Abstract
Drought is usually the precursor to large wildfires in northwestern boreal Canada, a region with both large wildfire potential and extensive peatland cover. Fire is a contagious process, and given weather conducive to burning, wildfires may be naturally limited by the connectivity of fuels and the connectivity of landscapes such as peatlands. Boreal peatlands fragment landscapes when wet and connect them when dry. The aim of this paper is to construct a framework by which the hydrological dynamics of boreal peatlands can be incorporated into standard wildfire likelihood models, in this case the Canadian Burn-P3 model. We computed hydrologically dynamic vegetation cover for peatlands (37% of the study area) on a real landscape in the Canadian boreal plain, corresponding to varying water table levels representing wet, moderate, and severely dry fuel moisture and hydrological conditions. Despite constant atmospheric drivers of fire spread (air temperature, humidity, and wind speed) between drought scenarios, fire activity increased 6-fold in moderate drought relative to a low drought baseline; severe (1 in 40 years) drought scenarios drove fires into previously fire-restrictive environments. Fire size increased 5-fold during moderate drought conditions and a further 20%–25% during severe drought. Future climate change is projected to lead to an increase in the incidence of severe drought in boreal forests, leading to increases in burned area due to increasing fire frequency and size where peatlands are most abundant. Future climate change in regions where peatlands have historically acted as important barriers to fire spread may amplify ongoing increases in fire activity already observed in Western North American forests.
Highlights
In boreal North America, peatlands cover 20% of land area, far more abundant than the 2.8% of global land area occupied by peat [1]
Peatlands in North America are primarily disturbed by wildfire [8], with the regions of highest wildfire occurrence [9] often overlapping with the Forests 2019, 10, 534; doi:10.3390/f10070534
We propose an empirical framework of fuel mapping and fire weather analysis in order to dynamically modify wildfire fuels maps to account for hydrological tipping points in boreal peatland flammability
Summary
In boreal North America, peatlands (wetlands with deep organic soils) cover 20% of land area, far more abundant than the 2.8% of global land area occupied by peat [1]. Boreal peatlands range from semi-aquatic treeless grass and sedge systems to closed-canopy forests, with all peatlands sharing a minimum 40 cm thick organic soil layer composed primarily of decomposed moss [2]. For upland boreal forests, where flammable forest floor vegetation is limited to a thin layer of undecomposed or partially decomposed material, fuel moisture is largely depleted after two weeks without precipitation [13]. In deep organic systems such as peatlands, this effect is more complex, owing to the connection of surface fuel conditions with the water table and numerous natural negative ecohydrological feedbacks that strive to maintain a high water table [14]. When the ecohydrological feedbacks are overwhelmed by prolonged drying, widespread burning of peatlands can result [15]
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