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Norway spruce (Picea abies (L.) Karst.) stump wood is a potential source of bioenergy in Finland. The heating value of stump wood depends on, among other things, the moisture, carbon and ash content of the wood. In this study the moisture content of Norway spruce stump wood was examined immediately after harvesting at the clear cutting area and after different drying times at the roadside storage sites. Immediately after stump harvesting the average moisture content (wet basis) was 53%. The stump wood dried fairly fast during spring and summer. One month after stump harvesting, the average moisture content was about 31%. If the stump wood had dried well once, water absorption became very weak and the moisture content increased only slightly in the late autumn. Each spring and summer the moisture content of the stumps was lower than during the previous year. Annually the lowest moisture content was observed at the beginning of July and the highest at both the beginning and the end of the year. The moisture content of stump wood followed an upwards opening parabola over a one year period and was repeated each year. Three years after harvesting the heating value of the stump wood was still 5.241 MWh/ton. Overall, when harvesting took place in the spring or early summer, the stump wood was combustible after a one month drying period immediately after harvesting.

The measurement of the amount of energy wood can be based on volume (m 3 ), weight (kg) or energy content (MWh). All of the previous units of measurement are being used today. However, measuring wood is problematic. Physically the measuring can be made in the forest, at the roadside storage site or at the heating plant. Nowadays crane scale weighing in the forest is the commonly used and accepted technique. In this study the differences, variations and correlations between the different energy wood measurement methods are examined. The whole supply chain from the forest to the heating plant was tracked. The material was collected from young stands and it was based on about 14,300 m 3 solid (12.7 million kg) energy wood from 75 worksites. There was a strong correlation (r 2 00.87Á0.98) between the values given by the different measurement methods throughout this study, although a remarkable weight loss (37%) between the forest and the heating plant was observed. Moreover, the solid volume factor 0.49 with SD 0.07 between the chips loose volume and the calculated solid volume, based on the crane scale, was higher than the 0.40 factor that is normally used in practice.

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