Greenhouse gas balance of harvesting stumps and logging residues for energy in Sweden

Abstract

In this case study, forest fuel procurement chains of stumps and logging residues were evaluated using a Life Cycle Assessment perspective. Direct emissions from combustion were not included, but soil organic carbon change was included as changes in carbon stocks in litter and soil. The results showed that primary forest biomass for energy has a climate impact which is time dependent. However, in long-time perspectives, there are large greenhouse gas (GHG) savings. In a short-term (20 years), there were no GHG savings when natural gas or coal was replaced. This is due to the fact that the harvest lead to decreased input of organic matter to the soil which is compared to a reference where biomass are left to decompose. The reduction in soil organic carbon may have been underestimated in the stump harvest systems studied, as the effect of soil disturbance per se was not included. Important factors when assessing GHG balance of forest fuels, besides the time horizon used, were site productivity, geographical position and forest fuel resource (stumps or logging residues). When assessing the greenhouse gas savings, efficiency of the end-use, allocation method between heat and power and type of fossil fuel replaced were also important.

Keywords:

• Bioenergy
• forest fuel
• greenhouse gas saving
• LCA
• logging residues
• soil organic carbon
• stumps

Acknowledgements

This study was carried out as part of the Stump Research Programme at the Swedish University of Agricultural Sciences. It was funded by the Swedish Energy Agency and the Swedish University of Agricultural Sciences. We also acknowledge the Editor and referees for their informed comments.