在共同时代之前,中部非洲西部雨林的潜在人类足迹已成为持续争议的焦点。在3000年前和2000年前之间,区域花粉序列表明成熟的雨林被包括先锋树的森林大草原马赛克所取代。尽管一些研究表明人为影响了这种森林破碎化,目前基于花粉数据的解释将雨林危机归因于气候变化向更干燥的方向发展,更多的季节性气候。对这一假设的严格检验,然而,需要独立于植被变化的气候代理。在这里,我们根据植物蜡的碳和氢同位素组成的变化,通过喀麦隆西南部Barombi湖的植被和水文变化的连续10,500年记录来解决这一争议。[公式:参见正文]13C推断的植被变化证实了Barombi湖流域C4植物的突出和突然出现,在公元1950年之前的2600个日历年(CALYBP),随后同样突然恢复到2,020calyBP的雨林植被。[公式:见正文]来自相同植物蜡化合物的D值,然而,显示没有同时的水文变化。基于这些数据与全面的区域考古数据库的结合,我们提供了证据,证明人类在2,600年前引发了雨林的破碎化。我们的研究结果表明,技术发展,包括农业实践和铁冶金,可能与班图人的大规模扩张有关,在共同时代之前对生态系统产生了重大影响。
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. [Formula: see text]13C-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. [Formula: see text]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.