成功大學校園中常見樹木傾倒行為研究

Many trees fell over and resulted in casualty and property loss in the cities and in NCKU campus even when winds were not strong. This study tries to develop a mechanical testing method to evaluate the strength of a tree against tipping using the results of pulling 120 trees in the Tainan city area . This research also use an electric winch to conduct pulling tests to draw the tipping curve of the Taiwanese tree species, and compare to Wessolly's generalized tipping curve. It is found that Alstonia scholaris, Cassia fistula, and Terminalia mantaly had different generalized tipping curve patterns. The speculated reason may be that the tree species tested in this study were broad-leaved tree species, while the Wessolly's generalized tipping curve is mostly tested with coniferous tree species in natural forest. This study also performed non-destructive pulling tests using winch with the limit inclination set at 0.25 degrees. We analyzed pulling load and inclination for the root plate stiffness, and compared among trees of the same species. The results showed that the root plate stiffness of dying trees was distributed more than 1.5 of standard deviations (SD) lower than the average healthy root plate stiffness. We recommend the root plate of unhealthy trees with lower stiffness than 1.5 SD should be protected to reduce the risk of overturn.