Late Holocene Fire and Vegetation Dynamics on Bonaire: A charcoal-based study of two hypersaline lakes on Bonaire examining human and climatic forcing of Late Holocene fire frequency and vegetation dynamics.

Abstract

This study presents the first high-resolution reconstruction of Late Holocene fire regimes and vegetation dynamics on Bonaire, a semi-arid island in the southern Caribbean. Using sediment cores from two hypersaline lakes (Saliña Slagbaai and Saliña Bartol), charcoal analyses (macro-, meso- and microcharcoal) were combined with pollen and geochemical proxies (LOI, CaCO₃, CaSO₄) to assess the interaction between climate variability, human activity, and the occurrence of fires over the past 2000 years. Charcoal morphology was used to infer fuel types. ImageJ software enabled standardized particle analysis. Both records show similar patterns in fire dynamics, indicating a strong spatial synchronicity. Three distinct fire phases were identified: 1) A pre-ceramic natural period (~CE 0– 867) with low fire activity (1 peak per ≥600 years) and open herbaceous landscapes (savannah-like). Fire regimes during this phase were likely driven by biomass availability, with limited to no human impact. 2) A phase of Indigenous land use (~CE 867–1520), indicated by Zea mays pollen, coincides with an increased fire frequency (1 peak per ~33 years). This period also corresponds to wetter environmental conditions, driven by a northern mean position of the Intertropical Convergence Zone (ITCZ) during the Medieval Warm Period. Increased precipitation led to greater biomass fuel availability, enabling both natural and human-caused fires. 3) A Colonial and modern phase (~CE 1520– present) characterized by fire suppression (no peaks), vegetation closure and the emergence of drought-tolerant species. Fire activity decreased before the arrival of Europeans. This decrease is linked to increased aridity associated with a southward shift of the mean position of the ITCZ during the Little Ice Age. Charcoal influx was mainly influenced by the availability of biomass fuel and anthropogenic land use, rather than increasing aridity. Despite changes in fire dynamics over time, charcoal morphology remained relatively stable (slightly dominated by woody charcoal particles). While charcoal is not a standalone climate indicator, combining it with pollen and geochemical data can provide valuable insights into past interactions between humans and the environment. This research improves the understanding of ecological transitions on Bonaire and informs future land management strategies for Caribbean dry ecosystems.