The effect of natural disturbances on the carbon balance of boreal forests

Abstract: Natural disturbances such as fires, insect outbreaks and windthrows are able to influence the balance between the ecosystem gain and loss of carbon in the boreal forest. This effect of natural disturbances on the ecosystem carbon balance has been proposed as one of the reasons why the CO2 concentration in the atmosphere varies between years. At present the boreal forest as a whole act to mitigate the high levels of CO2 in the atmosphere but the future of this balance is far from certain. In a changed climate the frequency and severity of natural disturbances are projected to increase which will enhance the transfer of terrestrial carbon to the atmosphere. If this loss of carbon is not compensated by an increased accumulation of carbon, the boreal forest will transform from an important carbon sink into a carbon source. Natural disturbances thus have the potential to act as a positive feedback between the boreal forest and the climate system. On account of the importance of natural disturbances these must be included in estimations of the carbon budget of the boreal forest. This review focuses on the effect of natural disturbances on the carbon balance in boreal forest in a current and future climate. Both direct and indirect emissions of CO2 from different natural disturbances have been collected from various regions. Different natural disturbances affect the carbon balance in their own way, and at different time scales. They are also more or less important in some regions. To be able to fully account for the carbon balance of the boreal forest biome the effect of natural disturbances must be understood. Methods are available but there are still information gaps to be filled since data have not been collected with enough spatial and temporal coverage.