Mean and maximum two dimensional wind force on an open-grown tree

The accurate quantification of the wind loading on trees is crucial for estimating the risk of tree damage. Here, we present an experimental quantification of the wind force on a rural, open-grown, deciduous tree. We first demonstrate that the amplitude and direction of the two-dimensional force vector can be estimated using two strain gauges mounted on the bottom of the stem. Secondly, we show that the dynamic response of the tree along the mean wind direction shows differences from that in the transverse direction, indicating the importance of studying both force components. Subsequently, the analysis is focused on the mean and maximum wind force over a wide wind speed range. During winter, both the mean and maximum force is described by a quadratic wind speed dependence, whereas during summer, an adjustment is needed to account for the reconfiguration of the leaves. This adjustment is parameterized using the same functional relationship for the mean and maximum force. Overall, in the wind speed range between 4–11 ms−1 the maximum wind load was 49%–66% and 52%–79% larger than the mean, during the summer and winter, respectively.