Changes in biomass, aboveground net primary production, and peat accumulation following permafrost thaw in the boreal peatlands of Manitoba, Canada

Permafrost thaw resulting from climate warming may dramatically change the succession and carbon dynamics of northern ecosystems. To examine the joint effects of regional temperature and local species changes on peat accumula tion following thaw, we studied peat accumulation across a regional gradien t of mean annual temperature (MAT). We measured aboveground net primary pro duction (AGNPP) and decomposition over 2 years for major functional groups and used these data to calculate a simple index of net annual aboveground p eat accumulation. In addition, we collected cores from six adjacent frozen and thawed bog sites to document peat accumulation changes following thaw o ver the past 200 years. Aboveground biomass and decomposition were more str ongly controlled by local succession than regional climate. AGNPP for some species differed between collapse scars and associated permafrost plateaus and was influenced by regional MAT. A few species, such as Picea mariana tr ees on frozen bogs and Sphagnum mosses in thawed bogs, sequestered a dispro portionate amount of peat; in addition, changes in their abundance followin g thaw changed peat accumulation. Pb-210-dated cores indicated that peat ac cumulation doubles following thaw and that the accumulation rate is affecte d by historical changes in species during succession. Peat accumulation in boreal peatlands following thaw was controlled by a complex mix of local ve getation changes, regional climate, and history. These results suggest that northern ecosystems may show responses more complex than large releases of carbon during transient warming.