How wind acclimation impacts Pinus pinaster growth in comparison to resource availability

Abstract

Abstract Key message Anthropic and natural disturbances in Pine pinaster forests may induce changes in tree wind exposure and resource availability. The wind acclimation has consequences on P. pinaster growth comparable to resource acquisition after sudden changes in micro-environmental conditions. Context More disturbances occur within the forest, resulting in the creation of inter-tree space. This increases resource availability for the remaining trees but also their wind exposure. Trees have the ability to acclimate to these changes in their micro-environmental conditions by modifying their development. Increase in both resource availability and wind-induced deformations (strains) are known to promote tree radial growth but their relative importance has not been previously analysed in field conditions. Aims This paper aims to study the Pinus pinaster growth in response to a sudden change in wind loading in comparison to a rapid increase in resource availability. Methods An experiment was established in a 16-year-old P. pinaster to create different conditions of wind loading and resources by guying trees with wires and removing their neighbours. The increase in trunk volume below 4 m was monitored for 3 years by measuring the stem radial growth at three stem heights. Results Acclimation to wind has important consequences for stem growth, comparable to that of the effect of greater resource availability after an increase in inter-tree spacing. The increase in trunk volume below 4 m induced by wind and by having more resources were quantitatively close and were equivalent after 3 years of treatment, to the trunk volume increase during the year before experiment. The observed wind acclimation was interpreted in terms of tree mechanical reinforcement by calculating the gain in the stem flexural rigidity: mechanical strength gains of 13.8 and 20.3% of swaying trees were observed in comparison to guyed trees for both high and low resource levels, respectively. Our analysis suggests that the relative effects of wind loading or higher resource are not modified over time by seasonable growth modulation. Both the effects of the wind acclimation and the higher resource were found to be independent and are likely to be cumulative. Conclusion This study highlights the importance of considering wind acclimation in the regulation of growth in forests after a sudden change in environmental conditions.