Wind-induced tree sways

Conclusions

The question of how the results of investigations on wind-induced tree sways can be used in practice is often posed. First, it must be said that, according to information in the literature, no tree species can survive violent storms (with mean wind speeds over a period of 10 min higher than 30 m/s) without any damage. This threshold value for wind speed is related to the height near the top of a forest stand. Taking the results of the spectral method as a basis for the reduction of storm risk of vital conifers, necessary silvicultural action must be: (1) to influence the amount and frequency distribution of the wind force in such a way that its shere of action becomes more and more unsuitable for tree sways, and (2) to raise the characteristic frequencies of the trees' primary sways because then effective wind force takes on lower and lower values due to narrow-band energy transfer.

Numerous silvicultural methods for achieving these objectives, such as cutting off the tops of crowns or chaining trees together, are described in detail by Rottman (1986).