Vegetation influence on retrogressive landslide deformation and sediment transport from multi-temporal UAV-LiDAR monitoring

Retrogressive landslides develop through progressive upslope retreat and long-term deformation, producing hazards to infrastructure, communities, and river systems. Vegetation is widely recognized as a stabilizing factor in shallow landslides, but its influence on deep-seated retrogressive landslides remains unclear due to limited empirical evidence. Multi-temporal UAV-LiDAR monitoring was applied to the Kalisari landslide, Central Java, Indonesia, which comprises a non-vegetated southern sector and a vegetated northern sector. Annual LiDAR surveys from 2020 to 2025 were analysed to quantify displacement, volumetric change, and displacement direction. Results show that both sectors remained active and vegetation had little influence on deformation behaviour. Volumetric analysis showed lower net material loss in the vegetated sector, suggesting that vegetation reduced sediment export by retaining displaced debris. These findings indicate that vegetation cannot prevent retrogressive landslide deformation but may help to moderate downstream consequences such as channel infilling or reservoir siltation. For hazard management, the results highlight the importance of integrating vegetation management with engineering measures to mitigate landslide risk.