Location and General Description
This ecoregion is made up of two isolated montane areas in the central part of the Sahara Desert. Lying halfway between Lake Chad and the Gulf of Syrte, the larger Tibesti Mountains area is found in the northern portion of Chad, and extends marginally into southern Libya. The Tibesti Mountains consist of seven inactive volcanoes, with the highest peak reaching 3,415 m. The second, smaller area is the Jebel Uweinat, located further to the east along the intersection of eastern Libya, southwestern Egypt, and northwestern Sudan. The Jebel Uweinat includes peaks reaching elevations just under 2,000 m.
Annual average rainfall in the surrounding Sahara Desert is under 100 mm, and extremely unreliable, as years may pass with no rainfall followed by a single thunderstorm lasting only a few hours. In the montane ecoregion rainfall is more regular, although still quite low. Lowland wadis areas receive their water from the mountains down storm channels. This water remains for a considerable period, as these areas have natural impermeable layers and shield-like sand covers that slow evaporation (Cloudsley-Thompson 1984). The mean maximum temperature is approximately 30°C in the lowlands and falls to 20°C in the highest elevations. Mean minimum temperatures are 12°C in the lowlands, but fall to 9°C over most of the ecoregion and are as low as 0°C at the highest elevations during winter months.
The geology of this ecoregion is volcanic in origin, with a large area of Tertiary basalt within an expanse of Nubian sandstones. The soils developed over the basalts are typically thin, with lithosols being predominant. Bare rock and regosols also occupy large areas of the ecoregion.
In terms of the phytogeographical classification of White (1983), this ecoregion is regarded as a part of the Saharan regional transition zone. The vegetation is mapped at the lower elevations as regs, hamadas, and wadis, and at the highest elevations as Saharomontane. The Tibesti mountain vegetation varies according to elevation and slope. Large wadis areas radiate from the southwestern slopes supporting tree species such as the doum palm (Hyphaene thebaica), Salvadora persica, Tamarix articulata, Acacia nilotica adstringens and Acacia albida, and other tropical herbs in the genera Abutilon, Hibiscus, Rhynchosia and Tephrosia (White 1983). The economically important doum palm and date palm (Phoenix dactylifera), together with other species of Hyphaene palms, also grow along deep gorges that hold water year round (White 1983). The Saharomontane vegetation of the higher elevations supports the endemic Ficus teloukat, which grows on the south and southwestern slopes, Myrtus nivellei and Nerium oleander on the western slopes, and Tamarix `gallica nilotica’ and Nerium oleander on the wetter northern slopes. The northern slopes also support wetland species such as Juncus maritimus, Typha australis, Scirpus holoschoenus, Phragmites australis and Equisetum ramosissimum (White 1983).
The peak of the Jebel Uweinat is virtually devoid of vegetation with only some shrub species like Lavandula and Salvia (White 1983). Scattered trees of Acacia tortilis prevent the classification of the Jebel Uweinat as montane vegetation, since they are not characteristically found in higher elevations (White 1983). Dominant species include Fagonia indica, Aerva javanica, Acacia tortilis, and Cleome chrysantha (Leonard 2000). The Jebel Uweinat, however, is not highly vegetated, with a total of only 87 species of plants recorded (Leonard 2000). The wadis support the greatest quantity of lower elevation desert vegetation, since they receive rainwater runoff from the mountain areas. In these Jebel Uweinat the wadis vegetation comprises open Acacia tortilis-Panicum turgidum plant communities of Mediterranean affinity (White 1983).
Remnant tropical and Mediterranean plant species are seen throughout this ecoregion, including palms, Hibiscus sp. and Rhynchosia sp. Others are Saharan endemics with tropical or Mediterranean affinities (White 1983). These species occur in this ecoregion because climate was wetter during the Pleistocene and there was continuous connection between this ecoregion, Mediterranean North Africa and tropical Africa. The past vegetation is documented by pollen grains found in the soils and sands of the desert and in the rock art of ancient people who depicted savanna woodland animals, including Elephants and various different kinds of antelope (Cloudsley-Thompson 1984).
Comprised predominantly of nomadic pastoralists, the current human population of the area is very small, and densities are low, with only 0-1 people per km2 recorded.
The presence of large numbers of species adapted to arid conditions, many of which are found in other regions of the Sahara, is one of the most important features of the flora and fauna from an evolutionary perspective.
