Urban Tree Root Stability Evaluation – Root Evaluation Based on the Trunk Inclination Baseline Shift

Currently, two widely accepted methods for evaluating tree root stability are the pulling test and the dynamic root stability test. While these methods are considered the most reliable for stability testing, arborists sometimes rely on a more subjective approach. While climbing or working on trees, they may sense that a tree is unsafe based on its movement. This subjective impression often proves accurate, as the tree may fail in high winds or be found unhealthy through instrumental testing. This observation suggests a potential new method for instrumental tree stability evaluation. In experimental work, we measured the inclination changes of several trees while arborists climbed them to capture the vibrations generated during their work. Inclination sensors were placed at the root collar. The test results revealed significant differences between stable and weak trees. For stable trees, the oscillation equilibrium level—essentially the baseline inclination value around which the tree's inclination fluctuated—remained constant. In contrast, this baseline shifted suddenly when climbing an unstable tree, as noted by the arborist. The "bad feeling" described by arborists likely stems from this abrupt change in the inclination baseline. Sudden baseline shifts were also recorded in windy conditions. This behavior presents a new approach to assessing the stability and safety of urban trees.