Vegetation succession on landslides in Hong Kong: Plant regeneration, survivorship and constraints to restoration

Abstract

Landslides often lead to a unique successional direction because the existing vegetation, seed bank and top soil including nutrient and mycorrhizal inoculum have been lost. This type of disturbance has attracted more attention in recent decades especially in mountainous regions experiencing regular severe rainstorm. In Hong Kong, urban development has been recently extended towards the natural terrain, which consequentially increased the social-economic impact brought by natural terrain landslides. In order to facilitate ecological restoration in such habitats, we studied the establishment and change of vegetation composition on eight landslide trails over the first 8.5 years after the disturbance. We conducted three censuses to measure the survivorship and height of woody individuals at these sites over the study period. We found that the woody composition did not vary across the censuses in terms of stem density, species richness, Shannon-Weiner's index and assemblage similarity. Most of the early-established individuals died in early succession which out-numbered the recruited individuals. Landslides became dominated by fern thickets formed by Dicranopteris pedata and Blechnum orientale which probably accounts for the suppressed colonization of woody plants. We identified fast-growing trees and species with highest survival rate which could potentially be used for future ecological restoration. They may serve as bird perches and facilitators of seed rain, while suppressing the expansion of fern thickets. Since fern clearance was practically difficult on landslide sites which are steep and remote, we recommended repeated sowing with woody pioneer seeds soon after the disturbance before the establishment of fern thickets. Using UAV for direct seeding could be tested on such remote and difficult terrain.