Location and General Description
This ecoregion extends across northern Africa and covers parts of Western Sahara, Mauritania, Morocco, Algeria, Tunisia, Libya, and Egypt. It is generally found inland of the coast, but stretches to the shore in areas where there is low rainfall. In Morocco, Algeria and Tunisia, this ecoregion forms a transition between the Mediterranean domain towards the north and the true desert in the south. The Saharan Halophytics ecoregion is also found scattered through this ecoregion in areas of suitable saline conditions.
Water is a serious constraint in this ecoregion. In the northern Sahara, the climate is hot and dry in the summer, and cooler with rain in the winter. Rains come from the Mediterranean and are associated with powerful depressions, which sometimes reach half-way across the Sahara. These occur mostly from October to April. Average annual rainfall varies from 50 mm in the south to 100 mm in the North, although there may be years where there is no rain at all (especially in the southern parts of the ecoregion). The highest temperature ranges between 40 and 45°C, creating evaporation that far exceeds the amount that falls as rain.
The extreme climate and varied geomorphologic conditions have assisted, nevertheless, to develop a significant diversity of landscapes and habitats adapted to drought. The ecoregion contains a number of geomorphologic features with different origins :
•The sandy systems : weever dunes, "placages", "nebkhas", "barkanes" form complex sequences that vary annually.
•Regs : Wide rocky plateaus where vegetation is relatively rare.
•Wadis : wide river beds, indicating an rainy past (as Oued Saoura, Oued M’Zi, Oued Mya) hosting "woodlands" of Acacia.
•Fesh fesh : are plateaus of soil that is not consolidated, almost mobile, with a rare vegetation.
•Dayas : depressions which are not salty and are favorable to the development of vegetation, with high number of Leguminosea, good for grazing.
•Mountains i.e. " Ougarta Mountains in Algeria": that dominate Beni Abbès plateaus covered by Acacia raddiana vegetation.
In terms of the phytogeographical classification of White (1983), the ecoregion occurs primarily within the Sahara regional transition zone, although it also extends into the Mediterranean/Sahara regional transition zone, most notably in Libya and Egypt. The flora comprises approximately 1,150 species (Le Houérou 1990) and is dominated by species belonging to families typical of the Palearctic Realm. Main depressions and major dune systems have vegetation comprised of tall shrubs (Retama raetam, Ziziphus lotus, Genista saharae, Calligonum comosum) and/or trees (Acacia raddiana, Pistacia atlantica, Tamarix aphylla, Calligonum azel, C. arich). There is great seasonal diversity in the plant communities of the Northern Saharan Steppe and Woodland. Some evergreen perennials, such as Pityranthus tortuosus and Stachys aegyptiaca, may flower all year, whereas others have restricted flowering during the summer (Zygophyllum coccineum) or autumn (Haloxylon salicornicum). There are also many ephemeral plant species in the northern desert that germinate in January during the wet season (Zahoran and Willis 1992).
Human populations are concentrated around water sources in oases that are characterized by particular models of water use (as foggaras), and palm agriculture (940 varieties have been listed in Algeria). Livestock is complementary to agriculture (e.g. camels, sheep "Daman race", and goats). Over recent decades the population has expanded greatly in the area. Now, some of the oases support moderate sized towns that are involved with oil exploration and production. These areas may also support tourist industries.
The ecoregion contains endemic species in both the plants and the animals, making it somewhat distinctive from other Saharan ecoregions where endemism is typically very low. The endemic plants in the ecoregion are distributed across the different geomorphological units. On sandy habitats there are several endemic plants, including Retama retam, Genista saharae, Rhanterium suaveolens, Calligonum comosum, Ephedra alata ssp alenda, Tamarix sp, Zilla spinosa, Oudneya africana, Panicum turgidim, and Aristida acutiflora. On dayas and bed wadis are woodlands of Acacia raddiana and Acacia seyal which support a number of endemic plant species including Panicum turgidum, Pithuranthos sp., Neurada procumbens, Anastatica hyrochuntina, and Astragalus gombo. The hammadas habitats also contain endemics, such as Pithuranthos chloranrhus, Helianthemum lippii, Gymnocarpos decander and Helianthemum kahirikum. Some hammadas are covered by the endemic species Anabasis aretioides and Arthrophytum schmittianum. (Quézel 1965).
The ecoregion is characterized by a number of Saharan endemic mammals that are very locally distributed in the dune systems. Most of these species are small mammals and include four-toed jerboa (Allactaga tetradactyla, EN), North African gerbil (Gerbillus campestris), James's gerbil (G. jamesi), pale gerbil (G. perpallidus), lesser short-tailed gerbil (G. simoni) and sand gerbil (G. syrticus, CR), fat-tailed gerbil (Pachyuromys duprasi), and Shaw's jird (Meriones shawi). Other common mammal species include the Atlas gundi (Ctenodactylus gundi) and the Sahara gundi (Ctenodactylus vali). Larger ungulate species that are found in the ecoregion include dorcas gazelle (Gazella dorcas, EN) which is endemic to the Sahara, mountain gazelle (Gazella cuvieri, EN) which is endemic to the northern Sahara and Maghreb areas, and slender-horned gazelle (Gazella leptoceros, EN) (Kingdon 1997).
