Assessment of the effect of thinning on the resistance of Pinus thunbergii Parlat. trees in mature coastal forests to tsunami fluid forces

Hiroyuki Torita; Kazuhiko Masaka; Norio Tanaka; Kenta Iwasaki; Satosi Hasui; Masato Hayamizu; Yasutaka Nakata

doi:10.1016/j.jenvman.2021.111969

Assessment of the effect of thinning on the resistance of Pinus thunbergii Parlat. trees in mature coastal forests to tsunami fluid forces

J Environ Manage. 2021 Apr 15:284:111969. doi: 10.1016/j.jenvman.2021.111969. Epub 2021 Feb 6.

Authors

Hiroyuki Torita¹, Kazuhiko Masaka², Norio Tanaka³, Kenta Iwasaki⁴, Satosi Hasui⁵, Masato Hayamizu⁵, Yasutaka Nakata⁵

Affiliations

¹ Forestry Research Institute, Hokkaido Research Organization, Japan. Electronic address: torita-hiroyuki@hro.or.jp.
² Environmental Sciences for Sustainability, Iwate University, Japan.
³ Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama-shi, Saitamaken, 338-8570, Japan.
⁴ Doto Station, Forestry Research Institute, Hokkaido Research Organization, Japan.
⁵ Forestry Research Institute, Hokkaido Research Organization, Japan.

PMID: 33561759
DOI: 10.1016/j.jenvman.2021.111969

Abstract

The Great East Japan Tsunami, triggered by the earthquake that occurred on March 11, 2011 in the Pacific Ocean, caused significant fatalities and socioeconomic damage. As recovery of a disaster area requires significant time, all possible mitigation measures must be prepared in advance for future events. As a tsunami countermeasure, coastal forests have been acknowledged to considerably reduce tsunami energy and decrease tsunami-related damage. In the Great East Japan tsunami, many trees of coastal forests were damaged by trunk breakage and overturning. This led to further infrastructural damage as the debris were transported landward and seaward by floodwaters. To better protect coastal areas from the secondary effects of tsunamis and reduce tsunami energy, coastal forests must exhibit higher resistance. This research investigated the effect of forestry management by applying different levels of thinning of trees as a means of resistance to tree damage under tsunami events. In October of 1999, study plots were established with different thinning intensities in a mature coastal forest of Pinus thunbergii trees. As a useful indicator of the resistance of coastal forests to tsunamis, the threshold tsunami velocities at which trees in these study plots begin to be destroyed were calculated using a mechanistic model. The results revealed that trunk diameter is the most important parameter for increasing resistance to tsunamis. An analysis of the generalized linear model for diameter growth showed that heavy thinning best enhanced the diameter growth. Therefore, heavy thinning is the most effective approach to increasing the resistance of trees to tsunamis. Considering the relationship between resistance to tsunami and inundation depth, the resistance to tsunami decreased rapidly with increasing inundation depth in all plots. Differences in the resistance to the tsunami were not observed across all plots when the inundation depth exceeded the mean tree height.

Keywords: Coastal forest; Mechanistic model; Resistance to tsunami; Thinning intensity; Threshold tsunami velocity; Tsunami.

MeSH terms

Forests
Japan
Pacific Ocean
Pinus*
Trees
Tsunamis*