Fig. 10.

Mean Fourier power spectra ($f{\stackrel{-}{S}}_{\mathrm{i},\mathrm{k}}(f)$) calculated from time series of wind-induced tilt ($D_{\mathrm{i},\mathrm{j}}$) of the stem of sample trees T1-T3 for the tree-specific momentum flux classes $M{C}_{\mathrm{i},\mathrm{k}}$. The mean frequency associated with the first and second vibration modes are highlighted by ${\stackrel{-}{f}}_{\mathrm{i},1}$ and ${\stackrel{-}{f}}_{\mathrm{i},2}$.