Succession and carbon dynamics of boreal permaforest peatlands during rapid climate warming

Permafrost thaw resulting from climate warming will dramatically change the succession and carbon dynamics of northern ecosystems. Two impacts are of special concern. First is a release of soil carbon to the atmosphere. Warming of northern soils can thaw permafrost, increase drainage, and hasten decomposition. Second is a northward movement of vegetation zones and permafrost in step with shifting isotherms. I studied four boreal permafrost peatland regions along a 4°C mean annual temperature gradient in northern Manitoba, Canada to determine the relative influences of local vegetation factors and regional climate factors on successional permafrost landscapes. Within this context of successional change, I measured annual and long-term peat accumulation to determine how succession impacts ecosystem function.; Succession in this system is characterized by a cycle of permafrost thaw, which forms unfrozen bog-fen communities, and formation to a Picea dominated “permafrost plateau.” I measured local and regional influences on the rates of permafrost thaw using dendrochronological techniques and by estimating thaw activity as a function of local species cover and azimuth. I documented how species and functional group changed following thaw by sampling plots in collapse scars and on plateaus and by measuring changes in peat bulk density with time. Permafrost formation was measured as a function of tree cover, mean annual temperature, and emergent organic depth. Carbon balance on plateaus and in collapse scars was assessed by measuring NPP, litterfall, and decomposition of major functional groups. Long-term peat accumulation was compared for plateaus and scars using 210Pb dating of peat cores.; Permafrost thaw and formation and peat accumulation were more strongly controlled by local processes than by regional climate. In many sites, permafrost thaw was stopped by a combination of hummock Sphagnum cover and shading of southern azimuths by Picea trees on plateaus. These results suggest that permafrost thaw will likely lag climate warming and that plateaus may exist out of equilibrium for several decades or more. The analysis of both short and long-term carbon accumulation suggest that these peatlands will accumulate significantly less carbon following permafrost thaw.