SECTION 4 ECOLOGICAL RESOURCES CAPITAL STOCK
4.2 Existing Capital Stock and Trends
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| 4.2.1.32 |
Degradation of mangrove habitats is one of the most conspicuous results of coastal and urban development, in particular it is noted by Tam and Wong (2000) that many mangrove resources have been destroyed in recent decades by reclamation and infrastructure development. A large proportion of the original stock of mangrove habitat in Hong Kong has been cleared from areas which historically featured the most significant of Hong Kong's mangrove stands, such as Tin Shui Wai, Tolo Harbour and Deep Bay. In these areas few healthy stands remain. Tam and Wong (1997) report that only 15% of the original mangrove stands now remain at the seaward fringe at Mai Po, and that more than 42% of the original mangroves along the coastline of Tolo Harbour have been destroyed by reclamation and the construction of new highways. In addition, mangroves are often regarded as convenient dumping grounds for construction, domestic, industrial and agricultural waste (Tam and Wong 1997). (See Paragraphs 3.5.3.10 - 3.5.3.11 - Solid Waste for further discussion of illegal dumping). Based on limited field surveys from 1994 to 1997 and aerial photography, Tam and Wong (1997) estimated Hong Kong's mangroves covered a total of 290 ha. Reference to Table 4.2a indicates that the more recent habitat mapping study estimates a figure of 3274 ha. The discrepancy arises due to differing methodologies for the two studies though it is suggested that the later survey, with its significant field survey, is likely to be a more accurate figure. |
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| 4.2.1.33 |
Most of the mangrove sites were considered to be of high ecological value after field assessment as they support moderate to high species diversity and are subject to little or no human disturbance. The largest patch of mangrove surveyed covered approximately 4.5 ha at Pak Nai. The mangrove at So Lo Pun (Northeast New Territories) was found to be densely vegetated with mangrove trees and supported high species diversity. Some mangrove patches, though small in size, eg Tai Ho Wan, support a comparable species diversity to those of larger sizes (eg So Lo Pun) and, therefore, a high ecological value was assigned. |
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| 4.2.1.34 |
The mangrove at Tai Tam has been reported to have totally disappeared based on the field visit conducted in May 1996 (Tam and Wong 1997). However, the mangrove there was found during the field surveys for SUSDEV 21 to support a number of mangrove species, diverse epifauna, and was free from human disturbance. Despite its small size, the habitat is believed to be expanding as many tree mangrove seedlings, especially Excoecaria agallocha, were observed. |
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| 4.2.1.35 |
Some of the identified mangrove sites have had their ecological value downgraded to medium because of the severe disturbance from pollution or development that the habitats are subject to. The mangrove located near the Yuen Long Industrial Estate, in particular, had been adversely affected by urban development and only a small patch was observed during the field visit. |
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| 4.2.1.36 |
Fishponds are generally small artificial ponds that have been constructed for the purposes of raising freshwater fish. They are mostly reclaimed from mangrove habitat or converted from shrimp ponds, market gardens or paddies. Gei wais are similar enclosures but contain brackish water and are often flushed through tidal action. Gei wais are either excavated from native mangrove forest or converted from rice paddies. Depending on the management scheme utilised, fishponds and gei wais can provide valuable habitat similar to that provided by natural wetlands. Further details on the pond culture production of fishponds and gei wais are presented under Paragraphs 3.3.1.5 - 3.3.1.6 - Pond CultureAgriculture and Fisheries. |
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| 4.2.1.37 |
Many of the fishponds surveyed were small in size (< 0.5 ha) and abandoned (ie not under active management). While some of the abandoned fishponds contain polluted water, some appear to have undergone succession and become higher ecological value habitats, eg wetlands (and thus have been re-classified as Freshwater/Brackish Wetland). Some ponds (eg at Kam Tin) have been partly infilled for urban development. Actively managed fishponds are generally of medium ecological value, except for those fish rearing fishponds in Ngau Tam Mei (Northwest New Territories) which, due to their concrete nature and lack of natural vegetation, are of low habitat value. |
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