Long-term reconstruction of rainfall and fire for the Kavango-East and Zambezi regions, Namibia and the impact of people on past fire regimes

Abstract

African savanna structure is driven by climate and fire, which have been well documented in modern observations and palaeo-studies, but is lacking on intermediate (decades to centuries) timescales where much of the ecosystem dynamics occur. Long term rainfall and fire records were generated from environmental proxies from the semi-arid Kavango-Zambezi region of South-Central Africa. The records were radiocarbon dated in high resolution and modelled with Bayesian accumulation models to generate ~600year chronologies. The proxy time series were analysed in time-frequency space to elucidate the relationship between rainfall and fire at different timescales within local and regional fire histories. Wavelet analysis shows periods of time in the past when fire had a positive relationship with rainfall, and also a negative relationship, and a switch from local to regional-scale fire response to rainfall is observed in the Little Ice Age (1700-750). A shift to regionally dominated fire regime thereafter is attributed to human population increase and associated land-use change. The results show that over time savanna landscapes can shift between load-limited and moisture-limited fire regimes and that savanna structure has been affected by human activities both directly, and via changes in fire regimes