Abstract
In boreal ecosystems, wildfire severity (i.e., the extent of fire-related tree mortality) is affected by environmental conditions and fire intensity. A burned area usually includes tree patches that partially or entirely escaped fire. There are two types of post-fire residual patches: (1) patches that only escaped the last fire; and (2) patches with lower fire susceptibility, also called fire refuges, that escaped several consecutive fires, likely due to particular site characteristics. The main objective of this study was to test if particular environmental conditions and stand characteristics could explain the presence of fire refuges in the mixedwood boreal forest. The FlamMap3 fire behavior model running at the landscape scale was used on the present-day Lake Duparquet forest mosaic and on four other experimental scenarios. FlamMap3 was first calibrated using BehavePlus and realistic rates of fire spread obtained from the Canadian Fire Behavior Prediction system. The results, based on thousands of runs, exclude the effects of firebreaks, topography, fuel type, and microtopography to explain the presence of fire refuges, but rather highlight the important role of moisture conditions in the fuel beds. Moist conditions are likely attributed to former small depressions having been filled with organic matter rather than present-day variations in ground surface topography.
Highlights
Fire is one of the dominant ecological drivers affecting vegetation patterns and dynamics in the circumboreal region [1,2]
At the end of the parameterization procedure, rates of spread (ROS) predicted by the FBP and BehavePlus systems were in good agreement (R2 = 0.8), ranging from 0.2 to 9 m/min
BehavePlus in conifer stands was noted, with the heaviest fuel loads under highest fire risk with windy conditions. This satisfactory agreement between both fire behavior models running at the stand level confirmed that the BehavePlus model could be adapted to the boreal mixedwood forest if the fermentation layer was taken into account in fuel load characterization
Summary
Fire is one of the dominant ecological drivers affecting vegetation patterns and dynamics in the circumboreal region [1,2]. A burned area usually includes residual patches that partially or entirely escaped fire [5,6,7,8]. Two types of post-fire residual patches have been distinguished in eastern North American boreal mixedwood forests [9]: (1) “transient residual patches” that only escaped the last fire, probably due to peculiar but temporary unsuitable conditions for fire propagation; and (2) “fire refuges” that escaped several consecutive fires, likely due to specific site conditions. Fire refuges represent a small proportion of the total area burned, they could provide unique habitats in post-fire successional landscapes [8]. The ecological continuity recorded in fire refuges (unlike in transient residual patches, which only escaped the last fire) [9] could provide refuges for species with specific biodiversity
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