A 16,000-year record of climate, vegetation and fire from Wallacean lowland tropical forests

Abstract

The tropical forests of Sulawesi represent some of the most diverse, biogeographically significant ecosystems globally. However, long-term ecological data for the region are scarce, making it difficult to predict vegetation response to future climatic and anthropogenic drivers of change. This is problematic as gauging the acclimation thresholds of forests within tropical Asia has been identified as an IPCC policy imperative. This study uses palynological and geochemical analysis of sediments from a tectonic basin – Lake Lantoa – to reconstruct the hydroclimatic, fire, and tropical rainforest dynamics of south Sulawesi over 16,000 years, and reveal the response of lowland ultramafic forest to large-scale environmental change. Our results show that the Late Pleistocene was characterised by a drier, more seasonal climate and persistent fire in the landscape. These conditions supported a slightly open, Gymnostoma-rich, semi-seasonal forest, and constrained the available habitat range for hydrophilic tropical conifers. Increased effective moisture in the Holocene, interpreted from the onset of periodic lake stratification under deeper conditions, appears to have precluded forest burning, and facilitated the expansion of a lowland ultramafic rainforest and upland tropical coniferous forest. An increase in garden/secondary forest taxa and ground ferns from ∼2 cal kyrs BP implies increased human management of the landscape. While these data highlight the compositional dynamism of lowland forest in Wallacea to seasonality, fire, and reduced precipitation, they demonstrate biome-scale resilience to glacial-scale environmental change. This contrasts with interpretations of forest sensitivity to climatic change drawn from analysis of leaf wax isotopes from adjacent lake basins, highlighting the value of adopting multi-proxy, taxonomically high-resolution techniques for reconstructing floristic histories. Show more