Forest biomass production potential and its implications for carbon balance

Sammanfattning: An integrated methodological approach is used to analyse the forest biomass production potential in the Middle Norrland region of Sweden, and its use to reduce carbon emissions. Forest biomass production, forest management, biomass harvest, and forest product use are analyzed in a system perspective considering the entire resource flow chains. The system-wide carbon flows as well as avoided carbon emissions are quantified for the activities of forest biomass production, harvest, use and substitution of non-biomass materials and fossil fuels. Five different forest management scenarios and two biomass use alternatives are developed and used in the analysis. The analysis is divided into four main parts. In the first part, plant biomass production is estimated using principles of plant-physiological processes and soil-water dynamics. Biomass production is compared under different forest management scenarios, some of which include the expected effects of climate change based on IPCC B2 scenario. In the second part, forest harvest potentials are estimated based on plant biomass production data and Swedish national forest inventory data for different forest management alternatives. In the third part, soil carbon stock changes are estimated for different litter input levels from standing biomass and forest residues left in the forest during the harvest operations. The fourth and final part is the estimation of carbon emissions reduction due to the substitution of fossil fuels and carbon-intensive materials by the use of forest biomass. Forest operational activities such as regeneration, pre-commercial thinning, commercial thinning, fertilisation, and harvesting are included in the analysis. The total carbon balance is calculated by summing up the carbon stock changes in the standing biomass, carbon stock changes in the forest soil, forest product carbon stock changes, and the substitution effects. Fossil carbon emissions from forest operational activities are calculated and deducted to calculate the net total carbon balance.The results show that the climate change effect most likely will increase forest biomass production over the next 100 years compared to a situation with unchanged climate. As an effect of increased biomass production, there is a possibility to increase the harvest of usable biomass. The annual forest biomass production and harvest can be further increased by the application of more intensive forestry practices compared to practices currently in use. Deciduous trees are likely to increase their biomass production because of climate change effects whereas spruce biomass is likely to increase because of implementation of intensive forestry practices.IIIntensive forestry practices such as application of pre-commercial thinning, balanced fertilisation, and introduction of fast growing species to replace slow growing pine stands can increase the standing biomass carbon stock. Soil carbon stock increase is higher when only stem-wood biomass is used, compared to whole-tree biomass use. The increase of carbon stocks in wood products depends largely on the magnitude of harvest and the use of the harvested biomass. The biomass substitution benefits are the largest contributor to the total carbon balance, particularly for the intensive forest management scenario when whole-tree biomass is used and substitutes coal fuel and non-wood construction materials. The results show that the climate change effect could provide up to 104 Tg carbon emissions reduction, and intensive forestry practices may further provide up to 132 Tg carbon emissions reduction during the next 100 years in the area studied.This study shows that production forestry can be managed to balance biomass growth and harvest in the long run, so that the forest will maintain its capacity to increase standing biomass carbon and provide continuous harvests. Increasing standing biomass in Swedish managed forest may not be the most effective strategy to mitigate climate change. Storing wood products in building materials delays the carbon emissions into the atmosphere, and the wood material in the buildings can be used as biofuel at the end of a building life-cycle to substitute fossil fuels.These findings show that the forest biomass production potential in the studied area increases with climate change and with the application of intensive forestry practices. Intensive forestry practice has the potential for continuous increased biomass production which, if used to substitute fossil fuels and materials, could contribute significantly to net carbon emissions reductions and help mitigate climate change.