The effect of a super typhoon to a mangrove forest in Iriomote island

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K14946
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Forest science
• Research Institution: University of the Ryukyus
• Principal Investigator: WATANABE Shin 琉球大学, 熱帯生物圏研究センター, 准教授 (10396608)
• Research Collaborator: MIYAGI Toyohiko ; UCHIYAMA Shoichiro
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: マングローブ / 大型台風 / ドローン

Outline of Final Research Achievements

In Iriomote island located at south western islands of Japan, we monitored mangrove forest hit by a super typhoon. As the result of the traverse survey, it was found that the ground level of the devastated area was lower by 30 to 50 cm than the ground level covered by mangrove trees. It was also revealed by our flight researches that the devastated area has been growing year and year.
It was thought that the mangrove forest collapse in a fairly large area by typhoons induced soil erosion because the forest floor lost the forest crown to protect from rainfall. At the same time, the complex root system to keep mangrove peat stably from daily inundation was lost. And it was also suggested that the dynamics of large-scale soil degradation and inundation has caused continuous soil erosion, thus the continuous forest degradation has been also induced like domino effect. The changed ground level might not provide suitable ecological niche for the present mangrove species anymore.

Free Research Field

森林科学

Academic Significance and Societal Importance of the Research Achievements

本研究ではドローンと実地調査によるモニタリングを3年間継続し、西表島のマングローブ林が年々大型化する台風の影響で失われ続けている現状を確認し、その崩壊メカニズムを解明した。そしてマングローブ林が失われることにより、大量の土砂が林外へ流出していることも明らかとなり、河口域の汽水生態系と沿岸域珊瑚礁生態系へ及ぼす悪影響が懸念された。また本研究対象のマングローブ林大規模倒壊現象は、70年以上前の太平洋戦争に伴う過度のマングローブ伐採と近年大型化した台風による被害との複合災害であることが示唆された。