Permafrost thaw as a mechanism for widespread boreal forest loss

Background/Question/Methods

Boreal forests occupy latitudes that are expected to warm most dramatically over the coming decades, and evidence indicates that changes are already underway in these systems. Much of the boreal is underlain by permafrost, which can be expected have important consequences for boreal forests as the climate warms. The southern margin of permafrost is especially susceptible to warming, since in this region, the permafrost is discontinuous, relatively thin (< 10 m), warm and ice-rich. In the zone of discontinuous permafrost, permafrost forms the physical foundation on which trees develop, forming tree-covered peat plateaus where trees are likely to contribute to permafrost maintenance and aggradation processes through reductions in radiation load and changes in snow accumulation. Forests are restricted to peat plateaus while wetland communities characterize the permafrost-free areas. The structure and composition of these communities and transitions among them are strongly influenced by hydrological inputs and connectivity. Evidence suggests that warming is leading to permafrost thaw and surface subsidence, which decreases forest cover while increasing wetland hydrological connectivity. In the present talk we investigate the implications of permafrost thaw on subarctic boreal forests. 

Results/Conclusions

We present 10-years of field-based evidence of substantial forest loss from a site at the southern limits of discontinuous permafrost in the Northwest Territories, Canada; between 1947 and 2008, approximately 30% of forested peat plateaus were in a 1km² area at this site with a corresponding increase in flat bogs. A process-based examination of the eco-hydrological mechanisms and feedbacks contributing to change in these systems will be presented and the implication of these changes to ecosystem function discussed. Finally, we will provide evidence that these changes are happening across Canada; such widespread land cover change has important implications for the function of these northern peatlands that play critical roles as reservoirs of fresh surface water and globally important carbon sinks.