http://hdl.handle.net/11375/25114

Wilkinson, S. (2019). Ecohydrological Thresholds to High Peat Burn Severity: Implications for Peatland Wildfire Management http://hdl.handle.net/11375/25114

Northern peatlands represent a globally significant carbon stock, equating to almost one-third of the world’s organic soil carbon. The largest areal disturbance to northern peatlands is wildfire where carbon loss, through peat smouldering combustion, is highly variable. The tightly-coupled ecohydrological nature of peatlands results in autogenic feedbacks and the occurrence of threshold behaviour. High depth of burn has been evidenced in black spruce dominated peatlands in the sub-humid Boreal Plains ecozone of Alberta, Canada so this was chosen as the area of study. A landscape-scale assessment of peat hydrophysical properties found that peat smouldering combustion vulnerability was greatest at stand-age > 80 years, in coarse/heterogeneous hydrogeological settings, and in peatland margins compared to peatland middles. In combination, and when exposed to a climatic water deficit, we found that these drivers of cross-scale variability could lead to high peat burn severity. Assessment of a partially-drained and burned peatland enabled the identification of a black spruce basal diameter threshold that corresponded to the occurrence of high peat burn severity. We suggest that the above-ground fuel load threshold could occur due to the initiation of a self-reinforcing feedback by anthropogenic disturbance or climate change. Moreover, surpassing a peat burn severity threshold can cause the breakdown of an important feedback that limits evaporation losses post-fire, likely leading to further carbon losses through increased decomposition rates and/or ecosystem regime shift. We found that although peat moisture content was increased by fuel modification treatment, combustion carbon losses were greater in fuel-treated areas compared to the control because of the addition of mulch (wood) to the surface. Hence, peatland wildfire management that integrates the modification of above- and below-ground fuels, considers ecohydrological thresholds, and drivers of cross scale variability, is required to effectively reduce the risk of high peat burn severity in black spruce dominated peatlands.

PhD, McMaster University, Boreal Water Futures

http://hdl.handle.net/11375/25114