Evaluating climatic and anthropogenic drivers of fire activity over four millennia at Eilandvlei, southern Cape coast, South Africa

Abstract

Fire is a key ecological force in South Africa's highly biodiverse Cape Floristic Region (CFR), yet the extent to which past changes in climate and anthropogenic activities have influenced fire activity over millennial timescales remains poorly understood. Here, we employ a continuous high-resolution (median 2-year/sample) sedimentary charcoal record spanning the last 4200 years to explore linkages between climate, vegetation, fire, and people from a southern Cape coastal lake, Eilandvlei. This record spans notable shifts in climate as well as subsistence and behavioral shifts among human populations living in this ecosystem. Pastoralists are first documented in the CFR ∼2000 years ago and European colonization commences in the mid-1600s CE. Fire activity at Eilandvlei generally decreased over the past four millennia, consistent with records of climate change from the region. This is reflected in the vegetation assemblage at Eilandvlei, which transitions from fynbos towards Afrotemperate forest dominance, in parallel with increased moisture availability and decreased fire activity. Linear regression modeling of the fire record identifies moisture availability as the most significant driver of fire at Eilandvlei over millennial timescales – outweighing all other variables, including proxy evidence for human population densities. The lowest fire activity of the record occurs in the past ∼140 years (since ∼1810 CE) – likely reflecting fire suppression practices enacted by colonial populations. This record suggests that increased moisture availability facilitates a shift in vegetation type and decreases fire activity as fuel becomes too wet to sustain burning. The record also suggests potential links between local-scale fire and global climate modes, including El Niño Southern Oscillation and related changes in ocean-atmosphere dynamics.