ENG-1973 — Page 273

NATURAL HISTORY

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isospondylous fishes) began to diminish-possibly due to an increasing disturbance of the local marine environment.

The full extent of Hong Kong's marine fauna is difficult to assess, but the diverse varieties of fish, crustacea, cephalopod, mollusc and seaweed indicate that the number of species involved is certainly high. The discharge of the largest freshwater system in South China to the west, and the prevailing Taiwan Current from the north-east, have created a situation where the westerly sector of Hong Kong has a predominantly brackish water fauna, while the eastern sector has a genuine marine fauna.

A notable marine animal which has been successfully introduced in the Deep Bay area is the Japanese oyster, Crassostrea gigas. It is now being cultivated.

The freshwater fauna of Hong Kong is relatively poor in variety compared with the Chinese mainland. This probably results from the absence of a perpetual system of rivers and lakes. Although there are large bodies of water stored in man-made reservoirs, only a few varieties of fish life have been introduced-primarily for water quality control purposes. The indigenous fauna comprises only limited species of cyprinid, loach and goby, while the African Tilapia has also established itself in local waters, but its initial introduction cannot be traced. Despite its limited size, Hong Kong has now some 2,900 acres of commercial fish ponds, where the grey mullet and seven species of Chinese carp are being produced at a rate of 1.2 tons per acre.

Flora

Hong Kong possesses a large and diverse flora of vascular plants-estimated at about 2,400 species, native and introduced-for so small an area. Generally Hong Kong offers the northern limit of tropical Asian flora.

Few high trees are to be found except in the fine fung shui groves preserved around many villages in the New Territories. After centuries of cutting, burning and exposure, the barren hillsides present a dry and arid impression. The ravines, saved from man and fire by their rugged character and more moist winters, contain a dense vegetation particularly rich in low trees, flowering shrubs and ferns. However, many hill slopes, particularly those in the water catchment areas, have been replanted by sowing tree- seeds or planting tree-seedlings raised in nurseries.

It is to conservation of wooded areas by the Agriculture and Fisheries Department that Hong Kong owes much of its mixed woodland. In a few large ravines, particularly Tai Po Kau and Pok Fu Lam Valley, autumn and spring colorations are particularly noticeable. There are several trees, shrubs and climbers whose leaves change to bril- liant colours in autumn. Plants which show richest autumn coloration continue their colours into February, before spring coloration takes over. Many trees, shrubs and vines help to produce this wonderful effect-Liquidambar formosana, Rhus spp, Sapium spp, Michilus thunbergii, Raphiolepis indica, Rourea microphylla, and Vitis

cantoniensis.

Many plants in Hong Kong are exceptional for the beauty or fragrance of their blossoms. The Bauhinia blakeana (Hong Kong orchid tree) was discovered in 1908 at