[H-GM04] Geomorphology

[HGM04-P07] An analysis on decadal-scale vegetation recovery after landslide events using LiDAR data: A case study of granitic slopes in the Echi River Basin, Shiga Prefecture, Japan

*Nanami Kinoshita¹, Tsuyoshi Hattanji², Takuro Ogura³, Toshiaki Mizuno⁴, Nagahiro Kojima⁴ (1.University of Tsukuba, Graduate School, 2.Institute of Life and Environmental Sciences, University of Tsukuba, 3.Graduate School of Education, Hyogo University of Teacher Education, 4.Lake Biwa Environmental Research Institute)

Keywords:LiDAR, Digital Elevation Model, Digital Surface Model, Elevation, Japanese red pine community

This study evaluated vegetation recovery in landslide scars in a granite area of the Echi River basin in Shiga Prefecture, Japan. This study used a digital surface model (DSM) and a digital elevation model (DEM) from airborne LiDAR data in 2022. The elevation data of the DEM was subtracted from the surface elevation data of the DSM to produce a map of canopy height, which indicates vegetation recovery from last landslide events. First, the effective range of the methodology in this study was investigated by comparing the actual canopy height measured at 12 sites with the canopy height map based on LiDAR data. These landslides were mapped with interpretation of aerial photographs in 1975. For landslides which occurred about 50 years ago, the canopy overhung the landslide scars by 4–6 m from the periphery slope, and the surrounding canopy completely covered the landslide scars for small landslides with an area of less than 320 m². The LiDAR data were applicable for vegetation recovery where the sites were not covered by the surrounding canopy. Within the area where the LiDAR data is available for vegetation recovery assessment, the following two indices were used for the assessment: the maximum canopy height, and the percentage of the area where the canopy height exceeds 0.1 m. These indices were calculated for 14 landslide sites that occurred prior to 1963, 9 sites that occurred from 1963 to 1975, and 9 sites that occurred from 1995 to 2015. These landslides were mapped with interpretation of aerial photographs in 1963, 1975, 1995, and 2015. Vegetation recovery was gradual in landslides that occurred from 1995 to 2015 beside landslides with the other ages, indicating that the approximately 20-year period was insufficient for tree growth. The vegetation recovered particularly in Japanese red pine communities at lower elevation (507–621 m) in the landslides that occurred from 1963 to 1975. Fast vegetation recovery was observed where vegetation invaded from adjacent intact forest or regrowth on remained in landslide scar.