Dr Hau is a terrestrial ecologist and a conservationist. He has been teaching ecology and biodiversity at HKU for more than 20 years. His research focus is ecological restoration, especially for terrestrial habitats in degraded tropical East Asia.  He aims to bring back native forest and the associated forest biodiversity into the degraded landscape in Hong Kong and South China. He founded the Native Tree Nursery of the Kadoorie Farm and Botanic Garden (KFBG) which promotes the use of native plant species in forest restoration work.

He has set up a 20 ha long term forest monitoring plot in Tai Po Kau Nature Reserve, Hong Kong under the Forest Global Earth Observatory (ForestGEO) programme of the Centre of Tropical Forest Science of the Smithsonian Tropical Research Institute. It is a global network of forest research sites that is strategically positioned for monitoring, understanding, and predicting forest responses to global climate change. He has been promoting urban biodiversity through applied research.

He is a local expert in ecological restoration and is often engaged by the Hong Kong Government and private sector in contract research projects on urban forestry, urban biodiversity and ecological restoration of man-made slopes and natural terrain landslides.

Abstract

Biodiversity Management in Seasonal Floodplain of Drainage Channels

The Drainage Services Department (DSD) has been promoting blue-green infrastructure and enhancing the biodiversity values of rivers and facilities they are managing. In recent years, many of the drainage channels were lined with grasscrete, riprap or gabion in the riverbed or embankment to allow vegetation to grow and develop into green channels. Vegetation removal is often required to maintain drainage capacity and address the concerns of local communities on environmental hygiene. Meanwhile, frequent and complete removal of vegetation may affect the ecology of the green channels. Since very little research had been done for the riverbed vegetation of these drainage channels, this study was commissioned to investigate, through a manipulative experiment in a selected green channel, the effect of different riverbed vegetation mowing regimes on biodiversity.

An experiment was conducted at a section of the channelized Tan Shan River in the northern New Territories.  Experimental plots were set up for testing different mowing frequency and intensity for a period of one year.  Biodiversity surveys were conducted in these experimental plots and treatment free control plots to assess the abundance and species richness. The results show that the effect of mowing regimes was taxa specific. Bird species richness in unmown and infrequently mown plots were significantly higher than frequently mown plots. Both abundance and species richness of butterflies were significantly enhanced by low intensity and low frequency mowing. The abundance of dragonflies, and the abundance and species richness of other macroinvertebrates remained high in low mowing intensity and control plots. The overall species richness of plants was not affected by mowing regimes, but the domination of tall invasive grass was suppressed by mowing.

In general, frequent intensive mowing are not favourable to biodiversity. It is recommended that a mosaic pattern of mowing should be maintained to strike a balance between drainage capacity, biodiversity, and environmental hygiene. Mowing at lower frequency and intensity, taking drainage capacity into account, could be considered. Patches of unmown areas could be retained where possible to provide additional refuges for grass-dependent specialists. On the other hand, for areas nearer to human dwellings, a relatively frequent mowing may still be conducted to ensure environmental hygiene.