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The West Saharan montane xeric woodlands is an ecoregion covering part of the Sahara.
The Sahara is the world's largest desert and is located in northern Africa. It streches from the Red Sea to the highlands of Ethiopia. However, the Sahara encompasses regions significantly different from an ecological perspective. The surface of the desert ranges from large areas of sand dunes (which are called erg), to stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. The northern and southern margins also receive more rainfall and have greater vegetation than central Sahara. The very scarse rain (less than 25 mm and even less than 5 mm per annum in the east) can fall in any season and in a very irregular way : some areas may receive no rain for years then suffer intense storms. Some areas encompass vast underground aquifers resulting in oases, while several other regions lack water reserves.
Some mountains (Ahaggar, Tassili NAjier, Tibesti, Aïr) also rise up in the desert and receive more rainfall and mostly present slightly cooler summer temperatures.
For such reasons, the great Sahara may be divided in several ecoregions and each of them be separately described.
Overview
The mountains of the West Saharan Montane Xeric Woodland ecoregion are found within the Sahara Desert and are predominantly of volcanic origin. The ecoregion covers Algeria, Mali, Mauritania, and Niger. The moutains rise from the surrounding flat desert landscape or from sand dunes. The boundaries for the largest part of this ecoregion, which includes the Tassili-n-Ajjer plateau, Ahaggar and Aïr ou Azbine massifs, follow the regs, hamadas and wadis above the 1000 m contour. This covers a good part of southeast Algeria. The highest point of these mountains is 2918 meters (Mount Tahat). Other high points are Mount Serkout (2,906m) and Mount Assekrem (2728m). Additional areas further south were included within this ecoregion, including the Aïr ou Azbine in northern Niger, Dhar Adrar in Mauritania, and Adrar des Iforas in Mali and Algeria, using the 500 m-elevation contour. The altitude allows slightly less hot and wetter areas to exist in an otherwise very dry and hot desert. Local spots of moister habitat with permanent water-holes (called guelta) support flora and fauna, in particular near-endemic species and threatened antelopes.
This ecoregion has an area of 258,100 km² (99,700 square miles)
Settings
Winters are quite rigorous, with amplitude in temperature over 20°C. Day temperatures may be over 20°C while nights are freezing (-3°C average at higher elevations). In summer, days are very hot (30°C at lower elevations, 15°C at highest), though less than in central Sahara. Rainfall is rare and sporadic (less than 100 mm per annum). Wind is frequent.
Most of the ecoregion is made of volcanic lava with very little soil. At higher elevations, the soils are a mixture of bare rock and lithosols, while yermosols exist at lower elevations. The Tassili present some clay-sandstones as well. In the past, some lakes existed, which left some great ergs and sand dunes, salt deposit. Remains of shells may also be found in the sand. However, most of the area is now very dry. Some running water may still be found in local spots, called guelta, usually in narrow-gorges where water is protected from the sun. These areas are very precious both for the local flora and fauna, and for the humans beings. Touaregs are very careful to protect gueltas from pollution.
Fauna and flora
Vegetation varies greatly depending on altitude and landscape (in particular wind protection). It is often relict of mediterranean vegetation.
In gueltas, vegetation is very diverse and hosts many animals. Trees may be found at lower elevations, while higher mostly host bushes. It is however possible to find olive trees (the olive tree on the right hand picture was found at 2300 m). Endemic and rare species includes Duprey-cypress (tarout) (Cupressus depreziana), wild olive (Olea lapperrini) and myrtle (Myrtus nivellei), all of which are relict Saharan-Mediterranean species. Olive and myrtle trees grow at the bottom of wadis, intermittent stream valleys, or beside gueltas, permanent or temporary waterholes.
Other species with a preference for moist habitats are Trianthema pentandra, Lupinus pilosus, and Convolvulus fatmensis. Silene kiliani, Acacia laeta, A. scorpiodes and Cordia rochii grow in wadis. Other representatives of the 28 national Algerian plant rarities found on Tassili-n-Ajjer include Ficus ingens and Anticharis glandulosa
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