At the Blackwater National Wildlife Refuge in Maryland, acres upon acres of dead tree trunks stand guard, their bases partially covered with salt water. In 2003, Hurricane Isabel hit the refuge before it could recover from an unusually dry summer. Storm surges brought salty seawater into the already parched landscape and essentially smothered salt-intolerant trees to death.
A 280 mile drive, at North Carolina’s Alligator River National Wildlife Refuge, it’s a similar story. A drought followed by a storm in 2011 killed huge swathes of trees on the refuge. And as climate change causes sea level to rise again, experts expect to see more of these haunting scenes called ghost forests. âIt’s a process that has been going on for some time, as the sea is rising,â explains refuge manager Scott Lanier. “It’s just now, it feels faster.”
People tend to phrase these changes in morbid terms: Apart from âghost forestsâ these rows of dead trees have been called âwooden tombstonesâ, evoking a sense of grim finality. But they are not necessarily an end. Ghost forests are markers of a habitat in transition, an intermediate phase between a forest and a swamp. The forest may die, but in its place a swamp is born.
For the birds of the mid-Atlantic marshes, these dead forests represent an opportunity. Some scientists and conservationists are working to ensure that this land turns into a quality swamp as the climate changes, providing a place for endangered coastal species to move inland when their current habitat is consumed by sea level rise. In Blackwater, old tree stumps in present-day marshes are a sign of how habitat has changed. âThese areas were once forests,â says Dave Curson, director of bird conservation for Audubon Mid-Atlantic. Now they have converted to quality marshes and marsh birds have settled there. Even in protected areas like the Blackwater Refuge, the new habitat created by inland swamp migration is unlikely to be enough to make up for all that is lost, Curson says. But these marshes could still be a lifeline for endangered birds.
The process of transforming a forest into a swamp begins with a flood of seawater, often caused by a hurricane or, in the longer term, by the rise in sea level. When salt water encroaches for the first time in a forest, it can kill mature trees, but it can prevent new ones from growing. With more frequent exposure to salt water, some trees may begin to die. Then, as more trees die and become snags, more sunlight can reach the ground, allowing salt-tolerant shrubs to colonize what was once the forest floor. Finally, the system will look like a swamp, with salt marsh grasses and only stumps left behind by the Ghost Forest, like in Blackwater.
This change occurs at the expense of forest habitat. Coastal forests are important spaces for migratory birds, and many species living in the canopy will lose their ranges with climate change. But other birds profit from their loss. From 2013 to 2015, environmentalist Paul Taillie, now a postdoctoral researcher at the University of Florida, and others bird species examined on North Carolina’s Albemarle-Pamlico Peninsula, home to the Alligator River National Wildlife Refuge. He found that although canopy birds lose some habitat, ghost forests can support a range of other species, many of which are endangered. Dead snags attract nesters to cavities such as woodpeckers and the Prothonotary Warbler, which has declined in recent years due to habitat loss. And where bushy vegetation grows, Taillie has found birds such as the Endangered Bobwhite quail, which declined by 85 percent in its range from 1966 to 2014.
Taillie encourages the transition from ghost forests to swamps as a conservation strategy. He argues that forest species that will lose out have ample space elsewhere, while birds that take advantage of snags and swamps are more in need of habitat. âThere are many reasons to be concerned about the death of trees, and I share that concern,â he says. âBut when it comes to animals, the coastal marshes are actually very important. They are home to many species that do not exist anywhere else.
Taillie encourages the transition from ghost forests to swamps as a conservation strategy.
A ghost forest does not always naturally turn into a quality swamp. In Blackwater, Curson saw habitat in transition become suffocated by Phragmites, an invasive grass that displaces native plants and wildlife. In other cases, small depressions form around dead trees as their roots shrink. Salt water fills these areas and further erodes the soil, ultimately turning the forest into open water rather than swamp. When these less-than-ideal alternatives present themselves, the ability of coastal birds to move through marshes at high altitudes is “severely compromised,” Curson says.
Curson and his colleagues experimented with ways to drain areas where the soil has subsided, such as digging canals to drain water. So far, they haven’t found success. âBut we will continue to work on the problem,â he said. In 2016, environmentalists sprayed a mixture of dredged sediment and water on 40 acres of swamp in Blackwater. Over the next several months, new marsh grasses were planted as the sediment settled in a 4 to 6 inch layer, increasing the elevation of the marsh. “TThis has resulted in firmer ground at the project site and will most likely extend the life of this marsh in the face of sea level rise, âCurson said.
Lanier, for his part, seeks a balance between strengthening the resilience of shorelines and supporting a future healthy marsh. He is working with partners such as The Nature Conservancy to make the Alligator River National Wildlife Refuge more resistant to rising waters. They built oyster reefs along the coast, which naturally break waves and slow down coastal erosion. They reintroduced prescribed burns to promote healthy swamps. And recognizing that more land will become swamps, they are investigating which plant species might be the most salt tolerant for future mass plantings, when they have more funding. âWe are not ready to end it,â he said. âIt’s still a good habitat for wildlife, and you can’t give it up. “
Realistically, more of the land that is now forested will become swamps due to climate change, even if the world stops burning fossil fuels today. Taillie suggests that land managers identify the most vulnerable forest areas and work to begin their transition to swamps. With more time to develop before oceans encroach, these swamps might have a better chance of accumulating sediment and becoming high enough to withstand sea level rise, he says.
Ghost forests show that when making decisions about climate change, it may be best to recognize how different the world will be as the results of our policies are felt. Taillie doesn’t want to lose any forests, but he recognizes that we most likely will. âIf we’re going to lose it, I want to make sure it moves on to something that will also contribute to biodiversity,â he says. âI like to see it as an opportunity. “