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Planet Earth

Mangrove, the Tree That Captures Carbon, Filters Saltwater, and Stops Storms

By Amy BarthJune 16, 2011 12:00 AM


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Mangroves are survivors, due to elaborate root systems that sprawl above and below the waterline. These so-called walking trees coolly shrug off extreme heat and muddy topsoil deficient in oxygen and filter the salty waters of southern Florida and tropical Southeast Asia, where the majority of the 73 known mangrove species live. Mangroves also help other species survive, forming dense forests that shelter monkeys, kangaroos, and tigers as well as shellfish and brightly colored corals. Even humans benefit as impoverished coastal communities exploit the tree for food, lumber, and medicine. But mangrove forests are dwindling. Relentless deforestation and powerful tropical storms have reduced their habitats by 35 percent (pdf) since 1980, prompting ecologists to step up their investigations into the unique ability of mangroves to survive and protect their coastal environments.


Slows Coastal Erosion Following the Indian Ocean tsunami of 2004, a study led by Danish ecologist Finn Danielsen reported that coastal areas flush with mangrove trees were markedly less damaged than those without. The findings suggest that the trees shield the coastline (pdf) by reducing the height and energy of ocean waves and offer hard evidence that deforestation could result in increased coastal damage from storms.

Captures Carbon Mangroves are expert carbon scrubbers. A global inventory by McGill University environmental scientist Gail Chmura found that mangroves pack away carbon faster than terrestrial forests. Every year they hoard some 42 million tons, roughly equivalent to the annual carbon emissions of 25 million cars.

Establishes Deep Roots The mangrove depends on its complex root system for stability, oxygen, and salt filtration. In 2007 U.S. Geological Survey scientists analyzing mangrove roots and soil up to 8,000 years old found that during periods of rising sea level, the roots grow faster and bolster the soil, which helps hoist the tree upward.

Survives Extreme Heat Mangroves love sunshine. Unlike many tropical plants that close the pores on their leaves at midday to reduce sun exposure, mangroves remain active, absorbing heat to prevent evaporation of the shallow waters they depend on. They also curb their thirst: A 30-foot mangrove sips about six gallons per day, while a similar-size pine tree guzzles more than three times that amount.

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