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 shaping the world's boreal landscapes. Changes in fire regimes are closely linked to a wide array of environmental factors, such as vegetation composition, climate change, and human activity. Arctic and boreal regions and, in particular, Siberian boreal forests are experiencing rising air and ground temperatures with the subsequent degradation of permafrost soils leading to shifts in tree cover and species composition. Compared to the boreal zones of North America or Europe, little is known about how such environmental changes might influence long-term fire regimes in Russia. The larch-dominated eastern Siberian deciduous boreal forests differ markedly from the composition of other boreal forests, yet data about past fire regimes remain sparse. Here, we present a high-resolution macroscopic charcoal record from lacustrine sediments of Lake Khamra (south-west Yakutia, Siberia) spanning the last ca. 2200 years, including information about charcoal particle sizes and morphotypes. Our results reveal a phase of increased charcoal accumulation between 600 and 900 CE, indicative of relatively high amounts of burnt biomass and high fire frequencies. This is followed by an almost 900-year-long period of low charcoal accumulation without significant peaks likely corresponding to cooler climate conditions. After 1750 CE fire frequencies and the relative amount of biomass burnt start to increase again, coinciding with a warming climate and increased anthropogenic land development after Russian colonization. In the 20th century, total charcoal accumulation decreases again to very low levels despite higher fire frequency, potentially reflecting a change in fire management strategies and/or a shift of the fire regime towards more frequent but smaller fires. A similar pattern for different charcoal morphotypes and comparison to a pollen and non-pollen palynomorph (NPP) record from the same sediment core indicate that broad-scale changes in vegetation composition were probably not a major driver of recorded fire regime changes. Instead, the fire regime of the last two millennia at Lake Khamra seems to be controlled mainly by a combination of short-term climate variability and anthropogenic fire ignition and suppression.

Holocene Fire Regime Changes in the Southern Lake Baikal Region Influenced by Climate-Vegetation-Anthropogenic Activity Interactions

“…Our assumption is that fire activity steadily increased as climatic variations became more favorable, with more fires during drier periods than during wetter periods. In addition, an increase in fire activity at the end of the Holocene is suggested by modern observations and increasing human activity [21,24].…”

“…North of Lake Baikal, in Yakutia, a recent study [21] indicates a decrease in fire activity since 1200 cal. yr BP and linked it to fire suppression by humans.…”

“…Another hypothesis would connect these shifts to the increase in human activity in the region. Indeed, human activities and settlement have often been linked to an increase in fire frequency and severity, for example because of human-induced fire for opening landscape and sustaining grasslands [21,49,82,83]. Bezrukova et al [36] discussed human activities around Lake Baikal over the Late Holocene period and indicated that archaeological research has shown that the region was inhabited by communities of huntergatherers and then pastoralists but that there were no traces of this occupation in the lake sediments for the Mid-to Late-Holocene.…”

“…To better understand the long-term impact of fire disturbance on boreal forests and the mechanisms linking fire, vegetation and climate, past fire activity has been widely studied, for example in Canada [6][7][8][9][10][11], in Fennoscandia [12][13][14][15] and in Russia [3,[16][17][18][19]. However, very few studies cover the region of Siberia and very little is known about past fire history during the Holocene [16,17,[20][21][22]. In eastern Siberia, a crown fire regime occurred between 11,000 and 9000 calibrated years before present (cal.…”

“…yr BP [16]. In southwestern Yakutia, Glückler et al [21] showed that during the last two millennia, fire dynamics have been particularly influenced by a combination of short-term climatic events and anthropogenic fire management. Their results showed that fire frequency has increased since 1750 CE.…”