HYDROMAN: Impacts of hydrological changes versus human activity on Central-West African forests during the Holocene

中西非拥有世界上第二大毗连的湿润热带森林，目前由于砍伐森林和森林火灾而受到人类的严重威胁。为了了解控制非洲热带森林变化的根本过程，重要的是确定造成过去森林干扰的驱动因素。在全新世(过去的11500年)，这些热带森林在气候变化的推动下经历了交替的扩张和收缩时期，尽管在过去的3000年里，与讲班图语的人的传播有关的人类活动可能产生了额外的影响。然而，过去是否存在明显的人类骚乱事件仍然非常含糊。为了解决在全新世期间影响中西非森林的驱动因素和机制，我建议分析直接记录水循环变化的新的气候指标，并结合植被指标和人为干扰指标。我将在喀麦隆的湖泊沉积物岩心上使用基于分子的替代物，特别是化合物特定的氢和碳同位素比率。我将应用一个新开发的沉积脂类生物标志物氢同位素值的区域传递函数，它被发现准确地记录了水循环中的现代变异性。植被组成的变化(例如，C3植物与C4植物)将使用脂质生物标记物碳同位素值来估计，而过去的人为干扰将通过结合X射线荧光扫描和农业活动、侵蚀和生物质燃烧的特定有机示踪剂来识别。这一完整的数据集将允许构建一个强大的古环境框架，以最终测试气候变化和人类活动对全新世期间中西非森林演变的作用。这些驱动因素如何影响过去热带森林的结构和构成的研究结果将有助于预测未来的全球变化将如何影响该区域的现有森林。

Central-West Africa hosts the second largest contiguous expanse of moist tropical forest in the world, which is currently under severe threat of humans through deforestation and forest fires. To understand the underlying processes controlling changes within tropical forests of Africa, it is important to determine the drivers responsible for the past forest disturbances. During the Holocene (the last 11,500 years) those tropical forests underwent alternating periods of expansion and contraction, driven by climate variability, although during the last ~3000 years human activity associated with the spread of the Bantu-speaking people may have had an additional effect. However, the existence of marked episodes of human disturbances in the past remains highly ambiguous. To resolve the drivers and mechanisms, which have affected the Central-West African forests during the Holocene, I propose to analyze novel climate-proxies directly recording changes in the hydrological cycle in combination with vegetation-proxies and indicators of anthropogenic disturbances. I will use molecular-based proxies, particularly, compound-specific hydrogen and carbon isotope ratios, on lake-sediment cores from Cameroon. I will apply a newly developed regional transfer function of sedimentary lipid biomarker hydrogen isotope values, which were found to accurately record the modern variability in the hydrological cycle. Changes in vegetation composition (e.g., C3 versus C4 plants) will be estimated using lipid biomarker carbon isotope values while past anthropogenic disturbances will be identified by combining X-ray fluorescence scanning and specific organic tracers for agricultural activities, erosion, and biomass burning. This complete dataset will allow constructing a robust paleo-environmental framework to ultimately test the role of climate change and human activity on the evolution of forests in Central-West Africa during the Holocene. The findings of how these drivers affected the structure and composition of past tropical forests will help to predict how future global changes would affect the present forests in the region.