Exploring charcoal as a natural archive for palaeofire and vegetation history of the Mayumbe, Democratic Republic of the Congo

Direct evidence for Central African vegetation history is primarily based on pollen analysis. In addition, charcoal analysis has proven successful for palaeobotanical reconstructions in moderate and arid regions. Yet in the tropics this discipline meets fundamental obstacles inherent in species-richness and the lack of a systematic identification procedure. Therefore, the first part of this PhD presents a transparent identification procedure for Central African charcoal, based on large databases and well-defined wood-anatomical characters. The procedure uses complementary imaging techniques and a methodology for the evaluation of identification reliability. The validity of the protocol has been proven by the mutual consistency of charcoal identification results and compatibility with vegetation history based on pollen research. In the second part of this PhD the charcoal identification and evaluation methodologies are applied on charcoal fragments found in 7 soil profiles excavated in the southern Mayumbe forest (Bas-Congo, DRCongo). Each soil profile yielded one or more charcoal assemblages, each archiving a palaeofire. Radiocarbon dating showed that all recorded palaeofires occurred during or shortly after one out of three well-known dry climate anomalies: the 8.2 ka BP event, the third millennium BP rainforest crisis (3000-2000 cal yr BP) and the Medieval Climate Anomaly (MCA, 1000 - 700 cal yr BP). During and after these periods the rainforests were very sensitive to drought and fire, primarily around open patches during the dry season. Charcoal identifications show that forests close to the Central African rainforest boundary were locally replaced by savanna and open forest types due to drought, whereas it remained relatively intact deeper in the heart of the rainforest. Moreover, forest regeneration during recovery periods was hampered by recurring forest fires, making it a very slow process. However, artefacts associated with some of the charcoal assemblages show that forest fragmentation was not a direct result of climatic drought only, but it was also reinforced by human disturbance, which started around the third millennium BP but probably became important only during the last millennium.