Competition and wind loading

Trees in a forest stand are permanently competing for resouurces like light and nutrions, which results in differences regarding the individual tree properties.

Influence of wind direction on wind loading

Wind direction has an impact on the turning moment that an individual tree experiences. For the same wind speed a tree experiences higher turning moment when the wind comes from a direction with less competition.

The plot below shows the competition for tree~4. An extraction track skirts in south-westerly direction of this tree, what results in lower competition than average from this sector. For comparsion the wind speed and turning moment relationship, was analysed for two different wind sectors. The first (blue sector) covers 150-190 degrees and the second (green sector) wind direction 240-280 degrees.

The regression lines for the relationship between squared wind speed and turning moment are statistically significant different. The slope for the two regresson lines are 2.12 (green) and 1.44 (blue), indicating that for the same wind speed the turning moment is higher if the wind is blowing from the direction with lower competition.