THE CHANGES OF TSUNAMI MITIGATION AND BREAKING RATE OF BLACK-PINE COASTAL FOREST AT DIFFERENT GROWTH STAGES UNDER THINNING MANAGEMENT OF TREES

Abstract

 Coastal forest has some advantages like a trapping of floating debris and/or reducing a tsunami energy, on the other hand, it also has a risk to increase the damage to houses behind forest when trees are broken and driftwoods are produced. However, if the breaking type of trees is an overturn, driftwoods are not produced and a forest still has an effect of trapping debris. If the tree trunk diameter at breast height is thick, the tree trunk is hard to be broken. Therefore, for the proper management of forest, thinning procedure of trees is needed to be periodically conducted. This study uses the characteristics of black pine in Hokkaido and numerical model which includes the tree breaking, and aims to clarify the effect of tsunami mitigation under breaking situation of the trees. To prevent the tree breaking, thinning procedure of trees should be held periodically to promote each tree growth. However, to reduce the tsunami energy through the forest, the density should be high and tree crown height should be small.