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Modelling the effects of timber length, stand- and tree properties on grade yield of Picea abies timber

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When the grade is determined by the worst part of a board, the grade yield will decrease with increasing timber length. This length effect varies due to longitudinal variation in the grading features and their appearance on the sawn surface. In this study models identifying the length effect's dependence on site, stand, tree and log-level characteristics have been developed. The study comprised boards from 160 Norway spruce trees (Picea abies (L.) Karst.) sampled from six sites in Norway which were selected based on variation in the occurrence of ramicorn branches, forked trees and sinuosity of stems. The boards were visually graded according to appearance by Nordic Timber and strength was graded by INSTA 142. The negative effect of increasing length on grade yield was strongest at stump level and decreased upwards in the trees. The biggest trees within a stand were most affected by an increase in length. In addition to timber length, position of the board within the tree was the most important factor influencing grade yield. The variation in grade yield within stands was greater than between stands for this material. The models predicting grade probabilities seemed to fit within a 10% margin.
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Keywords: Length effect; Norway spruce; Picea abies; multinomial logistic regression; timber grading

Document Type: Research Article

Affiliations: 1: Norsk Treteknisk Institutt (NTI), Oslo, Norway,Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences (UMB), Ås, Norway 2: Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences (UMB), Ås, Norway

Publication date: 2011-04-01

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