Landslide-induced changes of soil physicochemical properties in Xitou, Central Taiwan

- Landslide disrupted pedogenic development and left immature soil
- Soil properties were significantly changed after landslide deposition.
- Soil organic carbon and total nitrogen decreased following landslides.
- Landslides are expected to influence functions in forest ecosystems

Steep mountain terrain, fractured geological environments, and intense precipitation events are primary factors that contribute to frequent landslides in mountainous regions. Landslides exert an immense impact on forest ecosystems and substantially change soil properties; understanding these changes is crucial to facilitating subsequent forest revegetation and management. In this study, the effects of landslide on soil physicochemical properties were investigated in a moist montane forest ecosystem in Xitou, Central Taiwan. We established a dataset comprised historical soil survey data obtained in 1976 and data from soil samples taken in 2012 at the same locations to compare differences in soil properties after landslide deposition, and also conducted soil sampling along a landslide/nonlandslide affected sequence to determine how the degree of landslide deposition affected soil physicochemical properties. The results indicated that rock fragment content, soil pH value, bulk density, inorganic carbon, and base saturation increased following landslide deposition and that severe landslide deposition caused more substantial increases. By contrast, the thicknesses of the O and A horizons, soil organic carbon, total nitrogen, and cation-exchange capacity significantly decreased following landslides; these decreases were more substantial with increasing degree of landslide deposition. Exchangeable potassium, calcium, magnesium, and available phosphorus content, however, were unaffected by landslide deposition. The results demonstrated that soil physicochemical properties were significantly altered after landslide deposition; these resultant changes, particularly in regard to high soil pH value, poor structure, and low soil organic carbon and total nitrogen, are expected to influence functions in forest ecosystems.

Conceptual model for soil properties in Xitou, central Taiwan. (a) Landslide deposition occurs during the typhoon and rainstorm, and the geomorphological process disrupts pedogenic development and leaves behind immature soil with little development or low profile differentiation. (b) The pedological process on the nonlandslide areas allow soils to develop differentiated and organized profiles and accumulate more organic matter.144