout the region.
The ecoregion is one of the wettest parts of West Africa, with seasonal rains up to 3,300 millimeters (mm) per year soaking the region between Guinea and Liberia. A humid-equatorial climate ensures that certain locations, such as the No.2 River on the Freetown Peninsula in Sierra Leone, receive more than 5,000 mm precipitation annually. Weeks of heavy rain are punctuated by short but intense dry seasons. The seasonal variation in rainfall has a critical influence on the vegetation. Seasonal temperatures range between 30 and 33° C during the dry season and 12 and 21° C during the wet season. The cold, dry Harmattan winds sweep across the Sahara Desert from December to February, lowering temperatures to as cold as 12 and 15° C.
The generally warm and humid climate permitted the development of luxuriant forest vegetation along most of this coastal region. The vegetation of the Western Guinean Lowland Forest is comprised of many different plant associations, several of which are unique to the area. Human impacts on the vegetation have been severe and prolonged, and the closed canopy forest is substantially altered from the primary state. Today’s forests could be described as late secondary stands. The original forest here is often refered to as ‘Upper Guinea’, and classified as part of the Guineo-Congolian regional center of endemism.
There seems to be general agreement that the forest fragments that remain today can be grouped into moist evergreen forest and moist semi-deciduous forests. Many canopy trees are at least 30 m tall, with some emergent individuals reaching a height of 50-60 m. Tree density and species diversity per hectare are generally low, but stand basal area tends to be high because of the large girth of a small number of trees. Swamp and riparian forests can be found embedded within the moist evergreen and semi-deciduous forests. ‘Farmbush’, the degraded secondary growth derived from forest that follows slash-and-burn agriculture, is increasingly the most dominant vegetation type in this region.
The tree composition of this ecoregion is quite uniform over long distances, with species such as Dacroydes klaineana, Strombosia glaucescens, Allanblackia floribunda, Coula edulis and Diospyros sanza-minika being common in many places. However, different plant associations have been reported across the ecoregion. Local geo-climatic factors, as well as the level of past exploitation, undoubtedly play a large role in the distribution and dominance of different plant associations in a given region and even within the same vegetation type. In Côte d’Ivoire, two plant families dominate the moist evergreen forest; Mimosaceae and Caesalpiniaceae.
Typical plant associations include Anthonotha spp., Erythrophleum ivorense, Klainedoxa gabonensis, Parkia bicolor, Parinari excelsa and Piptadeniastrum africanum. In the Liberian mixed evergreen forest, Calpocalyx aubrevillei, Dialium spp., Heritiera utilis, Lophira alata and Sacoglottis gabonensis are typical, with some dominance either by Gilbertiodendron preusii, Parinari excelsa or Tetraberlinia tubmaniana. Typical canopy dominants of the moist evergreen forest of Sierra Leone include Heritiera utilis, Cryptosepalum tetraphyllum, Erythrophleum ivorense and Lophira alata, with small amounts of Klainedoxa gabonensis, Uapaca guineensis, Oldfieldia africana, Brachystegia leonensis and Piptadeniastrum africanum. The moist evergreen forests of southern Guinea have identical plant associations as those reported for Sierra Leone and Liberia.
Plant associations in the semi-deciduous forests of southwestern Côte d’Ivoire are comprised of Celtis spp., Mansonia latissima, Milicia excelsa, Nesogordonia papaverifera, Sterculia rhinopetala and Pterygota macrocarpa. In Liberia and in the semi-deciduous forests of Côte d’Ivoire, Entandrophragma spp. and Khaya spp., are often the dominant species. In Sierra Leone, common plant associations include species that are also common in the moist evergreen forest: Anthonotha fragrans, Bridelia grandis, Daniella thurifera, Parinari excelsa, Parkia bicolor, Pycnanthus angolensis, Terminalia superba and Terminalia ivorensis. Typical plant associations in the semi-deciduous forest of Guinea include Khaya senegalensis, Erythrophleum spp., Terminalia spp., Chlorophora regia and Antiaris excelsa.
The swamp and gallery forests of Sierra Leone possess some unique plant associations that include Pterocarpus santalinoide, Napoleonaea vogelii, Uapaca heudelotii, Newtonia elliotii, Myrianthus arboreus, Cynometra vogeli, Mitragyna stipulosa and Raphia spp. ‘Farm bush’ vegetation is made up of fast growing pioneers, including common species such as Funtumia africana, Holarrhena floribunda and Pycnanthus angolensis.
