Search

A suite of autogenic ecohydrological feedbacks and moss traits are important for protecting vast peatland carbon stocks following wildfire disturbance. Here, we examine how peat burn severity and water table depth (WTD) affect the strength of one such feedback—the hydrophobicity–evaporation feedback (HEF). The HEF is an evaporation‐limiting feedback known to minimize water loss following wildfire. The peatland surface becomes hydrophobic creating an evaporative cap and thereby reducing post‐fire evaporation; however, recent studies hypothesize that this is dependent on peat burn severity. To test this hypothesis, we studied plots along a peat burn severity gradient in a partially drained black spruce peatland that burned during the 2016 Fort McMurray Horse River wildfire. Evaporation rates were significantly lower in plots where hydrophobicity was present. Hydrophobicity was lowest in the severely burned area, and the average instantaneous evaporation rate (2.75 mm day−1) was significantly higher than moderately and typical‐lightly burned areas (0.82 and 1.64 mm day−1, respectively). Based on lab results, increasing WTD affected hydrophobicity within lightly burned (singed) feather moss samples but not in heavily burned feather moss, showing the importance of post‐fire ground cover and in situ WTD. Our results provide evidence of a burn severity threshold where increased depth of burn removes the feather moss evaporative cap and causes the HEF to break down. We argue that this threshold has important implications for boreal peatlands, which are predicted to undergo climate‐mediated pre‐fire drying and increasing burn severities, potentially leading to further carbon losses due to enhanced post‐fire drying and concomitant decomposition. [ABSTRACT FROM AUTHOR]

Peat properties such as bulk density, moisture retention and specific yield (Sy) influence water table fluctuations, drying rates and peat combustion vulnerability, therefore determining peat susceptibility and response to wildfire. Smouldering peat fires are challenging to suppress and emit vast quantities of carbon and particulate matter into the atmosphere. A 120-year peatland fire return interval was used to constrain a landscape-wide space-for-time chronosequence in the boreal plains ecozone of Alberta, where peat properties were assessed along spatial gradients within 26 peatlands. Bulk density depth profiles are different between microforms where hummocks < hollows < margins, correspondingly Sy followed the opposite trend. Hummock moisture retention parameters, modelled using the Van Genuchten-Mualem model, are maintained over time whereas hollows and margins experience changes due to wildfire impacts and subsequent recovery, causing decreased Sy immediately following fire but increased moisture retention. This trend is exacerbated in coarse and moraine hydrogeological settings which is also where margin: peatland proper area tends to be greatest. We find that only minimal increases in the annual water deficit would be required to cause high combustion vulnerability in some hydrogeological settings. This study provides the first landscape-wide assessment of peat properties across a fire return interval and assessment of potential smouldering vulnerability given increased water deficits under future climate change. Such studies will be useful to inform wildfire management decision-making especially at the wildland society interface. [ABSTRACT FROM AUTHOR]