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Early anthropogenic impact on western central African rainfrorests 2,600 y ago

  • Deschamps, Pierre
  • Ménot, G.
  • Saulieu, Geoffroy de
  • Schefuss, E.
  • Sebag, David
  • Dupont, L.M.
  • Oslisly, Richard
  • Brademann, B.
  • Mbusnum, K.G.
  • Onama, J.M.
  • Ako, A.A.
  • Epp, L.S.
  • Tjallingii, R.
  • Strecker, M.R.
  • Brauer, A.
  • Sachse, D.
Publication Date
Jan 01, 2018
Horizon / Pleins textes
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A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest–savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the "rainforest crisis" to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. δ13C-inferred vegetation changes confirm a prominent and abrupt appearance of C4 plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. δD values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era.

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