The effect of harvesting logistics on the fuel characteristics of non-comminuted Picea abies
(L.) Karsten (Norway spruce) logging residues from regeneration cuttings was studied in Southern Finland. Roundwood harvesting took place in the summer of 1999. Green residues were forwarded immediately to roadside storage areas for use during winter 1999-2000. Part of the material was left on the felling sites to dry for 4-8 weeks, after which the brown residues were also forwarded to the roadside for storage. Drying/ storage on the clearcut area continued into the fall. Altogether 12 roadside storage piles were made by mid-October 1999, half of them covered. Moisture, needles, and ash contents as well as element composition were analysed at the beginning and during the experiment.
Drying and storage conditions were exceptionally good during summer 1999. The cumulative evaporation of June through August was 150 mm, which was twice as high as the cumulative precipitation over the same period. As a result, the residues in roadside piles reached 22% moisture content in just 4 weeks. At the same time, the residues on the clearcut area in harvester-made heaps fell below the 20% mark, after which drying was much slower. With the approach of the fall and winter, the residue mass started to absorb moisture. As long as the weather was favourable, covering the piles did not seem to have much significance. However, with the increased precipitation, first rain and then snow, the uncovered roadside piles rewetted at a faster rate. This applied to both the green and the brown residues.
The fresh logging residues contained 19.1% needles. Seasoning the fuelstock lowered the percentage to 1.8% on the clearcut area and to 4.0% on the landing. This loss lowered the ash content from 2.1 % to 1.5% during the first month of storage. The concentrations of nutrient elements were correlated with the ash content. Seasoning helped to lower the amount of chlorine from 200 mg/kg to 50 mg/kg.