ENG-1987 — Page 341

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THE ENVIRONMENT

rocks are deeply weathered and are prone to landslides if disturbed, but they can be excavated quite easily for use as reclamation material. In the developed portion of the territory the natural landscape is changing dramatically as hills are removed and the fill is used at the various reclamation sites to be found around Victoria Harbour and in the New Territories.

Apart from providing decomposed rock as fill for reclamation, the hills that make up most of Hong Kong's land area have little practical use. Soils are thin and nutrient- deficient, supporting only a sparse cover of grass or scrub except in protected valleys or in water catchment areas where a policy of afforestation has succeeded in establishing hardy pines and some deciduous trees. Hong Kong possesses some deposits of iron, lead, zinc, tungsten, beryl and graphite, but these have been mined only in small quantities.

As Hong Kong lacks large rivers, lakes and underground water supplies, reservoirs have had to be constructed in large valleys such as Tai Lam Chung and in the coastal inlets of Plover Cove and High Island, where large dams have been built. These reservoirs have a dramatic impact on the environment and their water catchments form a part of the territory's 21 country parks.

The most important agricultural area Hong Kong possesses is the flat alluvium around Yuen Long in the New Territories. These alluvial lowlands have emerged from the sea only within the last 3 000 years, and some areas are still prone to flooding when heavy rainfall coincides with high tides. The natural deposition of sediment is continuing around the Deep Bay area, where brackish fish ponds have been established successfully in areas that were once mudflats, mangrove swamps or saltwater rice paddies.

On average, only two or three earthquakes are felt by the public each year. However, hundreds are detected by a seismometer network, comprising three short-period seismo- meters at Cheung Chau, High Island and Tsim Bei Tsui. Long-period seismographs record tremors from all over the world, and strong motion accelerographs are installed at two locations with different soil properties. This network is operated by the Royal Observatory. In recent years, about 150 earthquakes have been detected annually within 320 kilometres of Hong Kong.

Wildlife

The physical and climatic environment of Hong Kong provides woody and grassy habitats for a wide variety of native animal and plant life. Under the pressure of urbanisation, larger animal species are rarely seen, but reptiles and amphibians, birds and many kinds of insects

are common.

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Most of Hong Kong's countryside is protected by the Forests and Countryside Ordinance, the Wild Animals Protection Ordinance, the Country Parks Ordinance, and the Animals and Plants (Protection of Endangered Species) Ordinance.

One of the most important sites in Hong Kong for wildlife is the Mai Po Marshes. A restricted area under the Wild Animals Protection Ordinance and managed by the World Wide Fund for Nature (Hong Kong), it is an internationally significant site for migratory and resident birdlife. Its 380 hectares of mudflats, shrimp ponds and dwarf mangroves provide a rich habitat, particularly for ducks and waders. More than 250 species of birds have been observed in this area, and at least 110 of them are rarely seen elsewhere in the territory.

Yim Tso Ha, also a restricted area, is the largest egretry in Hong Kong. Five species, the Chinese Pond Heron, Night Heron, Cattle Egret, Little Egret, and the rare Swinhoe's Egret, nest there regularly. More than 1 000 egrets can be found there between April and