Influence of coastal forest width and stand density on tsunami mitigation in coastal forest management

Abstract

The concentration of population along coastlines increases vulnerability to climate change-related natural disasters, such as storm surges, wind damage, and tsunamis. Coastal forests, as infrastructure, play a crucial role in mitigating these risks. In tsunami-prone countries like Japan, coastal forests are particularly valuable. Coastal forests mitigate disasters during tsunamis and storm surges by reducing fluid force and trapping drifts; previous studies on tsunamis have confirmed the protective effects. However, since forests change their complex structure as they grow, the effects of tsunami mitigation also continue to change. To comprehensively understand the impact of forests on tsunamis and establish effective forest management methods, it is necessary to clarify the tsunami mitigation effect of forests according to their growth phases. This study conducted numerical simulations to investigate the effects of forest width and stand density on tsunami mitigation in nine coastal Japanese black pine forest patterns at different growth phases. Forest widths were set to 100, 200, and 300 m. Stand density was quantified using the relative yield index (Ry) and classified into high, medium, and low stand density, respectively. The results showed that increased stand density or forest width reduces fluid force. The tree destruction mode depended solely on forest management, which was linked to stand density. Furthermore, management patterns with medium or low stand density are preferable to avoid secondary damage from stem breakage caused by huge tsunamis. These results provide valuable insights into coastal forest management.