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A pollen diagram from Oursi in Burkina Faso is compared with anthracological (charcoal analysis) results from three sites in northeast Nigeria (Konduga, Gajiganna, Lantewa). The present-day vegetation at all four sites is Sahelian or Sahelo-Sudanian and under heavy human impact. At Oursi, a closed grassland with only few trees and almost no Sudanian elements can be reconstructed for the middle Holocene. At the Nigerian sites, on the other hand, Sudanian woody plants were present during this period. We assume that the Sahel was not a uniform zone during the middle Holocene but rather a mosaic of different vegetation types according to local site conditions. In the light of these results, a simple model of latitudinally shifting vegetation zones is not applicable. Around 3000 B.P. the closed grassland at Oursi was opened by agro-pastoral activities, and at Gajiganna, plants characteristic of pasture lands can be directly related with the presence of cattle. Human impact seems to have been the dominant factor in the vegetation history of the Sahel from 3000 B.P. until today, masking possible effects of climatic change.

Since the end of the 1950s it has generally been accepted that, during the mid-Holocene humid period, the central Saharan mountain vegetation (Ahaggar, Tassili-n-Ajjer and Tibesti) was clearly Mediterranean or even forest in nature. In addition to the present-day elements growing in North Africa the flora was supposed to have included some European arboreal species. This concept was mainly based on the results of pollen analysis. More recent pollen and macrofossil analysis of organic sediments from the Ahaggar massif show that mid-Holocene flora was actually very similar to that found at the present day. Earlier studies had included analysis of sediment contaminated by pollen transported long distances which had accumulated over a period of 4000 years. An endemic olive (Olea laperrini) and the Atlas pistachio tree (Pistacia atlantica), two species which are still well represented nowadays, dominated the vegetation. The new data question the extension of the Mediterranean vegetation towards the south and the amplitude of the associated climatic change.