Modelling the heartwood profile of Douglas fir in France based on the stem profile and other tree dendrometric characteristics - insights from experimental sites and commercial log data

Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) is a softwood species that is becoming increasingly important in Europe. To improve the quality of products for certain specific outdoor uses, there is an interest in limiting the amount of sapwood, the non-durable part, and in enhancing the amount of heartwood. The aim of this work was to develop a model of heartwood distribution in Douglas fir stems, taking tree dendrometric characteristics and silviculture into account. Several statistical models of varying complexity were developed, using sampling data from silvicultural experiments in France. Cross-validation and validation on an independent dataset of commercial logs demonstrated the good performance of the models. Stem size at any height in the tree was the major predictor of the longitudinal heartwood profile. The other dendrometric characteristics of the trees had only minor effects, suggesting limited silvicultural control of heartwood formation. Nevertheless, plausible model behaviour and interesting insights were found for two contrasting silvicultural scenarios, using a growth simulator. A more complete simulation study including additional wood quality criteria should be performed, in order to provide recommendations to forestry practice.