Mixed coastal forests are less vulnerable to tsunami impacts than monoculture forests

Previous studies have examined whether the magnitude of tsunami impacts on coastal forests differs according to the density and size structure of the trees. However, few studies have focused on how monoculture/mixed forest settings and tree spatial arrangements in coastal forests can mitigate tsunami impacts. Here, satellite images and aerial photographs taken before and after the tsunami events triggered by the Great East Japan Earthquake on March 11, 2011, were used to compare the degree of damage to coastal forests between monoculture (black pine only) and mixed forests (black pine and other broad-leaved tree species) as well as between forests with different tree planting spatial patterns. We found that mixed coastal forests were less vulnerable to tsunami impacts than were black pine monoculture coastal forests, and that mixed coastal forests with a more complicated spatial structure were less vulnerable than were simply structured mixed forests. The functional complementarity of mixed coastal forests leads to enhanced tree growth and physical stability, which may decrease the vulnerability of these forests to tsunami impacts. Maintaining mixed coastal forests with black pine and increasing forest spatial complexity is critical for the management of coastal forests to mitigate effects of tsunami disasters.