The role of fire in the boreal carbon budget

To reconcile observations of decomposition rates, carbon inventories, and n et primary production (NPP), we estimated long-term averages for C exchange in boreal forests near Thompson, Manitoba. Soil drainage as defined by wat er table, moss cover, and permafrost dynamics, is the dominant control on d irect fire emissions. In upland forests, an average of about 10-30% of annu al NPP was likely consumed by fire over the past 6500 years since these lan dforms and ecosystems were established. This longterm, average fire emissio n is much larger than has been accounted for in global C cycle models and m ay forecast an increase in fire activity for this region. While over decada l to century times these boreal forests may be acting as slight net sinks f or C from the atmosphere to land, periods of drought and severe fire activi ty may result in net sources of C from these systems.