Location and General Description
The Northwestern Congolian Lowland Forests ecoregion  stretches across four countries - Cameroon, Gabon, Republic of Congo, and the Central African Republic (CAR). It is bordered to the north and south by forest-savanna mosaics and to the east by swamp forest, while the western limit grades gradually into the lowland rain forests of the Atlantic Equatorial Coastal Forests ecoregion .
Most of the ecoregion lies at altitudes between 300 and 800 m, with the highest elevations towards the north and in the Chaillu Massif to the south. Mean annual rainfall ranges from 1,400 to 2,000 mm in the central portion of the ecoregion, with most rain falling during two distinct wet seasons. Temperatures are tropical, with an annual mean maximum of 27o to 30o C and an annual mean minimum of 18o to 21o C. Humidity is high throughout the year.
The majority of the area overlies Precambrian bedrock, with pre-Cretaceous sediments in the northern sector (Juo and Wilding 1994). In most places a thick layer of heavily leached red oxisols overlies the bedrock. Alluvial deposits sometimes overlay and mix with these oxisols on the surface layer.
The human population of the ecoregion is low, but accurate population density data are lacking. Population density is generally under 5 persons per km2, although densities are higher around towns and major cities, including the capitals of Yaoundé and Bangui on the fringes of the ecoregion. Large areas of the interior, especially in Gabon and Congo, are almost devoid of human inhabitants, with population densities as low as one person per km2. Gabon and the Republic of Congo rank first and second, respectively, as the least populated, forested countries of Africa (Wilks 1990). In the remote inland areas most people live along roads and rivers, leaving the interior of the forest free of major settlements. In the forested interior most people are from the BaAka, BaKa, BaKola, and some smaller groups of traditional forest peoples, usually referred to as pygmies (Luling and Kenrick 1998); there are also Bantu cultivators who associate closely with them.
This ecoregion is a part of the Guineo-Congolian lowland rain forest within the Guineo-Congolian regional center of endemism (White 1983). Two types of forest are recognized: a mixed moist semi-evergreen Guineo-Congolian type and a single-dominant moist evergreen and semi-evergreen Guineo-Congolian type (White 1983). Knowledge of the flora of this region has been greatly improved in the last decade by the activities of organizations such as ECOFAC, WCS, WWF, and others (Blake et al. 1997; Dowsett 1996; Harris 1996; Harris in prep; Lejoly 1996; Motsambote 1994; White 1995; White et al. 2000). Some of the characteristic species of the ecoregion include emergent trees up to 60 m tall (Entandrophragma congoense, Pentaclethera eetveldeana, Pericopsis elata, Gilbertiodendron dewevrei), shrub species of Drypetes (D. calvescens, D. capillipes, D. chevalieri), and abundant lianas and rattans. The abundance of Raffia palms is noteworthy along the river valleys in the northern portion of the ecoregion, with pure stands of Raffia cf. monbuttorum and other species being common. Letouzey (1968b and 1985) and White (1983) present an overview of the vegetation of the region.
Species richness is high throughout the ecoregion, although large areas of the forest and most taxonomic groups have been under surveyed (WWF 2003). Data therefore tend to reflect what is known of a few well-studied areas and taxa. In general, rates of strict endemism are not particularly high, especially in plants (Harris 1999). However, the recent discovery of new species of birds and small mammals indicates that endemism might be higher than has been previously assumed, especially in the Sangha Basin (Beresford and Cracraft 1999, Ray and Hutterer 1996, Colyn 1999).
There are an estimated 7,151 vascular plants found in Gabon, over 3,600 in the Central African Republic, 8,260 in Cameroon (Stuart and Adams 1990; WCMC 1992) and 6,000 in Congo (Hecketsweiler 1990). A study in Gabon has shown that these forests are richer in plant species than those of West Africa (Wilks 1990). Reitsma (1988) found over 200 different species of plants in a 0.02 ha plot in Gabon, and Letouzey (1968a) found 227 in a 0.01 ha plot in Cameroon. These are among the highest species/area counts for any vegetation the world (WWF and IUCN 1994).
