The Climate Mitigation Potential of Managed Boreal Forests Exceeds Their Carbon Store Effect

Abstract:

Boreal forests has important role for the mitigation of adverse effects of climate change. They form 1/5 of terrestrial carbon sink and secondary organic aerosols (SOAs) production through biogenic volatile organic carbon emissions further increase the cooling effect of this biome. The balance between these and the warming effect through surface albedo effects is still unclear. Moreover, boreal forests provide up to 17% of the global industrial roundwood harvest thus substituting other carbon intense materials. Here we modeled this integrated effect of boreal forest management on Earth radiative forcing (RF) using Finland as a case. We made analyses both in current climate and in the projected climate of year 2050.

At the stand level, the carbon sequestration effect and avoided CO₂ emissions due to substituted materials dominated in net RF in current climate. The warming effect of low surface albedo of forest cover was lower or of same magnitude than cooling effect of SOAs. The cooling effect of net radiative forcing increased along the increasing site fertility. Although the carbon stocks of broadleaved trees were smaller than that of conifers their total radiative cooling effect was larger due to the integrated albedo and aerosol effects. In the projected climate of 2050, the radiative cooling of aerosols increased to the level equaling forest carbon fixation.

Landscape level analyses emphasized the broad range of options to reach the cooling effect. The lowest harvest regime, 50% of current annual increment (CAI), yielded the largest cooling effect. Yet, harvests up to CAI produced only slightly less cooling RF if avoided emissions were considered. This result was highly sensitive to used substitution factors. If the goal is to mitigate climate change, boreal forest management should favor mixed forest stands and intensive harvests are preferable only if coupled with long lasting end products.