Different regional climatic drivers of Holocene large wildfires in boreal forests of northeastern America

Abstract

Global warming could increase climatic instability and large wildfire activity in circumboreal regions, potentially impairing both ecosystem functioning and human health. However, links between large wildfire events and climatic and/or meteorological conditions are still poorly understood, partly because few studies have covered a wide range of past climate-fire interactions. We compared palaeofire and simulated climatic data over the last 7000 years to assess causes of large wildfire events in three coniferous boreal forest regions in north-eastern Canada. These regions span an east-west cline, from a hilly region influenced by the Atlantic Ocean currently dominated by Picea mariana and Abies balsamea to a flatter continental region dominated by Picea mariana and Pinus banksiana. The largest wildfires occurred across the entire study zone between 3000 and 1000 cal. BP. In western and central continental regions these events were triggered by increases in both the fire-season length and summer/spring temperatures, while in the eastern region close to the ocean they were likely responses to hydrological (precipitation/ evapotranspiration) variability. The impact of climatic drivers on fire size varied spatially across the study zone, confirming that regional climate dynamics could modulate effects of global climate change on wildfire regimes.

Tracking Open Versus Closed‐Canopy Boreal Forest Using the Geochemistry of Lake Sediment Deposits

“…The fire history reconstructed from the lakes in the study was consistent with a regime that would maintain the current ecosystem structure that has persisted over the last 1,000 years (unpublished data). This is also consistent with Remy et al () findings that showed that the fire regime, the main disturbance factor prone to cause sudden vegetation changes, had not fluctuated much at the regional scale during the last 1,000 years. We therefore hypothesized for the present study that no major changes in vegetation had occurred in both watershed types (MF vs LW) during this period, and we focused only on the top 10‐ to 50‐cm lacustrine sediment sequences.…”

Holocene vegetation dynamics and hydrological variability in forested peatlands of the Clay Belt, eastern Canada, reconstructed using a palaeoecological approach

“…Thesusceptibilityofthepeatlandtofire may have increased due to autogenic-driven drying and the related increase in aboveground biomass. However, charcoal reconstructions from nearby sites (<20 km from Villebois peatland) also suggested higher fire frequencies during the late Holocene (Carcaillet et al 2001;Ali et al 2008) althoughadecreaseinfirefrequencyisdocumented in the boreal biome of northeastern America during this period (Ali et al 2012;Remy et al 2017).…”

The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model

“…However, it has been increasingly recognized that such an assumption is invalid and that modern observations are not a good analogue for prehistoric variability (Kelly et al, 2016;Hudiburg et al, 2017). For example, fire activity over much of the Holocene was higher in terms of frequency and fire size than the current levels across broad areas of eastern Canada (Girardin et al, 2013a;Remy et al, 2017). It is likely that not accounting for such variability may introduce biases in forest productivity dynamics and levels, more specifically on soil carbon dynamics (Hudiburg et al, 2017).…”