The current biodiversity patterns of plant and animal endemism in the Western Guinean Lowland Rainforest date from the Pleistocene epoch 15,000-250,000 B.P. The climatic fluctuations during this period created isolated forest refugia during drier periods, with the forest expanding again in wetter periods, only to contract once more when the conditions became drier. These changes, together with similar phases of tropical forest expansion and contraction over millions of years, have caused species of flora and fauna to become isolated, which has resulted in speciation and relictualisation. Despite their apparent small size, important refugia during this period included Cape Palmas, Cape Three Point and the Gola Forest region between Sierra Leone and Liberia. Two designated national parks, Taï (in Côte d’Ivoire) and Sapo (in Liberia) are also located within such putative refugia.
Recent estimates indicate there are more than 200 plants endemic to this ecoregion, with an endemic liana family Dioncophyllaceae containing three monotypic genera. In the vicinity of the Sassandra River in southwestern Côte d’Ivoire, 72 endemic plant species have been reported. One endemic species, Didelotia idae, is confined to the Gola forest complex between Sierra Leone and Liberia. The Taï Forest is the largest tract of protected lowland forest in the region with 1,300 vascular plant species recorded.
This ecoregion also has a diverse fauna. There are nearly 1,000 vertebrates recorded in Taï National Park, and the park holds viable populations of the near-endemic pygmy hippopotamus (Hexaprotodon liberiensis, VU). In the order Artiodactyla, two duikers, Jentink’s duiker (Cephalophus jentinki, VU) and zebra duiker (Cephalophus zebra, VU) are strictly endemic to this ecoregion. The Liberian mongoose (Liberiictis kuhni, EN) is also strictly endemic, and another small carnivore, Johnston’s genet (Genetta johnstoni, DD), is known from small populations in Liberia and Côte d’Ivoire. Miller’s striped mouse (Hybomys planifrons) is the only other strictly endemic mammal, although more than 15 species of mammal are regarded as near-endemic, with all of these species shared only with the adjacent Eastern Guinea Lowland Forest and/or the Guinea Montane forest ecoregions.
Non-human primates are also diverse and include endemic subspecies of the Diana monkey (Cercopithecus diana diana, EN), red colobus (Procolobus badius badius), lesser spot-nosed monkey (Cercopithecus petaurista petaurista), and sooty mangabey (Cercocebus torquatus atys). Other near-endemic primates include olive colobus (Procolobus verus), and the Western chimpanzee (Pan troglodytes verus, EN). Some of these species are threatened as a result of hunting for bushmeat and habitat loss. Other important large mammals in the Western Guinean Lowland Forest include the leopard (Panthera pardus, EN) and forest elephants (Loxodonta africana cyclotis, EN). The forest elephants in Taï and Comoé National Parks are considered to be priority baseline populations for West Africa, with the Gola Forest reported to have a potential viable population in Sierra Leone. Maxwell’s duiker (Cephalophus maxwelli), bushbuck (Tragelaphus scriptus) and the red river hog (Potamochoerus porcus) are among the wide-ranging mammals that are common in this ecoregion.
Forest birds are diverse and include a number of endemic and rare species. Three bird species are strictly endemic to this ecoregion: the Liberian greenbul (Phyllastrephus leucolepis, CR), Liberian black-flycatcher (Melaenornis annamarulae, VU) and Ballman’s malimbe (Malimbus ballmanni, EN). Other species considered endemic include chestnut owlet (Glaucidium castaneum), brown-cheeked hornbill (Ceratogymna cylindricus), Turati’s bushshrike (Laniarius turatii), iris glossy-starling (Coccycolius iris), rufous-winged illadopsis (Illadopsis rufescens), white-breasted guinea-fowl (Agelastes meleagrides, VU), Ghana cuckoo-shrike (Campephaga lobata, VU), and Sierra Leone prinia (Prinia leontica). While not endemic, there are several other species only shared with the Eastern Guinean Lowland Forest ecoregion or the Guinean Montane Forest Ecoregion. The most important of these include the yellow-headed rockfowl (Picathartes gymnocephalus, VU), rufous fishing owl (Scotopelia ussheri, EN), and yellow-throated olive greenbul (Criniger olivaceus, VU).
The herpetofauna is also diverse, and contains a large number of endemic species. In the amphibians there are 13 strictly endemic species and a number of others shared with the Eastern Guinea Lowland Forest ecoregion. The strict endemics include the rare frog Merlin’s clawed frog (Pseudhymenochirus merlini) known only from Guinea and Sierra Leone, and the Freetown long-fingered frog (Cardioglossa aureoli), which is only known from the mountains close to Freetown in Sierra Leone. Other notable endemics include the Tai River frog (Phrynobatrachus taiensis), Liberian long-fingered frog (Cardioglossa liberiensis) and Ivory Coast toad (Bufo danielae). The reptile fauna is less rich in endemics, with three strictly endemic species and thirteen shared only with other ecoregions in the Upper Guinea forest block. The strict endemics are Los Archipelago worm lizard (Cynisca leonine), Benson’s mabuya (Mabuya bensonii) and Liberia worm snake (Typhlops leucostictus).
