Radial trends in black spruce wood density can show an age- and growth-related decline

Context: Wood density variation affects structural timber performance and is correlated with several potentially confounding factors, such as cambial age, position in the stem and growth rate. To date, these relationships have not been comprehensively quantified in black spruce (Picea mariana (Mill.) B.S.P.). Aims: The aim of this study was to describe the variation in annual ring density in black spruce as a function of cambial age, stem height and growth rate. Methods: Radial density profiles from 107 black spruce trees were analysed using a two-stage modelling approach. First, the parameters of a nonlinear function were estimated separately for individual samples. Linear regression was then used to model the parameters obtained in the first stage as functions of internal and external tree descriptors. Results: Annual ring density was high near the pith and declined rapidly in the first 15 annual rings before increasing to more stable values between rings 25 and 60. However, just below 25 % of the samples showed a gradual decline towards the bark, typically after ring 60. Conclusion: Describing and quantifying radial density patterns, including the decline close to the bark, will help further our understanding of the links between tree growth and ring density over the life of the tree.