Forest biomass for energy is harvested on sites where it is profitable. The criteria include demand, sufficient volume and ecological factors such as nutrient status. The drain of nutrients is prevented by delimbing thinning wood and by restricting residue harvesting to areas where it is not harmful, as proven by studies. At least a third of the residues are always left on the site.
Metsähallitus harvests biomass together with other logging, collectively known as integrated harvesting. With the increasing use of biomass, nowadays there is need for wood obtained from first-thinning sites as well.
Forest biomass includes residues, whole trees, small-diameter stemwood and stumps. Small-diameter stemwood may contain minor amounts of timber suitable as pulpwood and sawlogs, if this is a way to get a better margin on the wood through higher price or lower cost.
Forest biomass is sold to regular business partners including delivery, i.e. it is supplied to power plants either as ready-made chips or as stems and tops. Some biomass lots for sale are announced in a sales catalogue issued once a year. These lots are sold according to offers, and the wood is delivered either to the power plant or to the roadside with the buyer responsible for chipping and transportation. Metsähallitus normally deals in wood-based energy by the megawatt hour.
Forest biomass is sold after a minimum of one drying season. Trees and stumps are dried either in the forest or at the roadside. If the moisture content of the biomass is 40%, one tonne will yield some 3 Mwh of energy. At a moisture content of 25% one tonne gives nearly 4 Mwh, but if the wood has become wet or the load contains snow and ice, the yield may remain below 1.5 Mwh/t.