Past fire dynamics in sub-Saharan Africa during the last 25,000 years: Climate change and increasing human impacts

The aim of this study is to provide the drivers of long-term fire dynamics in various regions of Sub-Saharan Africa using a synthesis of updated sedimentary charcoal records, from 25,000 years ago to the present. We used the charcoal data currently available in the Global Paleofire Database, updated with the most recent published charcoal data, to reconstruct past biomass burning across the continent. We analyzed standardized charcoal data grouped by region (central Africa, eastern Africa, southern Africa, and Indian Ocean) and by vegetation type (forest, savanna, and shrubland). Within this framework, we found that quality data were lacking to reconstruct a robust trend in biomass burning before 5000 years at the continental scale. This large spatial scale was indeed masking regional peculiarities. Our results suggest that past changes in biomass burning were nuanced and cannot be simply attributed to either climate- or humans, and that they varied from each sub-regions and vegetation type history. In central Africa, biomass burning increased after the end of the African Humid Period and the first wave of Bantu-speaking people migration, whereas in East Africa and the Indian Ocean islands, it seems that human population growth was the main driver of fire activity. In South Africa, reduced rainfall seemed to offset fire activity due to population growth by reducing potentially flammable biomass. While the diversity of methodological techniques used to produce charcoal quantification made comparisons difficult, regional patterns still emerged from these data. This synthesis thus highlights the need to increase the number of sites with charcoal data and to harmonize charcoal extraction and quantification methods across Africa to improve regional to continental assessments of fire histories.