Coastal forest ecosystems

In each of the climatic regions of the world, inland forests and woodlands may extend to the sea and thus form part of the coastal area. In addition to such formations, which are controlled by climatic factors, special forest communities, primarily controlled by edaphic factors and an extreme water regime, are found in coastal areas and along inland rivers. Such forest communities include: mangroves, beach forests, peat swamps, periodic swamps (tidal and flood plain forests), permanent freshwater swamps and riparian forests. Of these, the first three types are confined to the coastal area, whereas the remaining types can also be found further inland.

Mangroves

Mangroves are the most typical forest formations of sheltered coastlines in the tropics and subtropics. They consist of trees and bushes growing below the high water level of spring tides. Mangrove forests are characterized by a very low floristic diversity compared with most inland forests in the tropics. This is because few plants can tolerate and flourish in saline mud and withstand frequent inundation by sea water. Most of the animal species found in mangroves also occur in other environments, such as beaches, rivers, freshwater swamps or in other forest formations near water. On the whole, animal species strictly confined to mangroves are very few (crabs have a maximum number of species in mangroves). In many countries however, the mangroves represent the last refuge for a number of rare and endangered animals such as the proboscis monkey (Nasalis larvatus) in Borneo, the royal Bengal tiger (Panthera tigris) and the spotted deer (Axix axis) in the Sundarbans mangroves in the Bay of Bengal. Mangroves are also an ideal sanctuary for birds, some of which are migratory.

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Beach forests

This type of forest is in general found above the high-tide mark on sandy soil and may merge into agricultural land or upland forest. Sand dune and beach vegetations are mostly scrub-like with a high presence of stunted tree growths. These coastal forest ecosystems are adapted to growing conditions that are often difficult as a result of edaphic or climatic extremes (strong winds, salinity, lack or excess of humidity). They are very sensitive to modifications of the ecosystem. A slight change in the groundwater level for example might eliminate the existing scrub vegetation. Sand dune and beach vegetations have an important role in land stabilization and thus prevent the silting up of coastal lagoons and rivers, as well as protecting human settlements further inland from moving sand dunes. The dominant animal species on the adjacent beaches are crabs and molluscs. The beaches are also very important as breeding sites for sea turtles and therefore attract predators of turtles' eggs, such as monitor lizards (Varanus sp.).

Peat swamp forests

This is a forest formation defined more on its special habitat than on structure and physiognomy. Peat swamp forests are particularly extensive in parts of Sumatra, Malaysia, Borneo and New Guinea, where they were formed as the sea level rose at the end of the last glacial period about 18 000 years ago. Domed peat swamps can be up to 20 km long and the peat may reach 13 m in thickness in the most developed domes. Animals found in peat swamps include leaf-eating monkeys such as the proboscis monkey and the langurs found in Borneo.

Periodic swamps

As with peat swamp forests, these are defined mainly by habitat and contain a diverse assemblage of forest types periodically flooded by river water (daily, monthly or seasonally). Periodic swamps can be further subdivided into tidal and flood plain forests. Tidal forests are found on somewhat higher elevations than mangroves (although the term is sometimes used to describe mangroves as well). Such forests are influenced by the tidal movements and may be flooded by fresh or slightly brackish water twice a day. Tidal amplitude varies from place to place. Where the amplitude is high, the area subject to periodic tidal flushing is large and usually gives rise to a wide range of ecological sites. The natural vegetation in tidal forests is more diverse than that of mangroves, although still not as diverse as that of dense inland forests. Flood plains are areas seasonally flooded by fresh water, as a result of rainwater rather than tidal movements. Forests are the natural vegetation cover of riverine flood plains, except where a permanent high water table prevents tree growth. The Amazon, which has annual floods but which is also influenced by tides to some 600 km inland, has very extensive permanent and periodic swamp forests. The alluvial plains of Asia once carried extensive periodic swamp forests, but few now remain as these have mostly been cleared for wetland rice cultivation. The Zaire basin is about one-third occupied by periodic swamp forests, many disturbed by human interventions, and little-studied (Whitmore, 1990). Throughout the world, flood plains are recognized as being among the most productive ecosystems with abundant and species-rich wildlife.

Freshwater swamp forests

The term is here used for permanent freshwater swamp forests. As opposed to periodic swamps, the forest floor of these is constantly wet and, in contrast to peat swamps, this forest type is characterized by its eutrophic (organomineral) richer plant species and fairly high pH (6.0 or more) (Whitmore, 1990).

Riparian forests

Also called riverine or gallery forests. These are found adjacent to or near rivers. In the tropics, riparian forests are characterized as being extremely dense and productive, and have large numbers of climbing plants. In addition to their aesthetic and recreational values, riparian forests are important in preserving water quality and controlling erosion and as wildlife refuges especially for amphibians and reptiles, beavers, otters and hippopotamus. Monkeys and other tree-dwelling mammals and birds are often abundant in riparian forests.

Other coastal forest ecosystems

Other coastal forest ecosystems include: savannah woodlands, dry forests, lowland rain forests, temperate and boreal forests and forest plantations. Many of the natural coastal forests are under severe threat. Most of the lowland rain forests have vanished as a result of the ease with which commercial trees, standing on slopes facing the sea or other accessible coastal waters, could be harvested merely by cutting them down and letting them fall into the nearby water. As a consequence, most coastal dry forests and savannah woodlands have been seriously degraded by overexploitation for fuelwood and construction poles, and conversion to agriculture or to grazing lands through the practice of repeated burning. Coastal plantations have often been established for both production and protection purposes. As an example of the latter, coastal plantations were established in Denmark as far back as the 1830s to stabilize sand dunes which were moving inland and which had already covered several villages.

Extracted from:Integrated coastal area management and agriculture, forestry and fisheries, FAO Guidelines, FAO, Rome, 1998.
Whitmore, T.C.
1990. An introduction to tropical rain forests. Oxford, UK, Clarendon Press Ltd. 226 pp.
last updated:  Thursday, November 3, 2005