Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia documented by a lake-sediment charcoal record

Abstract

Abstract. Wildfires, as a key disturbance in forest ecosystems, are\nshaping the world s boreal landscapes. Changes in fire regimes are closely\nlinked to a wide array of environmental factors, such as vegetation\ncomposition, climate change, and human activity. Arctic and boreal regions\nand, in particular, Siberian boreal forests are experiencing rising air and\nground temperatures with the subsequent degradation of permafrost soils\nleading to shifts in tree cover and species composition. Compared to the\nboreal zones of North America or Europe, little is known about how such\nenvironmental changes might influence long-term fire regimes in Russia. The\nlarch-dominated eastern Siberian deciduous boreal forests differ markedly\nfrom the composition of other boreal forests, yet data about past fire\nregimes remain sparse. Here, we present a high-resolution macroscopic\ncharcoal record from lacustrine sediments of Lake Khamra (south-west Yakutia,\nSiberia) spanning the last ca.\xa02200\xa0years, including information about\ncharcoal particle sizes and morphotypes. Our results reveal a phase\xa0of\nincreased charcoal accumulation between 600 and 900\u2009CE, indicative of\nrelatively high amounts of burnt biomass and high fire frequencies. This is\nfollowed by an almost 900-year-long period of low charcoal accumulation\nwithout significant peaks likely corresponding to cooler climate\nconditions. After 1750\u2009CE fire frequencies and the relative amount of\nbiomass burnt start to increase again, coinciding with a warming climate and\nincreased anthropogenic land development after Russian colonization. In the\n20th century, total charcoal accumulation decreases again to very low\nlevels despite higher fire frequency, potentially reflecting a change in\nfire management strategies and/or a shift of the fire regime towards more\nfrequent but smaller fires. A similar pattern for different charcoal\nmorphotypes and comparison to a pollen and non-pollen palynomorph (NPP) record\nfrom the same sediment core indicate that broad-scale changes in vegetation\ncomposition were probably not a major driver of recorded fire regime\nchanges. Instead, the fire regime of the last two millennia at Lake Khamra\nseems to be controlled mainly by a combination of short-term climate\nvariability and anthropogenic fire ignition and suppression.\n