Wildfire history of the boreal forest of southwestern Yakutia (Siberia) over the last two millennia documented by a lake-sedimentary 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 (SW Yakutia, Siberia) spanning the last c. 2200 years, including information about charcoal particle sizes and morphotypes. Our results reveal a phase of increased charcoal accumulation between 600–900 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 colonisation. 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 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.

Comment on bg-2021-39

“…29 cal. ka BP agrees with the timing of cold conditions during MIS2 recorded by other regional records and Alaskan lake records (Asikainen et al, 2007;Finkenbinder et al, 2014;Vyse et al, 2020). Basal ages of several large northern latitude lakes show 400 similar ages to basement sediments at Lake Rauchuagytgyn (Anderson and Lozhkin, 2015;Brosius et al, 2021;Finkenbinder et al, 2014).…”

“…In addition, pollen reconstructed July temperatures were 4-5 °C lower than modern in agreement with unfavourable climate conditions for organic carbon productivity (Andreev et al accepted). Sedimentological records from Lake Ilirney during MIS2 also agree with extremely low within-lake productivity represented by very low TC and absent diatoms (Vyse et al, 2020). Preliminary diatom analyses also show a complete absence of diatoms within LU-III 420 in line with unfavourable conditions (Biskaborn, unpublished data).…”

“…The timing of these system responses is generally consistent with 485 depositional changes recorded at Lake Ilirney in response to deglaciation ca. 20 ka (Vyse et al, 2020) and those proposed for Alaskan glacial retreat (20-19 ka BP) (Elias and Brigham-Grette, 2013 and references therein).…”

“…This is further supported by abundant minerogenic elements Ca, Ti and K and a light sediment colouration that may support glacially derived material possibly in the form of rock flour (Fig. 7) (Vyse et al, 2020). The fingerprint of glacigenic sediment is recorded clearly by strongly negative PC1 scores from principal component analysis clustered as "Early MIS2" (Van der Bilt et al, 2015).…”

“…Sediment accumulation preserved within LU-III can be attributed regionally to the MIS2 "Sartan" glaciation recorded within Chukotka (Anderson & Lozhkin 2015;Brigham-Grette et al, 2003;Melles et al, 2012;Vyse et al, 2020) and the Itkillik II glaciation in Alaska, eastern Beringia (Hamilton and Ashley, 1993). Glaciation during this time was associated with asynchronous glacial advances in Alaskan mountain ranges between 31 and 28 cal.…”