The study is based on data from the first 6 sites of a 14 sites survey, covering a range of growing conditions in south-eastern Norway. The timber was strength-graded with Dynagrade before modulus of elasticity (MOE), modulus of rupture (MOR) and density were tested. Linear mixed models with random effects of tree and site were used to analyze the variations in the bending properties, and preliminary models based on objective parameters from simple measurements in the forest were developed. Models based on IP-value from Dynagrade were used for comparison, and the additional effects of data measured on tree-, log- and board level were quantified.
The results show that using only IP-value obtained from Dynagrade as fixed effect in models predicting MOE and MOR, respectively, explains almost the same amount of variance as a combination of stand- and tree characteristics. It can also be shown that different parts of the variance are explained. While the stand- and tree variables explain more of the site effect, IP-value explains more of the tree effect. The best models used IP-value and density as fixed effects, and reduced the residual variance of MOE with 68 % and that of MOR with 53 %. Models combining IP-value with stand- and tree characteristics were almost as good. These models show a potential in using forest inventory data to increase the accuracy of strength grading by Dynagrade. A MOR model using IP-value, site index, altitude and relative breast height diameter as fixed effects reduced the variance with 49 %. This shows that such models can be used for presorting of logs in order to locate proper resources for particular products, and it can be used for optimizing the bucking and allocation of logs to the sawmill.
Keywords: strength grading, stand characteristics, tree characteristics, Norway spruce
Authors
Fischer C.
Norwegian University of Life Sciences (UMB), Department of Ecology and Natural Resource Management, Ås, Norway
Vestøl G. I.
Norwegian University of Life Sciences (UMB), Department of Ecology and Natural Resource Management, Ås, Norway
Høibø O. A.
Norwegian University of Life Sciences (UMB), Department of Ecology and Natural Resource Management, Ås, Norway
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