Will climate change exceed the resilience limits of western Canadian peatlands?

Abstract:

Northern peatlands have served as persistent, small sinks of atmospheric CO₂ throughout the Holocene. In western Canada, peatlands exist on the drier spectrum of global peatland distributions. As a result, peatlands in this region are drier (e.g., no/few open pools in bogs and poor fens) and all bogs are treed. Because they occupy this climate space, continental peatlands might be regarded as being vulnerable to future warming and drying. On the other hand, these peatlands and their plant communities might already be adapted to drier conditions, conferring some resistance to climate change.

The position of the water table within a peatland serves as a dominant control on peat accumulation rates, as it influences plant structure and productivity, decomposition, and dissolved carbon export. Many studies predict that lower water table position, in response to enhanced evapotranspiration or drought, will cause peatlands to release stored C back to the atmosphere, indicative of a state change to an ecosystem type that no longer supports long-term peat accumulation. A 10-yr drainage experiment at the Alaska Peatland Experiment (APEX) sites showed that lowering the water table made a rich fen more of an atmospheric C source, primarily by altering plant species composition and lowering plant primary production rather than by increasing soil CO₂ flux. Multi-decadal drainage of Canadian peatlands also resulted in changes in plant species composition, with increasing tree and shrub canopy coverage and declines in moss abundance. Increased forestation in western Canadian peatlands will have large impacts on fire danger, which also has the potential to cause long-term shifts in plant and ecosystem structure, either through severe burning of surface peat layers or by inducing permafrost thaw. This talk will present findings from empirical and modeling studies examining peatland responses to warming, drought, permafrost thaw, and wildfires. Within the context of these dominant western Canadian disturbances, we will interpret our data within a resiliency framework, considering peatlands as complex adaptive systems that are resilient to some level of perturbation. However, we will present evidence that peatlands in some cases will experience state changes at higher levels of disturbance.