Location and General Description
The Northeastern Congolian Lowland Forest is located in the northeastern portion of the Democratic Republic of Congo (DRC) and extends into the Southeastern portion of the Central African Republic (CAR). It occupies a roughly triangular area of land supporting lowland and sub-montane rainforest vegetation. The northern margin fixed by the transition to savanna and woodland habitats, the eastern border is bounded by the Albertine Rift Montane Forests , and the southern and western margins are delimited by the Congo River and its tributaries, primarily the Elila River.
The ecoregion declines in elevation from east to west, from the Albertine Rift Mountains towards the Congo River. Vegetation undergoes a gradual transition from submontane forests, to lowland forests. Patches of swamp forest are found throughout the ecoregion. On the eastern and northeastern margins the topography is varied, with numerous rolling hills and escarpments, with elevations normally over 1,000 m in altitude. In the western portions topography is subtle with few variations and descends to around 600 m. The topographic diversity results in different forest habitat types across the ecoregion. There is also an important chain of inselbergs that cut east to west across the northern portions of the ecoregion. .
Climatically, the ecoregion lies within the humid tropics. Rainfall averages are between 1,500 mm and 2,000 mm per annum. Rainfall is seasonal with a well-marked dry season from January to March. Current climatic models indicate that the highest rainfall is found in the lower elevations of the western portion. Rainfall levels decline moving eastward as the land starts to rise towards the Albertine Rift Mountains. The mean annual maximum temperature is between 27oC and 33oC and the mean minimum is between 15oC and 21oC, with variation mostly dependent on elevation.
Precambrian basement rocks underlie the eastern and northern margins of the ecoregion. Further south the rocks are of more recent origin associated with sedimentation in the Congo Basin. Rocks are overlain by thick and heavily leached oxisols in the many parts of the ecoregion. In the southern portion of the ecoregion the soils are comprised primarily of nitosols, which are less weathered and better for crop cultivation. To the east volcanic activity within the Albertine Rift has also improved the fertility of the soils.
The human population of the ecoregion is greatest in the eastern portion, close to the Albertine Rift, reaching densities of 50 persons per km2. Human populations are lowest in the center of the rainforest, falling to less than 5 persons per km2. Some areas, notably the Maïko region, have no permanent settlements.
In terms of the phytogeographical classification by White (1979, 1983), this entire ecoregion falls within the Lower Guinea Rain Forest Block of the Guineo-Congolian regional center of endemism. The ecoregion contains the eastern limits of the Lower Guinea Rain Forest block at Semliki in Uganda, with only a few outliers of this forest type further to the east in Uganda, Tanzania and Kenya. The main vegetation type is lowland moist forest, with some transitional submontane forest in the east, where it borders the Albertine Rift Valley, and some drier transitional types in the north (White 1983). Although most of the area is covered in mixed-species moist evergreen and semi-evergreen rainforest, single-species dominated forest is also found in small to fairly large patches (White 1983, Hart et al. 1989, Hart 1990). The most common mono-dominant stand is largely made up of Gilbertiodendron dewevrei, which also forms mono-dominant stands in other ecoregions of the Guinean-Congolian Forest Region (Blom, pers. obs.).
Overall the flora is diverse and has high levels of endemism. Around 1500 species of plants are known from the Ituri part of the ecoregion, and others are found in Maïko National Park (WWF and IUCN 1994), and elsewhere. The flora contains high rates of plant endemism, and has many relict species. Some of the relicts indicate former connections to the lowland forests of Cameroon and Gabon. Recent plant collections in the central Ituri forest include several new species, and remarkable range extensions, including a Sapotaceous tree of a South American genus (John Hart pers com). The inselberg flora of the northern part of the ecoregion also contains interesting plants with links to the mountains of eastern Africa (John Hart, pers com).
This ecoregion also contain a number of narrowly endemic animals. Levels of endemism are highest on the lower slopes of the Albertine Rift Mountains at the eastern extremes, and remain high for some distance within the eastern portion of this ecoregion. The more central and western portions have yielded fewer restricted range species, however, this may be a collecting artifact caused by fewer biologists reaching this area.
Mammals in this ecoregion display high levels of endemism, with 16 species considered either strictly endemic or near-endemic, including the okapi (Okapia johnstoni; Hart 1992, Hart and Hart 1988a,b, 1989), giant genet (Genetta victoriae), and aquatic genet (Osbornictus piscivora). Four endemic species of shrew are found only in these forests; the mountain shrew (Sylvisorex oriundus, VU), African foggy shrew (Crocidura caliginea, CR), Congo shrew (C. congobelgica, VU), and the fuscous shrew (C. polia, CR) (Hilton-Taylor 2000). Ten additional species are considered near endemic, including the owl-faced monkey (Cercopithecus hamlyni), L'Hoest's monkey (C. lhoesti), the pied bat (Chalinolobus superbus, VU), Allen's striped bat (Chalinolobus alboguttatus, VU), Misonne's soft-furred mouse (Praomys misonnei), and Verschuren's swamp rat (Malacomys verschureni). This ecoregion also contains the most important population of the eastern lowland gorilla (Gorilla gorilla graueri, EN).
The avifauna of this region includes two strictly endemic species Neumann's coucal (Centropus neumanni) and the golden-naped weaver (Ploceus aureonucha, EN). Near-endemic species include Nahan's francolin (Francolinus nahani, EN), Ituri batis (Batis ituriensis), Turner's eremomela (Eremomela turneri, EN), Congo peacock (Afropavo congensis, VU; Hart 1994, Hart and Upoki 1997), Sassi's greenbul (Phyllastrephus lorenzi), Bedford's paradise-flycatcher (Terpsiphone bedfordi), and on the eastern margins with the Albertine Rift Chapin's mountain-babbler (Kupeornis chapini).
