Location and General Description
This ecoregion lies south of the Sahel in central and eastern Africa, and is divided into a western block and an eastern block by the Sudd swamps in the Saharan Flooded Grasslands ecoregion. The western block stretches from the Nigeria/Cameroon border through Chad and the Central African Republic to western Sudan. The eastern block is found in eastern Sudan, Eritrea, and the low-lying parts of western Ethiopia, and also extends south through southern Sudan, into northwestern Uganda, and marginally into the Democratic Republic of Congo around Lake Albert.
Topographically, the ecoregion is flat, mainly lying between 200 m and 1,000 m in altitude, although elevation rises slightly in western Ethiopia and around Lake Albert. The climate is tropical and strongly seasonal. Mean monthly maximum temperatures range from 30° to 33°C and mean minimum temperatures are between 18°C and 21°C. The annual rainfall is as high as 1,000 mm in the south, but declines to the north with only 600 mm found on the border with the Sahelian Acacia Savanna. Rainfall is highly seasonal, and during the rainy season from April to October, large areas of southern Chad and northern parts of the Central African Republic become totally inundated and inaccessible. During the dry season most of the trees lose their leaves and the grasses dry up and may burn.
Geologically, the ecoregion overlies a mixture of Precambrian basement rocks, and a number of post-Jurassic sedimentary basins. The soils are mainly ultisols and alfisols in the south with entisols in the north. Some oxisols and vertisols are also found in the east. The ecoregion is sparsely populated, with typical population densities ranging between 1 to 5 people/km2, although there may be as many as 20 to 30 people/km2 in some places.
White (1983) classified this region phytogeographically within the Sudanian regional center of endemism, as it supports more than 1,000 endemic species of plants. The vegetation is mapped as undifferentiated woodland that comprises trees, which are mainly deciduous in the dry season, with an understory of grasses, shrubs and herbs. Typical trees in the western block of the ecoregion include Anogeissus leiocarpus, Kigelia aethiopica, Acacia seyal and species of Combretum and Terminalia. In the eastern block woody vegetation is dominated by Combretum and Terminalia species, as well as Anogeissus leiocarpus, Boswellia papyrifera, Lannea schimperi and Stereospermum kunthianum. The solid-stemmed bamboo Oxytenanthera abyssinica is prominent in the western river valleys of Ethiopia, and dominant grasses include tall species of Hyparrhenia, Cymbopogon, Echinochloa, Sorghum, and Pennisetum (Tilahun et al. 1996).
The East Sudanian Savanna ecoregion closely resembles the West Sudanian Savanna in habitat structure and species composition. The two ecoregions differ somewhat in terms of their species assemblages and the degree to which the habitat and mammal assemblages are intact. The East Sudanian Savanna is not typified by high rates of faunal endemism, with only one strictly endemic mammal (a mouse, Mus goundae, VU), and two strictly endemic reptiles (Rhamphiophis maradiensis and Panaspis wilsoni). Five bird species are considered endemic, including two strict endemics, Reichenow's firefinch (Lagonostica umbrinodorsalis) and Fox’s weaver (Ploceus spekeoides). The near-endemic Karamoja apalis (Apalis karamojae) is found elsewhere in East Africa, while two other near-endemic species, the white-crowned robin-chat (Cossypha albicapilla) and Dorst’s cisticola (Cisticola dorsti, DD) are shared with the West Sudanian Savanna ecoregion. However, the situation is different for plants since the ecoregion is largely congruent with part of the Sudanian regional center of endemism, and is thus part of an important area for endemic plants. There are approximately 2,750 species of higher plants within the entire Sudanian regional center of endemism, and roughly one-third are endemic (White 1983). However, this ecoregion is immense in size, and as a result, the rate of floral endemism per unit area is rather low.