Mammalian richness is amongst the highest of any forest ecoregion in Africa. Gabon and Congo are estimated to have 190 and 198 mammal species respectively (Stuart and Adams 1990). Dzanga-Sangha National Park in CAR alone contains 105 species of non-volant mammals (Blom 1993). The species richness of primates is the highest in Africa. Cameroon has 29 species of primate recorded from its forests (Gartlan 1992) and Gabon has 19 (Blom et al. 1992), including mandrill (Mandrillus sphinx, VU) (Harrison 1988, Blom et al. 1992, Brugière et al. 1998, Brugière and Gautier 1998). The great apes are of particular interest: this ecoregion harbors more gorillas, and possibly more chimpanzees (Pan troglodytes, EN), than any other ecoregion in Africa (Tutin and Fernandez 1984, Carroll 1997, Fay and Agnagna 1992, Blom et al. 2001). Other forest dwelling mammals include forest buffalo (Syncerus caffer nanus) (Blake 2002a), and larger forest antelopes such as bongo (Tragelaphus euryceros) (Elkan 1996; Turkalo and Claus-Hugi 1999) and sitatunga (Tragelaphus spekei). The ecoregion is also well known for its large population of forest elephants (Loxodonta africana cyclotis, EN) (Alers et al. 1992; Barnes et al. 1993, 1995a, 1995b; Blake 2002b; Carroll 1988, 1997; Fay 1989; Fay and Agnagna 1991; Strohmayer and Ekobo 1992). In some parts of this ecoregion, such as Mouabale Ndoki National Park in Congo and Langoue in Gabon, these elephant remain relatively undisturbed (AECCG 1991).
At least 13 species of mammal are near-endemic and three are strictly endemic to this ecoregion. Strict endemic mammals are Dollman's tree mouse (Prionomys batesi), Remy's shrew (Suncus remyi, CR), and the recently discovered shrew, Sylvisorex konganensis (Ray and Hutterer 1996). Near-endemic species include sun-tailed monkey (Cercopithecus solatus, VU), black colobus (Colobus satanas, VU), elegant needle-clawed galago (Euoticus elegantulus), Glen's wattled bat (Chalinolobus gleni), forest horseshoe bat (Rhinolophus silvestris) and five species of shrew (Crocidura attila, VU, C. crenata, C. ludia, VU, C. manengubae, C. mutesae).
The bird fauna is also diverse. Gabon, which is mostly closed forest, contains 695 species (Dowsett and Forbes-Watson 1993), although the savanna patches in the center of the country and along the coast add species not found within this ecoregion. Odzala National Park alone contains 442 species (Dowsett-Lemaire 1997). The Trinational area of Nouabale-Ndoki National Park in the Republic of Congo, Lobeke National Park in Cameroon, and Dzanga-Sangha National Park in the Central African Republic contain at least 428 species (Christy 1999; Dowsett-Lemaire 1996, 1997), including one recently discovered endemic forest robin, Stiphornis sanghensis (Beresford and Cracraft 1999). The ecoregion lies within the eastern portion of the Cameroon and Gabon Lowlands endemic bird area (EBA), and includes forest batis (Batis minima), Rachel's malimbe (Malimbus racheliae), and forest swallow (Hirundo fuliginosa) (Stattersfield et al. 1998). Important Bird Areas include Ipassa Strict Nature Reserve and Minkébé Forest Reserve in Gabon and Nouabale-Ndoki National Park complex and Odzala National Park complex in Republic of Congo, Dja Faunal Reserve, Boumba-Bek, Nki, and Lobéké National Park (Christy 2001, Dowsett-Lemaire 2001, Fotso et al. 2001).
The species richness of amphibians and reptiles is also high. Among the amphibians are two endemic clawed frog species, Xeropus boumbaensis and X. pygmaeus. Endemic reptiles include the gray chameleon (Chameleo chapini), crested chameleon (C. cristatus), Grant's African ground snake (Gonionotophis grantii), Fuhn's five-toed skink (Leptosiaphos fuhni), Peter's lidless skink (Panaspis breviceps), Cameroon stumptail chameleon (Rhampholeon spectrum), and Zenker's worm snake (Typhlops zenkeri).
A map of the priority sites for biodiversity conservation has been proposed in IUCN (1989), with more details in Gartlan (1989), Hecketsweiler (1990), Hecketsweiler et al. (1991), Hecketsweiler and Mokoko Ikonga (1991), Wilks (1990) Dowsett and Dowsett-Lemaire (1991), WWF (2000), and Fishpool and Evans (2001).
This ecoregion contains large areas of forest and forms a part of one of the world's last remaining tropical forest wildernesses (Mittermeier et al. 1998). Around one third of the forest is classified as "frontier forests" that are largely in their natural state (Bryant et al. 1997).
Many of the most pristine areas of forest are located within protected areas, including Lobéké, Nouabale-Ndoki, Odzala, Dzanga, Ndoki, and Mbam Djerem. These comprise approximately 22,690 km2 or roughly 5.2 percent of the ecoregion. When other reserves such as the Dzangha-Sangha Special Reserve, Minkébé, Dja, Boumba-Bek, Nki, and Ngotto are also included, the total area under protection is 44,166 km2, or roughly ten percent of the ecoregion (Fiona Maisels pers. comm).
