North Saharan steppe and woodlands
Steppe with rocky stream, eastern Morocco. @ C. Michael Hogan
The North Saharan steppe and woodlands ecoregion forms the northern and the western border of the greater Sahara Desert region. This ecoregion was originally much biologically richer, especially in regard to large mammals and birds; however, climate desiccation beginning at least 2000 years before present, 20th century overhunting and recent indigenous warfare have caused severe reduction and in numerous cases extirpation of such fauna. Rainfall occurs chiefly during the cooler winter, nourishing a variety of plants that flower prior to the hot, dry summer. Compared to the South Saharan Steppe and Woodland, this ecoregion harbors a significant number of plant and small animal endemics. In the past the ecoregion also supported large numbers of desert-adapted African mammals, but many have been extirpated from the area due to decades (in some cases centuries) of over-hunting, and more recently indigenous warfare. Some of the remaining desert adapted species, such as the Dama gazelle and Houbara and Nubian bustards are still facing extreme hunting pressure and habitat reduction, and in some portions of the ecoregion they too have been extirpated.
Contents
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 (Mediterranean Sea) 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 chiefly from October to April. Average annual rainfall varies from 50 millimeters (mm) in the south to 100 mm in the north, although there may be years where there is a complete absence of rain (especially in the southern parts of the ecoregion). The highest temperature ranges between 40 and 45°C, creating evaporation which far exceeds the precipitation level.
Souss-Massa National Park, Morocco. (Photograph by WWF-Canon/ Hartmut Jungius) 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 (such as Oued Saoura, Oued M?Zi, Oued Mya) hosting Acacia woodlands.
- Fesh fesh: Plateaus of soil that are unconsolidated, almost mobile, with 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:Such as the Ougarta Mountains in Algeria, which dominate Beni Abbès plateaus covered by Acacia raddiana vegetation.
In terms of the phytogeographical classification of White, 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 is comprised by approximately 1150 species 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, Spartidium saharae, Calligonum comosum) and/or trees (Acacia raddiana, Pistacia atlantica, Tamarix aphylla). There is great seasonal diversity in the plant communities of the Northern Saharan Steppe and Woodland. Some evergreen perennials 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.
Human populations are concentrated around surface 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, "Daman race" sheep, and goats). Over recent decades the population has expanded greatly in the area. At present, some of the oases support moderate sized towns that are involved with oil exploration and production. These areas had supported tourist industries prior to the regional indigneous warfare and unrest that began in early 2011.
Biodiversity features
Dorcas Gazell (Gazella dorcas). (Photograph by Caribbean Gardens: The zoo in Naples) The ecoregion contains endemic species with regard to both plants and the animals, making it 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, Henophyton deserti, Panicum turgidum, 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 hierochunticaand Astragalus gombo. The hammadas habitats also contain endemics, such as Helianthemum lippii, Gymnocarpos decandrus and Helianthemum kahiricum. Some hammadas are covered by the endemic species Anabasis aretioides and Arthrophytum schmittianum.
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).
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 present in the ecoregion: the Changeable agama (Trapelus mutabilis) and Natterer's pygmy gecko (Tropiocolotes nattereri). Common reptiles in the ecoregion include the horned viper (Cerastes cerastes) and desert varan (Varanus griseus). Not surprisingly, the amphibian fauna is quite depauperate, and there are few taxa of particular note apart from Pseudepidalea brongersmai, which occurs in the [[coast]al] and near-coastal western Morocco and an element of the lowland interior valley south and east of the Atlas Mountains.
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 considered rare. Moreover, the wild boar (Sus scrofa) used to occur in the wadis areas, and the cheetah (Acinonyx jubatus hecki, EN) also occurred twenty 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 (Vulpes 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 Desert formed an effective [vicariance] for many species distributions.
Current status
The habitat is largely intact in drier areas, but can be quite severely 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 square kilometers). 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 (1500 square kilometers) and the Sidi Toui National Park created in 1993 (63 square kilometers).
Recently UNDP/GEF approved a three-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 2000 years this list could be expanded to include other large African mammals.
Water pollution is also major threat in this ecoregion with regard to surface water supplies, 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 "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.
References
- 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. ISBN: 0713665130
- 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. ISBN: 0412315106
- White, F. 1983. The vegetation of Africa: a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa. UNESCO, Paris, France. ISBN: 9231019554
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