Forest type drives the response of boreal forested peatlands to wildfire: a simulation study

Boreal black spruce forests contribute to climate change mitigation by accumulating large amounts of carbon (C) in moss-derived peat. When left undisturbed, a thick peat layer can inhibit tree growth, and this trade-off between peat and tree biomass can have implications on the forest C dynamics. Similarly, wildfire severity and frequency can modify C accumulation patterns, but this impact remains poorly documented. We used the Carbon Budget Model of the Canadian Forest Sector version 3 (CBM-CFS3) to explore over a 400-year simulation period, the effects of high-severity fire (HSF) and low-severity fire (LSF) on C dynamics of two forest types (black spruce–Sphagnum (BSSP) and black spruce–feathermoss (BSFM)). We found that total C stocks increased to higher levels after LSF than after HSF in BSSP due to peat accumulation. Conversely, in BSFM, HSF resulted in greater C storage than LSF due to tree biomass. The tree component is key to the rapid recovery of C pools in both BSSP and BSFM forests specifically after HSF, while mosses maintain C sinks over the long term. This study suggests that a good characterization of forest type is key to better predictions of the effects of a change in fire regime on ecosystem C dynamics.