Location and General Description
The Central Congolian Lowland Forests ecoregion lies in the central part of the Congo Basin, south of the wide arc formed by the Congo River. The network of rivers function as distribution barriers to many species, thereby isolating this lowland basin along its northern, eastern and western limits. The headwaters of the Lopori, Maringa, Ikelemba, Tshuapa, Lomela, and Lokoro Rivers lie within this ecoregion, while their lower drainage basins are included in the Eastern Congolian Swamp Forests ecoregion. Because of the relatively flat topography of the area, most of these rivers are slow flowing with heavy sediment loads, and numerous alluvial islands.
Topographically, the ecoregion is low-lying, with the central portion around 400 m above sea-level. The elevation and topographical complexity increases towards the southeast, where hills up to 700-800 m are found. The ecoregion has approximately 2,000 mm of rainfall annually. The mean maximum temperature is around 30o C in the central portion of the ecoregion, and falls to around 27o C along the southeast margins. The mean minimum temperature is between 18 and 21o C, with little seasonality and high humidity.
This ecoregion occupies an ancient part of the African landscape, eroded over millennia, and subject to considerable alluvial deposition in some places. Many of the soils are nutrient poor oxisols developed over ancient 'dune fields' believed to date from the Quaternary Ice Ages (Juo and Wilding 1994) or are more recent alluvial deposits from the many rivers. Part of the area is a proposed forest refuge where forest survived during the drier periods associated with Ice Ages (Axelrod and Raven 1978, Colyn et al. 1991, Louette 1984, Mayr and O'Hara 1986, Prigogyne 1988). Other research indicates that most forest may have been lost, or at least severely fragmented during arid phases associated with Ice Ages (Maley 1991, 1994), with the most recent arid phase ending around 2,500 B.P (Maley 2001). In wetter climatic periods, a large inland lake may have submerged the entire area of this ecoregion (Kingdon 1990).
Human populations are typically small and the highest densities are found along the rivers where people engage in fishing, cultivation of cassava, and hunt animals from the forest (Lanjouw 1987). Most areas support fewer than 5 people per square kilometer of forest, concentrated along rivers.
This ecoregion forms part of the Guineo-Congolian regional center of endemism (White 1983, 1993), and is quite complex in its major vegetation types. The northwestern portion is a mosaic of seasonally inundated and permanent swamp forest with mixed terra-firma moist evergreen and semi-evergreen rain forest components along levees and other areas of relief. Evergreen ombrophile forests are dominated by stands of Gilbertiodendron dewevrei. Areas of seasonally inundated forests and numerous sizeable clearings (bais) occur along the major rivers in the northern, eastern, and western portions. To the south the forests become drier and there is a transition to peripheral semi-evergreen rain forest, and finally a mosaic of Lower Guinea rain forest and grasslands. Semi-deciduous forest covers almost all areas between the major river systems, and is characterized by Staudtia stipitata, Polyalthia suavaeoleus, Scorodophloeus zenkeri, Anonidium mannii and Parinari glaberrimum.
The vegetation in this region is diverse, with estimates of between 1,500 and 2,000 vascular plant species, of which about 10 percent are endemic (WWF and IUCN 1994). However, further research is necessary to establish base-line data on the diversity of the flora, and hence allow an accurate assessment of the species richness and endemism values.
In terms of the fauna this ecoregion, scientist are just beginning to understand and document the complexity and distributions of species (Thompson 2001, 2003). In common with other large forested ecoregions of the Congo Basin, this ecoregion is primarily noted for its size and intactness, with populations of most species fluctuating within normal ecological limits. Much of the ecoregion remains as a rainforest wilderness and little explored by humans.
Vertebrate species richness and endemism levels in this forest area are markedly lower than in other moist forest ecoregions of the Congo Basin. This may be misleading and due to under-collecting within the area, although formidable riverine barriers to the north, east, and west may have prevented interchange of widespread vertebrate species from outside the ecoregion (e.g. Cephalophus leucogaster and Neotragus batesi) (Grubb 2001). The relatively low levels of species richness and endemism may also reflect recent climatic history. Maley (1991, 1994, 2001) and others indicate that forest may have been lost from these areas during the last million years, probably in association with ice ages, which resulted in dry periods in Africa. The presence of 'dune fields' beneath the forest indicates that the area may have become dry enough to turn into desert, although this is quite controversial and not accepted by all paleoecologists. At other periods, it is believed that the area was covered by a huge freshwater Lake.
From the little knowledge available, it seems that the density of large mammal species is also naturally lower in this ecoregion than other parts of the Congo Basin (Alers et al. 1992, Krunkelsven et al. 2000, Malenky et al. 1989). Heavy hunting has also lowered the population densities of forest elephants (Loxodonta africanus cyclotis, EN) (Alers et al. 1992). However, the Central Congolian Lowland Forests ecoregion houses a number of important mammal populations, including a top priority forest elephant population in Salonga National Park (AECCG 1991), and the largest remaining populations of bonobo (Pan paniscus, EN) in the world (Thompson-Handler et al. 1995, Thompson 2003). The bonobo populations are especially important and the species has been studied in detail at several sites, most notably in Wamba and in Lomako (e.g. Bermejo et al. 1994, Doran 1993, Furuichi et al. 1998, Hashimoto 1997, Hashimoto et al. 1998, Hohmann and Fruth 1993, Kano et al. 1994, Kano and Mulavwa 1984, Kortlandt 1996, Krunkelsven et al. 2000, Malenky and Wrangham 1994, Malenky et. al. 1989, Mitani and Gros Louis 1995, Reinartz and Boese 1997, Thompson-Handler et al. 1995, Krunkelsven et al. 1999, White and Chapman 1999).
