Influence of biomechanics and growing space on tree growth in young Pinus sylvestris stands

We tested hypotheses on the effect of growing space and biomechanics on tree growth, using data from two field experiments where Scots pine seedlings had been planted in a fixed but systematically irregular pattern. After 16 or 18 years, respectively, stem diameter was measured at 1.3 m (d1.3) and 0.3 m above ground (d0.3). Total tree height, length and diameter of the crown, and height to crown gravity point were also measured. Analyses were split in two parts: influence of growing space on tree and crown dimensions, and biomechanical influence of the crown on stem diameter. The results showed that crown size was closely related to tree height, and that there was a small but statistically significant effect of growing space on both crown size and shape. The biomechanical model explained about 85% of the variation in stem diameter, but growing space had no influence on this relationship, indicating that the wind load absorbed by a given crown size was not affected by growing space. The results were discussed in relation to future growth modelling and new ways of estimating site productivity.

Research highlights▶ The growing space available to young Scots pines had a small positive effect on tree growth (total height and stem diameter) and crown size, and a small negative effect on crown slenderness. ▶ Stem diameter at different heights can be estimated with high precision using the biomechanical approach. ▶ The wind load absorbed by a given crown size was not affected by the growing space available to a specific tree.