Responses of Scots pine trees to dynamic wind loading

Measurements of wind-induced tree displacement were used to analyze responses of 10 adjacent trees to dynamic wind loading in a planted Scots pine forest. In order to identify the turbulent airflow properties that contribute to the wind energy transfer into tree displacement, the Fourier and wavelet transform were applied. The wavelet transform was used to detect coherent structures in the time series of the fluctuations of the streamwise velocity component above the Scots pine forest canopy. The results demonstrate that strong increases in tree displacement are primarily caused by the passage of coherent structures. However, the coherent structures were superimposed by short-lived gusts. Using Fourier analysis it could be shown that wind energy transfer into tree displacement was very efficient in the range of the natural sway frequency of the sample trees. The findings suggest that greatest tree displacements result from the combined effects of wind loads exerted on the sample trees by coherent structures and short-lived gusts in the range of the natural sway frequency of the sample trees.