Ecohydrological Drivers of Boreal Shield Peatland Fire Refugia

Boreal peatlands play an important role in the global carbon cycle and can provide extensive buffering against climate change by acting as fire refugia. As wildfire extent, frequency and severity increase under climate change, it is critical to identify the characteristics and drivers of boreal peatland fire refugia in different hydroclimatic and hydrogeological settings to inform ecosystem management and conservation planning. We examined the ecohydrological characteristics of eight peatland fire refugia and eight unburned reference sites 3 years after an 11,362 ha wildfire in an eastern Boreal Shield landscape. We found that the vascular and bryophyte understorey vegetation composition within the peatland fire refugia was significantly different from the reference sites. Significant predictors of the difference in vascular vegetation composition were (i) median peat depth, (ii) maximum water table depth during the growing season and (iii) pH, where median peat depth was the only significant predictor identified for the bryophyte composition. While there was no clear evidence supporting any vascular indicator species, Sphagnum rubellum and Sphagnum medium were strongly associated with peatland fire refugia in this landscape. Peatland fire refugia also had a slower water table drawdown during the longest rain-free period of the growing season and a generally shallower growing season maximum water table depth than the reference sites. We suggest that peatland ecohydrological traits such as vegetation composition and water table drawdown rate may be useful to identify potential peatland fire refugia as they are indicators of negative ecohydrological feedbacks that maintain high peat moisture during drying.