A new contribution to the Holocene vegetation history of the West African Sahel: pollen from Oursi, Burkina Faso and charcoal from three sites in northeast Nigeria

Population dynamics and Paleoclimate over the past 3000 years in the Dogon Country, Mali

“…An abrupt and early climate break can be noted from 3500 BC in the Sahara (DeMenocal et al, 2000), but further south, it occurred much later. Hydrological functioning of Sahelian lakes demonstrates an increasing trend to drying between 1400 and 1000 BC (Ballouche and Neumann, 1995;Lézine and Casanova, 1989;Maley, 1981;Salzmann and Waller, 1998). At this time, the dune fields in the Malian Gourma between Douentza and Timbuktu were reactivated (Stokes et al, 2004).…”

“…For the historical period, natural sciences data are rare and come primarily from studies of variation in the level of Lake Chad (Maley, 1981) or ponds deposits, such as at Oursi and Kissi in northern Burkina Faso (Ballouche, 1998(Ballouche, , 2001Ballouche and Neumann, 1995) as well as in Lake Bosumtwi of Ghana (Russel et al, 2003) and in the Manga Plains of Nigeria (Salzmann and Waller, 1998;Salzmann et al, 2002). Very recently, a study of the Malian dunes of Gourma, based on a series of OSL dates, has yielded new data (Stokes et al, 2004).…”

“…Reichelt et al (1992) and Maley (1981) emphasize the continuation of population movement towards the south. In northern Burkina Faso, at Oursi (Ballouche and Neumann, 1995) and at Kissi (Ballouche, 2001), the retreat of savannah formations, as well as the degradation of the riparian banks along the ponds, are clear but the cause-climatic desiccation or anthropic desertification-cannot be isolated. It is also at the time, 600-500 years ago, to which Stokes et al (2004) date by OSL a reactivation of the dune fields in the Timbuktu region.…”

“…The intensification of pastoralism, the diversification in cultivated species and the development of an agro-forestry system, all of which accompanied the process of sedentarization, can be observed (Kahlheber et al, 2001). This shift can be linked to the changing climatic conditions documented locally, notably in Lake Oursi, whose deposits record a high frequency of drying with a retreat of species typical of permanent lakes (Ballouche and Neumann, 1995).…”

“…In contrast to the schema developed by R. McIntosh showing a second humid period starting in the 15th century, a certain number of evidences suggest an accentuation of aridification. These are the retreat of savannah formations and the degradation of the riparian banks along the ponds in northern Burkina Faso (Ballouche, 2001;Ballouche and Neumann, 1995), as well as the reactivation of the dune fields in the Malian Gourma 500-600 years ago (Stokes et al, 2004). Variations in the level of Lake Chad permit distinction of two phases: the first (15-16th centuries) marked by significant regressions, and the second in the 17th century during which the lake recovered levels comparable to those during the 1st millennium AD before undergoing regressions leading to current conditions (Maley, 1981).…”