Integrating fire-scar, charcoal and fungal spore data to study fire events in the boreal forest of northern Europe

Abstract

Fire is a major disturbance agent in the boreal forest, influencing many current and future ecosystem conditions and services. Surprisingly few studies have attempted to improve the accuracy of fire-event reconstructions even though the estimates of the occurrence of past fires may be biased, influencing the reliability of the models employing those data (e.g. C stock, cycle). This study aimed to demonstrate how three types of fire proxies – fire scars from tree rings, sedimentary charcoal and, for the first time in this context, fungal spores of Neurospora – can be integrated to achieve a better understanding of past fire dynamics. By studying charcoal and Neurospora from sediment cores from forest hollows, and the fire scars from tree rings in their surroundings in the southern Fennoscandian and western Russian boreal forest, we produced composite fire-event data sets and fire-event frequencies, and estimated fire return intervals. Our estimates show that the fire return interval varied between 126 and 237 years during the last 11,000 years. The highest fire frequency during the 18th–19th century can be associated with the anthropogenic influence. Importantly, statistical tests revealed a positive relationship between other fire event indicators and Neurospora occurrence allowing us to pinpoint past fire events at times when the sedimentary charcoal was absent, but Neurospora were abundant. We demonstrated how fire proxies with different temporal resolution can be linked, providing potential improvements in the reliability of fire history reconstructions from multiple proxies.

Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El'gygytgyn sediments

“…While Simoneit et al (1999) and references therein suggest that MAs form at burn temperatures > 300 • C, several studies that have analysed the influence of various combustion conditions in natural samples indicated that MAs are thermal dehydration products at burning temperatures < 350 • C, mainly under smouldering as opposed to flaming conditions (Pastorova et al, 1993;Gao et al, 2003;Engling et al, 2006;Kuo et al, 2008Kuo et al, , 2011. A recent review of Suciu et al (2019) attributes the dominant low-temperature production to depolymerization, fragmentation and inter-and intramolecular transglycosylation during pyrolysis, while a minor fraction of MAs can attach to charcoal during higher temperatures, when smoldering overlaps with or follows flaming conditions. In Holocene lake sediments, MAs provide complementary fire proxies to sedimentary charcoal (Elias et al, 2001;Schüpbach et al, 2015;Battistel et al, 2017;Schreuder et al, 2019;Dietze et al, 2019).…”

Relationships between low-temperature fires, climate and vegetation during the last 430 kyrs in northeastern Siberia reconstructed from monosaccharide anhydridesin Lake El’gygytgyn sediments

“…To reconstruct long-term fire regime shifts, sedimentary charcoal can be used as a classical proxy of fire of various combustion efficiencies (Whitlock and Larsen, 2001;Conedera et al, 2009). Yet, fire intensity reconstructions and 110 the differentiation between surface and crown fires is difficult to specify, especially on long timescales, as well as when considering other fire proxies such as fire scars and fungal spores (Stivrins et al, 2019). Molecular burning proxies are currently being explored to infer source-and temperature-specific fire histories (Kehrwald et al, 2016;Kappenberg et al, 2019;Dietze et al, in review).…”

Long-term ecological consequences of forest fires in the continuous permafrost zone of Siberia

“…Dendroecology, however, can provide insights of unique temporal resolution, because tree rings may allow fire histories to be reconstructed (McBride 1983, Stivrins et al 2019. A recent example of the successful utilization of tree rings in wildfire dendroecology is the precise dating of moss buried stems to quantify postwildfire dynamics of the ASL thickness and ground vegetation recovery in northern Siberia (Knorre et al 2019).…”