Swamps – Wooded Wetlands

Swamps are wooded wetlands and include forested and shrub wetlands. Swamp is used in many European and African countries and elsewhere to refer to a wetland that is dominated by tall emergent plants, whether woody or herbaceous. The herbaceous ‘swamps’ under those systems of classification are referred to as marshes in this encyclopedia and are covered elsewhere. The Sudd swamps in Africa, for example, are marshes for the most part following the definition above. Swamps or wooded wetlands occur on hydric soils, are flooded or saturated for part of the growing season in most years, and support a canopy of trees and/or shrubs that cover 25–30% or more of the wetland; wetland trees or shrubs are adapted for wetland life or can tolerate periods of inundation. Adaptations of trees and shrubs for wetland life often include development of aerenchyma tissue that ‘form channels’ that allow gases to diffuse or be transported by differences in canopy and root temperatures and concentrations from aerial parts of the plant to and from the roots. Another adaptation in some species includes adventitious roots that extend from the aerial parts of the plant to or into the sediment or below the water surface and support the plant (stilt roots) and/or function in transporting oxygen to underground/underwater roots via lenticels (pores) that allow gases to enter and exit the aerial root and be transported to and from the underground roots via aerenchyma tissue. Another adaptation is the development of pneumatophores or roots that extend from the sediment to above the water surface and also function to allow gases to exchange between the atmosphere and roots buried in sediments and/or help to hold the tree or shrub in place. Seed dispersal in swamps include dispersal by a variety of birds, mammals, fish (especially in the tropics), and other animals, and by wind and water. Forested swamps are dominated by trees that are 6 m tall or taller and may include one or more shrub layers and an herbaceous layer of plants. Shrub swamps are dominated by woody plants that are less than 6 m tall. Swamps are found on nearly every continent around the world and in all wetland habitats including in and along the margins of lakes and streams, in floodplains and deltas, in isolated depressions, in seepage areas on hill slopes, and on waterlogged soils on flats. Swamps that are underlain by peat deposits include boreal forested and shrub bogs and fens and tropical forests on waterlogged soils. Nonpeat swamps are estimated by one author to cover up to 15% of the world's wetlands. It is estimated that peat swamps cover at least that much land surface, although data on them are limited. Major peat swamp areas include swamps in the boreal and Northern Temperate Zones of Canada, Russia, Alaska, and Scandinavia. Tropical peat swamps occur widely on waterlogged soils in southeast Asia with smaller areas in Africa and elsewhere. It is estimated that swamps (wooded wetlands) cover about 30% or more of all wetlands and occupy 2% or more of land globally. This is a conservative estimate. Swamps range in productivity from 200 to 1800 g m−2 yr−1 depending on flow and hydroperiod. They supply a multitude of ecosystems services to humans that have been estimated to be as high as $7000 per hectare annually. They also support a high diversity of organisms including millions of birds, fish, crocodilians, snakes, turtles, and amphibians.