Triangle of statics
Trunk geometry and the material properties of green wood determine the load-bearing capacity of a tree. For a structure to remain safe the applied load must not exceed the bearing capacity of the structure. This principle is represented by the “triangle of statics” (Wessoly & Erb 2014).
To estimate the worst-case wind load to be considered, the load that a tree must carry at the lower end of a Beaufort 12 storm (hurricane) is estimated using the tree height, the estimated crown area, and the tree species-specific drag coefficient. The influence of tree location on wind speed is also considered (Wessoly & Erb 2014).
Measuring the diameter of the trunk, with a simplified assumption of a circular (or elliptical) cross-section and taking into account tree species-specific material properties, provides an approximate estimate of the load bearing capacity of the stem, in bending ,assuming a solid, defect-free cross-section.