If any single event was a watershed for conservation of the world's mangrove forests, it was the Indian Ocean tsunami of 2004. The day after Christmas that year, a magnitude 9.1 earthquake thundered along a fault line on the ocean floor with a force that sent waves — some a hundred feet high — surging toward the densely populated coasts encircling the Indian Ocean. The disaster took more than 225,000 lives.
In the aftermath of the tsunami, some scientists reported that settlements behind swampy, shoreline mangrove forests often suffered less damage, and fewer casualties, than areas where the forests had been cleared for aquaculture or coastal developments. Although the mangroves provided only modest protection against such a devastating tsunami, the ordeal was nevertheless a powerful reminder that mangroves can be vital buffers against storm surges, floods and the normal hazards of coastal life.
Many took the lesson to heart: Mangroves had to return.
In several affected countries, nonprofits and government agencies swiftly began planting mangrove seedlings; in Sri Lanka, plantings were made at more than 20 sites around the island’s rim. But when University of Ruhuna botanist Sunanda Kodikara visited those sites between 2012 and 2014, he was shocked to find mangroves regrowing on only about 20 percent of the area planted. Elsewhere, just a few saplings persevered, or none at all. “I saw so many dead plants,” Kodikara recalls. Especially disheartening, he says, was the fact that some $13 million had been spent on the efforts.
Such results are particularly frustrating to experts, as the need for protecting and restoring the world’s “blue forests” is greater than ever. Mangroves are mighty sponges for climate-warming gases — which makes large companies increasingly eager to pay for mangrove conservation to offset their own emissions. Mangroves are also havens for biodiversity, and living dikes that help shield against storms and waves that are growing ever stronger in a warming climate. And yet, they remain one of the world’s most threatened tropical ecosystems; we’ve lost over 35 percent of the world’s total in two recent decades, largely due to clearing of mangroves for aquaculture, agriculture, urban development and timber.
CREDIT: CURIOSO PHOTOGRAPHY / SHUTTERSTOCK
That’s why there’s rising interest from governments, nonprofits and local communities around the world in rebuilding these vital systems. But, as Kodikara saw in Sri Lanka, such endeavors often fail. In the Philippines, for instance, less than 20 percent of planted saplings survive, on average, while a large-scale study estimated a median survival rate of roughly 50 percent. Now Kodikara and other scientists are increasingly urging organizers to abandon old approaches to regrowing mangroves and the misdirected incentives that drive them. Instead, they argue for a science-based approach that takes into account the forests’ sensitive ecology and tendency to regenerate naturally, and the needs of people who live around them.
As coastal and marine ecologist Catherine Lovelock of the University of Queensland in Australia notes, “We all understand exactly how you grow a mangrove forest, and it’s been known for quite some time.” The problem, she says, has much more to do with people than with science.
Indispensable swamps
When colonial-era seafarers first encountered the stout, tangled forests that fringe the world’s tropical shorelines, they despised them for their swampy stench and dangerous inhabitants like alligators and snakes. But today, there’s a growing worldwide appreciation for these coastal jungles. Mangroves are valuable precisely because they thrive in one of the harshest environments known to trees: the intertidal zone. Salt exposure from daily inundation with seawater can cause physiological stress, and the fine-grained, waterlogged sediments the trees grow in contain little oxygen for roots to breathe.
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