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Doctoral thesis, 2014

Impacts of stumps and roots on carbon storage and bioenergy use in a climate change context

Melin, Ylva


As a result of national and international greenhouse gas emissions reduction targets, economic incentives and political desires to be more independent regarding energy supplies, there is interest in substituting fossil fuels with renewable energy sources, such as forest fuels. Stump harvesting could be an option to further increase the bioenergy potential in forested countries; currently stump harvesting is carried out on a pilot basis in Sweden. In this thesis, the Swedish stump harvest potential is studied in a national and European climate change mitigation context. One main objective was to develop a general system for estimating and monitoring carbon stocks and carbon stock changes in stump and root systems on a national scale. A core part of this system was a decomposition function for Norway spruce stumps and roots that was developed as part of this thesis. The decomposition rate in Norway spruce stumps and roots was estimated to be 4.6% annually. Another objective included assessment of the carbon balance trade-offs between the use of stumps for either bioenergy or carbon sequestration. This was carried out over different time scales and harvest intensities and, further, the substitution effect of using stumps for bioenergy in comparison with coal was investigated. The risks of nutrient loss linked to stump harvesting were also studied and discussed. Data from the Swedish national forest inventory and from specifically designed studies on stumps and roots were used for the analyses. The results showed that it takes about nine years for a stump harvest scenario to become more climate-friendly than if coal were used i.e. there is a certain lag period during which the CO₂ emissions from the stump harvest scheme exceed the emissions from utilizing coal as fuel; this is due to higher calorific value in fossil fuels. However, in the long-term, the CO₂ emissions decrease if stumps and roots are used instead of coal. In the medium scenario studied, the CO₂ emissions decreased by 5.0 Tg CO₂ yr-1 - this corresponds to 8.6% of Sweden's current greenhouse gas emissions. It was also shown that the Swedish carbon pool in stumps and roots would start to decrease if more than approximately 107 PJ were harvested annually. Without stump harvesting, the carbon pool in stumps and roots increased over the study period (1984 – 2003) by, on average, 6.9 Tg CO₂ yr-1. Also, the nutrient pools would be at risk if intensive stump harvest schemes after stem and slash harvesting were implemented. However, from a nutrient perspective, depletion of forest soils would be at least risk if a proportion of slash rather than stumps and coarse roots were left after harvesting.


stump; root; carbon; biomass; bioenergy; forest fuel; climate change; substitution

Published in

Acta Universitatis Agriculturae Sueciae
2014, number: 2014:79
ISBN: 978-91-576-8106-5, eISBN: 978-91-576-8107-2
Publisher: Department of Forest Resource Management, Swedish University of Agricultural Sciences

    Associated SLU-program


    UKÄ Subject classification

    Climate Research
    Forest Science

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