Early anthropogenic impact on Western Central African rainforests 2,600 y ago

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

Pollen analysis of ODP Hole 159-958A

Palynological investigation (pollen, spores, and dinoflagellate cysts) of 39 samples from the upper 50 m of Ocean Drilling Program (ODP) Site 958 provides some complementary information about the history of the northeast trade winds and the African Easterly Jet. Unfortunately, with the exception of upper Pliocene sediments from Hole 958A between 31 and 41 mbsf and one other sample at 22.25 mbsf, most of the investigated sediments being of late Pliocene and Pleistocene age showed a poor pollen preservation. Samples with good pollen preservation showed a flora dominated by pine pollen. Pollen from the Sahara was infrequently found indicating that the African Easterly Jet was very weak. The dinoflagellate cyst assemblage is typical for the oceanic environment of the North Atlantic. A hiatus between 44 and 42.50 mbsf is confirmed by the last occurrence of cysts of Invertocysta