The decline of Pinus thunbergii and P. densiflora trees in coastal forests from the mega-tsunami following the Great East Japan Earthquake

Abstract

The mega-tsunami generated by the Great East Japan Earthquake on 11 March 2011 devastated coastal forests on the Pacific seaboard in northeastern Japan, mainly composed of Pinus thunbergii and P. densiflora. After the tsunami hit, decline and resulting death occurred in the remaining pine trees, which arouse concern about the availability of pine trees in restoring the devastated coastal forests, although the extent and factors of the tree decline were unclear. We monitored the decline and death of P. thunbergii and P. densiflora trees individually at the study plots set in six locations showing different types of tsunami damage for two years. During the monitoring period, mature P. thunbergii trees showed good survival, suggesting their resistance to the tsunami damage, unless they seemed to suffer from strong stress from shading before the disaster, physical damage by the tsunami or poor drainage condition of the soil. By contrast, P. densiflora was more vulnerable to seawater inundation. From those results, we could present aconcrete argument for the relevance of P. thunbergii for use in coastal plantations, as is historically approved in Japan, and the importance of securing drainage to make coastal forests more resistant to tsunami damage.