Location and General Description
The South Saharan Steppe and Woodlands ecoregion extends in a narrow band from central Mauritania, through Mali, southwestern Algeria, Niger, Chad, and across Sudan to the Red Sea, covering the southern fringes of the Sahara Desert. Rainfall occurs mainly during the summer months of July and August, but is unreliable and varies greatly from year to year. On average, annual rainfall is between 100 and 200 mm, declining along a gradient from south to north. However, droughts lasting several years often occur. Except near the coast of Sudan, mean annual temperature throughout the Sahelian portion of the ecoregion is between 26ºC and 30ºC. Pastoralism and domestic grazing are the foundations of the economy in the Sahel Region. Rainfall in this ecoregion is insufficient for rain-fed agriculture, but some irrigated agriculture is practiced near water points and along wadis (seasonally dry watercourses).
In terms of the phytogeographical classification of White (1983), the ecoregion is within both the Sahara regional transition zone and the Sahel regional transition zone. It serves as a transition from the Sahara to the Sahel. Delineated by White’s regs, hamadas and wadis vegetation type, the northern border of the ecoregion lies several hundred kilometers north of the 100 mm rainfall isohyet, which is the northern limit of summer grassland pasture composed of the grasses Eragrostis, Aristida, and Stipagrostis spp. with the herbs Tribulus, Heliotropium, and Pulicharia. Woody species include Acacia tortilis, Acacia ehrenbergiana, Balanites aegyptiaca, and Maerua crassifolia, which mainly grow along wadis. In the south, the vegetation of the ecoregion grades into the Sahelian Acacia Savanna ecoregion, and includes steppes of Panicum turgidum perennial tussock grass.
This ecoregion has few endemic plants. The Mediterranean flora that are characteristic in the Northern Sahara are almost completely absent from the Southern Sahara, where tropical flora dominate (White 1983). The higher massifs surrounded by this ecoregion, i.e. the Termit Massif in Niger, the Adrar des Iforas in Mali and Jebel Elba and Jebel Hadai Aweb in Sudan, which do have endemic species (White 1983; WWF and IUCN 1994), have all been assigned to montane ecoregions within the Greater Sahara ecosystem.
Notable animal species that once occurred throughout the ecoregion, but have now been reduced to extremely small and scattered populations include the following: addax (Addax nasomaculatus, CR), slender-horned gazelle (Gazella leptoceros, EN), Dorcas gazelle (Gazella dorcas, VU), dama gazelle (Gazella dama, EN), striped hyena (Hyaena hyaena, LR/DD), cheetah (Acinonyx jubatus, VU), wild dog (Lycaon pictus, EN), and ostrich (Struthio camelus). Small populations of the Barbary sheep or aoudad (Ammotragus lervia, VU) may exist on scattered rocky outcrops. The once-widespread scimitar-horned oryx (Oryx dammah, EW) and bubal hartebeest (Alcelaphus buselaphus buselaphus) have been exterminated entirely from the region (East 1999). Only one species of vertebrate is strictly endemic to the South Saharan Steppe, the gerbil Gerbillus dongolanus. Other near endemic mammals found here are two more species of Gerbil Gerbillus mauritaniae and G. principulus.
The habitats of this ecoregion are heavily influenced by drought, the effects of which are exacerbated by the large numbers of domestic livestock. In wetter years, there can be an abundance of forage, and in the past considerable numbers of large migratory ungulates used these temporary grasslands (Newby 1988). Tree cover in the south and along wadis has declined. Many trees have been cut for charcoal, firewood, and building materials. The recruitment of young trees into mature age-classes is almost non-existent in many areas due to overgrazing.
The Aïr and Ténéré National Nature Reserve in Niger and the Ouadi Rimé-Ouadi Achim Faunal Reserve in Chad are the two most important protected areas in the Sahelian subdesert zone of Africa. They probably contain the last viable populations of many of the larger ungulates of this ecoregion. However, both reserves have been plagued by political insecurity and civil unrest, and the current situation of their wildlife is far from certain. There are no protected areas in this ecoregion in Mauritania, Mali or Sudan, leaving huge expanses of habitat unprotected.
Types and Severity of Threats
Niger, Mali, Sudan, and Chad have suffered severe degradation of their natural resources in recent decades. Prolonged droughts and overgrazing by livestock are primarily responsible. The most severe degradation has occurred in the higher rainfall areas, or around boreholes, due to overwhelming local pressure on resources. Threats to the larger animals are quite intense. The populations of many ungulate species and ostriches have been greatly reduced by subsistence and recreational hunting, particularly by military personnel and rebel forces, as well as through intense competition with humans and their livestock. Predators, including the striped hyena, have been persecuted throughout the ecoregion by the widespread use of poisons such as strychnine because they kill livestock (MH/E, WWF and IUCN 1996). The under-representation of the desert and semi-desert habitats of this ecoregion in the protected areas systems of the Sahelian countries poses a threat to their long-term stability and conservation.
Justification of Ecoregion Delineation
This ecoregion is delineated from White's (1983) ‘regs, hamadas and wadis’ and ‘desert dunes with perennial vegetation’ units south of the Sahara Desert. Although these vegetation types surround the Sahara Desert, the southern habitats were delineated as a distinct ecoregion from the northern unit due to different rainfall regimes and the presence of Afrotropical species.
East, R. (comp.) 1999. African Antelope Database 1998. IUCN/SSC Antelope Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. x + 434 pp.
MH/E, WWF and IUCN. 1996. La Réserve Naturelle Nationale de l'Aïr et du Ténéré. Ministère de l'Hydraulique et de l'Environnement, World Wide Fund for Nature and World Conservation Union, Gland, Switzerland, 712 pp.
Newby, J.E. 1988. Aridland wildlife in decline: the case of the scimitar-horned oryx. Pp. 146 - 166 in: Dixon, A. and Jones, D. (eds). Conservation and Biology of Desert Antelopes. Christopher Helm, London, U.K.
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 and IUCN. 1994. Centres of plant diversity. A guide and strategy for their conservation. Volume 1. Europe, Africa, South West Asia and the Middle East. IUCN Publications Unit, Cambridge, U.K.
Prepared by: Chris Magin
Reviewed by: In progress