Uh-Oh, the Mangroves Are Rapidly Migrating North
Mangroves have started shifting toward the poles, signifying a movement of the subtropics.
The salt-water based shrub-like trees move to where the temperatures suit their needs.
Scientists have tracked the mangrove migration for decades, a phenomenon seen across the world.
The mangrove is a demanding tree. It needs salt water to thrive and dips its roots along coastline. Those roots eventually become a tangled mass that eventually traps deposits and forms a land-like buffer between the ocean’s waves and the true shoreline. That buffer has long protected coastal areas from erosion and damage brought by hurricanes and tsunamis while sucking carbon from the air. Along with the salt water, though, mangroves require a location where temperatures never dip into freezing ranges. That’s why these trees are common in subtropical areas like Florida, South America, and Australia.
In a piece for Scientific American, writer Michael Adno spoke to ecologist Ilka Feller, who started investigating the movement of mangroves over two decades ago when she noted that the plant was showing up in locations farther north than it was believed to have done before. The movement hasn’t stopped, pushing the border of the subtropics closer to the poles. In North America, that means the northernmost mangroves have now slid north past the Florida-Georgia line.
And according to a story published by the U.S. Fish and Wildlife Service, Feller isn’t the only ecologist to have noticed. Coastal ecologist Ches Vervaeke recalled seeing these trees in January of 2024. “Holy cow, there are mangroves in Georgia,” he said. “This is climate change, there’s no denying it, this is proof. You can take the public out and show them the trees that are not supposed to be here. These are tropical plants migrating north because of climate change.”
The shift isn’t just happening in Florida, but across the globe. And it won’t just affect the trees. Mangroves have proven a robust home for plenty of creatures and their movements could provide new areas for animals and birds. It could also remove habitats for others, as the mangroves often replace marshy areas.
In the long term, this has happened before. Because these trees have such specific climate needs, their range has fluctuated right along with the temperature fluctuations of the planet. “There’s no telling how many times they’ve been [this far North] before,” ecologist Candy Feller told the U.S. Fish and Wildlife Service. “There have always been periods of expansion, and periods of contraction, based on whether or not we had a freeze event to kill them back. It’s got to be cold enough to do the damage and, then—bang—everything, including mangroves, are dead.”
As for the short-term, it has been shorter than many people expected. “We thought it would take longer to creep up from Florida, but now we’re learning that maybe we shouldn’t have been so surprised,” Jill Andrews, chief of the Coastal Management Section for the Georgia Department of Natural Resources, told the U.S. Fish and Wildlife Service. “But now it’s like, ‘OK, they’re here.’ So, we immediately shifted into making sure we understand what that means.”
Samantha Chapman—a biology professor at Villanova University—told Scientific American that not every area will see a full transition, even if some do. “I think these places are going to be a matrix of both salt marshes and mangroves,” she said.
The push-and-pull of mangrove movement and the delineating line of the subtropics is once again on the move. This time, though, scientists wonder if it will become more permanent.
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