Towards more accurate grading: non-destructive methods for assessing low-quality sawlogs

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Abstract

At times of bark beetle infestation, the sawmill industry uses mainly low-quality logs with a high proportion of salvage logging. Some countries of Central Europe, including the Czech Republic, have been greatly affected by such insect attacks as they significantly reduce the quality of sawn timber. To minimise the losses, non-destructive methods are needed to detect infestation early. Thirty Norway spruce sawlogs from loggings affected by bark beetle were processed and visually graded according to EN 1611-1 (CEN (1999) EN 1611-1:1999 – sawn timber – appearance grading of softwoods – part 1: European spruces, firs, pines and douglas firs. Brussels: European Committee for Standardization). The commonest defects were knots, but other defects such as soft rot, deep insect attack, and deep cracks had the most significant effect on quality. These defects were best detected by computed tomography using a MiCROTEC CT log scanner. The frequency-resonance method resulted in poorer coefficients of determination from R 2 = 0.004 to R 2 = 0.29 when predicting qualitative yield and therefore cannot be recommended when visually grading sawn timber. The Recommended Rules for Measuring and Grading of Roundwood in the Czech Republic 2008 should be adapted to the current situation in the industry by dividing grade III.D into two subclasses.

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