Calculations of carbon circulation made by Mr Göran ?gren and Ms Riitta Hyvönen, researchers at the Swedish University of Agricultural Sciences, demonstrate that bio energy from forests and cultivated fields are practically carbon dioxide neutral and that they do not disturb natural circulation.

Their calculations also demonstrate that multi annual energy crops bind more carbon dioxide than what alternative, annually renewable cultivated plants do.
When harvesting more bio-fuel from forests, not only tree trunks, but also wood left over at thinning, fungus infested wood, branches and tree tops are collected.
Needles and leaves should be left lying in the forest in order to leave most of the nitrogen in the growth place. Nevertheless, some nitrogen fertilizing is probably necessary in the long term. Considerable quantities of calcium, magnesium and potassium remain in the ashes after combustion. These wood ashes should be recycled to the forest, or to the bio energy cultivation.
An important additional aspect is that wood energy works as a substitute to other fossil fuels and therefore when used decreases the carbon dioxide emissions.