Biomass burning response to high-amplitude climate and vegetation changes in Southwestern France from the Last Glacial to the early Holocene

The main drivers of fire regimes in southern Europe are climate, vegetation and land-use changes that interact at different spatio-temporal scales. These complex interplays between ``natural'' and anthropogenic forcings hinder the identification of fire-climate linkages on the long time scale. In this paper, we focused on the Last Glacial-Holocene transition, which is the last time Europe experienced rapid warming of similar magnitude and rate of change as predicted for the future, and with minimal human impact (no agricultural activities). We derived fire activity from two neighbouring lacustrine macrocharcoal records, Ech paleolake and Lake Lourdes, located 3 km apart. To understand the effect of external forcings, we reconstructed summer TA degrees changes and vegetation dynamics from two independent proxies. We then compared both paleofire records with chironomid-inferred summer air temperature reconstruction from Ech paleolake. We discuss the role of vegetation type, structure and biomass availability using pollen analysis from Ech paleolake and Lourdes. Fire activity is strongly modulated by summer TA degrees oscillations as shown by the highly contrasted responses between the Oldest Dryas/Interstadial and Younger Dryas/Holocene transitions. However, vegetation type and biomass availability act as limiting factors: the slight increase in fire activity at the onset of the Interstadial is triggered by a 7 A degrees C summer TA degrees increase but remains limited by low availability of woody biomass in a steppe environment. On the contrary, the onset of the Holocene is characterised by a 2 A degrees C summer TA degrees increase and an unprecedented increase in fire activity, conditioned by the establishment of dense deciduous forests.