Can restoring mangroves protect Miami from rising seas?

Miami Beach, Florida — As the 20th century dawned, mangroves blanketed this Florida island, which, at the time, was more of a swampy sandspit than solid land. Their gnarled roots standing knee-deep in tidal waters, mangroves were mainly known as the haunts of alligators, other reptiles, and blizzards of mosquitoes. And by 1915 they were gone. Carl Fisher, one of the founders of Miami Beach, had stripped the island bare as his first step toward transforming it into the fabled tourist playground it is today. 

The 21st century vision of the future is different: City leaders see a resilient Miami Beach at the front lines of climate change, adapting to rising seas and worsening storms by installing massive pumps, elevating streets—and, yes, bringing back the lowly mangrove, nature’s buffer against storm tides. Next week, volunteers plan to plant 680 mangrove trees in the city’s largest park to create a “living shoreline” along the same stretch where mangroves were hacked down a century ago.

Mangroves may have been destined for eradication back then, but today they stand almost unequaled for their benefits to the environment. They’re still not an easy sell here though—even after Miami-Dade County recently rejected a proposal by the Army Corps of Engineers to construct a massive seawall. The county put forward no alternative plan—but mangroves, goes the argument, would spoil the view. 

The trees are usually not very tall, but they’re scruffy and gangly limbed. Not to mention the mosquitoes.

“I don’t think individuals generally think of mangrove shorelines as a desirable way to stabilize their properties,” says Lisa Spadafina, assistant director of the Miami-Dade division of environmental resources.

Yet the mangrove forest’s ability to buffer against the energy of hurricane-force winds and surging waves is well documented. Mangroves annually shield 15 million people globally from harmful violent storms and save $65 billion in property damages, according to 2020 research published in Scientific Reports. A dramatic confirmation of their value occurred in 2004, when a giant tsunami, one of the deadliest in history, swept through the Indian Ocean. Villages in India and Malaysia that stood behind mangroves suffered less damage and had fewer deaths. In 2005, the Indian government banned deforestation of mangroves.

Even small stands of mangroves can stabilize coastlines against erosion and cleanse polluted water of toxins. Mangroves also act as a nursery for birds, fish, shellfish, and even sharks by providing food, shade, and protection from predators, tidal surges, and heat. As a bonus, mangroves store copious amounts of carbon emissions, as much as five times more, acre for acre, than terrestrial forests.

All that would seem to make the new mangrove seedlings arriving at Brittany Bay Park in Miami Beach central players in the $1.8 million makeover of the waterfront park. There, the living shoreline will include natural material (the mangroves) paired with hard material (the seawall) to bolster efforts to fight flooding, as South Florida faces the prospect that seas will rise two feet by mid-century.

“As seas rise, it is easier to build up a living shoreline rather than reconstructing an entirely new seawall,” says Amy Knowles, Miami Beach’s resilience officer, as she shows off some of the city’s elevated streets and massive pumps on a recent morning walk. “Is it the Number 1 protection? It’s part of the entire toolbox of options that we have.”

But there are limits to how much the city can do. It has 55 miles of coastline, and all but five miles is privately owned. 

Every day should be mangrove day

If Knowles was looking for a strong voice to defend the planting of hundreds of mangroves in Brittany Bay Park, UNESCO could lend a hand: Today is International Day for the Conservation of the Mangrove Ecosystem. UNESCO created the holiday in 2015 at the urging of Ecuador, home to towering 200-foot mangroves, to draw attention to mangroves’ virtues, as well as to the decimation of mangrove forests globally. 

Since 1980, more than half the world’s mangrove forests have disappeared, victim primarily to urban coastal development, road-building, and farming. Much of the loss has occurred in Southeast Asia, where nearly a third of the world’s mangroves grow, and where they are logged for charcoal production and cleared to make room for aquaculture ponds, mostly for shrimp farming.

Rafael Araujo, a University of Miami mangrove researcher, grew up in Colombia and assists Asian and Latin American countries in devising mangrove protections. He says he has seen a reversal of thinking about mangroves—and that’s a good sign.

“When I was young, mangroves were thought of as a wasteland, full of mosquitos, and we should chop them down,” he says. “None of my students today think of mangroves that way. That gives me hope for the ecosystem and the benefits they provide.”

Mangroves thrive in conditions that would kill their terrestrial cousins. Although they live in saline swamps, they extract freshwater from seawater through their roots and excrete salt through their leaves and bark. 

“The most incredible thing about mangroves is that they live in conditions that are stressful constantly,” Araujo says. “With salinity, they have found a way to cope. In high temperatures, which are quite challenging for trees, they have found a way to cope. In soils without oxygen, which would be death for other trees, they found a way. I find that inspiring. Even with adversity, you can cope.”

What mangroves can’t do, of course, is stop sea level rise. In fact, by mid-century, scientists predict they could become a casualty themselves. To survive, mangrove’s roots must be exposed to air twice daily with the changing tide. As seas rise, and the tidal zone moves inland, mangroves would have to migrate inland with it, or they won’t survive.

Raising mangrove 'pups'

Mangroves can still be found across South Florida, fringing parks and other areas. But efforts to add more of them to densely populated urban spaces have run into resistance.  

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In Miami proper, opposition to a plan to add more mangroves to an upgrade of the flood-prone Morningside Park prompted the Miami City Commission to consider a proposed ordinance outlawing the planting of mangroves on public property. After an outcry, the measure was shelved. 

Mangroves still have many fans. The garden club in Coral Gables, near Miami began raising and planting red mangroves in 2020, after Rhonda Anderson, a club member and Coral Gables city commissioner, rescued 300 mangrove propagules, or “pups,” that had washed onto a bike trail after a king tide. This year, with the help of a local scout troup, the club is raising 1,500 mangroves in plastic kiddie pools, to be distributed along the Florida coastline.

Naysayers, Anderson says, “might want to opt for some mangroves so they can clean up the water. It gives people a different perspective on nature and what it can do for you.”

North of Miami, Palm Beach County has been installing small, artificial islands, planted with mangroves in Lake Worth Lagoon to restore bird and wildlife habitat lost to dredging and other causes. The county also has partnered with The Nature Conservancy to expand and restore habitat to Palm Beach Resilient Island, which plans to plant mangroves there next month.

In a separate project to demonstrate mangroves’ value as protector, scientists at the group used an insurance industry model to estimate property damage losses after Hurricane Irma pummeled Collier County, on the Gulf Coast in southwest Florida, in 2017. The group concluded that every 2.4 acres (1 hectare) of mangroves with properties behind them had prevented an average of $7,500 in damages The Nature Conservancy urged county officials to invest in mangrove restoration.

If there is any downside to using mangroves in living shorelines, it’s that small clusters may not buy much protection from wind and flooding. Scientists have long argued that only wide stands of mangroves can truly provide protection against violent storms. 

“You have to have 100 meters if you want to cut down a storm surge,” says Peter Sheng, a University of Florida engineering professor who has analyzed storms and wetlands along the East Coast.

On the other hand, here’s where mangroves’ other attributes come into play: Even a narrow strip of trees can stabilize the shoreline or improve water quality. “Yes, I do agree, every bit helps,” Sheng says. “If you have a few meters of mangroves, it is better than nothing.”