Stubbrytningens klimatpåverkan : en studie av stubbrytningens kortsiktiga effekter på koldioxidbalansen i boreal barrskog

Sammanfattning: Harvesting stumps for biofuel purposes has the potential to reduce the amount of fossil fuel that we use. The climate gain from exchanging fossil- for biofuel can however be offset if the harvesting technique results in higher decomposition rates. Stump extraction causes a significant disturbance of the soil that could result in a net CO2 efflux from increased decomposition. The aim of this study was to determine whether or not stump harvesting can be considered climate neutral in terms of CO2 emissions in a short term perspective. To do this, NEE (net ecosystem exchange) for three years from two areas in a former coniferous boreal forest in central Sweden was investigated. The reference site was clear felled and site prepared, the control site was clear felled, stump harvested and then site prepared. For comparison, the reduced amount of decomposable substrate on the stump harvested site had to be accounted for. This was achieved by calculating the total amount of stump biomass that was removed and then by modelling respiration from its decay using a negative exponential function. The results indicate no increase in CO2 emissions from the stump harvested site, on the contrary it was found to be a smaller CO2 source annually than the reference site. The difference in CO2 fluxes was however not significant (p<0,05). In conclusion stump harvesting can be considered climate neutral in terms of CO2 emissions in a short term perspective. The long term effects of stump harvesting are however still unknown.