Northern ecosystems are experiencing rapid climate and environmental changes. In the face of such change, considerable progress has been made towards understanding boreal forest and arctic tundra ecosystems in the context of resilience theory. For example, there is clear evidence that wildfire activity is overwhelming the resilience mechanisms of conifer species, shifting forest composition toward deciduous cover in some boreal regions. Relative to forests and tundra; however, we have less knowledge on what governs the response of northern peatlands to disturbance. It was only recently appreciated that fire serves as an important agent of successional change in northern peatlands, and recent studies show that the defining function of peatlands as net carbon sinks requires light to moderate fire activity. Peatlands often are regarded as adaptive resilient systems, in part due to the high porosity and storage coefficient of surface peat that maintains wet conditions. As a consequence, resistance to fire has increased carbon storage in undisturbed boreal and tropical peatlands over long time scales. In this presentation, I will evaluate aspects of ecological and hydrological resilience in northern ecosystems, particularly in light of recent documented changes in two disturbance regimes: wildfire and permafrost thaw.
Results/Conclusions
Multiple lines of empirical evidence shows that drying as a result of climate change and anthropogenic activity lowers peatland water tables, overwhelming the resilience of moss and increasing their vulnerability to burning. Long-lived smouldering can lead to deep burning of peat, which releases ancient carbon to the atmosphere, exposes mineral soils, and can lead to loss of critical species (moss, conifer species) that underpin peat accumulation.
Across northern ecosystems, deep peat burning also reduces the insulative qualities of surface soil and makes permafrost more vulnerable to post-fire thaw. When permafrost is ice-rich, warming and thaw of permafrost leads to surface deformation, thermokarst, and ecological state changes, such as replacement of forested permafrost plateaus with thaw lakes or collapse scar wetlands. These thaw features are formed through abrupt structural changes in vegetation composition, soil structure and albedo. However, they also undergo significant shifts in ecosystem function, as most permafrost systems upon thaw are converted from net carbon sinks to large emitters of legacy carbon to the atmosphere. While succession can cause northern ecosystems to regain aspects of pre-disturbance form or function, there is increasing evidence that ongoing climate change is triggering novel pathways of change across a range of ecosystem types.