Notable threatened mammal species include large herds of elephant (Loxodonta africana, EN) in Chad and Central African Republic (DPNRF 1997), wild dog (Lycaon pictus, EN), cheetah (Acinonyx jubatus, VU), leopard (Panthera pardus, EN) and lion (Panthera leo, VU). Black rhinoceros (Diceros bicornis, CR) and northern white rhinoceros (Ceratotherium simum cottoni, CR) have been extirpated from the ecoregion, although occasional unconfirmed reports of the former (from southern Chad, for example) continue to be received (DPNRF 1997). The eastern giant eland (Taurotragus derbianus gigas) still survives in good numbers in the Central African Republic, especially in the western regions of the country, out of reach from Sudanese poachers (East 1999). Giant eland are less susceptible to poachers than other more sedentary and less wary antelope species, but have been almost completely eliminated from Sudan. The roan antelope’s (Hippotragus equinus) cautious behavior has also allowed it to withstand poaching pressure to some degree and it is widespread throughout the Central African Republic, in low to moderate densities. However, uncontrolled poaching in Chad and Sudan has resulted in decreasing roan antelope populations in the rest of this ecoregion.
The original wooded savanna habitat has been significantly reduced, although to a lesser extent than in the West Sudanian Savanna, primarily due to the lower human population density. There are a good number of protected areas and outside formal protection, habitats remain in reasonable condition in many regions.
The total area of protected lands is over 136,000 km2. This is approximately 18 percent of the ecoregion that is quite high. However, many of these protected areas are not adequately enforced or policed. They include Dinder, Radom, and Boma National Parks in Sudan, as well as Zakouma N.P. in Chad, Manovo-Gounda-Saint Floris and Bamingui-Bangoran N.P. in Central African Republic, and Gambella N.P. in Ethiopia, and Mt Kei in Uganda.
Types and Severity of Threats
The habitats of the ecoregion are principally threatened by the agricultural and herding activities of the local populations. Threats include seasonal "shifting" cultivation, over-grazing by livestock, cutting trees and bushes for wood, burning woody material for charcoal, and uncontrolled wild fires. Climatic desiccation is a further threat, exacerbating the impacts of human activities, as the ability of the ecosystem to recover from overuse is reduced when there is little rainfall. The main threats to the species of the ecoregion are over-grazing and, in the case of larger animals, over-hunting for meat or poaching for trophies. Poaching of wildlife is particularly pronounced in politically unstable areas such as southern Sudan.
Justification of Ecoregion Delineation
This ecoregion, along with the West Sudanian Savanna, forms part of the Sudanian regional center of endemism, and contains two vegetation units, the ‘Sudanian undifferentiated woodland’ and ‘Sudanian woodland with abundant Isoberlina’ (White 1983). Although these two units differ in the presence of Isoberlina, with the northern unit being slightly drier, they share similar animal assemblages. The West and East Sudanian Savannas are also similar in terms of their broader species assemblages, but they were split into two separate ecoregions near the Mandara Plateau because a number of plant taxa do not cross this boundary (WWF 1998). Several modifications to White’s boundaries have been made, including an extension of the Sahelian Acacia Savanna below Lake Chad, and a northern boundary considerably further south than White’s boundary (WWF 1998). Edaphic grassland and communities of Acacia and broadleaved trees identified by White have also been largely excluded. The eastern portion of this ecoregion forms an extension of undifferentiated woodland, following White’s ‘Ethiopian undifferentiated woodland’ and ‘Ethiopian transition from undifferentiated woodland to Acacia deciduous bushland and wooded grassland.’ This area was extended to include ‘Sudanian undifferentiated woodland’ south towards Lake Albert and Mount Elgon. Udvardy (1975) delineates a biogeographic boundary between the Western and Eastern Sahel, which would effectively split the western section of this ecoregion in half.
DPNRF, 1997. Zakouma: Projet Conservation de l'Environnement dans le sud-est du Tchad. Rapport d'Activité 1996-1997. Direction des Parcs Nationaux et Réserves de Faune, Ministère de l'Environnement et de l'Eau, République du Tchad. 77 pp + Annexes.
East, R. compiler. 1999. African Antelope Database 1998. IUCN/SSC Antelope Specialist Group. IUCN, Gland, Switzerland and Cambridge, United Kingdom
Tilahun, S., S. Edwards, and T. B. G. Egziabher. editors. 1996. Important Bird Areas of Ethiopia. Ethiopian Wildlife and Natural History Society. Semayata Press. Addis Ababa, Ethiopia.
Udvardy, M.D.F. 1975. A classification of the biogeographical provinces of the world. IUCN Occasional Paper No. 18. International Union of Conservation of Nature and Natural Resources, Morges, Switzerland.
White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris.
Prepared by: Chris Magin
Reviewed by: In progress