Wind Measurements in a Pine Forest During a Destructive Gale

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Abstract
Anemometer readings were recorded during a gale which blew down some of the trees in an even-aged 16 m stand of Pinus sylvestris on sandy soil at Thetford forest. Gusts at the top of the canopy attained 17⋅5 m/sec. Wind profiles agreed well with the theoretical logarithmic profile above the canopy and the exponential profile below. During the gale the zero plane displacement and roughness length values were similar to those at lower wind speeds. It is therefore possible to estimate wind profiles and the forces to which a tree in the crop is subjected from measurements of wind speed at a single point within or above the forest. The wind speeds which blew trees down were much lower than those predicted as necessary from ‘tree pulling’ studies in the same forest. This discrepancy suggests that any consideration of windthrow must take into account the effects of tree vibration on the deterioration in the strength of the root-soil complex.