Landslide Susceptibility Mapping for Subalpine Grassland Using Frequency Ratio and Landslide Index Model

Abstract. Subalpine ecosystems are highly fragile as compared to biological and environmental factors. Landslide is one of the ruinous upshots of this ecosystem. One of the impressionable areas in the cause of natural factor is Masoleh watershed in western Alborz Mt, (Iran). In order to landslide hazard zonation, landslide index and frequency ratio method based on twelve causative factors such as slope, slope aspect, land use, lithology, distance from faults, distance from road, distance from stream, rainfall, range condition, Stream Power Index (SPI), Component Topographic Index (CTI) and elevation Receiver Operator Characteristic (ROC) curve analysis method was also used to evaluate the model. The results showed that geological, physiographical and grassland conditions have an important role in landslide area. Overgrazing, grazing in forth of season, early grazing, late term egression, and excess livestock are considered as direct affecting factors on vegetation, so that they have simultaneous role to make the landslide risk. The verification results via ROC curve showed that the landslide index model (85%) performed slightly better than the frequency ratio model (82%). It was concluded that managers and protectors of this ecosystem can inhibit and conserve the landslide by decreasing the amount of livestock, and short-term exclosure on critical area, and biomechanical dams in landslide-occurred area.