Revegetation on steep slopes prone to shallow landslides in an abandoned clear-cut plantation forest, Kuma-mura, Kumamoto Prefecture

Abstract

This paper addresses present conditions of revegetated steep slopes susceptible to shallow landslides; and temporal changes in the role of root networks in preventing shallow landslides due to vegetation recovery in abandoned forests after plantation clear cutting. The study site is 0.89 km² and is located near Kuma-mura, Kumamoto Prefecture. To conduct vegetation surveys of present revegetation conditions, we installed quadrats on four slopes: three with steeps lopes of not less than 40 degrees and one with a relatively gentle slope of 30 degrees. Vegetation on steep slopes prone to shallow landslides was poorer than that on the relatively gentle slope. When clears slope are reforested immediately after harvesting, the prevention function increases over time and is restored after approximately 20 to 30 years. Conversely, on slopes abandoned after clear cutting the prevention function is restored after 50 to 60 years due to the slower processes of natural vegetation succession. This indicates that the risk of landslides on steep slopes in abandoned plantations persists for 40 to 60 years after abandonment, considerably longer than in actively managed and re-planted forestry plantations