Niger Delta swamp forests
The Niger River swamp forests occupy the inner reaches of the expansive Niger Delta. The Niger Delta, though having played an important role in the global economy (through the slave trade, palm oil trade, and now fossil fuels) over the last 400 years, has escaped close biological scrutiny. The first systematic surveys of the delta's flora and fauna were conducted during the past decade, and revealed several species previously not known to occur in the delta, including the Niger Delta red colobus (Procolobus badius epieni) which was new to science. These surveys also indicate that the forests and animal populations of the delta are under severe threat. Nigeria's second most important timber species, abura (Hallea ledermannii), once common in the delta, has been removed by extensive logging since the late 1950's. Pressure on the delta's remaining forests comes from a growing native Nigerian population, and improving infrastructure that makes it easier to access remaining areas of swamp forest. There are no protected areas in the delta and the rapid rates of destruction paint a bleak picture for the future of its habitats and species.
Location and General Description
The Niger Delta Swamp Forests ecoregion is contained in a triangle with the town of Aboh on the Niger River being the northernmost tip. The Benin River forms the western boundary of the ecoregion where this ecoregion merges into the Nigerian Lowland Forest ecoregion. The Imo River forms the eastern side where this ecoregion merges into the practically vanished Cross-Niger Transition Forests ecoregion. Along its southern side the Niger Delta Swamp Forests is separated from the Atlantic Ocean by a band of mangroves, which can reach up to 10 kilometers (km) inland. In front of the mangrove belt and close to the sea are ephemeral coastal barrier islands often clothed in transitional vegetation. The ecoregion's total area of approximately 15,000 square kilometers is contained within three states, Rivers, Bayelsa, and Delta, of the Nigerian Federation.
The soils of this ecoregion are all of fluviatile origin, except for the Coastal Barrier Islands that consist of marine sand overlain with an organic surface layer. The continuous movement of the delta's creeks has resulted in a mosaic of soil types. Remnants of old levees consist mostly of water permeable sand and loam. The soil of the depressions behind them (backswamps) consist mostly of water-logged heavy clay covered by peat, while higher lying sections consist of silty loam and clay.
The climate of the Niger Delta is characterized by a long rainy season from March-April through October. Precipitation increases from the north of the delta (with an average of 2,500 millimeters) to the coastal area where mean annual rainfall averages around 4,000 millimeters (mm), making it one of the wettest areas in Africa. The wet season peaks in July, and the only dry months are January and February. However, even during this dry period an average monthly mean of 150 mm rainfall is recorded in the delta. Relative humidity rarely dips below 60% and fluctuates between 90% and 100% for most of the year. During most of the rainy season cloud cover is nearly continuous resulting in 1,500 mean annual sunshine hours and an average annual temperature of approximately 28°C.
The most important determinant of biological variation in the delta is its hydrology. In addition to precipitation, the major variation in the hydrological regime comes from the Atlantic Ocean's tidal movements and the Niger River flood. This flood begins toward the end of the rainy season in August, peaks in October, and tapers off in December. Some fluctuation in flow is determined by the yearly variation in rainfall, but after the completion of the Kainji dam on the Niger at Bussa in 1968 the timing and level of flooding is also determined by the opening and closing of the dam's sluices.
