Crown structure of European beech (Fagus sylvatica): a noncausal proxy for mechanical–physical wood properties

The current tendency towards the silvicultural promotion of mixed tree species has increased the variability in the crown structure within stands. This study shows how neighbouring trees can influence both the external crown features and internal wood properties of trees. Using terrestrial laser scanning, the crown features of 100 European beech trees (Fagus sylvatica L.) from pure beech stands and mixed stands of beech with Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Norway spruce (Picea abies (L.) Karst.), sessile oak (Quercus petraea (Matt.) Liebl.), and Scots pine (Pinus sylvestris L.) were recorded. After felling and sawing, the dynamic modulus of elasticity was determined on 1623 boards from the two lowest 4.1 m logs. Significant differences were found between beech trees from pure stands and those from beech–pine mixed stands in terms of crown volume (415 vs 766 m3), crown ratio (50.0% vs 71.5%), crown projection ratio (0.182 vs 0.253 m·cm−1), and branch angle (30.7° vs 54.1°). Multiple regression mixed models revealed significant relationships between timber stiffness and crown volume (–1.7 N·mm−2·m−3), crown ratio (–28.4 N·mm−2·%−1), and crown projection ratio (–9835 N·mm−2·m−1·cm). Thus, the crown morphology of broad-leaved species reflects the tree’s long-term competitive status and suggests indicators for the assessment of mechanical–physical wood properties.