Prof. Shuin and his research group found that landslides vary with forest maturity.

2023.09.09 Environment & Sustainability

＊The following sentences are translated by the automatic translation function.

POINT

In Japan, landslides caused by heavy rainfall vary with the maturity of forests.
We compared the amount of rainfall that caused landslides and the amount of driftwood that occurred in artificial forests of different ages. The positive and negative effects of forest maturity on landslides were clarified.
The results of this study are expected to be useful in considering the direction of landslide countermeasures and management of forest resources under climate change.

SUMMARY

It is clear that the landslide prevention function of forests improves with forest maturity. In Japan, landslides caused by heavy rainfall have been decreasing nationwide due to the maturation of forests. On the other hand, recent landslide disasters have seen large-diameter trees washed away as driftwood, increasing the damage. In order to develop landslide countermeasures and to manage forest resources, it is necessary to comprehensively examine the effects of forest maturity on landslides.
In this study, we clarified the positive and negative effects of forest maturity on landslides by comparing surface failures (*1) that occurred in artificial forests of different ages.
A research group led by Tadamichi Sato, a doctoral student at Kyushu University's Graduate School of Bioresource and Environmental Sciences, Yoh Katsuki, a master's student at Kyushu University's Graduate School of Bioresource and Environmental Sciences, and Professor Yasuhiro Shuin of the Department of Environmental Agriculture, Graduate School of Agricultural Science, Kyushu University, compared the 1988 landslide in the former Kakemachi, Hiroshima Prefecture (landslide in a young forest) with the 2017 They compared the rainfall that caused the landslides and the amount of driftwood that occurred in Asakura City, Fukuoka Prefecture, in 2017. The results showed that mature forests are capable of preventing larger-scale heavy rainfall disasters compared to younger forests. However, the mature forests also showed a greater volume of woody debris generated during landslides than the young forests.
In Japan, 67% of the national land area is forested, of which approximately 40% is planted forest. At present, most of the planted forests are in a mature state. In addition, extreme rainfall events are expected to increase in the future due to climate change. This research is expected to contribute to the development of effective countermeasures against landslides and management methods for forest resources under such circumstances.
The research results were published in the British journal Scientific Reports on Thursday, August 31, 2023 (Japan Standard Time).

Figure-1 Radial time variation of the reproduction period of each tank storage volume in the three-stage series tank model for the Kake and Asakura disasters (The black arrows in the figure indicate that the reproduction period of the first-stage tank storage volume is the largest at the time of the occurrence of the disaster, suggesting that the first-stage tank storage volume is involved in the occurrence of the surface failure. The reproduction period for the Kake and Asakura disasters is 23.6 years and 69.8 years, respectively).

Research-related inquiries

Shuin Yasuhiro,Professor

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