The swamp forest can be further subdivided into three zones based on hydrological variation. Each zone appears to support its own floral and faunal assemblage. The first zone is the flood forest. This zone shows strong seasonal variation. During the dry season the soil is dry save for the seasonal flood channels, a few permanent creeks, and some lakes. During the rainy season water levels slowly rise, eventually leading to complete inundation during the Niger River flood, which lasts generally from October through December. Some of the more common tree species here are; Lophira alata, Pycnanthus angolensis, Ricinodendron heudelotii, Sacoglottis gabonensis, Uapaca spp., Hallea ledermannii, Albizia adianthifolia, Irvingia gabonensis, Klainedoxa gabonensis, Treculia africana, and Ficus vogeliana. The oil palm (Elaeis guineensis) is common, and the understory is often dominated by rattans (e.g. Calamus deerratus). The second zone is the eastern delta flank, which is shrinking relative to the western flank. Some lowland forest non-swamp species are found here (e.g. Ogilby's Duiker Cephalophus ogilbyi and Sclater's Guenon Cercopithecus sclateri). The third zone is the central backswamp area of the delta, crossed by old creek levees. This area is not often flooded and is not influenced by the tides, and hence relatively stable. Most of the forest here is always waterlogged. The only systematically collected data for the Niger Delta's vegetation comes from this zone. The distribution of tree species in the forest is determined by hydrology with drier remnants of levees being more diverse than the waterlogged back swamps. The forest is dominated by the following tree species: Euphorbiaceae (Uapaca spp., Klaineanthus gaboniae, Anthostema aubreyanum, Macaranga spp.) Annonaceae (Xylopia spp., Hexalobus crispiflorus) Guttiferae (Symphonia globulifera, Pentadesma buteraceae), Rubiaceae (Hallea ledermannii, Rothmannia spp.), Myristicaceae (Coelocaryon preussii, Pycnanthus marchalianus), and Ctenolophonaceae (Ctenolophon englerianus). Average tree height (20-25 meters) is relatively low for rain forest, and emergents, which can reach heights of 35 to 40 meters (m), occur at low densities. In drier sections the most common emergents, Lophira alata, Sacoglottis gabonensis, Irvingia gabonensis, and Klainedoxa gabonensis, while in the wetter sections Alstonia boonei and Ctenolophon englerianus dominate. The middle story also shows variation determined by hydrology with Klaineanthus gaboniae dominating in the drier areas, and Raphia spp. in the wetter areas (which can, in the western part of this zone, form large single-species dominant forests). In some sections of this zone small single-species stands of Oxystigma mannii (Ceasalpinioideae) can also be found. The shrub layer is dominated by Diospyros preussii augmented with Ouratea spp., Massularia acuminata, Monodora myristica, Homalium spp., and Alchornea cordifolia. The forest floor number is covered by a number of small palms (Eremospatha and Podococcus spp.) and by members of the Marantaceae and Zingiberaceae.
Presently there is little information available on the species composition of this ecoregion. Wildlife surveys in the delta were not conducted until the late 1980s. A number of species that were not known from the delta, and new for Nigeria were discovered as recently as the 1990s.
The Upper and Lower Guinean biota, which was once considered to be separated by the Dahomey Gap, overlaps in the delta. The Delta's floral assemblage appears to be unique, although endemic plants are not known. The presence of two endemic animal subspecies, the Niger Delta or Pennant's red colobus (Procolobus badius epieni, EN) and the Niger Delta or Heslop's pygmy hippopotamus (Hexaprotodon liberiensis heslopi, CR), supports Grubb's suggestion that the Delta is a small center of endemism. Although the Niger presents a zoogeographic barrier to some degree, the situation in reality is far more complex since the narrower distributary delta channels allow species to move from one side of the Niger River to the other.
There are no endemic animal species in this ecoregion, but there are two threatened endemic mammal subspecies, the Niger Delta red colobus and the Niger Delta pygmy hippopotamus. There are also two near-endemic species of monkeys, the white-throated guenon (Cercopithecus erythrogaster, EN), and Sclater's guenon (Cercopithecus sclateri, EN). A number of other species have been recently discovered in the Niger Delta that are either new to Nigeria or had not been observed west of the Cross River, such as black-fronted duiker (Cephalophus nigrifons), pygmy scaly-tailed flying squirrel (Idiurus sp.), and small green squirrel (Paraxerus poensis). This suggests that more endemic subspecies may be present.
The African elephant (Loxodonta africana), chimpanzee (Pan troglodytes), Sclater's guenon, white-throated guenon, and crested genet (Genetta cristata) are all classified as endangered. There is evidence indicating that chimpanzees in Nigeria and western Cameroon may be a different subspecies from those in the west and south. Moreover, it may even be that there is a significant difference between populations in western and eastern Nigeria, with the Niger Delta forming a meeting point. Further research on these chimpanzee populations is an urgent priority, because if these populations are distinct at the subspecies level they will be critically endangered. Of this ecoregions other endemic subspecies the Niger Delta pygmy hippopotamus, if it indeed survives, would be critically endangered while the Niger Delta red colobus is considered endangered.
