Peat accumulation and succession following permafrost thaw in the boreal peatlands of Manitoba, Canada

Permafrost thaw in boreal peatlands may be widespread as climate warms over the next century. Thaw will lead to dramatic changes in vegetation, and an understanding of the patterns and rates of succession following thaw is important for assessing future ecosystem changes, such as carbon accumulation and the likelihood of permafrost formation during climate warming. This paper describes the autogenic processes of peat accumulation and succession from recently thawed, aquatic Sphagnum communities to lawn and hummock Sphagnum communities favorable for permafrost formation. Peat cores were used to construct bulk density profiles in aquatic, lawn, and hummock habitats. Soil bulk density increased over time from the edges to the centers of thawed bogs. These changes corresponded to changes from aquatic to lawn/hummock communities. Macrofossils from Pb-210-dated peat cores were used to document historical changes to hummock communities. Succession to hummock communities capable of forming permafrost was less than 80 years. Picea mariana seedlings colonized emergent Sphagnum hummocks in collapse scars, which may lead to permafrost formation. However, permafrost formation in today's discontinuous permafrost landscape is unlikely during future climate warming because of limited tree establishment and shifting mean annual temperature isotherms.