Assessing carbon balance trade-offs between bioenergy and carbon sequestration of stumps at varying time scales and harvest intensities

Mitigating climate change and securing a supply of energy may be achieved, in part, by substituting fossil fuels with bioenergy from stumps and roots. However, the use of stumps would result in a reduction of the carbon pool and thus, from a greenhouse gas emission perspective, there is a trade-off between using stumps for bioenergy and retaining them in the carbon pool associated with dead organic matter. The objective of this study was to show whether, from a carbon balance perspective and over the short and long-terms, stumps are more important as a source of energy that replaces fossil fuels, or as a carbon sink.The study was based on the estimated bioenergy potential of stumps for three harvest scenarios and the corresponding effects on stump–carbon sequestration, if stump harvesting had been practiced in Sweden during the period 1984–2003. Approximately 30,000 permanent plots from the Swedish National Forest Inventory (NFI) were used for estimates of bioenergy potential. For the scenario “Medium intensity”, the bioenergy potential was estimated to 51 PJ yr−1 (or 5.7 Tg CO2 yr−1). The corresponding carbon sequestration potential from the retained biomass in the ground was 15 Tg CO2 yr−1. Using these stumps and roots as bioenergy substituting coal would result in a reduction of emission from coal combustion of 5.0 Tg CO2 yr−1. In the short-term, the choice of coal or stumps as an energy source has a minor effect on the gross emissions to the atmosphere but the removal from an increasing stump–carbon pool would slightly favor the use of coal. However, this study indicates that the most effective way of achieving a net reduction of emissions in the long-term is to burn stumps.