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Long-term fire regime shifts are major unknowns in the prediction of future environmental change in the high northern latitudes. Lake El'gygytgyn (ICDP Site 5011-1), northeastern Siberia, provides the only continuous Pliocene-Pleistocene sediment record of environmental conditions in the Arctic. Several proxies suggested prominent climate and biome shifts in the past under different boundary conditions – beyond human influence. Hence, El'gygytgyn sediment cores are unique archives to analyze high northern fire regime shifts on long time scales and during different climate states, with some past interglacials serving as natural analogues of predicted future climate change. Here, we study the long-term fire regime history of Chukotka, and focus on two intervals of the last 270,000 years that are characterized by similar summer insolation, but different global ice volume, and different vegetation composition (i.e., MIS 5e and MIS 7e). We aim to test (i) how far varying climate conditions and biome configurations are reflected in multiple fire regime proxies that are fire-intensity and severity specific, and (ii) how far external feedbacks as determined from climate and ice volume relationships and/or internal vegetation-permafrost feedbacks drive fire regime shifts in the high-northern latitudes. We present centennial and millennial scale records of multiple fire proxies from the same samples of core PG1351 that allow to characterize past fire regimes. Charcoals and spores of Gelasinospora (a fire disturbance indicator) were microscopically analyzed from pollen slides, whereas ultra-high performance liquid chromatography-high resolution mass spectrometry was used to determine, for the first time, records of the low-temperature biomass combustion residues levoglucosan, mannosan and galactosan. We find significantly different fire proxy ranges, variability and ratios that allow characterizing different fire regimes during the two interglacials and their preceding glacials. The comparison with climate and vegetation reconstructions from the same lake and same samples, respectively, suggests that not only temperature, but also internal vegetation-permafrost feedbacks determine the specific configuration of fire regime parameters such as fire intensity, severity, type and amount of biomass burnt, on long time scales. These new results provide a step forward to understanding long-term feedbacks that are crucial for model predictions of future fire regime shifts in the high northern latitudes. [ABSTRACT FROM AUTHOR]

Climate and natural vegetation composition determine the biome-specific fire regimes, but shifts in regional to global fire regimes can also be strongly affected by human land management. Among the last 250 years, fire occurrence increased globally during the mid-19th century, which was explained mainly by natural changes, but also related to increased human population growth. Yet, it is poorly known how exactly humans have influenced fire regimes prior to active wildfire suppression, which led to a global decrease in fire occurrence since the onset of the 20th century. To improve predictions of current and future fire risk, the human dimension of fire regime shifts requires more interdisciplinary research.Here, we investigate the influence of climate, land cover change, and human activity on fire regimes in northern Poland using multiple highly resolved lake-sedimentary fire proxies (i.e., charcoal and the fire biomarkers levoglucosan and its isomers). Supported by a review of historical documents, we robustly classify source area- and temperature-specific fire regimes (biomass burnt, fire episodes). We find two prominent fire regime shifts during the 19th and 20th centuries, driven by an adaptive socio-ecological cycle in human forest management. Although individual fire episodes were triggered mainly by arson during dry summers, the biomass burnt increased unintentionally during the mid-19th century due to the plantation of flammable, fast-growing pine tree monocultures needed for industrialization. State forest management reacted with active fire management and suppression during the 20th century. Similar scenarios are likely also in other industrializing regions worldwide, where not only pine but also flammable Eucalyptus monocultures have been planted. In the light of climate projections that predict increasingly dry conditions, a renewed need for adaptations to increasing fire risks becomes necessary. [ABSTRACT FROM AUTHOR]