Three-dimensional model for size and location of resin pockets in stems of Norway spruce

Resin pockets, being an important natural characteristic for wood quality and tree physiology, were observed on the surfaces of boards sawn from four large Norway spruce (Picea abies (L.) Karst.) trees and analysed for size and distribution. Axial length varied between trees and increased from pith to surface and from butt to top; however, three quarters of the variation were random and normally distributed. Also resin pocket frequency varied between trees. Within the stem, the resin pockets remained independent and randomly distributed following the exponential distribution in all three directions: radial, angular and axial, corresponding to a constant probability during the lifespan of the tree. No association between size and frequency was identified. The initiation and the expansion of a resin pocket appear to be controlled by two different physiological processes. The findings should add to the understanding of resin pocket formation in spruce and should be applicable to wood quality modelling.