Biome: Montane Grasslands and Shrublands
Size: 5,100 square miles
Conservation Status: Critical/Endangered
Location and General Description
The Jos Plateau Forest-Grassland Mosaic ecoregion is located on the boundary between the Guinean Forest-Savanna Mosaic ecoregion in the south and the Lake Chad Flooded Savanna ecoregion in the north. The Plateau is the largest landmass above 1,000 m in Nigeria and is approximately 250 km by 150 km in size. It comprises high plains about 1,300 m above sea level and a number of granite hill ranges that can reach heights of over 1,900 m. On the west and south sides the plateau is demarcated by a scarp 500 m to 700 m in height, but on the plateau’s northern side the transition to the lower plains is less abrupt.
The rocks of the Jos Plateau are mainly granites that are part of the Pre-Cambrian Basement Complex, an ancient group of crystalline rocks that used to form part of the land surface of the Gondwanan supercontinent (Buchanan and Pugh 1955). The granites are particularly resistant to erosion, and generally form shallow and sandy soils. In some areas there are also basaltic rocks, which weather to form relatively deep clay loams (Buchanan and Pugh 1955). The latter of these have reasonable agricultural potential and are farmed for crops including potatoes.
Temperatures on the Jos Plateau are lower than the surrounding areas, with minima of 15.5°C to 18.5°C to maxima of 27.5°C to 30.5°C. On the Plateau, the rainfall is around 2,000 mm in the wetter southwest, and declines to around 1,500 mm in the northeast. Average rainfall for the town of Jos is 1,411 mm per year (Payne 1998). These figures compare with 1,000 mm to 1,200 mm per annum in the surrounding savannas (Happold 1987). The heavier rains in the south and west are due to the moisture-bearing winds meeting the escarpment at this point. The watershed pattern on the Jos Plateau is unusual in that its streams can drain into three different larger river systems. Some streams flow northeast to Kano and Lake Chad, east to the Gongola River (which enters the Benue), south to the Benue, and west ot the Kaduna River which feeds into the Niger River (Payne 1998).
White (1983) identifies this ecoregion as an isolated vegetation unit within the Guineo-Congolian/Sudanian Regional Transition Zone. Savanna woodland is likely to have been the climax ecotone of this ecoregion, but human activities have resulted in extensive and severe degradation. Presently, only a few remnants of woodland remain, and they are restricted to the steep and less accessible margins of the plateau, with open grassland occupying the remainder of the plateau. Forests are limited to the southern and western escarpments, river edges, and along the base of rocky outcrops (Payne 1998). The vegetation is dominated by savanna species, but also includes a number of species with South or East African affinities (Buchanan and Pugh 1955). The most numerous tree species in the remaining woodland is Isoberlinea doka, with Vitex doniana, Lannea schimperi, and Uapaca somon also being common. Along streams Syzygium guineense and a Berlinea sp. are common (Netting 1968). White (1983) lists the following rupicolous species found in bushland and scrub forest on the Plateau: Carissa edulis, Dalbergia hostilis, Diospyros abyssinica, D. ferrea, Dodonaea viscosa, Euphorbia desmondii, E. kamerunica, E. poissonii, Ficus glumosa, Kleinia cliffordiana, Rhus longipes, R. natalensis, Ochna schweinfurthiana, Olea capensis, Opilia celtidifolia, and Pachystela brevipes. The domination by species common to the lowland savanna areas that surround the Plateau may not be a natural occurrence. The destruction of the original woodland over at least several hundred years, and the presumed increased incidence of fires, may have allowed these elements to spread to the Plateau.
The ecoregion, though small, contains a relatively large number of endemic species. Two small mammals are strictly endemic to the Jos Plateau, Nigerian mole rat (Cryptomys foxi) and Fox's shaggy rat (Dasymus foxi). Several other mammals occur in Nigeria only on the Jos Plateau, including the bushveld horseshoe bat (Rhinolophus simulator), the high-crowned bat (Miniopterus inflatus), dark-eared climbing mouse (Dendromus melanotis), and the West African subspecies of klipspringer (Oreotragus oreotragus porteousi, EN). The two bat species and the dark-eared climbing mouse are also found in the Cameroonian highlands, suggesting that there may have been a faunal and climatic link between these two areas in the past (Happold 1987).