The herpetofauna has not been well studied. In the reptiles there are five endemic species, including the Zaire dwarf gecko (Lygodactylus depressus). Among amphibians there are seven endemic species: the olive shovelnose (Hemisus olivaceus), Kigulube reed frog (Hyperolius diaphanus), Kunungu reed frog (H. schoutendeni), Mertens' running frog (Kassina mertensi), Buta River frog (Phrynobatrachus gastoni), Christy's grassland frog (Ptychadena christyi) and Pangi Territory frog (Rana amieti). A further nine amphibians are regarded as near-endemic.
As with all other central African countries, a map of the priority sites for biodiversity conservation in this region was proposed in IUCN (1989) and has been updated recently (WWF 2003).
Currently, no accurate data are available on the status of the habitats in this ecoregion (but see Doumenge 1990, Sayer 1992 and Witte 1995 for general information). Forest cover of the ecoregion has fluctuated over time, with forest declines associated with climate desiccation events which occurred during the Pleistocene ice ages and also since the end of the last ice age, e.g. during the period 2000 - 2500 BP (Hart et al. 1994). Much of this ecoregion now comprises lowland rain forest, often in a seemingly primary state. Although the full extent of forest is unknown, it easily exceeds 100,000 km2, and much of this is continuous.
In the DRC, an important part of the Ituri forest is now protected within the Okapi Faunal Reserve. Other lowland forest areas are protected within the Kahuzi-Biega National Park, the Maïko National Park and the Yangambi Reserve (UN 1993, IUCN 1998, WWF 2000). At present the Yangambi reserve is seriously compromised, and of uncertain conservation value. Further reserves which should be assessed to determine their values are the Rubi Tele Domaine de Chasse, the Maika Penege Reserve (near Isiro), and on the ecoregions northern border, the Bili-Uere Domaine de Chasse. The total area under protection is roughly 31,000 km2, representing around 6 percent of the ecoregion. Lowland forest of the Itombwe Massif is currently unprotected, but of high conservation value.
The ecoregion contains part of one of the great rain forest wildernesses in the world. This is particularly true in the central part of the ecoregion where the extensive forests support a low density of forest dwelling Mbuti pygmies (Luling and Kenrick 1998), and associated agricultural peoples (Wilkie and Curran 1993, Wilkie et al. 1998a, 1998b, Wilkie and Finn 1990). Soils and agriculture potential are better in the east and south of the ecoregion, especially in Kivu Province. This land is suitable for cattle ranching and plantation agriculture, including coffee. The wars in Rwanda and Burundi and in eastern Congo have displaced many people into the eastern part of the ecoregion. However, these wars have also led to the depopulation of other areas, allowing for potential regrowth of forest cover in the future.
Types and Severity of Threats
The main threats to this ecoregion are mining, logging, large-scale human population movements as a result of war, and the bushmeat and wildlife utilization often accompany these other threats. Gold, diamonds, and the rare metal coltan are mined (Hart and Mwinyhali 2001). Mining has already seriously impacted many important forest areas, such as Maïko, Ituri and the Kahuzi Biega lowlands (in the latter there are currently 15,000 miners).
Bushmeat hunting, often associated with illegal mining, is a major threat to the larger animals, even in the remote Ituri forest (Wilkie and Carpenter 1998, Alers et al. 1992, Hall et al. 1997, 1998, Hart and Hall 1996). Elephant poaching has also had a major impact in this region, even in protected areas such as Kahuzi-Biega and Maïko National Parks, and Okapi (Ituri) Faunal Reserve (Alers et al. 1992, Hall et al. 1997, 1998, Hart and Hall, 1996, Blom, Hall, Hart and Hart, pers. comm.).
Logging has also occurred in several locations, but was largely interrupted due to the war in the DRC. Huge logging concessions are planned and some are underway. Recently the logging industry has been moving in from Uganda, taking advantage of the relative security in the east (especially Ituri region).
The recent wars in Rwanda, Burundi, and eastern Democratic Republic of Congo have had serious impacts on protected area management capabilities, and have led to the widespread migrations of refugees. In some places these refugees have cleared large areas of forest for subsistence agriculture, especially in the eastern sector (Klug, pers. comm.).
There are fewer threats in the central part of the ecoregion, as population density is low and most of the pygmy inhabitants practice subsistence survival techniques, which are generally compatible with the survival of the forest.
Justification of Ecoregion Delineation
The Northeastern Congolian Lowland Forests ecoregion is a part of the Guineo-Congolian regional center of endemism (White 1983). The ecoregion is distinguished by high rates of endemism. It is bound by the Uele River in the northeast, the Congo River and its tributaries (primarily the Elila River) in the south, and the Bomu River as it flows into the Oubangui River in the west. These rivers form distribution boundaries to some mammal species, such as the fishing genet (Osbornictis piscivora). The eastern flank of the ecoregion is comprised of 'transitional forest' in the foothills of the Albertine Rift Mountains and our boundary is placed arbitrarily at around 1,500 m. The majority of the southern boundary of the ecoregion abuts swamp forests, with the remaining portion following White's delineation between wetter and drier lowland rainforest.
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Prepared by: Allard Blom, Jan Schipper
Reviewed by: In progress