Only long-term environmental gains from forest fuel
Stumps and roots are not exactly an ideal fuel if you are looking to achieve an immediate climate effect. In fact, according to a recent doctoral thesis, they are worse than coal.
If half of the production capacity at Ringhals Nuclear Power Plant, corresponding to 14 TWh, were to be replaced with harvested stumps, it would take nine or ten years for the stumps to be more climate friendly than if an equivalent amount of coal were used. Initially, burning stumps releases more CO2 emissions than using fossil fuel, since fossil fuels generate more energy per unit of CO2 emissions.
However, the level of CO2 emissions generated using stumps and roots instead of coal decreases after ten years due to the decomposition rate of the different fuels when left untouched in nature. When stumps and roots are used instead of coal, the only emissions produced are from the combustion of the stumps and roots, rather than from both combustion and decomposition, which is the case with coal. Over time, using stumps in the same scenario of 14 TWh would reduce the level of fossil-fuel CO2 emissions by five million tons per year, corresponding to 8.6% of Sweden’s current annual greenhouse gas emissions.
Ylva Melin has compared the amount of carbon dioxide released into the atmosphere and the amount of carbon remaining in stumps and roots, from year to year in various scenarios. A central component of the project is the speed at which the stumps decompose, specifically the delay in the release of carbon dioxide when stumps are left untouched rather than immediately incinerated.
For environmental reasons, deciduous stumps are currently left in nature, as is a large portion of spruce and pine stubs in certain areas.