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Wildfire is the largest disturbance affecting peatland ecosystems and can typically result in the combustion of 2-3 kg C m−2 of near-surface peat. We hypothesized that organic soil burn severity, as well as the associated carbon emissions, varies significantly as a function of hydrogeological setting due to groundwater impacts on peat bulk density and moisture content. We measured depth of burn (DOB) in three peatlands located along a hydrogeological and topographic gradient in Alberta's Boreal Plains. Peatland margins across all hydrogeological settings burned significantly deeper (0.245 ± 0.018 m) than peatland middles (0.057 ± 0.002 m). Further, hydrogeological setting strongly impacted DOB. A bog with an ephemeral groundwater connection in a coarse-textured glaciofluvial outwash experienced the greatest DOB at its margins (0.514 ± 0.018 m) due to large water table fluctuations, while a low-lying oligotrophic groundwater flow-through bog in a coarse-textured glaciofluvial outwash experienced limited water table fluctuations and had the lowest margin burn severity (0.072 ± 0.002 m). In an expansive peatland in a lacustrine clay plain, DOB at the margins bordering an isolated domed bog portion (0.186 ± 0.003 m, range: 0.0-0.748 m) was considerably greater than the DOB observed at fen margins with a longer groundwater flow path (<0.05 m). Our research indicates that groundwater connectivity can have a dominant control on soil carbon combustion across and within hydrogeological settings. We suggest that hydrogeological setting be used to identify potential deep burning 'hotspots' on the landscape to increase the efficacy of wildfire management and mitigation strategies. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary Wildfire is the largest disturbance affecting boreal peatlands, however, little is known about the controls on post-fire peatland vegetation recovery. While small-scale variation in burn severity can reduce post-fire moss water availability, high water table (WT) positions following wildfire are also critical to enable the re-establishment of keystone peatland mosses ( i.e. Sphagnum ). Thus, post-fire moss water availability is also likely a function of landscape-scale controls on peatland WT dynamics, specifically, connectivity to groundwater flow systems ( i.e. hydrogeological setting). For this reason, we assessed the interacting controls of hydrogeological setting and burn severity on post-fire moss water availability in three burned, Sphagnum -dominated peatlands in Alberta’s Boreal Plains. At all sites, variation in burn severity resulted in a dichotomy between post-fire surface covers that: (1) exhibited low water availability, regardless of WT position, and had minimal (<5%) moss re-establishment ( i.e. lightly burned feather mosses and severely burned Sphagnum fuscum ) or (2) exhibited high water availability, depending on WT position, and had substantial (>50%) moss re-establishment ( i.e. lightly burned S. fuscum and where depth of burn was >0.05 m). Notably, hydrogeological setting influenced the spatial coverage of these post-fire surface covers by influencing pre-fire WTs and stand characteristics ( e.g. , shading). Because feather moss cover is controlled by tree shading, lightly burned feather mosses were ubiquitous (>25%) in drier peatlands (deeper pre-fire WTs) that were densely treed and had little connection to large groundwater flow systems. Moreover, hydrogeological setting also controlled post-fire WT positions, thereby affecting moss re-establishment in post-fire surface covers that were dependent on WT position ( e.g. , lightly burned S. fuscum ). Accordingly, higher recolonization rates were observed in a peatland located in a groundwater flow through system that had a shallow post-fire WT. Therefore, we argue that hydrogeological setting influences post-fire recovery in two ways: (1) by influencing vegetation structure prior to wildfire, thereby controlling the coverage of post-fire surface covers and (2) by influencing post-fire WT positions. These results suggest that post-fire moss recovery in peatlands isolated from groundwater flow systems may be particularly susceptible to droughts and future climate change. [ABSTRACT FROM AUTHOR]

In the Boreal Plain of Canada, the margins of peatland ecosystems that regulate solute and nutrient fluxes between peatlands and adjacent mineral uplands are prone to deep peat burning. Whether post-fire carbon accumulation is able to offset large carbon losses associated with the deep burning at peatland margins is unknown. For this reason, we examined how post-fire hydrological conditions ( i.e. water table depth and periodicity, soil tension, and surface moisture content) and depth of burn were associated with moss recolonization at the peatland margins of three sites. We then interpreted these findings using a hydrogeological systems approach, given the importance of groundwater in determining conditions in the soil-plant-atmosphere continuum in peatlands. Peatland margins dominated by local groundwater flow from adjacent peatland middles were characterized by dynamic hydrological conditions that, when coupled with lowered peatland margin surface elevations due to deep burning, produced two common hydrological states: 1) flooding during wet periods and 2) rapid water table declines during dry periods. These dynamic hydrological states were unfavorable to peatland moss recolonization and bryophytes typical of post-fire recovery in mineral uplands became established. In contrast, at a peatland margin where post-fire hydrological conditions were moderated by larger-scale groundwater flow, flooding and rapid water table declines were infrequent and, subsequently, greater peatland-dwelling moss recolonization was observed. We argue that peatland margins poorly connected to larger-scale groundwater flow are not only prone to deep burning but also lags in post-fire moss recovery. Consequently, an associated reduction in post-fire peat accumulation may occur and negatively affect the net carbon sink status and ecohydrological and biogeochemical function of these peatlands. [ABSTRACT FROM AUTHOR]