A model of stem growth and wood formation in Pinus radiata

Numerous factors determine how wood properties vary as a tree grows. In order to model wood formation, a framework that considers the various xylogenetic processes is required. We describe a new model of xylem development and wood formation in pines (parameterised for the commercially important species, Pinus radiata D. Don). In this paper, we use as inputs simulated daily data from the CaBala stand growth model which, in turn, takes into account site and daily weather conditions, and silviculture. It incorporates a first attempt at predicting microfibril angle (the angle of cellulose microfibrils relative to the vertical axis of the cell, MFA) based on metrics of cambial vigour and carbohydrate allocation. It also predicts tracheid dimensions and wall thickness, and from these data, wood density. Pith-to-bark and intra-annual variation in predicted wood properties was realistic across a wide range of site types, although juvenile wood properties were weakly predicted. The model was able to explain 50 % of the variation in outerwood MFA and 70–80 % of the variation in outerwood and mean sample wood density respectively, from 17 study sites. The model, early results from which are very promising, provides a useful framework for testing concepts of how formation occurs, and to provide insights into areas where further research is needed.