Gilman, E.F., J. Miesbauer and F. Masters

Structural pruning effects on stem and trunk strain in wind

Arboriculture & Urban Forestry 41 (1): 1-8

Pruning removes mass and reduces bending in the wind on the pruned stem. However, little is known about the impacts of structural pruning, which leaves some parts of the tree not pruned. This study was designed to measure change in stem and trunk strain (ε) in turbulent wind from reducing the length of one side of a codominant stem pair. Trees were placed in front of a storm simulator with airfoils directing 22 m/s wind at four frequencies f(a) = 0.3, 0.5, 0.7, and 0.9 Hz. Trees were subjected to 30 cycles at each f(a) at each of four pruning doses - 0%, 33%, 66%, and 100% foliage (and associated branch mass) removed from the smaller codominant stem. This resulted in 16 trials on each of five trees. The non-pruned stem of a codominant pair experienced no ε change in wind following reduction or removal of the competing codominant stem. Strain (ε) on the pruned codominant stem and on the trunk below the union where stems join decreased linearly with pruning dose and increased with f(a).