Validation of saw log and technological wood assortment recovery and reduction predictions based on cut-to-length harvester data

In this study, assortment yields were studied for Scots pine, Norway spruce, birch spp. (silver and downy birch), European aspen, black alder, and grey alder stand elements. Theoretical assortment yields were calculated using the Ozolinš’ stem taper curve, incorporating tree diameters and heights. The modelled results were compared with actual yields provided by the State Forest Management Centre. During the study, differences in timber assortments and firewood yields were modelled compared to actual data. Changes in wood assortment yields, compared with undamaged and straight trees, depended on the tree species, stand site index, and stand element age. For Scots pine, depending on the stand site index and age, the reduction in log volume ranged from 7 to 28% of the total volume of all assortments. For Norway spruce, it was 5–30%, for birch spp. 30–70%, for aspen 50–90%, for black alder 20–50% and grey alder 5–30%. The increase in firewood volume according to the volume of all assortments was 3–4% for Scots pine, 5–14% for Norway spruce and birch spp., and 5–16% for European aspen. The difference between log and firewood changes represents the change in pulpwood. Over time, the need for new studies arises to adapt to evolving industry practices, including changes in log diameters and quality criteria. The appendix outlines steps that programmers can take to utilize the developed model.