Wildfire in Swedish boreal forests - Impacts of fire severity and salvage logging on tree seedling regeneration and the belowground system

Abstract: Wildfires are projected to occur more frequently and become more severe as the climate warms. The increasing release of carbon to the atmosphere from more severe fires may contribute to climate warming, and thus initiate a positive feedback loop. Following wildfire, salvage logging is a common management practice, but the impact on soil and vegetation may vary depending on fire severity. Hence, it is important to understand how wildfire severity and salvage logging affect soil abiotic and biotic properties and tree seedling regeneration. Also, in the future, forest recovery from fire and salvage logging may be affected by climate warming. In this thesis, I have conducted laboratory and greenhouse experiments to investigate the abiotic and biotic effects of fire severity and post-fire management on biomass production of Betula pendula, Picea abies and Pinus sylvestris seedlings regenerated from seeds and associated soil processes. Further, I have performed a mesocosm field experiment to investigate the impacts of fire severity, salvage logging and experimental warming on P. abies and P. sylvestris nursery seedlings in situ, and undertaken field measurements of soil N transformation rates and C fluxes in stands of varying fire severity and management. This thesis shows that the effect of fire severity on the soil system is stronger than that of salvage logging and that the impact of salvage logging on forest regeneration varies depending on fire severity; these effects can further be directly or indirectly altered by experimental climate warming. This thesis also shows that the effect of soil abiotic and biotic properties following fire on tree seedling regeneration are species specific. Altogether, it contributes with new fundamental knowledge about the interactive effects of multiple drivers of seedling regeneration and soil processes in the post-fire boreal forest landscape. The conclusions of this thesis can be applied, in combination with other research, in decision making about management of boreal forest following wildfire.