As Sea Levels Rise, So Do Ghost Forests
Up and down the mid-Atlantic coast, sea levels are rising rapidly, creating stands of dead trees — often bleached, sometimes blackened — known as ghost forests.
The water is gaining as much as 5 millimeters per year in some places, well above the global average of 3.1 millimeters, driven by profound environmental shifts that include climate change.
Increasingly powerful storms, a consequence of a warming world, push seawater inland. More intense dry spells reduce freshwater flowing outward. Adding to the peril, in some places the land is naturally sinking.
All of this allows seawater to claim new territory, killing trees from the roots up.
Rising seas often conjure the threat to faraway, low-lying nations or island-states. But to understand the immediate consequences of some of the most rapid sea-level rise anywhere in the world, stand among the scraggly, dying pines of Dorchester County along the Maryland coast.
Chesapeake Bay’s migrating marshes
People living on the eastern shore of Chesapeake Bay, the country’s largest estuary system, have a front-row view of the sea’s rapid advance, said Keryn Gedan, a wetland ecologist at George Washington University.
Part of the reason for the quickly rising waters may be that the Gulf Stream, which flows northward up the coast, is slowing down as meltwater from Greenland inhibits its flow. That is causing what some scientists describe as a pileup of water along the East Coast, elevating sea levels locally.
The effects of climate change are also exacerbated by land that is sinking as a result of geological processes triggered by the end of the last ice age.
Because of the extraordinary speed at which the water is rising here, Dr. Gedan said, “I think of this area as a window into the future for the rest of the world.”
In Dorchester County, where dead and dying loblolly pines stand forlornly, Dr. Gedan has learned to “read” these forests from the mix of species present.
As saltwater moves into the ground, oak and other sensitive hardwoods die first. Loblolly pine, the most salt-tolerant, is often the last tree standing until it, too, is overwhelmed.
Then the saltwater marsh plants move in. If you’re lucky, velvety tufts of cordgrass sprout. If not, impenetrable stands of cane-like Phragmites, an invasive species, take over.
One reason the effects of rising seas are so noticeable here is that the land has very little slope. Those five millimeters of sea level, a rise that’s only slightly more than two half-dollar coins stacked, can translate into saltwater pushing 15 feet inland per year, according to Dr. Gedan.
Shoots of sweet gum, a tree with star-shaped leaves and bark like alligator skin, have more tolerance for salt than other hardwoods, such as oak. They can endure for a time as groundwater becomes more saline.
But eventually, the sweet gum dies as well.
The Blackwater National Wildlife Refuge, where Dr. Gedan does research, lost 3,000 acres of forest and agricultural land between 1938 and 2006. More than 5,000 acres of marsh became open water.
At first, this trend depressed Matt Whitbeck, a biologist with the Fish and Wildlife Service who works at the refuge. Saltwater marshes are important nurseries for the fish and crabs people like to eat.
But in 2012, he realized the marsh wasn’t entirely disappearing; it was migrating. Some of the 3,000 acres of forest that the refuge had lost had transformed into saltwater marsh.
His outlook changed. “We need to think about where the marsh is moving, not where it is,” he said.
But in nearby Smithville, a historically African American town, this movement poses an existential threat. Backyards have been gobbled up by advancing marsh, basketball courts overgrown. What were once thick stands of pine near the water’s edge have greatly thinned.
The marsh now menaces a historic graveyard.
Residents have battled the advancing wetlands for years, said Roslyn Watts, 60, who grew up here. All that time, she and her neighbors thought the inexorable advance was simply the price of living near water’s edge.
But in 2010, she learned about global warming and sea level rise, she said. She understood that what was happening wasn’t entirely natural.
“I was angry,” she said, and particularly incensed by the idea that retreat was the only workable strategy. The Dutch didn’t retreat, she said. They built dikes. Why couldn’t Smithville?
“These families have been here since at least the late 19th century,” she said. “There’s a connection to the land.”
But Smithville, small and with few resources, has little money to adapt.
Further south in Somerset County, numerous “for sale” signs stand in front of houses along the back roads. Some are abandoned, their yards overgrown by Phragmites. On Deal Island, ditches once dug to drain the land for farming and to help manage flooding from high tides now stand full of stagnant water.
Today, in fact, these ditches are part of the threat: Instead of draining water out to sea, they can accelerate the movement of saltwater inland, said Kate Tully, an agroecologist at the University of Maryland.
In general, saltwater can seep into the soil before sea level rise becomes obvious in other ways, killing sensitive plants far from the shore. “We call it the invisible flood, because you can’t really see it,” she said.
Elizabeth van Dolah, an anthropologist at the University of Maryland who works with rural communities along the eastern shore, noted that residents here are accustomed to marsh migration and flooding. “But they’re probably seeing it happening at a much quicker pace than in the past,” she said.
“Many of them recognize that, yes, they eventually have to leave. But for the time being, they intend to stay in place.”
Bob Fitzgerald, 80, has farmed near the town Princess Anne his whole life. Driving the back roads in his four-seater pickup, he pointed out fields that, just five years ago, grew corn but have since become too salty for crops.
“You can’t give property away down here,” he said.
The asphalt roads are occasionally tinted red along the edges. That, too, is an effect of the floodwater “over-topping” the roads, Mr. Fitzgerald said.
