Is charcoal reflectance a palaeofire intensity proxy?

Variations in wildfire are a hot topic due to concerns linked to the current climate crisis. Although an increasing number of studies focus on how the coupled climate and anthropogenic forcings influence fire frequency and behaviour in highly fire-prone regions, there has been less research in more temperate ecosystems.

Analyzing charcoal records yields insights into the fire regimes in a given area, including the fire frequency, type, and intensity. Recent research suggests that measuring the amount of light reflected from charcoals can provide information about the energy flux during the pyrolysis of plant material, which can be further translated into a proxy for fire intensity. To assess the use of reflectance as a post-fire tool for palaeofire intensity reconstructions, we used annually laminated (varved) sediment record from Lake Żabińskie, north-eastern Poland.

We provide both quantitative macrocharcoal, and charcoal reflectance measurements of individual charcoal particles as well as semi-quantitative morphotypes analysis. These data were compared with palynological analysis of the vegetation shifts and evidence for the impact of humans in the lake area. Our preliminary research indicates that lower reflectance measurements (mean value around 1%) most likely relate to the litter fires as the charcoals show features of biodegradation before the fire. Higher values (mean 1-3%) represent surface understory fires (undergrowth burning) while the highest reflectance values (mean >3%) can be related to the crown fires. Our measurements are the first of this kind in this part of the world.