The secondary growth response of <i>Pinus pinaster</i> to induced strains demonstrates sensitivity to the full range of chronic winds

Abstract Thigmomorphogenesis, the process by which plants acclimate to mechanical stress through growth modulation, significantly affects biomass allocation but remains underrepresented in integrative tree response models. Specifically, the contribution of chronic, non-injurious wind-induced strains to growth acclimation remains poorly quantified in natural environments. We characterized the secondary growth response to experimental strain stimulus in the stems of Pinus pinaster under forest conditions. Eighteen 12-year-old trees were subjected to transient bending treatments replicating the range of trunk strains generated by local chronic winds, while six trees served as controls. Radial growth was monitored continuously at three trunk positions. The thigmomorphogenetic response was quantified using growth rate amplification and cumulative growth gain, then related to the estimated strain intensity at each position. Mechanical strain induced an immediate, sustained increase in radial growth along trunks. This stimulation persisted over extended periods, pausing only during drought or winter before resuming. Growth modulation scaled proportionally with strain intensity across the full natural range, with no detectable threshold. A consistent strain–response relationship was observed across all trunk positions, indicating spatially homogeneous sensitivity. These results demonstrate that secondary growth in P. pinaster is sensitive to the full spectrum of chronic wind-induced strains. This supports the view that non-injurious winds drive continuous mechanical acclimation contributes to a growth-mediated margin of safety in trees.