Abstract/Summary

Fire is an important environmental process in the northern extratropics (NET), with various regions predicted to experience the highest magnitude increases in fire activity compared to other global regions in future. Previous NET palaeofire studies are limited by poor data availability and a lack of quantitative methods. A synthesis of charcoal records is conducted to reconstruct sub-continentalscale Holocene fire histories across the NET (>45°N) and to understand their environmental controls. A circum-NET-scale analysis, and a more spatially resolved analysis at the European scale (n of 21 regions) are conducted. At the NET scale, simulated palaeo climate and plant productivity data are used in a novel clustering method to define a stratification that delineates spatial units of coherent fire-relevant environmental change. At the European scale, this is done using pollen-based reconstructions of Holocene forest cover, summer temperature and precipitation change. Fire histories are reconstructed by aggregating charcoal records from the Reading Palaeofire Database within clusters. Fire reconstructions are correlated with climate and land cover reconstructions at 4000-year intervals. Fire responses of 20 regions show correlation values of >= |0.75| with at least one environmental variable for at least one 4000-year interval. Across Europe, fire increased over the Holocene, initially in response to the Fennoscandian Ice Sheet collapse and associated climate drying and forestation. Mid-to-late Holocene fire increases were caused by forest compositional shifts, human deforestation, and agricultural expansion. Across North America, the early-Holocene collapse of the Laurentide Ice Sheet caused continent-wide productivity increases leading to fire increases. A subsequent long-term moisture increase drove late-Holocene fire declines across most of the continent. In central Asia, a general Holocene-wide moisture increase drove a long-term fire decline. The results support previous study showing that sub-continental palaeofire histories in the NET are explained by variations in climate variables influencing fuel moisture and load, but that these effects can be modulated by land cover processes influencing fuel structure and composition. The results provide a basis for spatial prediction of fire regime changes in response to future climate, vegetation and human land use processes.