Models of internal knot properties for Picea abies

Abstract Models describing the variation in internal knot properties of Norway spruce (Picea abies (L.) Karst.) in Sweden were developed. The sawlog portion of 114 mature trees was scanned using computer tomography in order to identify internal knots and measure knot dimensions (knot size, sound-knot length, loose-knot length). The variation of both maximum and mean knot diameter per whorl was described in terms of a non-linear segmented (hyperbolic–quadratic–quadratic) model, and as a function of several stand variables, tree variables, and height above ground. The number of knots per whorl was described in a linear model as a function of the distance between whorls and site index. Sound-knot length was modelled in a linear mixed model with knot diameter, height above ground, and diameter at breast height (DBH) as predictors. Loose-knot length was described as a function of relative knot diameter and DBH in a mixed log-linear model. This family of models was intended to be integrated in a decision support system for sawmill conversion simulation studies applicable to merchantable trees in mature stands.

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