Wildfire overrides hydrological controls on boreal peatland methane emissions

Abstract

Abstract. Boreal peatlands represent a globally important store of carbon, and disturbances such as wildfire can have a negative feedback to the climate. Understanding how carbon exchange and greenhouse gas (GHG) dynamics are impacted after a wildfire is important, especially as boreal peatlands may be vulnerable to changes in wildfire regime under a rapidly changing climate. However, given this vulnerability, there is very little in the literature on the impact such fires have on methane (CH4) emissions. This study investigated the effect of wildfire on CH4 emissions at a boreal fen near Fort McMurray, Alberta, Canada, that was partially burned by the Horse River Wildfire in 2016. We measured CH4 emissions and environmental variables (2017–2018) and CH4 production potential (2018) in two different microform types (hummocks and hollows) across a peat burn severity gradient (unburned (UB), moderately burned (MB), and severely burned (SB)). Results indicated a switch in the typical understanding of boreal peatland CH4 emissions. For example, emissions were significantly lower in the MB and SB hollows in both years compared to UB hollows. Interestingly, across the burned sites, hummocks had higher fluxes in 2017 than hollows at the MB and SB sites. We found typically higher emissions at the UB site where the water table was close to the surface. However, at the burned sites, no relationship was found between CH4 emissions and water table, even under similar hydrological conditions. There was also significantly higher CH4 production potential from the UB site than the burned sites. The reduction in CH4 emissions and production in the hollows at burned sites highlights the sensitivity of hollows to fire, removing labile organic material for potential methanogenesis. The previously demonstrated resistance of hummocks to fire also results in limited impact on CH4 emissions and likely faster recovery to pre-fire rates. Given the potential initial net cooling effect resulting from a reduction in CH4 emissions, it is important that the radiative effect of all GHGs following wildfire across peatlands is taken into account.

Oil palm ‘slash-and-burn’ practice increases post-fire greenhouse gas emissions and nutrient concentrations in burnt regions of an agricultural tropical peatland

“…CH4 emissions were also significantly higher in the burnt region than in the non-burnt region and stayed at similar higher levels even into the wet-season, five months after the fire event (Fig 3b). It was previously observed that fire would make the peat dry and effect lower CH4 emissions from the burnt areas because of the lack of moisture (Davidson et al, 2019), but this study has shown that at similar moisture levels, burnt peat has a potential for higher CH4 emissions than the non-burnt peat. This higher CH4 emissions in the fire-affected region may be due to the availability of more labile C due to the denaturation of peat by fire and resultant heat (Sazawa et al, 2018).…”

Constructive criticism of “Misinterpreting carbon accumulation rates in records from near-surface peat” by Young et al: Further evidence of charcoal impacts in relation to long-term carbon storage on blanket bog under rotational burn management

“…For example, (i) net C fluxes at the three Heinemeyer et al sites [2] (see the Peatland-ES-UK website [12] ) indicate a potentially high net C uptake on regrowing burnt plots (possibly higher than that of unburnt plots with aging/degenerating heather and soon to offset combustion losses, but this requires a complete burn rotation to allow comparing cumulative C flux budgets versus C stocks estimates); (ii) recent work [14] adds to the prescribed heather burning work [2,3] in highlighting the positive role that charcoal (produced during cool burns or low-severity fires) can have on peatland C storage (e.g. it has the potential to increase peat C stocks by adding recalcitrant Corg in the form of charcoal and further reducing C losses via decomposition of soil organic matter); finally, (iii) a recent study suggests that low-severity fires may reduce methane emissions relative to no burning or high-severity fires in cooler climates [15] . Our greatest concern is that Young et al's unjustified criticisms of specific studies [2,3] have been reproduced within publications of important peatland conservation bodies, such as in the IUCN UK Peatland Programme [16] , which explicitly refer to the two heather burning studies [2,3] as having "presented misleading conclusions" (n.b.…”

Soil carbon flux research in the Asian region: Review and future perspectives

“…Wildfires may have positive and negative effects on R s , as fire-induced heat suppresses microbes, whilst post-fire ash supplies a greater volume of substrate for microbes and reduces rhizospheric respiration by inhibiting photosynthesis and the development of roots and mycorrhizae Irvine et al, 2007;Kuzyakov and Gavrichkova, 2010 . Based on the large spatial heterogeneity of vegetation cover, fire regime, and increasing deforestation/degradation fires, there is a need for a greater number of studies on the impact of fire on R s and its components across diverse ecosystems, to obtain a better understanding on future C cycles Smith et al, 2018;Hu et al, 2020 . At present, there are very few studies on the fire impacts on CH 4 uptake in the Asian region to reliably assess post-fire impacts on CH 4 flux compared to northern peatlands Davidson et al, 2019;Kumar et al, 2020. Kim 2013 reported that in a white birch forest located at the Teshio Experimental Forest, northern Japan, a low-intensity experimental surface fire did not affect CH 4 uptake, finding no significant alterations in soil properties such as soil moisture, pH, and inorganic N concentrations.…”