Description: 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.

Description: Sedimentary ancient DNA is becoming more widely used in paleoeocology, as methods for sampling of sediments, as well as for extraction and sequencing of sedimentary ancient DNA have become more efficient and retrieval success has increased. To date, investigations of ancient DNA have concentrated on sites with low temperatures, as these display optimal preservation conditions. Remote, high latitude sites are ideal to track environmental changes that are not directly induced by human activity. Current climate changes are causing particularly strong ecosystem perturbations in the Arctic, and sedimentary archives allow a comparison of the current situation with past changes throughout the Holocene. Sites from temperate and tropical regions have been studied to a lesser extent, but are important for the analysis of human history and anthropogenic ecosystem modifications. Preservation conditions are less optimal, but ancient DNA has been retrieved on centennial to millenial timescales - corresponding to a period of time, in which anthropogenic impact has been strongest. Given good preservation conditions coupled with adequate precautions to ensure clean subsampling of the inside of sediment cores and for work with ancient DNA, a high diversity of authentic taxa can be retrieved. Plant DNA metabarcoding of Arctic lake sediment cores and ancient permafrost from Siberia can yield, for example, up to over 90 or 100 plant taxa from single samples, including both terrestrial and aquatic taxa, as well as bryophytes. Inferences of spatial and temporal vegetation change correspond very well to those from pollen, and DNA can potentially offer a higher degree of resolution. Using the same approaches as for Arctic samples, we are currently investigating a sediment core from Lake Barombi Mbo in Cameroon, concentrating on samples spanning the Holocene. Here, we give an overview of our approaches and comparatively assess the potential of sedimentary DNA as a paleoecological tool in different settings.