Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 13, Pages 3261-3266Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1715336115
Keywords
Western Central Africa; late Holocene; rainforest crisis; paleohydrology; human activity
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Funding
- ISIS-888 Project
- French National Research Institute for Sustainable Development (IRD), its local office in Yaounde
- LMI DYCOFAC
- Deutsche Forschungsgemeinschaft (DFG) [GA1629/2]
- Ministry of Science, Research, and Culture des Landes Brandenburg
- Labex OT-Med project
- EQUIPEX ASTER-CEREGE project
- DFG-Research Center/Cluster of Excellence The Ocean in the Earth System at MARUM-Center for Marine Environmental Sciences
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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. delta C-13-inferred vegetation changes confirm a prominent and abrupt appearance of C-4 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. delta D 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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