Among the mammals, there is only one known strictly endemic species, the Salonga monkey (Cercopithecus dryas). Other near-endemic mammal species include the golden-bellied mangabey (Cercocebus chrysogaster), bonobo (Pan paniscus, EN), okapi (Okapia johnstoni), Allen's swamp monkey (Allenopithecus nigroviridis), Angolan cusimanse (Crossarchus ansorgei), Thollon's red colobus (Procolobus tholloni) and Wolf's monkey (Cercopithecus wolfi). In the smaller mammals near-endemic species include a brush-furred rat species (Lophuromys huttereri), and a shrew (Crocidura latona, VU). However, because this region is so poorly surveyed, the information on species numbers and endemics should be viewed as incomplete.
There are no known strict endemic species among the avifauna, but two species represent near-endemics with restricted ranges. These are the Congo peacock (Afropavo congensis, VU) and the yellow-legged malimbe (Malimbus flavipes) (Thompson 1996). The known herpetofauna also shows low rates of endemism. One amphibian is strictly endemic to the ecoregion, the Gembe reed frog (Hyperolius robustus), and another is nearly endemic, the Lomami screeching frog (Arthroleptis phyrynoides). There are no strictly endemic reptiles, but near-endemic reptiles include Vanderyst's work lizard (Monopeltis vanderysti), Gastropholis tropidopholis, Mehelya laurenti, Polemon robustus, and Zygaspis dolichomenta. This ecoregion also offers critical habitat to the African slender-snouted crocodile (Crocodylus cataphractus). As with the mammals and birds it is very likely that further survey work in this ecoregion will discover additional species of amphibians and reptiles that are either strictly or nearly endemic to the ecoregion.
Further information on the ecoregion can be found in Happold (1994), IUCN (1989), Doumege (1990) Sayer (1992) and Ngjelé (1988).
Much of the forest habitat of the ecoregion remains intact, even to the south where the transition to savanna woodland is the result of climatic rather than anthropogenic effects. It is estimated that over 100,000 km2 of forest still occurs, much of which is continuous, or at least connected. However, as little recent data is available from this ecoregion, this information may be outdated.
There is one very large protected area within the ecoregion, Salonga National Park (36,500 km2). One of the largest national parks in the world, and the second largest tropical forest national park in the world (Tumucumaque in Brazil is the largest), it is found in two distinct patches. Although poorly surveyed, this park holds important populations of forest elephants and bonobos (Alers et al. 1992, Krunkelsven et al. 2000). Several other areas in the ecoregion have been proposed for protection, most notably Lomako and Lomami-Lualaba. Lomami-Lualaba might be of significant biogeographic importance due to its location between two main rivers (WWF 2003).
There are few larger settlements in this region, and little evidence of agricultural clearance can be seen on satellite images presented in Sayer et al. (1992). Huge areas of forest appear to be in almost pristine condition, particularly those that lie far from the rivers (the main access routes in the area).
The human population of the area is low with densities around 5-10 persons per km2, although it is much lower in some areas. Most people live in the forest and derive their livelihood from it, although there are increasing numbers of fisherpeople found along the rivers, and in cleared forest areas where shifting agriculture is practiced.
The habitats of the ecoregion have some natural fragmentation due to the numerous rivers and the patchy formations of vegetation types through the areas, including forest/swamp mosaics and forest/savanna mosaics. These may present a barrier to species that are not able to swim, or to cross via the canopies of trees growing above the smaller rivers. However, this level of natural fragmentation is probably not significant to the conservation of the species or the ecological functions of the area. Fragmentation of the forest by people is not an important issue at present.
Types and Severity of Threats
Overall, the threats to the habitats in this ecoregion are low and the conservation potential is very high. There has been some forest lost to farming and logging; however, the rates are low and do not pose a significant threat to either the habitat or species at this time. Poaching poses a serious threat to the elephants of this ecoregion (Alers et al. 1992, Krunkelsven et al. 2000).
Justification of Ecoregion Delineation
This ecoregion is a part of the Guineo-Congolian regional centre of endemism of White (1983). Located under the arc of the Congo River, it is distinguished from neighboring ecoregions by its relatively isolated position, lower rates of species richness and endemism, and the presence of endemic primates such as the bonobo (Pan paniscus). The ecoregions northern limit is the Eastern Congolian Swamp Forest ecoregion . The southern boundary follows the line just north of the Fimi River, where White (1983) distinguished wetter lowland rainforest from drier lowland rainforest.
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Prepared by: Allard Blom
Reviewed by: In progress