Outline of the biological history of the Sahara

Abstract

The Sahara has not always been desert; desert and semi-arid conditions have alternated on many occasions. At the junction of the Pliocene and Pleistocene conditions were probably more or less as they are now. Desert conditions, however, were interrupted on at least eight to 10 major occasions during the past 2 to 3 million years. The optimal conditions of the Holocene lasted from c. 9000 to 4000 years BP. The Sahara was then a semi-arid, locally humid, tropical savanna sprinkled with many lakes. It harboured a rich Afro-tropical fauna and was inhabited by both Protomediterranean cromagnoids and African melanodermic hunters; bovine pastoralists moved in and, later, so did white horsemen, the People of the Sea, probable ancestors of the Tuareg. Remnants of the Afro-tropical fauna survived in montane refuges until the early 20th Century. Some relicts are still in existence: e.g. the Duprez cypress in the Tassili of Ajjers, represented by some 200 trees in Wadi Tamrit. The flora comprises about 2800 species of flowering plants while the fauna includes 70 species of mammals, 90 resident birds (30 endemic), 100 reptiles (30 snakes and 70 saurians) and a large number of arthropods (e.g. 66 species of ants). This biological richness and diversity is seriously threatened by desertisation, mainly on the margins and in the montane refuges, as a combined result of increasing human population pressure, hunting and climatic fluctuations. There is no doubt that the Sahara is biologically impoverished and expanding. Most of the 20 species of large mammals fairly common at the beginning of this century have become rare or extinct over the past five decades. A number of rare tree and shrub species are also endangered. If the trend that has prevailed over the past 50 years continues, all large mammals will become extinct, not only in the Sahara, but also in the arid zones bordering it. Man-made desert will also expand over the entire North African steppes and the Sahel until human life becomes untenable outside oases—unless the 10 governments concerned enforce appropriate conservation.