Western Congolian swamp forests
This ecoregion, combined with the neighboring Eastern Congolian Swamp Forests, contains one of the largest continuous areas of swamp forest in the world. Although relatively few species have been recorded, it remains largely intact and contains large populations of western lowland gorilla (Gorilla gorilla gorilla). Poaching is thought to have reduced populations of forest elephants (Loxodonta africana cyclotis) along the navigable waterways. Little research has focused on this region, and further efforts are necessary to better understand these forests and their species composition. There are no protected areas.
Location and General Description
The Western Congolian Swamp Forests ecoregion stretches from eastern Republic of Congo through to the western portion of the Democratic Republic of Congo (DRC), and into the Central African Republic. This ecoregion lies on the western bank of the Congo River, which forms a major biogeographic barrier to the Eastern Congolian Swamp Forests and Central Congolian Lowland Forests. The [[[river]] in this section can be up to 15 kilometers (km) wide, and becomes braided in a maze of alluvial islands. The Western Congolian Swamp Forests have an irregular shape (reflecting riparian habitats) bounded by the right bank of the Congo River between the confluence of the Lualaba (Upper Congo) and the Lomami Rivers to the confluence of the Lefini and the Congo Rivers.
These swamps are found in the Cuvette Congolaise, a sedimentary basin that straddles the equator. In the relatively recent geological past (the past four millennia), the area may have supported a lake over much of its extent. There is, however, considerable debate on the climatic history of the area. What is generally accepted is that at one or more times during the driest periods associated with the Pleistocene Ice Ages, climatic desiccation caused the forests to retreat to the wetter areas alongside the river systems.
The Congo River and its tributaries play an important role in this ecoregion, not only as barriers to species dispersal, but also by providing the water for the swamp forests. These forests grow extensively along the meandering tributaries, and often form the predominant forest type between neighboring rivers, especially in the area between the Congo and the Oubangui Rivers. The major tributaries to the Congo that support marginal swamp forests are the Mangala, Giri, Likouala aux Herbes, Sangha, Likouola, and the Kouyou Rivers.
The topography is predominantly a featureless alluvial plain at an altitude of 380-450 meters (m). Climatically, the area is part of the wet tropics with mean annual rainfall around 1,800 millimeters (mm) per annum. Mean maximum temperatures are around 30°C, and mean minimum temperatures are between 21-24°C. There is little seasonality, and humidity levels are normally high. In the wet season, the forests are mainly flooded, usually to a depth of 0.5 to 1.0 meters; and during the dry season, they dry out again. The soils of the ecoregion are classified as gleysols, due to the flooding and waterlogging throughout the year. The human population is low and typically involved with hunting and fishing activities in the forest and its rivers.
This ecoregion contains swamp forest, flooded grasslands, open wetlands, rivers, and some drier forest areas on slightly raised land. The seasonal floods are characteristic features of the riparian habitats of both the Congo and its tributaries, and determine the structure and species distributions in these areas. Species such as Guibourtia demeusei, Mitragyna spp., Symphonia globulifera, Entandrophragma palustre, Uapaca heudelotii, Sterculia subviolacea, Alstonia congensis, and species of Manilkara and Garcinia characterize the swamp forests. Permanently flooded swamp regions host almost monospecific stands of Raphia palm, which can occupy significant areas within the ecoregion. Levee forests occur on higher ground and host a high diversity of liana species as well as Gilbertiodendron dewevrei and Daniekkia pynaertii. Open areas are home to giant ground orchids (Eulophia porphyroglossa), and riverbanks are often lined with arrowroot (Marantochloa spp).
This ecoregion is believed to possess similar, and low, levels of species richness and endemism. Available data indicate that faunal endemism is lower in this ecoregion than in the Eastern Congolian Swamp Forest ecoregion, but this may be due to differences in the intensity of biological study. Together with the Eastern Congolian Swamp forest and the Central Congolian Forests, this area has been interpreted as a possible forest refuge during the drier climatic periods associated with Ice Ages. During the Belgian colonial period there was some study of this ecoregion and many specimens of the flora and fauna are found in museum collections in Belgium. Many of these data have never been fully compiled.
One of the primary values of this ecoregion is its intact forest wilderness where most species populations fluctuate within natural ecological limits. The Congo River is a highly navigable waterway, making some areas accessible to poachers. Despite this, large tracts of low-access forest remain in the ecoregion since swamp forests are not easy to log.
