Peat Depth as a Control of Peat Burn Severity: Implications for Peatland Fire Management, Restoration and Refugia Formation

Abstract:

As wildfires increase in severity, frequency, and areal extent, the slowly-accumulating carbon in northern peatlands is becoming increasingly threatened. While previous research has examined the controls of wildfire and drought resistance in deep peatlands with persistent water tables, shallow peatlands and peat deposits, which may be most vulnerable to climate-mediated drying, are relatively understudied. To examine control that peat depth has on peat burn severity, we measured the depth of burn (DOB) in peat deposits 0.1 to 1.6m deep within a rock barrens landscape in the Boreal Shield. We found that DOB, and the percent of the peat profile that burned, were negatively correlated with pre-fire peat depth. A breakpoint analysis revealed a threshold of 0.66m of pre-fire peat depth, where peat deeper than this was generally more resistant to wildfire, while shallower peat experienced a relatively high peat burn severity (median percent burned = 2.2 and 65.1, respectively). Furthermore, peat shallower than this threshold exhibited faster rates of water table drawdown, where nearby unburned peatlands with a maximum depth < 0.66m had lost their water table by the time the fire started. These results suggest that peat depth acts as a control of peat burn severity by regulating the feedbacks controlling water table drawdown. This has broader implications for fire management and restoration of northern peatlands, where younger, shallower peatlands should be targeted for proactive restoration and conservation. Additionally, this suggests that older, deeper peatlands may have a greater potential to act as fire and climate refugia in the future.