Wind load estimation on an open-grown European oak tree

In this study, we investigate the relationship between the mean wind-induced load on an open-grown oak tree and the mean wind speed. The estimation of the wind load is based on bending moment observations on the stem, using strain gauges installed close to the base of the tree. The measurement campaign included periods where the crown was both with and without foliage. A new post-processing method to compensate for time- and temperature-dependent drifts of long-term strain gauge measurements is presented. The timescale, at which the method is applied, is determined from the observed high coherence between the wind speed and the induced bending moments. The analysis shows that the wind load on the tree is proportional to the wind speed raised to an exponent of 1.60-1.68 and 1.90-2.01 in the case of a crown with and without leaves, respectively. The results indicate that the presence of foliage increases the wind-induced load by a factor of 2-3. The impact of the wind speed range on these results is discussed and compared to the measured wind deficit in the lee of the tree. The application of this method can potentially be extended to other tree mounted sensors.