Predicting wood and tracheid properties of Norway spruce

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Models were developed for predicting the proportion of latewood and average tracheid length in earlywood, as well as wood density, tracheid width, and ratio of cell wall thickness to tracheid diameter in early and latewood, in individual annual rings of Norway spruce ( Picea abies (L.) Karst.). The models had to be applicable as a part of a stand growth simulation system that is based on growth models for individual trees. Data were collected from long-term thinning and fertilisation experiments in Finland and Sweden. The wood and tracheid properties were mainly related to the radial increment rate and ring number counted from the pith outwards. Site index was also a statistically significant variable in most of the models. Increasing the increment rate, caused by thinning or fertilisation, resulted in similar kinds of changes in the wood and tracheid properties, irrespective of the factor promoting radial increment. Even though most of the average values of the wood and tracheid properties were predicted unbiased, there was large random variation between individual trees and annual rings. The variation that accounted for the fixed part of the models was: tracheid length 82.8%, tracheid width 64.9%, cell wall percentage 48.0%, latewood proportion 24.8%, and wood density 21.2%. Thus, the best prediction was for tracheid length. This relationship between radial growth and wood properties will enable the application in growth models aimed at predicting the effects of stand management and environmental factors.