2.1 Study site
The experiment was conducted on three recent natural terrain landslides (approximate 200m altitude) in the New Territories of Hong Kong, China (Figure. 1; 22° 27ʹ 35ʺ N, 114° 06ʹ 13ʺ E). The three selected landslide sites were formed in late August 2018 under a rainfall exceeding 200 mm within a day in the New Territories (Hong Kong Observatory, 2021). Prior to the landslides, grassland and shrubland were the most abundant vegetation types in these sites due to repeated human-induced hill fires in the surrounding areas. After the disturbances, the landslide scars remained barren for two years, and were not even occupied by pioneer grasses or ferns. Soil in these three sites was composed of highly decomposed crystal tuff with decomposition grade VI to VII (Geotechnical Engineering Office, 1988). The soil was shallow, with good drainage and aeration, but low in fertility. The terrain is unstable and easy to collapse.