Validating a continental European charcoal calibration dataset

Abstract

Large-scale training sets enabling quantitative reconstructions of past fire parameters are needed to better assess potential effects of increased fire hazard under global warming conditions. The aim of this article is to validate recently developed continental regression equations for the reconstruction of fire number, intensity and size. These transfer functions were built by linking satellite data and charcoal collected in annually sampled sediment traps. We apply these European regression equations to four annually layered lakes located on a North–South gradient in Europe. Down-core annual microscopic charcoal (MIC) and macroscopic charcoal (MAC) influx values were compared with satellite-derived time series of fire number, fire intensity and area burned. Results show that the match between predicted and observed values improves when the overall mean and median of sampled years (12 and 9 years) are considered. Especially, the comparisons of median values show a very good agreement between charcoal-inferred and satellite-observed fire-regime parameters. MIC-based predictions underestimate the variability of the observed fire parameters and MAC-based predictions overestimate it. Our results imply that median values of the fire parameters can be reconstructed well by using MIC and MAC, while it is more difficult to infer the variability of fire-regime parameters. However, when MIC- and MAC-based predictions are pooled together, the fit between observed and predicted values increases for both medians and variability. This finding suggests that MIC and MAC are complementary proxies, thus best sedimentary fire reconstructions may be achieved when they are used together. We conclude that sediment traps can be used for the construction of continental-scale training sets and that their results can be applied to Holocene sedimentary charcoal sequences.

The reconstruction of burned area and fire severity using charcoal from boreal lake sediments

“…Some studies have attempted to linearly link charcoal number with local fire characteristics such as burned area and fire occurrence. No significant relationship has been found within grassland ecosystems (Duffin et al, 2008; Leys et al, 2015), but charcoal number has been shown to be linearly correlated with more regional events (Adolf et al, 2018; Asselin and Payette, 2005). Using the variable classification, we found that no local variables (within the smallest zone) explained the median surface area of charcoal particles but only semi-regional (15-km zone) and regional (30-km zone) scale variables.…”

“…Conversely, low severity fires produce few charred particles relative to burned biomass, and the energy released by the fire front is too low to allow their suspension and thus their transportation away from the burned area (Ohlson and Tryterud, 2000). Studies have only considered burned area or fire occurrence when investigating the role of components on charcoal measurements (Adolf et al, 2018; Leys et al, 2015). The present study thus highlights the importance of fire severity in understanding the charcoal time series (Figures 6 and 7).…”

“…Calibration can enable the reconstruction of past fire characteristics on a quantitative basis (Higuera et al, 2011) and improves our understanding of the taphonomic processes affecting the dispersal of charcoal particles, from the production source, via transportation by wind (primary) and water bodies (secondary) and deposition processes, to conservation in natural archives. Charcoal production (in terms of number and surface area of particles) during a fire has been linked to fire characteristics such as burned area, distance from fire, number of fires or fire intensity in a wide range of ecosystems, including grass-dominated ecosystems (Aleman et al, 2013; Duffin et al, 2008; Leys et al, 2015), temperate forests (Adolf et al, 2018; Clark and Royall 1995), boreal forests (Higuera et al, 2011; Ohlson and Tryterud, 2000; Oris et al, 2014) and mountain forests (Adolf et al, 2018; Higuera et al, 2011). Dispersion and deposition of charcoal particles have also been studied using experimental fires in boreal ecosystems, with traps located at the fire edge, within and outside the fire perimeter to a distance of a few tens to hundreds of metres (Clark et al, 1998; Lynch et al, 2004; Ohlson et al, 2011).…”

A palynological perspective on the impacts of European contact: Historic deforestation, ranching and agriculture surrounding the Cuchumatanes Highlands, Guatemala

“…Linking the charcoal influx values to MODIS-inferred modern day burning regimes, an approach used by Adolf et al (2018b), showed that the source area for macroscopic and microscopic charcoal is estimated to be 16 km for macroscopic charcoal and 180 km for microscopic charcoal, assuming that distance is indicated by the strongest correlations between charcoal and satellite data (Fig. 6).…”

“…The size of the source area for macroscopic charcoal and microscopic charcoal into a depositional environment is contentious. Macroscopic charcoal is widely suggested to reflect burning from a local to sub-regional source area between 0 and 10 km radius (Gavin et al 2003;Lynch et al 2004;Petersn and Higuera 2007;Higuera et al 2007Higuera et al , 2011Anderson and Wahl 2016), while microscopic charcoal is suggested to primarily reflect regional burning within a radius of up to several hundred kilometres (Clark 1988); however, recent validation of charcoal dispersal across Europe linked both macroscopic and microscopic charcoal influx to a regional source area of around 40 km radius (Adolf et al 2018b). Our results from Cenote Kail indicate that the catchment area for macroscopic charcoal and microscopic charcoal varied by a degree of magnitude.…”