ABSTRACT
Wetlands represent only 6 per cent of the Earth’s surface, but it is believed that in 1900 this percentage might have been twice as much (Barbier et al. 1994). Wetlands include a wide array of habitats, ranging from fens and marshes to mangrove forests and rice paddies, and are considered one of the most threatened landscapes in the world (Gardiner 1994). A simple definition is ‘land with soils that are permanently flooded’ (Williams 1990: p. 1). The Ramsar Convention, an international treaty to conserve wetlands, defines wetlands as: ‘areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres.’ This encompasses a wide range of habitats, the main types being shown in Figure 20.1). Surveys have established the extent of wetlands, both past and present, in different areas of the world, leading to the compilation of inventories of wetland sites, particularly for plants, birds and mammals, and investigations into physical, chemical and biological processes. Collectively, these have developed a real insight into wetland ecology.
