Abstract: [Objective] The theory and method of tree stem strength analysis under wind disaster is studied. The strongest wind that tree could resist is predicted by building the relationship between tree stem strain and square of wind speed. [Method] A new method to measure the combined deformation of tree stem was designed: two strain meters were attached to the stem in orthogonal direction, and another two strain meters were attached to the trunk in the ”X“ pattern with 45° and -45°, then the maximum bending linear strain(stress) and maximum torsional shearing strain(stress) caused by combined deformation of bending and torsion of tree stem can be measured. The maximum strain(stress) had no direct relation to wind direction. [Result] Four spicy camphor trees(Cinnamomum camphora) were selected to perform pulling tests under measurable load to verify the new method, and the results indicated that the measured maximum strain only depended on the output values of the sensors and in no relation with the direction of load. Moreover, the stress transformed by Hooke’s law coincided with the theoretical results. Practical test was carried out on a spicy camphor tree in Hefei, China by combining the technique with anemograph under strong wind. The relationship between tree stem strain and square of wind speed was established, due to which the critical wind speed when tree fractured and the failure mode were predicted, and they conformed to the actual situation.[Conclusion] The tree stem strength analysis method proposed here could be applied to measure and analyze the strain(stress) of tree stem subjected to bending and torsion combined deformation under wind load, and predict the maximum wind speed that tree could bear. As crown area, ventilation rate, height of crown center and eccentric distance of crown and some other parameters that difficult to measure did not need to estimate, the new tree stem strength analysis method could provide forest and city garden trees a direct and effective method to assess the resist ability to wind disaster.

Key words: wind disaster, stem strength