Mangrove forests: ecology

Mangrove roots, Mafia Island, Tanzania. / ©: Edward Parker / WWF-Canon
Mangrove roots, Mafia Island, Tanzania.
© Edward Parker / WWF-Canon
Mangrove forests consist of diverse, salt-tolerant tree and other plant species, ranging from small shrubs to tall trees tens of metres high.
These forests are found between 32 degrees north and 38 degrees south of the equator, in sheltered, inter-tidal areas that receive a high annual rainfall.

The most extensive area of mangroves is found in Asia, followed by Africa and South America. According to the FAO, the total mangrove area is around 150,000 km2. Four countries (Indonesia, Brazil, Nigeria, and Australia) account for about 41% percent of all mangroves.

Although a wide variety of plant species are found in mangrove forests, only some 54 species belonging to 16 families are recognized as "true mangroves" - species which are rarely found outside mangrove habitats.

Mangrove trees have various adaptations that allow them to live in saline, tidal areas. Their dense root systems give support in the soft, water-logged sediment. In most species, the roots protrude above the soil to absorb oxygen from the air, as the sediment is oxygen-poor.

In addition, the trees either actively exclude salt when they take up seawater through their roots, or else excrete the salt from their leaves, roots, or branches. Most mangrove species also have special adaptations for reproduction, including viviparity where seed germination begins on the tree itself.

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