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 im portant for assessing future ecosystem changes, such as carbon accumulation and the likelihood of permafrost formation during climate warming. This pa per describes the autogenic processes of peat accumulation and succession f rom recently thawed, aquatic Sphagnum communities to lawn and hummock Sphag num communities favorable for permafrost formation. Peat cores were used to construct bulk density profiles in aquatic, lawn, and hummock habitats. So il bulk density increased over time from the edges to the centers of thawed bogs. These changes corresponded to changes from aquatic to lawn/hummock c ommunities. Macrofossils from Pb-210-dated peat cores were used to document historical changes to hummock communities. Succession to hummock communiti es capable of forming permafrost was less than 80 years. Picea mariana seed lings colonized emergent Sphagnum hummocks in collapse scars, which may lea d to permafrost formation. However, permafrost formation in today's discont inuous permafrost landscape is unlikely during future climate warming becau se of limited tree establishment and shifting mean annual temperature isoth erms.