In order to quantitatively assess the spatial distribution of the various types of wetlands on a functional basis, it will be necessary to compile wetland inventories from wetland sites. There is information available from all regions, but coverage is poor in intermittent wetlands.
Information is more comprehensive for permanently inundated wetlands.
Wetland areas are often underestimated. Some of the major gaps, including the Siberian wetlands, are mainly due to lack of access. Wetlands in forested areas are difficult to determine, especially in those areas where the water table is below the surface. 1987 Hughes and Hughes 1992 IUCN, Gland, Switz. African wetlands and shallow waterbodies.