Mangroves have declined by nearly half in the last 50 years. This is disconcerting to scientists because the hardy brackish tidal tree is an important bulkhead against climate change, according to findings is a recent study published in the journal Nature Geoscience.

Tropical mangrove trees are better at storing climate-warming carbon than most other forests, so cutting them down unleashes far more greenhouse gas than deforestation elsewhere, scientists reported in the study.  In fact they store two to four times the carbon that tropical rainforests do according to Daniel Donato, U.S. Forest Service scientist and lead author of the study.

Destruction of these tropical coastal woodlands accounts for about 10 percent of carbon dioxide emissions from deforestation, the second largest source of CO2 after fossil fuel combustion, the study found.

Mangroves — whose twisted, exposed roots grace coastlines in more than 100 countries — provide many benefits. The trees act as a natural nursery for dozens of species of fish and shrimp essential to commercial fisheries around the world. They also serve as a natural bulwark against hurricanes and storm surges.

Donato, based in Hilo, Hawaii, and an international team of researchers examined the carbon content in 25 mangroves scattered across the Indo-Pacific region. The trees stored atmospheric carbon just as well as land-based tropical forests, they found. Below the water line, mangroves were even more efficient, hoarding five times more carbon over the same surface area.

“Mangroves are among the most carbon-rich forests in the tropics,” Donato said. “Our data show that discussion of the key role of tropical wetland forests in climate change could be broadened significantly to include mangroves.”