Explainer

Mangroves are a group of plants that have adapted to extreme climate conditions on coasts and river deltas. They are frequently inundated with salt water due to the tidal activity of gulfs, seas and oceans. Some 60 trees and shrubs belong to the mangrove group. Some are as high as 60 meters and others are just knee-high shrubs.

Natural habitat

Just like the rainforest, mangroves provide a natural habitat for several animal species. Crustaceans, oysters, snails and sea anemones find shelter in the trees' massive root systems. Insects, mammals as well as several crab and fish species thrive in the tidelands where mangroves grow. Mangroves serve as rookeries, or nesting areas, for coastal birds such as brown pelicans and roseate spoonbills. The importance of mangroves as spawning grounds for offshore fish is now being researched.

The trees grow between the 30th latitudes north and south of the equator, but also in pockets in Japan, Florida, the Bermudas, in Australia and New Zealand. The “Sunderbans” on the Ganga river delta between India and Bangladesh are some of the most famous mangrove swamps in the world.

A vital carbon sink

Much like rainforests and coral reefs, mangroves are considered one of the most productive ecosystems in the world. They use carbon dioxide, filtered from the air, to “produce” shells, nails, mosquitoes, leaves and branches.

A hectare of mangrove forest can draw one and a half to three tons of carbon dioxide from the atmosphere each year. A large part of this carbon-heavy waste, for instance consisting of dead leaves, is transported large distances into the deep sea by the high tide. There, it settles at the bottom of the sea, having no effect on the climate.

A natural wave-breaker

With its dense network of roots, mangroves protect the coasts from erosion and flooding. Intact mangroves can save many coastal regions at a time of rising sea levels. A study in Australia has long proven that the forests can also grow when sea levels rise gradually.

Their protective role was demonstrated most spectacularly during the 2004 tsunami. In places where mangroves were intact, the destruction was much less than in areas where they had been cleared.

The threat

“Mangroves can be considered the most threatened forests of the world,” ecologist Michael Succow, winner of the Alternative Nobel Prize once said.

Around the world, the coastal forests are disappearing twice as fast as tropical rainforests. Two decades ago, there were an estimated 30 million hectares of mangrove forest in the world. Today, that number has dropped by half. Every sixth mangrove species is now on a red list of endangered species.

In the Phillipnes, over 70 percent of mangrove forests has been destroyed. Most disappear when coastal tidelands are drained to make way for urban planning and plantations. Huge areas of mangrove forests have also been cleared in recent years for conventional shrimp farms.

The hope

But there's new good news – mangroves can be reforested relatively quickly as numerous UN projects in Vietnam, Thailand or Indonesia have shown. The European Union, too, is involved in reforestation projects in Asia. But reforesting former shrimp farms remains problematic. That's because the ground is often contaminated with chemicals, making it unfertile.

Author: Oliver Samson (sp)
Editor: Jennifer Abramsohn