Did enhanced afforestation cause high severity peat burn in the Fort McMurray Horse River wildfire?

Abstract

Climate change mediated drying of boreal peatlands is expected to enhance peatland afforestation and wildfire vulnerability. The water table depth-afforestation feedback represents a positive feedback that can enhance peat drying and consolidation and thereby increase peat burn severity; exacerbating the challenges and costs of wildfire suppression efforts and potentially shifting the peatland to a persistent source of atmospheric carbon. To address this wildfire management challenge, we examined burn severity across a gradient of drying in a black spruce dominated peatland that was partially drained in 1975−1980 and burned in the 2016 Fort McMurray Horse River wildfire. We found that post-drainage black spruce annual ring width increased substantially with intense drainage. Average (±SD) basal diameter was 2.6 ± 1.2 cm, 3.2 ± 2.0 cm and 7.9 ± 4.7 cm in undrained (UD), moderately drained (MD) and heavily drained (HD) treatments, respectively. Depth of burn was significantly different between treatments (p < 0.001) and averaged (±SD) 2.5 ± 3.5 cm, 6.4 ± 5.0 cm and 36.9 ± 29.6 cm for the UD, MD and HD treatments, respectively. The high burn severity in the HD treatment included 38% of the treatment that experienced combustion of the entire peat profile, and we estimate that overall 51% of the HD pre-burn peat carbon stock was lost. We argue that the HD treatment surpassed an ecohydrological tipping point to high severity peat burn that may be identified using black spruce stand characteristics in boreal plains bogs. While further studies are needed, we believe that quantifying this threshold will aid in developing effective adaptive management techniques and protecting boreal peatland carbon stocks. ORCID iDsS L Wilkinson https://orcid.org/0000-0002-4043-6277 M D Flannigan https://orcid.org/0000-0002-9970-5363 J M Waddington https://orcid.org/0000-0002-0317-7894

Hydrogeologic setting overrides any influence of wildfire on pore water dissolved organic carbon concentration and quality at a boreal fen

“…Fens are typically more species rich (dominated by graminoid species and brown mosses) and have water tables that are typically closer to the surface than those measured in bogs in similar climatic settings (Chee and Vitt, ; Vitt & Chee, ; Graham et al, ). The terrestrial carbon stored within these peatlands are vulnerable to degradation and subsequent release through a number of anthropogenic and natural disturbances that can be exacerbated by climate change (Turetsky, Wieder, Halsey, & Vitt, ; Wilkinson, Moore, Flannigan, Wotton, & Waddington, ).…”

Wildfire overrides hydrological controls on boreal peatland methane emissions

“…The higher CH 4 production found at the MB hummocks is likely due to the small methanogen community surviving the fire, due to the resistance of S. fuscum to fire (Benscoter et al, 2011). After fire, there could be chemical changes in the soil substrate, such as an increase in availability of terminal electron acceptors, that could contribute to the reduction in CH 4 production and emissions (Wilson et al, 2017). Therefore, there is a potential long-term impact on the biogeochemical processes of peatlands (Danilova et al, 2015), and in order to fully understand the overall impact of wildfire on CH 4 emissions, additional studies at other sites encompassing the full range of boreal peatland types would be key.…”

“…Fire can remove surface vegetation, increasing net radiation at the ground surface (Brown et al, 2015), and can "re-set" vegetation communities back to the primary succession stage (Johnstone, 2006;Benscoter and Vitt, 2008). Fire can alter soil organic matter quality in the soil column (Neff et al, 2005;Olefeldt et al, 2013a) and reduce belowground C stores in peatlands (Wilkinson et al, 2018). Overall, wildfire can lead to a decrease in C accumulation rate through combustion loss, reduction in vegetation productivity, and increased organic matter decomposition post-fire (Ingram et al, 2019;Robinson and Moore, 2000;Wieder et al, 2009).…”

Postfire Soil Carbon Accumulation Does Not Recover Boreal Peatland Combustion Loss in Some Hydrogeological Settings

“…In the Boreal Plains (BP), wildfire is the largest disturbance affecting these ecosystems (Turetsky et al, ). Peatlands in Canada's subhumid BP region burn as frequently as every 100–120 years (Turetsky et al, ), and the drier peatlands in this region can emit considerable amounts of CO 2 (e.g., Turetsky et al, ), releasing long‐term stored carbon through deep smoldering combustion (Turetsky et al, ; Wilkinson et al, ). While moss traits and peatland ecohydrological feedbacks generally minimize wildfire peat burn severity (depth of burn = 0.05 to 0.10 m) in the interiors of BP peatlands (Benscoter et al, ; Thompson & Waddington, ), BP peatland margins are especially vulnerable to smoldering in some hydrogeological settings (depth of burn >1.0 m; Hokanson et al, ; Lukenbach, Hokanson, et al, ).…”