Climate, flora and fauna changes in the Sahara over the past 500 million years

The present-day Sahara occupies an area of slightly over 8 million km2in Africa, between latitudes 16 and 32° N, circumscribed within the isohyet of 100 ± 50 mm mean annual rainfall. The hyperarid area alternately expanded and shrank on both sides of a seemingly narrow semi-permanent eremitic zone along the Tropic of Cancer during the course of the Quaternary epoch (1•7 Ma). The Cenozoic, Mesozoïc and Paleozoïc Sahara, in turn, has undergone drastic climatic changes as the African continent drifted northward from its Antartic position to reach its present latitudinal situation. But, seemingly the Sahara was never the large desert it now is, with the exception perhaps of the Upper Triassic Lower Liassic epochs. The Pleistocene and Holocene contrasting climate changes induced large variations in flora and fauna distribution, as well as in geomorphic processes. The flora shifted from that of typical desert to tropical savanna and Mediterranean forest or steppe, depending on period and location. Fauna, in turn, changed more in abundance than in nature, since the same groups have been in existence since the Upper Pliocene–Lower Pleistocene. Large mammals, for instance, were mainly of Afro-tropical kinship throughout the Pleistocene and Holocene, while small mammals, in contrast, were predominantly of Mediterranean origin over the same periods. And such is still the case. There were varying large degrees in density of occurrence, but relatively minor fluctuations in nature, in response to such environmental changes as lake and dune expansion and retreat, and even glacier expansion and melting at higher elevations. The present-day man-made expansion of desertic conditions to the north and south actually threaten both flora and fauna alike in the short- and medium-term. Most African large mammals, still present in the desert until the second half of the 19th century, have now become extinct, or are on the very verge of extinction in the Sahara (some may be surviving further south, and/or in the East Africaʹs parks network). The situation, however, is far less dramatic for the flora, which still includes almost 3000 species of vascular plants, although some species — of economic value or not — are in danger from the man-made destruction of their habitat.