Climate and Human Impacts on Neotropical Vegetation and Fire Regimes since the Last Glacial Maximum

Vegetation and fire regimes in the Neotropics have fluctuated in response to past climate oscillations, yet the drivers of these changes remain complex and regionally variable. Based on analyses of large datasets of pollen and charcoal records, we addressed how climate changes since 21 ka drove major trends of vegetation and fire changes across the Neotropics. Our findings suggest that temperature, atmospheric CO₂ concentrations, and precipitation exert distinct and alternating roles as primary drivers of tree cover and fire regime changes, with additional impacts from vegetation-fire feedbacks and human activities. During the Last Glacial Maximum, tree cover in high elevation sites and at sub- and extra-tropical latitudes was mainly limited by low temperatures and reduced atmospheric CO₂ concentrations, while fuel-limited conditions and/or low temperatures restrained fire activity. In the warmer tropical regions, moisture availability was likely the main controlling factor of both vegetation and fire, with the effects of low CO₂ amplifying these constraints. Deglacial warming and rising CO₂ promoted biomass expansion and intensified fires in temperate areas. Meanwhile, precipitation variability associated with millennial-scale events was positively correlated with tree cover and negatively correlated with fire regimes. Throughout the Holocene, relatively stable temperatures and CO₂ shifted the primary control to precipitation patterns, with human activities increasingly impacting vegetation and fire regimes in the late Holocene, particularly in Central America and tropical Andes. These findings highlight the complex interplay of climate factors and anthropogenic influences shaping Neotropical ecosystems over millennia.