Although the diversity of reptiles is moderately high in the ecoregion the number of endemic species is lower than in semi-desert areas of Southern Africa. Here there are two strict endemic reptiles (Agama mutabilis and Tropiocolotes nattereri). Common reptiles in the ecoregion include the horned viper (Cerastes cerastes) and desert varan (Varanus griseus). Not surprisingly, the amphibian fauna is very poor and there are no species of particular interest apart from Bufo brongersmai, which is confined to coastal North Africa.
In the past, the fauna of this ecoregion was significantly richer because it included a number of large mammal and bird species that have since been extirpated. The dorcas gazelle was common in the area until the 1950s and is now rare. Moreover, the wild boar (Sus scrofa) used to occur in the wadis areas, and the cheetah (Acinonyx jubatus hecki, EN) also occurred 20 years ago, but both have probably been extirpated from this ecoregion. Other carnivores have also declined greatly in the ecoregion since the 1960s, including the fennec fox (Fennecus zerda) and the striped hyena (Hyaena hyaena barbara, DD). Fewer predators means that desert rodents can be extremely numerous in favorable years. The ostrich (Struthio camelus) was fairly common in the northern Sahara at the end of the 19th century, but was extirpated from the area by the early 20th century. The populations of the Houbara bustard (Chlamydotis undulata) and Numbian bustard (Neotis nuba) have been greatly reduced in the area over the last decades. Most of these declines can be attributed to hunting activities of people, but over the last few thousand years there has also been a great change in the fauna due to climatic desiccation. By the time of the Romans many of the formerly present large Afrotropical mammals (e.g. rhinoceros and giraffe) had already disappeared from the ecoregion, and the Sahara formed an effective barrier for many species distributions (Le Houérou 1991).
The habitat is largely intact in drier areas, but can be quite badly degraded close to the coast or where there is higher rainfall and more grazing animals. However, the ecoregion is extensive, with habitat in good condition over vast areas.
The ecoregion is poorly protected officially, with one protected area in Mauritania (Iriki permanent hunting reserve, 100 km2). One other area in Algeria (Taghit) is proposed to be classified as a nature reserve, but the area is not yet delineated. There are also two national parks in Tunisia: Jebil National Park created in 1993 (1,500 km2) and the Sidi Toui National Park created in 1993 (63 km2) (Chaieb and Boukhris 1998).
Recently UNDP/GEF approved a 3-year project on " Nature resources management in semi-arid and arid zones." One of the proposed sites in this project is Taghit in Algeria. The project will be implemented by a network of 26 NGOs (Comité National des ONGs Algériennes- CNOA) belonging to the RIOD (International NGOs Network to combat desertification). The main project objectives are to develop a management plan for nature resources, legally gazette the nature reserve, and build capacity of grass-roots organizations in co-management of the reserve through training and pilot demonstration activities.
Types and Severity of Threats
In general, the drier parts of this ecoregion are not threatened by human activities. Threats are concentrated in areas with more rainfall, or around water sources, where the local pressure on resources can be intense. Overgrazing by livestock is a serious problem that has resulted in severe environmental degradation in many areas. The cutting of woody vegetation for fire-wood is also a problem.
The threats to the remaining populations of larger animals adapted to desert conditions are intense. The populations of many species have been greatly reduced by hunting for food, and also through hunting for sport and recreation (e.g., Houbara bustard and Nubian bustard). Some species listed above have been entirely removed from the ecoregion in the last 100 years. Over a period of 2,000 years this list could be expanded to include other large African mammals.
Water pollution is also major threat in this ecoregion, as many cities have been developed in this part of the desert. Development of tourism (mostly in Tunisia) also poses a threat to water systems.
Justification of Ecoregion Delineation
This ecoregion is delineated from White's (1983) ‘regs, hamadas and wadis’ and ‘desert dunes with perennial vegetation’ units north and west of the Sahara Desert. Although these vegetation types surround the Sahara Desert, the northern habitats were delineated as a distinct ecoregion from the southern unit due to different rainfall regimes and the presence of Mediterranean plant and vertebrate species.
Chaieb, M. and M. Boukhris. 1998. Parcs Nationaux de la Tunisie aride et saharienne. In Flore Succinte et illustrée des zones arides et sahariennes de Tunisie. Edition l’Or du Temps. Pages 242-249.
Kingdon, J. 1997. The Kingdon field guide to African mammals. Academic Press. London, UK.
Le Houérou, H.N. 1990. Recherches écoclimatique et biogéographique sur les zones arides de L’Afrique du Nord. CEPE/CNRS, Montpellier, 600pp.
Le Houérou, H.N. 1991. Outline of a Biological History of the Sahara. Pp.146-174. In. McNeely, J.A., and V.M. Neronov, editors. Mammals in the Palaearctic Desert: status and trends in the Sahara-Gobian region. The Russian Acedemy of Sciences, and the Russian Committee for the UNESCO programme on Man and the Biosphere (MAB).
Quézel, P., 1965. La végétation du Sahara, du Tchad à la Mauritanie. Fisher Verlag, Stuttgart.
Zahoran, M.A. and A.J. Willis. 1992. The vegetation of Egypt. Chapman and Hall, London
White, F. 1983. The vegetation of Africa: a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa. UNESCO, Paris, France.
Prepared by: Nora Berrahmouni and Neil Burgess
Reviewed by: In progress