Peat properties and water retention in boreal forested peatlands subject to wildfire

Peat cores from a recently burned peatland and one over 75 years since fire in Alberta, Canada were analyzed for physical properties and water retention. Wildfire exposed denser peat at the peat surface, more so in hollow than hummock microforms. Water retention in peat has implications for postfire Sphagnum regeneration, as this more dense peat requires smaller volumes of water loss before a critical growth‐inhibiting pore‐water pressure of −100 mb is reached. Simulations of water retention after fire showed that hollow microforms are at a higher risk of losing low‐density surface peat, which moderates water table (WT) declines via high specific yield. Exposure of dense peat to the surface after fire increases surface moisture under a constant WT. The net effect of decreasing specific yield and increasing water retention at the surface has implications on hydrologic stability and resilience of boreal peatlands to future wildfire risk under a changing climate. Earth system models incorporating wildfire disturbance in boreal peatlands would benefit from the inclusion of these hydrological feedbacks in this globally significant carbon reservoir. Wildfire in boreal peatlands exposes more dense peat to the surface Denser peat contributes to faster water table decline Humified or rooty peat retains less water per unit dry mass