Variations in Brinell hardness of Scots pine wood from mature mineral soil stands in five regions in Finland and Sweden were studied by means of linear mixed models. Hardness was studied from planed tangential surfaces of the specimens, i.e., the force acted in radial direction. One model consisted of only readily available background variables, whereas, in the other model wood density was included as an independent variable. Geographical origin, as well as the longitudinal and radial location of the specimens within a tree was significantly affecting hardness. In addition, if the indentation was placed on latewood section the hardness was clearly higher compared to earlywood and combined earlywood and latewood. With the best fit model approx. 50% of the hardness variation could be described. Wood density was the most important variable affecting hardness and simple linear relationship was found between hardness and wood density. Hardness values based on the diameters of the residual indentations and the initial depths of the indentations were compared, and the differences between these two, as well as the possible sources of error were discussed.

Key words: Brinell hardness, linear mixed model, Pinus sylvestris L., Scots pine, wood quality