Multi-millennial reconstruction of fire return intervals from a fynbos – Afrotemperate forest ecotone in the Cape Floristic Region, South Africa: Paleoecological implications for present-day management

In South Africa's highly biodiverse and fire-adapted Cape Floristic Region, fire is critical to maintaining ecosystem health and for the reproductive strategies of many endemic species. Ecological studies have identified fire return intervals (FRIs) of approximately 10–15 years. However, the short timescale of these observations, derived from anthropogenically impacted systems, means that the extent to which these FRIs are maintained over millennia, and how vegetation dynamics co-vary with fire frequency is poorly resolved. Here, we analyze a high resolution macrocharcoal record from a lacustrine sedimentary archive to reconstruct fire return intervals over four millennia at a fynbos-afrotemperate forest ecotone along South Africa's southern Cape coast. We address variability in fire activity (i.e., more or less burning) and FRIs in relation to pollen-derived reconstructions of local vegetation change and regional shifts in moisture availability over the past 4200 years. We document a range of FRIs between 10.5 and 166 years. We find that FRIs shift towards longer intervals, fire activity decreases, and afrotemperate forest vegetation becomes more abundant during periods of increased moisture availability. Our historical (1890–2013 CE) FRI reconstruction is consistent with ~10–15 years between burns, but one must only look back a few centuries to see FRIs far outside the range of variability observed today. This suggests that our present-day ecological lens is not representative of the full range of natural variability experienced at this site over the past four millennia. This work provides long-term ecological context to land managers working towards the conservation and protection of fynbos.