Although the Niger Delta is wedged between two of Africa's most densely populated areas, for a while it escaped some of the habitat destruction associated with these areas due to its relative inaccessibility. Roads stop at the delta's boundaries and further travel is either by dug-out canoe, or for those who can afford it, by motorized boats. As a result the delta used to support low population densities and little socioeconomic activity other than fishing, some farming in the drier sections, and the collection of forest products. Two events, which happened to occur at about the same time, changed this. In the 1950s oil was discovered in the Niger Delta and the associated activities (road and canal building) opened large sections of remote delta habitat up for exploitation. The second event was that abura (Hallea ledermannii) had become the most important timber species after Triplochiton scleroxylon. In 1938 there were no abura exports from Nigeria, but, as of 1949, it became the second most important income earner and by 1951 export volume had increased more than five times from 626,133 to 3,497,549 logs. Most of the abura came from the swamp forest situated between the Nigerian Lowland Forests ecoregion and the mangrove belt, which were soon depleted. As a result loggers started to focus more on the delta where exploitation was at the same time facilitated by increasing oil exploration efforts. Presently there are few abura left in the delta and logging has shifted to other species that float, a requirement in an area where transportation is restricted to waterways.
There are no effectively protected areas in the Delta. A number of forest reserves exist, but these areas are under control of forest department and are generally exploited for their timber. In addition, nine of these forest reserves have only been proposed. The three existing forest reserves are Upper Orashi, Nun River, and Lower Orashi, all in Rivers State, which comprise a total of 239 km2. The only effective habitat protection is found in sacred groves protected by communities. However, these areas are never very large. Other forms of community protection are restricted to certain species of wildlife. In a number of lakes crocodiles receive protection and in one area, Nembe, chimpanzees receive protection.
Types and Severity of Threats
The Niger Delta provides a small-scale representation of many of Africa's problems. A growing population, conflicts between different ethnic groups, national political instability, unsustainable exploitation of natural resources; all of these factors play a significant role in the problems the delta is presently facing. The single most pressing problem facing the delta presently is a lack of development, despite most of Nigeria's revenues coming from the oil found in this area. There is electricity only in a few of the delta's towns and fresh water and health care facilities are basically absent. Rightfully or not, the delta's inhabitants hold the oil industry responsible for this situation, and dissatisfaction has now reached such levels that the seizure and destruction of oil company property, as well as the kidnapping of oil company personnel, has become a common occurrence. As a result it has also become extremely difficult to engage in research or conservation activities.
At the same time the human population of the Niger Delta is growing rapidly, with the result that most of the natural resources (e.g., fish, timber) there have either been reduced to a level where they are insufficient to meet the local needs, or, as in the case of abura, have been depleted altogether. Buying fish now requires money, and as a result the delta's population has been forced to focus more and more on activities that provide cash. The oil industry, which is not labor intensive, provides only a very small number of jobs and, therefore, provides no alternative for government supported development. As a result the only local large-scale economic activities that provides cash come from the exploitation of the delta's other natural resource: trees. This is a significant departure from the barter system that up to not long ago was the most important form of economic exchange.
The inhabitants of the densely populated ecoregions next to the delta have depleted most of their wildlife and fish, with the result that they have started looking elsewhere for protein sources. The improving infrastructure in the delta has now made it possible for its inhabitants to transport more fish to the surrounding area, but also for outsiders to travel into the delta. The areas to the northeast and west of the Niger Delta harbor two of Nigeria's three largest ethnic groups, the Ibo and Yoruba. This southern part of Nigeria has reached one of Africa's highest population densities - 20 years ago already between 200 and more than 400 persons/km2. This means that the demand for smoked fish and timber is high, and most these commodities now come from the delta. A good indicator of the human pressure on the Niger delta is that people from as far as Ogoni, located more than 50 km to the east of the delta, come to its central area for part of the year to fish. Overfishing is the result, fish populations are declining, and frozen marine fish is now for sale in the larger towns of the delta. Tension between different ethnic groups, but also within the same ethnic groups, is now resulting in an increase of communal clashes, which often result in the deaths of people and halts all human activities (e.g., fishing, farming) in the involved communities' vicinity.
Recent surveys of the delta, especially the central part, have shown that small logging efforts have had a devastating cumulative effect on animal populations, through both loss of habitat and increase in localized hunting. This situation is growing worse as outsiders move into the Delta and hunting pressures grow.
Justification of Ecoregion Delineation
The swamp forests of the Niger Delta comprise the second largest swamp forests on the continent after the Congolian swamp forests. This ecoregion is based on the 'swamp forest' vegetation mapped by White. However, the southern boundary has been modified based on reference to a classified AVHRR 1km satellite image of the continent. The swamp forests is biologically distinct as it harbors endemic mammal subspecies, Pennant's red colobus (Procolobus pennantii epeini) and Heslop's pygmy hippo (Hexaprotodon liberiensis heslopi).
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