Stubblyftningens initiala effekt på emissioner av växthusgaser från en granmark i Småland

Sammanfattning: In order to reduce greenhouse gas emissions from human activities fossil fuels will have to be replaced with renewable energy alternatives, such as bioenergy. Sweden has a great potential to produce bioenergy derived from forest products and there is currently a great interest within Sweden in using stumps for bioenergy production. However, the environmental consequences of the method need to be investigated before stump removal can be performed on a large scale. Swedish forest soils contain large carbon pools and a different land use may change conditions so that soils that presently act as sinks of carbon could potentially turn into sources of carbon release instead. This study investigates the initial effects of stump harvesting on the emissions of three greenhouse gases, carbon dioxide, methane and nitrous oxide. The emissions were measured from the soil surface in a Norway spruce forest located in the southern part of Sweden. The study was conducted during May and June in 2008. The greenhouse gas emissions were measured from five different parcels, of which 3 were harvested and 2 were controls with no stump harvesting. During this study the emissions of carbon dioxide were 26 % higher from the harvested parcels than the emissions from the controls. There where no emissions of methane or nitrous oxide from the controls or the harvested parcels. There are several factors controlling the rate of decomposition of organic matter. The period when the study was performed was very dry and the decomposition process was probably limited by the low levels of soil water content. Changes in soil temperature and soil water content followed the same pattern on both the harvested and the unharvested parcels (the controls) thus indicating that the increased decomposition of organic matter in the harvested parcels probably was due to a superior oxygen supply. The amount of organic matter was also a determining factor behind the levels of carbon dioxide emissions.