Klipspringer distribution is of special biogeographic interest because this is the only West African population of klipspringer. With the exception of some small, isolated populations in Central African Republic (East 1999), the Nigerian klipspringers are separated by about 3,000 km from the nearest East African population, and much of that interlying habitat is not suitable for them, as they exclusively inhabit rocky outcrops and inselbergs. Now one of the rarest savanna antelopes in Nigeria, klipspringer were at one point found in Bauchi, Bornu and Zaria provinces, and were widespread on the Bauchi Plateau (Happold 1987).
Two endemic birds include the rock firefinch (Lagonosticta sanguinodorsalis) and the brood-parasitic Jos Plateau indigobird (Vidua maryae). The Jos Plateau indigobird mimics the rock firefinch’s song, which resulted in the discovery of this bird (Payne 1998). Anther bird species illustrates the link between the fauna of the Jos Plateau and the Cameroonin Highlands. This is the Adamawa turtle dove (Streptopelia hypopyrrha), which is found on the Adamawa Plateau and some other parts of the Cameroonian Highlands ecoregion and on the Jos Plateau (Payne 1998). There are no known strict or near-endemic reptiles or amphibians on this plateau.
The human population of the area is high with a density of around 200 to 300 persons per km2. Jos was a mining center through the 1920s and development workers and Christian missions have been located here for decades (Payne 1998). The relatively fertile soil and favorable climate make intensive farming with short fallow periods possible. Other than conversion to farmland the collection of firewood has been another major cause of deforestation. In and around villages, except for an occasional sacred grove, most trees are useful species such as the oil palm (Elaeis guineensis), canarium (Canarium schweinfurthii) and mango trees (Mangifera indica) (Netting 1968), many of which are planted. Natural trees are largely to wholly absent in most areas.
Types and Severity of Threats
With most of the original woodland vegetation having been lost, or restricted to inaccessible areas or river margins, this ecosystem faces a bleak future. The area is highly threatened by agricultural activities, particularly in the regions located over basalt where the soil is more fertile and well suited for crops that cannot be grown in most other parts of Nigeria. This includes potatoes. Though the threats are lower in areas where the substrate is granite the collection of firewood has resulted in extremely high levels of deforestation as well.
Presently there are no activities to preserve the few remaining remnants of this ecosystem. The Forestry Department is considering the replanting of trees but unfortunately they are considering exotic species such as eucalyptus (Eucalyptus camaldulensis).
Justification of Ecoregion Delineation
The Jos Plateau ecoregion follows the ‘Jos Plateau mosaic’ delineated by White (1983). It includes a number of species with South or East African affinities, such as the West African population of Klipspringer, as well as a number of endemic mammals and birds. Although it shares some biological affinities with the Cameroonian Highlands, it was considered geographically distinct to warrant a separate ecoregion (WWF 1998). The boundary of the ecoregion is taken from White (1983), but has been modified using the 1000 m elevation contour.
Buchanan, K. M. and J. C. Pugh. 1955. Land and People in Nigeria. University of London Press, London.
East, R. 1999. African Antelope Database 1998. IUCN/SSC Antelope Specialist Group, IUCN, Gland, Switzerland and Cambridge, United Kingdom.
Happold, D. C. D. 1987. The Mammals of Nigeria. Oxford University Press, New York.
Payne, R. B. 1998. A new species of Firefinch (Lagonosticta sanguinodorsalis) from northern Nigeria and its association with the Jos Plateau Indigobird (Vidua maryae). Ibis 140:368-381.
Netting, R. M. 1968. Hill Farmers of Nigeria. University of Washington Press, Seattle and London.
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.
WWF. 1998. A conservation assessment of terrestrial ecoregions of Africa: Draft proceedings of a workshop, Cape Town, South Africa, August 1998. World Wildlife Fund, Washington, DC, USA.
Prepared by: Jan Lodewijk R. Were
Reviewed by: In progress