There are numerous information gaps in the invertebrate fauna for this ecoregion, but several recent inventories conducted in Sierra Leone have led to the discovery of several new species, especially among the order Coleoptera (Euconnus spp., and Termitusodes spp.). New discoveries in the orders Lepidoptera and Diptera have also been made, with two endemic species of dragonfly, Argiagrion leoninum and Allorhizucha campioni, also known from Sierra Leone.
Much of the natural forest in this ecoregion has been lost to human activities, with almost all remaining forest modified by past human disturbance. The loss has been severe in Côte d’Ivoire, where the national priorities favored export crops, which led to vast forests being cleared. Sierra Leone has also experienced severe loss of its natural forest, dating back to the 19th century when timber was exported during British colonial administration. Subsistence agriculture in the wake of commercial logging has reduced the area of primary forest in Sierra Leone from more than 70 percent to just under 6 percent. Further losses in forest coverage are projected at five percent should the trend in deforestation continue. Both Côte d’Ivoire and Sierra Leone show the greatest level of fragmentation of natural forests, while Liberia still retains large forest blocks. The largest stands of high forest in all of these countries are found within so-called ‘protected areas’ and ‘forest reserves’. Despite these titles, the management of protected areas and reserves is currently poor or non-existent, especially in Guinea, Sierra Leone and Liberia where civil conflicts drain resources to other areas. The total area of protected forest in this ecoregion is just under 3 percent for all National Parks and other reserves (IUCN levels II-IV) with international designations.
Guinea appears to lack any protected forests within the ecoregion, while Sierra Leone barely makes the list, with only the small Tiwai Island wildlife sanctuary (12 km2). There are still important forest blocks within both countries that could complement the overall biodiversity of this ecoregion but these have not been elevated to the status of conservation areas. For example, in Sierra Leone, forests such as the Golas, Western Area Forest Reserve, Kangari Hills, Tama-Tonkoli Forest, Dodo Hills, Nimini Forest and Geboi Hills all contain important and locally threatened plant and animal communities. There is also an important closed canopy forest on the Kounounkan massif (approximately 50 km2), located southeast of Conakry in Guinea, at the northern end of the Western Guinean Lowland Forest. Despite its small size, wildlife surveys have identified threatened and endangered forest species living alongside savanna species. The avifauna is allied to that of the Western Area Forest Reserve and Gola Forest of Sierra Leone, and the presence of the yellow-headed rockfowl further extends the natural range of this species as far as the northern limit of the Western Guinean Lowland Forest. Other threatened and candidate threatened species found at this site include chimpanzees, yellow-casqued hornbill (Ceratogymna elata), Sharpe’s apalis (Apalis sharpii) and red-cheeked wattle eye (Platysteira blissetti). The Ziama and Diecke Forest Reserves in Guinea have outstanding biological importance, and should be adequately protected.
Sapo National Park (1,292 km2) is by far the largest protected area in Liberia, it is about onethird the size of the Taï Forest National Park in Côte d’Ivoire, which is by far the largest protected area in this ecoregion at over 3,500 km2. Other protected areas in Côte d’Ivoire that contain habitats of this ecoregion are Mont Peko National Park (340 km2) and Nzo Faunal Reserve (950 km2). Despite the relative lack of National Parks in Liberia there are, however, a large number of forest reserves. While they lack designation as biodiversity conservation areas, they still contain sizeable tracts of lowland forest. Some of the larger reserves include: Gola (2,070 km2), Kpelle (1,748 km2) and Lorma National Forests in northwestern Liberia (435 km2); the Krahn-Bassa National Forest (5,140 km2); and Grebo National Forest (2,673 km2). These areas are allocated for logging.
