THE ENVIRONMENT
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discharge from the Pearl River has a marked influence on Hong Kong waters. In addition, three different ocean currents affect Hong Kong during the year.
During the summer, an oceanic flow from the south-west to the north-east brings the warm, high-salinity water of the Hainan Current into Hong Kong waters. This interacts with fresh water from the Pearl River and divides Hong Kong into three distinct sections. In the west, where the fresh water influence is greatest, the environment is estuarine and the water is brackish. In the east, the water is mainly oceanic with relatively minor dilution from direct monsoonal rainfall and runoff from small streams. The limits of the central transitional zone vary depending upon the relative influence of Pearl River water and marine currents.
During the winter, the Kuroshio oceanic current brings warm water of high salinity from the Pacific through the Luzon Strait. The fresh water of the Pearl River has a lesser influence than in summer and water salinity is more uniform across Hong Kong. Besides the Kuroshio current, the coastal Taiwan current brings cold water down the South China coast, which affects inshore waters, making the surface water cold during the winter.
The normal tidal range in Hong Kong waters is between one and two metres, depending on the relative influence of the moon and sun. The tidal pattern is complex due to the relative effects of the diurnal and semi-diurnal components. The basic pattern during flood tides is for oceanic water to flow north into Mirs Bay, west through Victoria Harbour and north through Kap Shui Mun and the Ma Wan Channel. Maximum tidal currents generally range from 0.5 to 1.5 knots and locally up to 5 knots at narrow channels. This flow is reversed during the ebb tide, though currents in some parts may be stronger due to the influence of the Pearl River.
Flora
Hong Kong is near the northern limit of the distribution of tropical Asian flora and has an estimated 2 800 species of vascular plants, both native and introduced. Various conservation measures have transformed the formerly bare hillsides and slopes into areas with plants of local and introduced species. Besides greening and beautifying the countryside, woodlands are important habitats for wildlife and are essential in protecting water catchments from soil erosion and in providing recreational opportunities for the public.
Remnants of the original forest cover, either scrub forest or well-developed woodlands, are still found in steep ravines. They have survived the destructive influences of man through their location in precipitous topography and the moist winter micro-climate.
Terrestrial Fauna
Hong Kong's physical and climatic environment provides woody and grassy habitats for a wide variety of animals and plants. Under the pressures of urbanisation, larger animal species are rarely seen, but reptiles, amphibians, birds and insects are still
common.
The Mai Po Marshes form one of the most important wildlife conservation sites in Hong Kong. Together with the Inner Deep Bay area, the Mai Po Marshes were listed as a 'Wetland of International Importance Especially as Waterfowl Habitat' under the Ramsar Convention in September 1995. Some 835 hectares of mudflats, fish