Forest Biomass Production Potential and its Implications for Carbon Balance

Sammanfattning: An integrated methodological approach is used to analyse the forestbiomass production potential in the Middle Norrland region of Sweden, and itsuse to reduce carbon emissions. Forest biomass production, forest management,biomass harvest, and forest product use are analyzed in a system perspectiveconsidering the entire resource flow chains. The system-wide carbon flows as wellas avoided carbon emissions are quantified for the activities of forest biomassproduction, harvest, use and substitution of non-biomass materials and fossil fuels.Five different forest management scenarios and two biomass use alternatives aredeveloped and used in the analysis. The analysis is divided into four main parts. Inthe first part, plant biomass production is estimated using principles of plantphysiologicalprocesses and soil-water dynamics. Biomass production is comparedunder different forest management scenarios, some of which include the expectedeffects of climate change based on IPCC B2 scenario. In the second part, forestharvest potentials are estimated based on plant biomass production data andSwedish national forest inventory data for different forest managementalternatives. In the third part, soil carbon stock changes are estimated for differentlitter input levels from standing biomass and forest residues left in the forestduring the harvest operations. The fourth and final part is the estimation of carbonemissions reduction due to the substitution of fossil fuels and carbon-intensivematerials by the use of forest biomass. Forest operational activities such asregeneration, pre-commercial thinning, commercial thinning, fertilisation, andharvesting are included in the analysis. The total carbon balance is calculated bysumming up the carbon stock changes in the standing biomass, carbon stockchanges in the forest soil, forest product carbon stock changes, and the substitutioneffects. Fossil carbon emissions from forest operational activities are calculated anddeducted to calculate the net total carbon balance.The results show that the climate change effect most likely will increaseforest biomass production over the next 100 years compared to a situation withunchanged climate. As an effect of increased biomass production, there is apossibility to increase the harvest of usable biomass. The annual forest biomassproduction and harvest can be further increased by the application of moreintensive forestry practices compared to practices currently in use. Deciduous treesare likely to increase their biomass production because of climate change effectswhereas spruce biomass is likely to increase because of implementation ofintensive forestry practices.Intensive forestry practices such as application of pre-commercialthinning, balanced fertilisation, and introduction of fast growing species to replaceslow growing pine stands can increase the standing biomass carbon stock. Soilcarbon stock increase is higher when only stem-wood biomass is used, comparedto whole-tree biomass use. The increase of carbon stocks in wood productsdepends largely on the magnitude of harvest and the use of the harvested biomass.The biomass substitution benefits are the largest contributor to the total carbonbalance, particularly for the intensive forest management scenario when wholetreebiomass is used and substitutes coal fuel and non-wood constructionmaterials. The results show that the climate change effect could provide up to 104Tg carbon emissions reduction, and intensive forestry practices may furtherprovide up to 132 Tg carbon emissions reduction during the next 100 years in thearea studied.This study shows that production forestry can be managed to balancebiomass growth and harvest in the long run, so that the forest will maintain itscapacity to increase standing biomass carbon and provide continuous harvests.Increasing standing biomass in Swedish managed forest may not be the mosteffective strategy to mitigate climate change. Storing wood products in buildingmaterials delays the carbon emissions into the atmosphere, and the wood materialin the buildings can be used as biofuel at the end of a building life-cycle tosubstitute fossil fuels.These findings show that the forest biomass production potential in thestudied area increases with climate change and with the application of intensiveforestry practices. Intensive forestry practice has the potential for continuousincreased biomass production which, if used to substitute fossil fuels andmaterials, could contribute significantly to net carbon emissions reductions andhelp mitigate climate change.