The ecoregion supports populations of several important Saharan large mammals. For example, addax (Addax nasomaculatus, CR), scimitar -horned oryx (Oryx dammah, EN), dorcas gazelle (Gazella dorcas, VU), dama gazelle (Gazella dama, EN), Barbary sheep (Ammotragus lervia, VU) and cheetah (Acinonyx jubatus, VU) have been recorded (Hilton-Taylor 2000). The scimitar-horned oryx is now regarded as extinct in the wild (Hilton-Taylor 2000). Dorcas gazelle (Gazella dorcas) and moufflon (Ammotragus lervia) were recently documented in the Jebel Uweinat portion of the ecoregion (Leonard 2000).
Small mammals and their predators are also abundant,, including hyrax (Procavia capensis), brown hare (Lepus capensis), spiny mouse (Acomys spp.), large North African gerbil (Gerbillus campestris), Nigerian gerbil (G. nigeriae), bushy-tailed jird (Sekeetamys calurus) and three different fox species, Rueppel’s sandfox (Vulpes rueppelli), sand fox (Vulpes pallida) and Fennec fox (Fennecus zerda) (Boitani 1999). Other predators found in the ecoregion include the African wildcat (Felis silvestris), African wild dog (Lycaon pictus), striped hyenas (Hyaena hyaena), honey badger (Mellivora capensis) and common jackal (Canis aureus), primarily in the Tibesti Mountains (Boitani 1999; Le Berre 1989).
The reptile and amphibian fauna is poor in this area, although reptiles include the hookbilled blindsnake (Leptotyphlops macroshychus), cliff racer (Coluber rhodorachis) and white-spotted gecko (Tarentola annilaris) (Schleich et al. 1996).
Schouwia-Tribulus habitats, which grow in the wadis of this ecoregion, are well known for their role in the life cycle of the desert locust. The female locusts lay their eggs in the moist soil. When these hatch, Schouwia-Tribulus provide food and moisture necessary for the maturation of the locust (Cloudsley-Thompson 1984). These insects are responsible for plagues including the devastating and far reaching damage from 1980-81 when large swarms reached distant areas of Africa and Europe, destroying crops (Cloudsley-Thompson 1984).
The steep, rough terrain of this ecoregion, and its location deep within the Sahara Desert make it relatively intact. Almost all species, both plant and animal, can seek refuge in remote parts of the ecoregion. Currently there are almost no people living in the area, allowing vegetation to regrow from previous degradation caused by grazing (Le Houérou 1998). Nomadic people and soldiers still use resources, however, and practice unregulated hunting. Climatic desiccation over thousands of years has affected the vegetation of the area, as with other parts of the Sahara.
Types and Severity of Threats
Although habitats are largely unthreatened, an established protected area may be needed in the long run to conserve the species and habitats in this ecoregion. Hunting continues to be a major threat to large mammals. Since its war with Libya ended in 1987, Chad has been fairly stable politically, with only occasional security problems in the North (East 1999). Fighting between armies along the border of Libya and Chad occurs mainly in the Tibesti Mountains, with one group even referred to as the Tibesti rebels. Reports noting the heavy use of landmines in the area have led to the assumption that some species loss is occurring. This political and economic instability limits the resources available for protection of the habitats and biodiversity located in this ecoregion. Even with the end of the war, time will have to pass before the region is stable enough for surveys and conservation work to be carried out.
The most recent study of the fauna of the Jebel Uweinat is that of Leonard (2000), who studied the effects of grazing by Dorcas gazelle (Gazella dorca) and Barbary sheep (Ammotragus lervia) on the vegetation of the area. Dorcas gazelles mainly graze on the lower parts of the sandstone habitats, and were not found to have an impact on plant distribution. However, moufflon overgraze the higher parts of the massif where the flora is poor, leading to the decline of high altitude plant species and an increase in inedible species.
Justification of Ecoregion Delineation
These high elevation areas, reaching over 3,400 m, are unique geological formations with distinct biota within the Sahara Desert. The boundaries of the ecoregion are taken from White’s (1983) ‘Saharamontane vegetation’ unit with the lower elevation vegetation type, ‘regs, hamadas, wadis.’ Given the distance between the higher elevation areas comprising the two other montane ecoregions within the Sahara Desert, the Tibesti and Jebel Uweinat were defined as a separate ecoregion (WWF 1998).
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Prepared by: Christine Burdette
Reviewed by: In progress