Fire, climate change, carbon and fuel management in the Canadian boreal forest

Fire is the dominant stand-renewing disturbance through much of the Canadia n boreal forest, with large high-intensity crown fires being common. From 1 to 3 million ha have burned on average during the past 80 years, with 6 ye ars in the past two decades experiencing more than 4 million ha burned. A l arge-fire database that maps forest fires greater than 200 ha in area in Ca nada is being developed to catalogue historical fires. However, analyses us ing a regional climate model suggest that a changing climate caused by incr easing greenhouse gases may alter fire weather, contributing to an increase d area burned in the future. Direct carbon emissions from fire (combustion) are estimated to average 27 Tg carbon year(-1) for 1959-1999 in Canada. Po st-fire decomposition may be of a similar magnitude, and the regenerating f orest has a different carbon sink strength. Measurements indicate that ther e is a net carbon release (source) by the forest immediately after the fire before vegetation is re-established. Daytime downward carbon fluxes over a burned forest take 1-3 decades to recover to those of a mature forest, but the annual carbon balance has not yet been measured. There is a potential positive feedback to global climate change, with anthropogenic greenhouse g ases stimulating fire activity through weather changes, with fire releasing more carbon while the regenerating forest is a smaller carbon sink. Howeve r, changes in fuel type need to be considered in this scenario since fire s preads more slowly through younger deciduous forests. Proactive fuel manage ment is evaluated as a potential mechanism to reduce area burned. However, it is difficult to envisage that such treatments could be employed successf ully at the national scale, at least over the next few decades, because of the large scale of treatments required and ecological issues related to for est fragmentation and biodiversity.