Billy C.H. Hau

Effects of Plant Transpiration on Suction Distribution in a Vegetated Soil Slope

Extensive studies have been carried out to investigate the use of plant roots as a mechanical reinforcement for slope stabilisation. However, although plant is well-recognised to induce soil suction via transpiration, any of its contribution to slope stability is rarely investigated. The objective of this study is to investigate the plant-induced suction distribution on a slope vegetated with multiple plants. A series of parametric study is conducted to investigate the effects of plant number and spacing on induced suction and its influence zone. In each analysis, the ground is subjected to 6-month drying under a constant potential transpiration rate. Any computed variations of plant-induced suction influence zone in each case are discussed.

Growth Rate and an Evaluation of Age Estimation for the Endangered Big-Headed Turtle (Platysternon megacephalum) in China

Abstract Understanding growth patterns is critical for determining age and size at sexual maturity and longevity in species that are severely threatened by over-collection and habitat loss, particularly in poorly understood species in tropical East Asia. Using data collected during a 9-year mark–recapture study, we fit the von Bertalanffy and logistic growth models to examine growth patterns of the endangered Big-headed Turtle (Platysternon megacephalum). Growth rate of P. megacephalum was best described by the von Bertalanffy model. Mean age at maturation for female and male P. megacephalum was 8 and 13 years. At maturity for female and male P. megacephalum, mean carapace length was 100 mm and 130 mm, respectively. We determined that counting growth rings on the carapace and plastron was not a reliable method for estimating ages. The long time to maturation in P. megacephalum may be costly in harvested populations, with individuals potentially being removed from populations prior to first reproduction. The growth patterns we have documented, and associated information on body size and age at sexual maturity, yield metrics that may be used to assess the effects of harvesting in populations and may contribute to conservation efforts for this endangered species.

Diet of the endangered big-headed turtle Platysternon megacephalum

Populations of the big-headed turtle Platysternon megacephalum are declining at unprecedented rates across most of its distribution in Southeast Asia owing to unsustainable harvest for pet, food, and Chinese medicine markets. Research on Asian freshwater turtles becomes more challenging as populations decline and basic ecological information is needed to inform conservation efforts. We examined fecal samples collected from P. megacephalum in five streams in Hong Kong to quantify the diet, and we compared the germination success of ingested and uningested seeds. Fruits, primarily of Machilus spp., were most frequently consumed, followed by insects, plant matter, crabs and mollusks. The niche breadth of adults was wider than that of juveniles. Diet composition differed between sites, which may be attributable to the history of illegal trapping at some sites, which reduced the proportion of larger and older individuals. Digestion of Machilus spp. fruits by P. megacephalum enhanced germination success of seeds by about 30%. However, most digested seeds are likely defecated in water in this highly aquatic species, which limits the potential benefit to dispersal. The results of our study can be used by conservation-related captive breeding programs to ensure a more optimal diet is provided to captive P. megacephalum.

Early Ecological Succession on Landslide Trails, Hong Kong, China

ABSTRACT In Southeast Asia, intensive rainstorms caused by strong monsoon and tropical cyclones can trigger landslides in mountainous or hilly regions, which may significantly impact the natural terrains. This mostly includes the loss of vegetation cover, the emptying of seed banks and degradation of the top soil. The objective of this study was to assess the spontaneous vegetation regeneration on nine landslide trails approximately 2.5 years after disturbance. A systematic vegetation sampling was conducted using 5 × 5 m quadrats. A total of 1,304 individuals from 72 tree and shrub species were recorded across the landslide trails, with a mean density of 1.09 ± 0.71 individual m-2. The woody component of the regeneration was dominated by birddispersed species, followed by wind-dispersed species. Ground cover was dominated by two matforming ferns Dicranopteris pedata and Blechnum orientale. In order to facilitate the vegetation restoration and to speed up ecological succession on landslides, it is recommended to establish pioneer trees to improve both the top soil stability and soil-building process. The importance of providing bird perches must be emphasized, as it improves seed rain to the disturbed landscapes, thus promoting the regrowth of trees and shrubs.