We studied the geomorphological and geological characteristics of four medium- to large-scale landslides that occurred in the alpine and subalpine zones of the northern Japanese Alps and assessed the relationship between landslide features and vegetation diversity in the landslide areas. To achieve this, we conducted field investigation and laboratory work including airphoto interpretation and radiometric dating of soils and fossil logs. Our field investigations indicate that, even in alpine and subalpine zones, landslide blocks (i.e., landslide deposition areas) display specific landforms such as scarplets, shallow depressions, and low mounds with linear or curved forms. Vegetation cover and aquatic areas such as peat bogs and moors also display linear or curved patterns that are superimposed on these small topographic features. We found that the highly diverse landscapes in landslide blocks were substantially different from those in present-day or fossil periglacial slopes near the main ridges, both of which displayed monotonous facies. The specific patterns of vegetation cover seen on landslide blocks probably formed under the influence of different slope environments, with variations of parameters such as inclination, soil properties, thermal-water regimes, and microclimate occurring as a result of landslide activities. Similarly, geomorphic changes such as channel migration and waterfall formation in and around areas of landsliding probably affected biological evolution and differentiation, and resulted in multiple modulations of the gene expression of aquatic organisms. Medium- to large-scale landslides are often reactivated by secondary movement. We suggest that subsequent variations of the landforms in the landslide blocks caused sudden or gradual changes in the surrounding natural environments, which had been forming since the initial mass movement. The biota present in a landslide block is the result of evolution and differentiation during geomorphic changes such as those described here; therefore, it is possible that secondary landsliding resulted in increased biological diversity and complexity.
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