Variation of moisture induced movements in Norway spruce (Picea abies)

This paper deals with the variability of moisture induced movements in Norway spruce wood. Totally 987 specimens from 12 well defined trees, six from a fast-grown and six from a slow-grown stand, were studied in detail. A large variation in moisture induced movements was found. The swelling coefficients in the longitudinal direction (alpha (1)) varied between 0.001 and 0.035, in the tangential direction (alpha (t)) between 0.18 and 0.46 and in the radial direction (alpha (r)) between 0.07 and 0.28. Especially for alpha (1) there was an individual variation with distance from the pith for each of the studied trees. For alpha (t) and alpha (r) there was a difference between the trees but no clear variation with distance from the pith. By excluding specimens containing knots and/or compression wood, the variability in swelling coefficients was decreased, especially for alpha (1). The eigenfrequency in the longitudinal direction was the single best parameter, measured in this study, to predict swelling coefficients in all three directions. The variation in eigenfrequency explained 52% of the variations in alpha (1), 67% of the variations in alpha (t) and 52% of the variations in alpha (r). Specimens from the fast-grown stand and specimens containing compression wood were less anisotropic than the other specimens.