“People who have built their homes here are damn fools,” he said, speaking near a place where pine trees appear to be dying around a house. “It should have been abandoned.”
As the years pass, he said, it will be.
‘Cedar cemeteries’ in New Jersey
For 33 years, Ken Able has walked the same causeway almost daily at the Rutgers University Marine Field Station in Tuckerton, N.J. In that time he has seen marsh become open water, and the fish population transform as cooler-water species decline and those that thrive in warmer waters move in.
Blue crab and summer flounder, both saltwater species, have pushed into freshwater rivers. Their arrival suggests the waterways are becoming saltier further inland.
All these signs of change come from the ocean, a fluid and often fickle environment. Which is why Dr. Able, a professor emeritus of marine and coastal sciences, so appreciates the ghost forests. They’re a signal of change from a stationary source: the trees themselves.
“A ghost forest is a way to capture geological history,” he said. “There’s not always a way to do that.”
The Atlantic white cedar, abundant around the Mullica River Estuary in stands such as this one, is an unusually durable parchment on which to capture that history.
Long prized for lumber, its wood is highly resistant to rot. But the tree is also very sensitive to salt. It can tolerate maybe three salty high tides before succumbing.
So when the trees begin dying, it’s a trustworthy indicator that conditions are becoming more saline. It is an age-old phenomenon, now happening faster.
Erosion of marshes and riverbanks has also accelerated, revealing buried cedar stumps from prehistoric ghost forests. Jennifer Walker, a frequent collaborator with Dr. Able who recently earned her Ph.D. in oceanography at Rutgers, dated one stump here to the fifth century. “Cedar cemeteries,” she calls these places.
As elsewhere, ghost forest formation seems to have sped up recently, particularly after Hurricane Sandy hit the region in 2012. “It’s a good example of a slowly encroaching process — and then storms making it worse,” Dr. Walker said.
She is studying sediment cores from salt marshes and dating ancient, dead cedars in order to reconstruct sea level rise and ghost forest formation through time.
The pace of sea level rise first quickened in the late 19th century after the Industrial Revolution, Dr. Walker said, and then sped up again in recent decades. It’s now rising faster than at any point in the past several thousand years.
Much of the Mullica River Estuary is a nature preserve, its many tributaries remote and undeveloped. But since 2015, Dr. Able and Dr. Walker have taken a series of helicopter rides over the area. “It’s not one giant ghost forest,” Dr. Walker said. “But the more you look, the more you find them.”
From above, they’ve seen swaths of dead trees along riverbanks many miles from the open ocean, suggesting that Sandy pushed seawater far up the river system.
“You get a slug of saltwater,” Dr. Able said, “and things die.”
On the North Carolina coast, fires and salt
Paul Taillie, a Ph.D. student at North Carolina State University, encountered a mystery: He wanted to know how quickly ghost forests form. So he repeated a study originally done 15 years earlier to see how plant life had changed over time.
As expected, saltwater marsh had advanced. Pond pine and other salt-sensitive trees were dying. Salt-tolerant plants, including sawgrass and black needle rush, were moving in.
But unexpectedly, the change wasn’t occurring evenly across the landscape. Trees were dying faster in some places than others.
What could explain this uneven emergence of ghost forests?
The study area had almost no slope — much of it was just inches above sea level — and the minor differences in elevation couldn’t explain the variation.
But a clue came from the soil. It tended to be saltier where trees were dying fastest.
The explanation Dr. Taillie, who’s now a post-doctoral researcher at the University of Florida, landed on had to do with drought. When droughts hit, the amount of freshwater emptying into the ocean from nearby rivers declines, making near-shore waters saltier in some places.
That saltier water then pushes inland unevenly, killing trees in an irregular pattern across an otherwise mostly uniform landscape. “It’s not just rising sea level” that creates ghost forests, Dr. Tallie said, but periods of dryness.
“It’s more during times of drought, when you have less freshwater, that the saltwater creeps in,” he said. “Salinity goes up.”
Wildfires are another accelerant.
Wetlands burn naturally here during dry years. Fires often travel on top of standing water, consuming grass and trees that rise above the muck.
In the past, young trees quickly sprouted after fires. But recently, some forests have failed to recover.
“There’s almost no regeneration,” Chris Moorman, a disturbance ecologist at North Carolina State University, said as we surveyed an expanse of dead, mostly branchless trees. He and Dr. Taillie said they think that wetlands like these have become too salty for young pond pines, which are more sensitive to salt than mature ones. They can’t gain a foothold in marshes their own forebears could tolerate.
Drought is predicted to become more frequent as the climate warms, Dr. Taillie said. That means wildfires, combined with intensified dry spells and amplified saltwater intrusion may, together, accelerate the formation of ghost forests independently of sea level rise.
The synergy of fire and salt produces particularly dramatic ghost forests. Along the Chesapeake Bay, stands of trees might gradually thin near open water, until just a few scraggly pines remain. But in some places here, acre upon acre of dead trees, sun-bleached and occasionally fire-blackened, stand sentinel over bubbling marshes.
Yet while the ghost forests may evoke graveyards, the salt marsh plants that advance into dead and dying stands of trees are themselves valuable. Marshes provide homes for birds; they serve as nurseries for young fish and other sea creatures.
And as the sea advances, the new marshes also provide a momentary buffer against the rising tide — protecting the forests whose time has not yet come.