Ecosystem scale evapotranspiration and CO2 exchange in burned and unburned peatlands: Implications for the ecohydrological resilience of carbon stocks to wildfire

摘要

Boreal peatlands represent a significant global store of soil carbon, which are subject to increasing natural and anthropogenic disturbance. Wildfire is the single largest disturbance to boreal forest and wetlands annually. Critical to the long-term carbon storage function in peatlands is the (re-)establishment of a near-surface water table following wildfire. This has been recently shown to in part be facilitated by post-fire reductions in water losses via evapotranspiration (ET). However, reduced ET may also have cascade impacts on other ecohydrological processes in recovering peatlands, such as a reduction in carbon sequestration. To investigate the linked cycles of evaporative loss and carbon exchange in burned peatlands, the burned and unburned peatlands in Alberta, Canada, were instrumented with eddy covariance systems to monitor continuous fluxes of energy, carbon dioxide, and water vapour, over two summer seasons (2013 and 2014; 2-3 years post-burn). The burned site showed significant changes to respiration and productivity and a shift in the partitioning of available energy (significantly larger Bowen ratio; mean values of 1.19 and 1.10 at the burned and unburned sites, respectively), as well as a significant reduction in ET rates. Decreases in respiration did not offset the decrease in primary productivity, and the burned site was significantly less productive than the reference site on a net production basis for the available data period. This provides direct observations of ET and CO2 fluxes at a novel ecosystem scale to show the impacts of fire on short-term (2-3 years) post-burn ecosystem ecohydrological function.