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Tropical forests are widely regarded as the Earth’s most important ecosystems, yet they are severely threatened by anthropogenic disturbances. Rapid and extensive monitoring of forest structure and biodiversity is crucial for developing ecologically sound conservation and restoration strategies. Airborne light detection and ranging (LiDAR) can effectively monitor three-dimensional forest canopy structures. Traditionally, LiDAR-based plant diversity estimation has relied on individual tree-based and area-based approaches. However, these approaches face significant challenges in tropical forests due to their complex canopy structures and diverse plant compositions. Therefore, by proposing a novel community-based approach, this study aims to examine the relationship between field-derived biodiversity indices and LiDAR-derived canopy structural metrics of plant communities in a species-rich ForestGEO forest dynamic plot in tropical Hong Kong. Our goal is to determine whether canopy structural metrics extracted from airborne LiDAR data can serve as a robust and efficient alternative for expediting plant diversity monitoring in highly dense and diverse tropical forests. Our results indicate that an integration watershed segmentation technique (for automatic patch-scale plant community delineation), LiDAR-derived canopy structural metrics, and machine learning-based random forest regression analysis can provide accurate predictions of community-based species diversity indices. Among various diversity indices, species richness and the Shannon-Wiener index are most accurately estimated using LiDAR-derived metrics. This study reveals that species richness is predominantly influenced by the existence of multi-layered canopy structures, whereas the Shannon-Wiener index is associated with both multi-layered structures and canopy morphologies. Overall, our findings showcase the immense potential of airborne LiDAR data in advancing the monitoring of structure and biodiversity in dense-canopy and species-rich tropical forests in a spatially explicit manner.

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.

Determines whether seed predation was a barrier to natural forest regeneration on degraded hillsides in Hong Kong, China. Percentage of land area covered by forests in the country; Reasons for seed predation.