Log end face image and stem tapering indicate maximum bow height on Norway spruce bottom logs

In cut-to-length logging, the harvester operator adjusts the bucking in accordance with visible defects on processed stems. Some of the defects, such as a sweep on the bottom of the stem, decrease the yield and quality of sawn products and are difficult for the operator to notice. Detecting the defects with improved sensors would support the operator in his qualitative decision-making and increase value recovery of logging. Predicting the maximum bow height of the bottom log in Norway spruce (Picea abies (L.) Karst.) with log end face image and stem taper was investigated with two modelling approaches. A total of 101 stems were selected from five clear-cut stands in southern Finland. The stems were crosscut and taper measured, and the butt ends of the bottom logs were photographed. The stem diameter, out-of-roundness, and pith eccentricity were measured from the images while the max. bow height was measured by a 3D log scanner at a sawmill. The bottom logs with an eccentric pith had higher max. bow height. In addition, a highly conical bottom part of the stem was more common on the bottom logs with a large max. bow height. Applying both log end face image and stem taper measurements gave the best model fit and detection accuracy (76%) for bottom logs with a large max. bow height. The results indicate that the log end face image and stem taper measurements can be utilised to aid harvester operator in deciding an optimised length for logs according to the bow height.

Taper modeling and economic evaluation of multi-products obtained from wood of short-rotation eucalyptus stands

This study aims at defining the appropriate model to describe the stem tapering of trees of Eucalyptus urophylla x Eucalyptus grandis hybrid, and at evaluating the economic viability of obtaining wood multi-products at different interest rates. The volume of 60 sample trees were determined, and stem tapering was described according to the models proposed by Demaerschalk, Prodan, Kozak, and Ormerod. The best model was used to convert the trees into assortments so that the wood could be optimized for the product that offers the maximum economic return with the minimum possible waste. Then, an economic viability analysis was performed for wood multi-product production, using the Net Present Value (NPV) and applying interest rates of 8 to 12% p.a. The Demaerschalk model is the most appropriate one for the study of stem tapering and assortment determination in short-rotation stands of the Eucalyptus urophylla x Eucalyptus grandis hybrid intended for multi-products in the region covered by the study. The allocation of wood for multi-products is a viable option for stands of the Eucalyptus urophylla x Eucalyptus grandis hybrid, according to the interest rates applied in the present study.