This study proposes an advanced evaluation method to assess the capacity of lodging trees to resist tsunami, considering environmental conditions such as root depth and tree density. Field experiments aimed at determining the resistance force of lodging trees were carried out. The results indicate that the critical moment of lodging trees corresponds to the bending strength of the trunk, the section modulus measured at chest height, and are related to the parameter β (representative of tree growth environment). The correlation between field measurements and the estimated value was better than the ones previously obtained. β depends on the diameter of trees at chest height, tree density and sand thickness above the top of the roots. Therefore, increasing sand thickness on top of the roots appears to be one of the strengthening methods which will maintain tree stability. However, it should be noted that the method can be applied only to Pinus thunbergii.
