Abstract
The aim of the study was to model and analyse the effect of length on grade yield of timber from different stem parts in Picea abies, and to use the models to simulate the cost of reduced grade yield due to increased length. The boards were simulated having lengths ranging from 20 to 60 dm starting at stump level, 4 m above stump level and 8 m above stump level, respectively. Logistic regression models showed that length had a significant effect on grade yield, and this length effect was stronger in strength grading according to INSTA 142 (IN) compared to appearance grading according to Nordic Timber (NT). The length effect was most pronounced in butt logs, and somewhat greater in middle logs compared to top logs. Also a smaller length effect in inner boards compared to boards farther from the pith was found for IN-grading. The cost of the decrease in grade yield with increasing length will depend on the assumptions about the price gap between the grades. Current market prices in both grading rules gave a decrease in value of the sawn timber in stock by about 6% with an increase in the log length from 45 to 60 dm. In addition, a decrease in yield of timber in longer logs will amplify this effect, while a higher efficiency in the production process will diminish it.
Zusammenfassung
Ziel dieser Untersuchung war es, den Einfluss der Länge auf die Ausbeute von Fichtenschnittholz aus verschiedenen Stammabschnitten in den einzelnen Sortierklassen zu modellieren und zu untersuchen und mit Hilfe der Modelle die Kosten des Ausbeuteverlustes aufgrund zunehmender Länge zu simulieren. Für die Simulation wurden Bretter von 2 bis 6 m Länge aus drei Stammhöhen (Fällschnitt, 4 m, 8 m) verwendet. Spezielle Regressionsmodelle zeigten, dass die Länge einen signifikanten Einfluss auf die Ausbeute in den Sortierklassen hatte und dass dieser Längeneinfluss bei der Festigkeitssortierung gemäß INSTA 142 (IN) stärker ausgeprägt war als bei der Sortierung nach dem Aussehen gemäß Nordic Timber (NT). Der Längeneinfluss trat am deutlichsten in den Erdstammstücken hervor und war im mittleren Stammabschnitt größer als im Zopfstück. Darüber hinaus war der Längeneffekt bei der Festigkeitssortierung bei marknahen Brettern geringer ausgeprägt als bei markfernen Brettern. Die Kosten einer sinkenden Ausbeute in den Sortierklassen aufgrund zunehmender Länge hängen von den angenommenen Preisscheren zwischen den Sortierklassen ab. Auf der Basis der derzeitigen Marktpreise führt ein Anstieg der Länge von 4,5 auf 6 m bei beiden Sortierverfahren zu einer Wertminderung von insgesamt 6%. Daneben wird dieser Effekt durch eine Abnahme der Schnittholzausbeute bei längeren Stammabschnitten verstärkt, wohingegen die höhere Produktionsleistung diesen mindert.
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Øvrum, A., Vestøl, G.I. Modeling the effect of length on yield of sawn timber grades in Norway spruce (Picea abies (L.) Karst.) . Eur. J. Wood Prod. 67, 63–70 (2009). https://doi.org/10.1007/s00107-008-0286-9
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DOI: https://doi.org/10.1007/s00107-008-0286-9