Improving fire history reconstructions

Occurrence of forest fires in the past has been extensively studied, using biological archives such as tree rings or charcoal in organic sediments. These proxies both have their advantages and disadvantages. Tree ring records are spatially and temporally accurate, but of limited time span. For sedimentary charcoal, the origin of the charcoal is not necessarily clear, and the temporal resolution is limited. However, sedimentary charcoal records often extend back to millennia.

In a recent study, lead by Normunds Stivrins as part of the project EBOR (Long-term Ecological History of the Boreal Forest), we demonstrated the applicability of another potential proxy for fires: the spores of the Neurospora fungi. This fungi develops its fruiting bodies when temperatures exceed 65°C, which in the boreal forest typically occurs only during forest fires. As the production of charcoal and the formation of fire scars have partly different requirements compared to the conditions that lead to Neurospora spore release, this proxy could bring valuable new insight into fire history reconstructions. Indeed, statistical tests showed a positive relationship between other fire event indicators and Neurospora occurrence, allowing us to locate past fire-events at times when the sedimentary charcoal was absent. These findings thus pave way for improvements in the reliability of fire history reconstructions from multiple proxies, and help understanding the long-term disturbance history of the boreal forest.

The full paper is now published in the Holocene.

Fire frequency for Kämmekkä (A), Polttiais (B) and Naava (C) hollow. Dots at the top of boxes indicate the sampling density, a higher row of crosses – the inferred fires and the lower row of crosses – the fires in 120-year bins. Black curve – the posterior mean of the fire frequency and gray band – the 95% highest density interval. X-axis – age and y-axis fire frequency data in 120-year bins