Types and Severity of Threats
Anthropogenic pressures for farmland, timber, bushmeat, fuelwood and mineral resources are reducing the size and biotic potential of the remaining forests. Most of the high forest areas that remain are late secondary stands, which are isolated from each other within a sea of ‘farmbush’ vegetation. Large tracts of moist forests remain in Liberia, but the recent civil conflict in the region creates doubts about the long-term survival of the forests and their resources (e.g bushmeat). Recent media accounts circulating on the Internet suggest that logging operations have increased in many of the forest reserves, and it is doubtful whether any protected forests will remain untouched when the war ends. Similarly, the Western Area Forest Reserve on the Freetown peninsula of Sierra Leone has experienced intense exploitation for timber because of the inaccessibility of timber resources in rebel-held territories. Two species, Heritiera utilis and Terminalia ivoriensis, are in high demand by furniture makers in Freetown and are experiencing intense exploitation. The global demand for valuable hardwoods continues to spur logging in most of the high forests in this region. The secondary impacts of this activity are perhaps more damaging to the forest than timber harvesting itself, since the roads used to access the timber invite subsistence agriculturists and cash croppers who clear more forest to cultivate. In this way, timber harvesting has accelerated forest fragmentation.
Hunting for bushmeat now parallels habitat loss as the major threats to the survival of mammals in this ecoregion. Recently, the extinction of Piliocolobus badius waldroni was attributed to hunting and the demand for bushmeat in the Eastern Guinean region. Bushmeat is a critical protein source for many people in the region and a large variety of species are hunted. Antelopes, forest pigs and primates dominate the bushmeat trade in urban areas, while grasscutter (Thryonomys swinderianus) and Gambian giant rat (Cricetomys gambianus) are widely preferred because they are readily available. The extent of such hunting has prompted governments to enact hunting bans, though the legislation is impractical and cannot be enforced. It is clear that if action cannot be taken to reduce bushmeat hunting, then it will continue to have a severe impact on the mammal fauna of the ecoregion.
Commercial fuel wood collection is an emerging threat to both protected and already degraded forests. It is exacerbated by reliance of a vast majority of urban dwellers on wood and charcoal for cooking. On the Freetown peninsula of Sierra Leone, charcoal consumption is reported to be higher now than in the last two centuries, with charcoal and firewood supplying 80 percent of the total energy demand. Fuelwood collection is a major factor in the shortening of in fallow periods because trees are continuously extracted until the land is farmed again.
Though regional instability may have provided respite to some forests and the species that inhabit them, civil war also translates into poor or non-existent management of parks and protected areas. The recent civil conflicts in Sierra Leone and Liberia have resulted in serious damage to forests, as a result of mining, logging and bushmeat hunting. Logging activities have increased considerably in the Western Area Forest Reserve, with a large number of unemployed refugees providing the man power needs for this illegal trade. The loggers are selectively targeting two species, Heritiera utilis and Terminalia ivorensis. In Liberia, an estimated 50,000 m3 of Heritiera utilis (Niangon) was exported in 1999 alone, and comprises a total round wood volume of 335,543 m3 exported by approximately 20 logging companies. As people repatriate, local demand for forest resources will undoubtedly rise. Demand for charcoal and fuel wood species such as Phyllocosmus africanus, Parinari excelsa and Xylopia quintasii has led to the over-exploitation of these species in some sections of the Western Area Forest Reserve in Sierra Leone.
Mining is a locally intense and destructive practice in Sierra Leone and a primary cause of habitat destruction in parts of that country. Mining has been closely tied to civil conflicts throughout this ecoregion, especially diamond mining. Mining of bauxite and titanium dioxide (rutile) in the southeast has resulted in forest loss, with the subsequent dredging leaving large bodies of deep water polluted with heavy metals. These mining activities have also caused perpetual displacement of people and have locally increased the pressure on remaining forests. In other regions of the country where mining for diamonds and gold has occurred, siltation is threatening freshwater fish populations, while hunters have increased their assault on the dwindling wildlife populations in nearby forests to supply bushmeat to the mining settlements.
Justification of Ecoregion Delineation
The Western and adjacent Eastern Guinean Lowland Forests comprise the Upper Guinea forest block, recognized as an Endemic Bird Area, Center of Plant Diversity, and Hotspot. They form part of White’s Guineo-Congolian rainforest and Udvardy’s Guinean rainforest biogeographic province. The two ecoregions are separated by the Sassandra River, which represents an important biogeographical boundary for primates, duikers, amphibians, lizards, and other groups. Differences are most pronounced in the amphibian fauna. The northern limit of the Western Guinean Lowland Forest primarily follows the vegetation unit delineation; however, the subdivisions of ‘wetter’, ‘drier’, and ‘mosaic’ within lowland rainforest have been generalized. Slivers of swamp forest and mosaics of ‘lowland rainforest and secondary grasslands’ have been subsumed to depict potential vegetation, rather than anthropogenic influences. One significant change from White’s vegetation unit is the northwestern extent of the ecoregion. The area of potential lowland rainforest is mapped to extend much further to the northwest, encompassing the coastal areas of Sierra Leone and Guinea.
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
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