Guidelines for the use and interpretation of palaeofire reconstructions based on various archives and proxies

Abstract

We present a comparative analysis of fire reconstructions from tree rings and from wood charcoal preserved in forest soils, peat and lake sediments. Our objective is to highlight the benefits and limits of different archives and proxies to reconstruct fire histories. We propose guidelines to optimize proxy and archive choice in terms of spatial and temporal scales of interest. Comparisons were performed for two sites in the boreal forest of northeastern North America. Compared to others archives, tree-ring analysis remains the best choice to reconstruct recent fires (<1000 years). For longer periods (from several centuries to millennia), lake charcoal can be used to reconstruct regional or local fire histories depending on the method used, but the focus should be on historical trends rather than on the identification of individual fire events. Charcoal preserved in peat and soils can be used to identify individual fire, but sometimes cover shorter time periods than lake archives.

Lacustrine charcoal peaks provide an accurate record of surface wildfires in a North European boreal forest

“…Our results suggest that even small concentrations and a very low number of charcoal particles may be indicative of local fires. In this study, the charcoal concentration was 0-7 particles in 1 cm 3 ( Figure 5), while the number of charcoal particles found in sediments receiving influx from crown fires usually ranges between 20 and 100 per cm 3 (Ali et al, 2009;Brossier et al, 2014; Higuera al., 2010;Remy et al, 2018). The observed pattern is consistent with the idea that boreal surface fires are characterized by a low accumulation of charcoal in the lake sediments.…”

Fire in the Swamp Forest: Palaeoecological Insights Into Natural and Human-Induced Burning in Intact Tropical Peatlands

“…To explore the relationship between fire, its drivers and vegetation change at a higher temporal resolution, further sampling, and the use of additional proxies, would be required. Though individual fire events can be identified from fossil charcoal records extracted from peat deposits, palaeoecological data is best suited to identifying historical trends in fire regimes (Remy et al, 2018). Observing a true response of the vegetation to an incidence of burning, or another form of disturbance, can also be challenged by differing rates of pollen production amongst species and varying distances over which pollen grains are transported, in turn affected by the changing characteristics of the canopy around the coring site, amongst other constraints (Davies et al, 2018).…”

Evidence of a historical frequent, low-severity fire regime in western Washington, USA

“…For example, Pellatt et al (2015) reported MFIs of 26-41 years for Pender Island and Vancouver Island, British Columbia (<20 km from our sites), and Lucas and Lacourse (2013) reported 15 fires over 1300 years on Pender Island, for a MFI of 88 years. Charcoal and pollen, however, are proxies for actual fires that are sampled over longer time frames and thus are recommended for identifying historical trends rather than individual fires (Remy et al 2018). There are several reasons for the differences between our results and those of these types of studies, including differences in sampling intensity (multiple trees vs. a single sediment core) and temporal resolution (Lucas and Lacourse (2013) report, for example, a standard deviation of 42 years around an estimated sediment date of 1851 (see their table 1)).…”