Biomass-modulated fire dynamics during the Last Glacial–Interglacial Transition at the Central Pyrenees (Spain)

• Late Quaternary fire regime is studied in a fuel-limited, high-altitude site.
• Biomass is a key factor accelerating fire frequency under a fire-conducive climate.
• Mesophytes enhance fires due to its flammability and fast spread.
• Frequent fire events between 10-8 kyrs BP avoided arboreal recovery after 7 kyr BP.
• Pollen richness is not influenced by fire but it covaries with landscape opening.

Understanding long-term fire ecology is essential for current day interpretation of ecosystem fire responses. However palaeoecology of fire is still poorly understood, especially at high-altitude mountain environments, despite the fact that these are fire-sensitive ecosystems and their resilience might be affected by changing fire regimes. We reconstruct wildfire occurrence since the Lateglacial (14.7 cal ka BP) to the Mid-Holocene (6 cal ka BP) and investigate the climate–fuel–fire relationships in a sedimentary sequence located at the treeline in the Central Spanish Pyrenees. Pollen, macro- and micro-charcoal were analysed for the identification of fire events (FE) in order to detect vegetation post-fire response and to define biomass–fire interactions. mean fire intervals (mfi) reduced since the Lateglacial, peaking at 9–7.7 cal ka BP while from 7.7 to 6 cal ka BP no fire is recorded. We hypothesise that Early Holocene maximum summer insolation, as climate forcing, and mesophyte forest expansion, as a fuel-creating factor, were responsible for accelerating fire occurrence in the Central Pyrenees treeline. We also found that fire had long-lasting negative effects on most of the treeline plant communities and that forest contraction from 7.7 cal ka BP is likely linked to the ecosystem's threshold response to high fire frequencies.