Conservation initiatives over the last decade have resulted in a number of newly gazetted areas. For example, the declaration of the Minkébé Forest Reserve (5,650 km2) marked a significant enhancement of the conservation area network in Gabon. In Congo, Odzala–Koukoua National Park (over 13,000 km2) has recently been extended. The Dzanga-Sangha forest in CAR is protected within the Dzanga-Ndoki National Park and the adjacent Dzanga-Sangha Faunal Reserve, totaling 4,347 km2, which is about eight percent of CAR's total closed forest estate (Blom and Yamindou 2001). While the forest around Ngotto in CAR currently has no official protected area status, the Forêt de Ngotto (730 km2) is in the final stages of gazettement. In Cameroon, Dja, Boumba-Bek, Nki and Lac Lobéké protected areas cover an extensive area of lowland forest in the southern part of the country. One of the largest areas under protection is the Sangha Trinational protected area (10,650 km2), which combines the Nouabalé-Ndoki National Park (over 4,000 km2) in northern Republic of Congo, Dzanga-Sangha complex in the Central African Republic (CAR), and the Lobéké National Park in Cameroon.
Types and Severity of Threats
Most of the ecoregion has been allocated to forestry concessions (Minnemyer 2002). Even within protected areas, logging is a concern. Although logging in the region is selective and habitat conversion is limited, the major issue is the depletion of wildlife in logging concessions through hunting for bushmeat and poaching for ivory (Auzel and Wilkie 2000; Fay and Vedder 1997; Putz et al. 2000b; Wilkie et al. 2000). There are also technical problems with the sustainability of logging operations (see Sayer et al. 1992) and also of the political will both of regional governments and the logging industry to operate sustainably (CARPE 2001; Minnemyer 2002; Putz et al. 2000a; Wilkie and Laporte 2001).
Logging roads and other infrastructure developments are contributing to the uneven loss of habitat throughout the ecoregion, with more accessible regions most affected (Wilkie et al. 2000). Although the impact of this fragmentation on biodiversity is still poorly understood, the population densities of sensitive species (e.g. chimpanzees) are known to decline (White and Tutin 2000).
Road and infrastructure developments increase interactions between humans and animals, to the usual detriment of the latter. One direct impact is the bushmeat trade, which primarily affects duikers (Cephalophus spp.) that can comprise up to 80 percent of the harvest in certain sites, and monkeys (Cercopithecus, Cercobcebus, Mandrillus, Colobus spp.). Larger antelopes, Tragelaphus spp., apes (Gorilla and Pan), buffalo and pigs (Potamochoerus, Hylochoerus) are also affected. Even top predators such as crowned eagle (Stephanoaetus coronatus), leopard (Panthera pardus) and golden cat (Felis aurata) are affected as their prey animals are hunted out. An overview of the bushmeat problem can be found in Auzel and Wilkie (2000), Bennet & Robinson (200a,b), Eves & Ruggiero (2000), Fimbel et al. (2000), and Noss (2000).
The logging industries' role in this trade has been heavily debated. However, there is little doubt that they provide a market (the logging camps), a transport system (the logging trucks), and a means of access (the logging roads) that are invaluable to the bushmeat industry (Minnemyer 2002; Putz et al. 2000a; Wilkie et al. 1998, 2000; Wilkie and Laport 2001).
In addition to the bushmeat industry some species are also hunted for trophies, fetishes and the pet trade. Elephants are still extensively poached for their meat and ivory. The trade in African gray parrots (Psittacus erithacus) is well developed in some parts, especially in Cameroon where it threatens the survival of this species. Certain other species, such as crocodiles and lizards, face similar threats (Thorbjarnarson 1999, 1992). Although professional safari hunting can be beneficial to conservation, this has rarely been the case in this ecoregion (Wilkie and Carpenter 1999). Future threats to the forest include immigration of agricultural peoples into the logged forest areas (Putz et al. 2000a; Wilkie et al. 2000; Wilkie and Laport 2001).
Justification of Ecoregion Delineation
This ecoregion forms part of the greater Guineo-Congolian regional center of endemism (White 1983). The northwestern limit of the ecoregion is the Sanaga River, a faunal boundary for such species as the golden angwantibo (Arctocebus aureus), white-bellied duiker (Cephalophus leucogaster), mandrill (Mandrillus sphinx), and elegant needle-clawed galago (Euoticus elegantus). The Oubangui River also represents a faunal boundary to the northeast. Other borders follow 'Guineo-Congolian wet and dry rainforest' delineated by White (1983). Small areas of swamp forest were subsumed within the ecoregion.
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Prepared by: Allard Blom
Reviewed by: In progress