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[HGG01-01] Landslide as a geomorphic process to cause the diversity of plant species in the Shirakami Mountains, Northeast Japan
★Invited Papers
Keywords:landslide, microtopography, forest, diversity, Shirakami Mountains
The Sirakami Mountains located in the Aomori and Akita prefectures in Japan which has been registered as a World Natural Heritage area are widely covered with deciduous broadleaved forests. Slopes formed by past slow movement landslides are densely distributed there. As landslides are the major geomorphic processes which often induce disasters tends to occur in relation to fragile geology mainly of the Tertiary strata, steep sloping terrain and heavy-snowfall climate. They often interrupt road traffics and supply heavy sediment load to downstream areas.
Since the rupture surface of a slow movement landslide is generally deeper than tree root depth, forest damage areas do not tend to extend widely in the slopes. Barren slopes appear at a head scarp which usually originates from the rupture surface and a steep toe of the landslide body due to slope failure and/or riverbank erosion. On a landslide body whose gradient is usually gentler than the head scarp, stress of tension and compression due to landslide movement forms cracks, hollows and upheaved hills resulting in fallen trees or lean of tree stems.
It was pointed out that complicated micro-topographies of a landslide slope often prepare spatial difference in soil moisture and surficial erosion and deposition conditions may cause the diversities of plant species in and around a landslide slope in the Shirakami Mountains (Mishima et al, 2009). Only shrub type plants or grass can grow on the steep slopes of a tall head scarp annually affected by snow avalanches.
Other study on the vegetation recovery after the landslide occurrence in 1999 reveals that the ratio of the pioneer species to the species of beech (Fagus crenata) forest and intermediate species originating from a small patch of beech forest on the landslide body decreased from 41.3% in 2007 to 31.0% in 2014 (Higaki, 2022). Plenty of slopes formed by landslides indicates various spatial and temporal occurrences of slope movements in the Shirakami Mountains. It is inferred that different succession stages of forest plant species after landslide occurrences might exist thus continuing various plant species.
Slow movement landslide might be a geomorphic process to cause the diversity of plant species in the cool-temperate deciduous broadleaved forest by producing complex slope microtopography and the space for forest plant succession in the Shirakami Mountains. While landslide disaster risk management is a quite important global issue, geo-ecological approaches to landslides especially of slow movement type also seem to be required.
Since the rupture surface of a slow movement landslide is generally deeper than tree root depth, forest damage areas do not tend to extend widely in the slopes. Barren slopes appear at a head scarp which usually originates from the rupture surface and a steep toe of the landslide body due to slope failure and/or riverbank erosion. On a landslide body whose gradient is usually gentler than the head scarp, stress of tension and compression due to landslide movement forms cracks, hollows and upheaved hills resulting in fallen trees or lean of tree stems.
It was pointed out that complicated micro-topographies of a landslide slope often prepare spatial difference in soil moisture and surficial erosion and deposition conditions may cause the diversities of plant species in and around a landslide slope in the Shirakami Mountains (Mishima et al, 2009). Only shrub type plants or grass can grow on the steep slopes of a tall head scarp annually affected by snow avalanches.
Other study on the vegetation recovery after the landslide occurrence in 1999 reveals that the ratio of the pioneer species to the species of beech (Fagus crenata) forest and intermediate species originating from a small patch of beech forest on the landslide body decreased from 41.3% in 2007 to 31.0% in 2014 (Higaki, 2022). Plenty of slopes formed by landslides indicates various spatial and temporal occurrences of slope movements in the Shirakami Mountains. It is inferred that different succession stages of forest plant species after landslide occurrences might exist thus continuing various plant species.
Slow movement landslide might be a geomorphic process to cause the diversity of plant species in the cool-temperate deciduous broadleaved forest by producing complex slope microtopography and the space for forest plant succession in the Shirakami Mountains. While landslide disaster risk management is a quite important global issue, geo-ecological approaches to landslides especially of slow movement type also seem to be required.