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THE ENVIRONMENT
plants including native camelias, magnolias, orchids, azaleas and the Chinese New Year Flower.
The Wild Animals Protection Ordinance prohibits hunting of wild animals and restricts the entry of unauthorised members of the public into two important wildlife habitats, the Mai Po Marshes and the Yim Tso Ha Egretry. Overall enforcement of the ordinances is carried out by nature wardens and park wardens. These officers provide information at visitor centres and at warden posts and also escort groups on guided visits.
In addition to general conservation of the countryside, Hong Kong has adopted the concept of identifying and conserving sites of special scientific interest to ecologists, such as a site where a rare tree or a rare species of butterfly can be found. More than 46 sites have been identified for future conservation action.
Topography and Geology
Hong Kong is part of an ancient Cathaysian landmass that some 1 000 million years ago extended from Shandong in northern China to the Gulf of Hainan. Following intensive folding of its metamorphic and crystalline rocks, intense mountain-building occurred with granitic and volcanic intrusions during the Mesozoic period, about 250 million years ago. From the beginning of the Quaternary period, between two to three million years ago, the lower-lying areas were alternately flooded or exposed as masses of water were locked up or released from ice sheets. The last marine incursion was about 10 000 years ago; since that time there have been sporadic depositions of sedimentary material eroded from the hills.
This erosion of the hills and deposition in the valleys increased rapidly following the widespread colonisation of the Hong Kong area during the Song Dynasty (960–1279).
Large volumes of sedimentary material are brought regularly to Hong Kong by the Zhu Jiang (Pearl) River, but this process has been accelerated in recent years by extensive reclamation projects along the coastline. Hong Kong's granitic and volcanic rocks are deeply weathered and are prone to landslides if disturbed, but they can be excavated quite easily for use as reclamation material. Much of the natural landscape is changing as hills are removed and the fill is used at the various reclamation sites to be found throughout the territory.
Apart from providing decomposed rock material as fill for reclamation, the hills that make up most of the total land area of Hong Kong have little economic value. 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. While Hong Kong does possess some deposits of iron, lead, zinc, tungsten, beryl and graphite, these have been mined only in small quantities.
Because 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 coastal inlets such as Plover Cove and High Island where large dams have been built. The areas surround- ing Hong Kong's reservoirs and their water catchments have become 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 2 000 to 3 000 years, and some coastal 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 successfully established in areas that once were mudflats, mangrove swamp or salt-water rice paddies.