Climate and biomass control on fire activity during the late-glacial/early-Holocene transition in temperate ecosystems of the upper Rhone valley (France)

The main objective of this study is to document paleofire activity during the late-glacial/early-Holocene transition in temperate ecosystems. For this purpose, we cored lakes Paladru and Moras (Rhone valley, France) and quantified sedimentary charcoal accumulation rate and fire frequency. To assess the role of climate and vegetation in paleofire activity, charcoal data were compared to vegetation dynamics based on pollen analyses and to climate reconstructions. The first increase in paleofire activity occurred at the beginning of the Bølling/Allerød Interstadial period (14,500 cal yr BP), synchronous with temperature and fire-prone vegetation increases. During the Younger Dryas, paleofire activity first decreased (12,600–12,200 cal yr BP) and then abruptly increased (12,200–11,600 cal yr BP). This change corresponds to a known climate partitioning that occurred during the Younger Dryas and implies that a sufficient quantity of biomass was available during the second period. At the beginning of the Holocene, fire activity remained high. This is in agreement with the increases in temperature and vegetation density. The change in forest composition since ca. 11,200 cal yr BP partly explains the decrease in paleofire activity, whereas warm climate conditions seem suitable for fire ignition and propagation.