This ecoregion supports a number of large mammal species, including important populations of western lowland gorilla (Gorilla gorilla gorilla, EN), chimpanzee (Pan troglodytes, EN), and forest elephant (Loxodonta africana cyclotis, EN). Large numbers of forest buffalo (Sycerus caffer nanus) were once found here, although most have been hunted out. Together with the elephants and gorillas, the few remaining forest buffalo make use of open grassland areas within the swamps. There may also be important seasonal migrations of elephants.
This ecoregion is separated from the Eastern Congolian Swamp Forest by the Congo River that forms an important biogeographical boundary for the radiation of species, with clear examples among the primates. For example, crowned guenon (Cercopithecus pogonias EN), moustached guenon (C. cephus), chimpanzee (Pan troglodytes, EN), agile mangabey (Cercocebus agilis), gray-cheeked mangabey (Lophocebus albigena albigenea), Guereza lowland colobus (Colobus guereza), potto (Perodicticus potto edwardsi), golden angwantibo (Arctcebus aureus), and western lowland gorilla occur only on the right bank of the Congo River. In comparison, Wolf's guenon (Cercopithecus wolfi), bonobo (Pan paniscus, EN), golden-bellied mangabey (Cercocebus galeritus chrysogaster), black crested mangabey (Lophocebus aterrimus), and dryad guenon (Cercopithecus dryas) occur only on the left bank of the Congo. The distribution of Demidoff's galago (Galagoides demidoff) subspecies follows a similar pattern, with G. d. anomurus and G. d. murinus found only on the right bank of the Congo and G. d. phasma found only on the left. Allen's swamp monkey (Allenopithecus nigroviridis) is found on both sides of the Congo River.
For other vertebrates there is generally a low rate of species richness and few endemics. In birds there are 2 near-endemic bird species - the African river-martin (Pseudochelidon eurystomina DD), and the Congo martin (Riparia congica). There is one near-endemic amphibian, the Yambata River Frog (Phrynobatrachus giorgii), and three near-endemic reptiles: gray chameleon (Chamaeleo chapini), Witte's beaked snake (Rhinotyphlops wittei), and Gastropholis tropidopholis. The apparently low number of endemic species may be due to the low rate of biological study.
The ecoregion contains one large (4,390 km2) Ramsar site in the Republic of Congo, Lac Tl-Likouala-aux-Herbes Community Reserve, which was gazetted in 1998. The reserve is located along the River Likouala-aux-herbes, with four major tributaries Tanga, Mandoungouma, Bailly, and Batanga and the lake, Lac Tl, which is the home of the mythical giant dinosaur-like animal called Mokele Mbembe. The area is a good example of a freshwater tropical African wetland ecosystem with a diversity of habitats, including swamp forest, inundated savannas and floating prairies along the watercourses. The site is public property, owned by the local communities. A special zone of firm land and seasonally flooded forests, named Zone d'Utilisation Rationelle (ZUR, zone with sustainable use) is used for hunting.
Types and Severity of Threats
The habitats of this ecoregion are becoming increasingly threatened by logging concessions in the Congo and DRC, which have been awarded over large areas. Roads have increased, facilitating hunting in areas that were once inaccessible. For example, along the northern and northwestern border of the Lac Tl-Likouala-aux-Herbes Community Reserve a road has been planned for transportation of wood from a logging concession located just outside the reserve. The main threat to some of the fauna is from hunting and poaching; in particular there is organized hunting of the larger species for bushmeat, elephants for ivory and meat, and gorillas for meat and fetishes. The potential increase in commercial bushmeat hunting may in the future cause a reduction in animal populations in the Likouala swamps. Closer to the Congo and Ubangui Rivers, poaching has probably already eliminated elephants.
Justification of Ecoregion Delineation
The boundaries of the Western Congolian Swamp Forest largely follow those of White. However, the sections of swamp forest that White extends along the Sangha, Dja, and Ngoko Rivers, were subsumed into the Northwestern Congolian Lowland Forest, to which they are thought to be more similar. Although the entire swamp forest is floristically similar (albeit relatively species poor), the definition into two ecoregions was based on differences in the fauna. For example the great apes chimpanzee and Western lowland gorilla are only present on the right bank of the Congo, and the bonobo is only present on the left bank.
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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- WWF. 2003. Biological Priorities for Conservation in the Guinean-Congolian Forest and Freshwater Region. Proceedings of Workshop held on March 30 - April 2, 2000 in Libreville, Gabon. Kamdem Toham, A., D. Olson, R. Abell, J. D'Amico, N. Burgess, M. Thieme, A. Blom, R. W. Carroll, S. Gartlan, O. Langrand, R. Mikala Mussavu, D. O'Hara, H. Strand, and L. Trowbridge (Editors). Available from http://www.worldwildlife.org/ecoregions
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