SECTION 4 ECOLOGICAL RESOURCES CAPITAL STOCK
4.2 Existing Capital Stock and Trends
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| Grassland |
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| 4.2.1.20 |
True grassland habitats are those where the land is covered by grasses and no visible woody plants. Grassland in which grasses are mixed with woody plants but still dominated by grasses (ie over 50% grasses) is referred to as shrubby grassland. Grasses may also be present in mixed or Baeckia shrubland but cover less than 50% of the area (see above). |
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| 4.2.1.21 |
Hong Kong's grasslands are highly varied, ranging from low communities with a mixture of herbs and small shrubs, to tall, dense strands of a single grass species (WWF 1999). Both flora and fauna change with altitude and fire frequency. Due to the variety of forms this habitat may take, the fact that it has the broadest area of coverage of any habitat in Hong Kong (Table 4.2a), and the frequency of fire disturbance, knowledge of the ecological characteristics of the habitat is rather limited. However, in general, grassland contains few native animal species, and has a low level of structural complexity, therefore it tends to be of generally low biodiversity potential. Shrubby grassland has a higher level of structural complexity and thus is expected to support a moderate level of biodiversity. |
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| 4.2.1.22 |
The majority of the shrubby grassland identified in surveys was regarded as having medium ecological value. Most of the shrubby grassland areas were relatively small in size (< 0.5 ha) and structurally less complex than most of the mixed shrubland surveyed. The habitat is relatively intact and subject to little or no disturbance due to human activities. A few of the identified surveyed habitats were downgraded to low habitat value due to human disturbance and comparatively poor species diversity. |
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Wetlands
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| 4.2.1.23 |
Wetlands are areas which are covered by or saturated with water. In the context of this discussion, wetlands refers to habitats such as ponds, tidal mudflats and marshland where the habitat is typically represented by shallow waters which are dominated by emergent hydrophytes. Wetlands can be categorised into freshwater and brackish types, based on the salinity of the water (if the salinity is less than 10 ppt, the habitat is generally regarded as a "freshwater" wetland). Hong Kong wetlands, particularly its freshwater wetlands, support a wide array of plants and animals, including submerged macrophytes (freshwater plants), amphibians, and a range of aquatic insects (eg dragonflies and damselflies) (Dudgeon and Chan 1996). |
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| 4.2.1.24 |
The wetlands identified in the SUSDEV 21 survey were found to exist in the form of marshes, pools or reedbeds. Large patches of wetlands (> 10 ha) were observed at South Lantau , Nam Sha Po (Northwest New Territories) and Ting Kok (Northeast New Territories). They are generally remote from urban areas and subject to little or no human disturbance, apart from one of the patches at Ting Kok which was found to have been disturbed by dumping of solid wastes (eg plastic containers) and urban development (building of houses near the habitat). Aside from the Ting Kok wetland, many other wetlands, generally of much smaller size, were also thought to have been disturbed by pollution as evidenced by the highly turbid, dark brown or black-coloured waters of the habitat. In many areas the odour of hydrogen sulphide was noted indicating poor water quality with low oxygen content. Impact on wetlands due to urban development was particularly obvious in such survey areas as Kam Tin and Ma On Kong where a number of the wetland patches have been developed or filled for construction purposes. |
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| 4.2.1.25 |
In-depth surveys have been conducted for 28 freshwater wetland sites identified in an AFCD Study by Dudgeon and Chan (1996). Examples include the species rich marshes at Yung Shue O, Luk Keng and Sam A Tsuen and the ponds at Cheung Sheung (supporting several rare species) and Lamma Island Most of the remaining Hong Kong freshwater wetlands are small on a global scale, but nevertheless may have particular local ecological importance. This applies especially if they are used as breeding, feeding or roosting sites where large numbers of a widely-distributed species become concentrated during certain periods (Davies and Giesen 1994). Some rare or endemic species (eg the Romer's Tree Frog Philautus romeri) are confined to small wetlands where predators or potential competitors are absent (Lau 1998). |
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| 4.2.1.26 |
The designation by Government in 1995 of the Mai Po Marshes and Inner Deep Bay as a Wetland of International Importance under the Ramsar Convention provides protection for the brackish and freshwater wetland in this area. This area contains the largest concentration of bird species in Hong Kong and is particularly important for migrant and wintering wildfowl. Increased urbanisation and development of the New Territories constitute the greatest threats to freshwater wetlands in Hong Kong. Most of these wetlands lie outside Country Park boundaries and are thus not afforded legal protection by existing legislation. The situation is exacerbated because unmanaged freshwater wetlands in Hong Kong comprise, in the main, abandoned fishponds or flooded fields associated with villages. Most of this land is privately owned and thus vulnerable to pressures arising from the desire to put the land to "productive use". (see Section 3.2 - Land Use and Land Supply for a further discussion of the dynamic between conservation and development). |
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