Post-Fire Chronosequence Analysis of Peatland Bog Vegetation Communities Across Hydrogeological Settings

Abstract

Canada’s Boreal Plains peatlands comprise 2.1% of the world’s terrestrial carbon store and are vital water supplies for adjacent upland ecosystems in this sub-humid climate. Projections indicate that future drought and wildfire events will be more frequent and severe, enhancing moisture deficits and threatening the functional role of peatlands as net carbon sinks. Peatland margins existing at the peatland-upland interface have been identified as deep smouldering hotspots on the landscape, where margin carbon loss accounts for 50 to 90% of total peatland carbon loss, dependent on hydrogeological setting. Previous chronosequence analysis of peatland bog recovery from wildfire disturbance has chronicled a return to carbon sink status within 20 years, but has not included margins nor peatlands located in coarse or heterogeneous-textured hydrogeological settings with varying degrees of groundwater connectivity. This analysis identifies and describes margin vegetation communities and recovery trajectories with time since fire and across hydrogeological settings. No significant differences were identified in margin area over time or margin peat depths across hydrogeological settings. Margin canopy composition consists of mixed coniferous and broadleaf deciduous species, with enhanced litterfall characterizing the dominant early to mid successional ground layer composition. Both peatland bog middle and margin vegetation communities were found to be dominated by feathermoss growth ~60 years following wildfire, which represents an accelerated trajectory from previous chronosequence analyses. Increased peatland and margin fuel loads with time since fire are also demonstrated using aboveground biomass calculations. Restoration practitioners can use this study to identify recovery milestones and altered trajectories, with their associated feedbacks, that perpetuate a broadleaf canopy and limited Sphagnum moss paludification. Fire managers should include confined peatlands in coarse-textured hydrogeological settings with deep smouldering margins in their management considerations and consider intervention (forest treatments) to open the canopy and prevent legacy carbon losses by severe wildfires.