Saltwater intrusion is killing the freshwater-dependent forests, leaving behind what looks like a desperate scene from a big-budget, post-apocalyptic summer blockbuster. But this is not a movie set. These are signs of climate change.
“A ghost forest is a stand of dead trees. It’s evidence of a mass mortality event,” said Dr. Emily Bernhardt, James B. Duke Distinguished Professor in the biology department at Duke University. “The phrase has been applied to other causes of mass forest mortality like drought and bark beetle infestations, but is most prominently used for the loss of coastal trees due to rising water levels and soil salinization.”
Bernhardt, an ecosystem ecologist and biogeochemist, was the guest speaker June 3 for the virtual Cary Science Conversation “Saltwater Intrusion, Sea Level Rise, and the Spread of Ghost Forests,” hosted by New York-based Cary Institute of Ecosystem Studies.
Bernhardt and her colleagues have been monitoring the transformation of North Carolina’s Albemarle-Pamlico Peninsula for nearly 20 years. An area with large-scale agriculture, salt water intrusion from sea level rise has been made worse by irrigation infrastructure. Increasing salinity is transforming forested wetlands into salt marsh, reducing carbon storage and crop productivity, and degrading freshwater resources, according to a release from Cary Institute.
Speaking before a screening of the short film “The Seeds of Ghost Forests,” produced by Luke Groski of public radio’s Science Friday, Bernhardt said that ghost forests are becoming increasingly prevalent features in North America’s coastal plains.
“One of the most important points I like to make when I talk about climate change on the coastal plain is that it’s not something that we need to talk about happening in the future. We don’t have to wait. We are already facing really rapid climate change induced shifts in our ecosystems,” she said.
Living on the edge
While a lot of the focus on the coastal changes is on the wealthy fringe, where the people have big houses, Bernhardt said the National Science Foundation is funding a research coordination network to focus on the much poorer, less empowered communities living in rural landscapes.
The Saltwater Intrusion and Sea Level Rise Coordination Network, which is still in its early stages, is pulling together researchers to study the problem of rural coastal climate change by linking environmental and social sciences.
“We’re looking at forests – and it’s because we can see them from space – but the same places where we’re seeing forest loss, we’re seeing loss of agricultural productivity, wholescale loss of agricultural fields to salinization, threats to drinking water supplies,” she said.
With the new network, Bernhardt hopes to help amplify the voices and the stories of why it matters to “keep these kinds of communities of plants and animals and people existing and healthy.”
“A lot of the places which are really vulnerable to rapid climate change on the coast also happen to be places where the people who live there are already living on the edge, and so this is going to be something that’s a real threat,” she said. “There’s an enormous environmental justice component to this story as well, that is going to be an important part of our work moving forward.”
She said certain landscapes are more likely to be vulnerable to hurricane or drought and salination. These types of landscapes often overlap with populations that have higher poverty levels.
“I think part of what we need to do as scientists is make sure we expand that conversation to include the people whose voices really should be heard, instead of ours,” she said.
“Canary in the coal mine”
Ghost forests are a concern, Bernhardt told Coastal Review during a follow-up interview, because they are a “canary in the coal mine” for all sorts of other subtle environmental changes along the coast. Only a few plants, and only one kind of woody plant — mangroves — can survive in saltwater.
“The ghost forests are obvious even from space, but in the same areas, landowners are reporting the salinization and flooding of agricultural fields – conditions which make it impossible to sustain crop yields,” she said.
As sea levels have risen and fallen over geologic time, the bands of salt marshes, freshwater marshes and freshwater forested wetlands have gradually migrated inland and seaward, Bernhardt explained.
The issue now is that the rate of sea level rise and the magnitude of droughts and hurricanes that contribute to salinization are increasing, and there is no way for many of these forested wetlands to migrate to higher ground. That’s because higher ground is being used for agriculture and lawns.
“We are losing this really special kind of ecosystem, the cypress and gum swamps that are home to so much wildlife and which sequester so much carbon, more than two times that found in a salt marsh,” she said.
The entire East Coast and Gulf Coast are subjected to significant disturbances from storm events that can push saltwater inland. It takes more than a year for rain to rinse the salt pushed inland, she explained during the presentation.
Increasingly severe or long-duration droughts are adding to saltwater intrusion as well. Drought in a flat landscape is another way that saltwater can move upland, inland or landward.
“We had such a drought on the coast of North Carolina between 2007 and 2012, punctuated by Hurricane Irene,” she said. “Three years of drought with a hurricane in between, that’s a pretty tough time to live as a tree.”
Bernhardt explained that many who live on the coastal plain in North Carolina don’t want to talk about climate change, but they are perfectly happy to talk to researchers about field flooding and salinization of their fields.
“It’s a big problem. It’s widely acknowledged. Everybody either has it happening on their land or know someone who is,” she said.
In some areas, farmers are starting to grow more salt-tolerant crops, a form of adaptation.
“In the coastal plain of North Carolina, we’re seeing less of that,” she said, attributing that to the high number of the farms owned by multinational companies and rented to individual farmers who operate in small areas.
“I think that’s an interesting difference regionally, but you’ve got sort of different farming communities facing this problem and the amount of economic or socioeconomic power they have to make change for protected fields really varies and that’s one thing we’re going to be spending a lot of time thinking about with our new research-coordinating network,” she said.
Wetlands provide important protections for coastal residents, their homes and their livelihoods from storm surges and saltwater intrusion. But this buffer is vulnerable.
“I think if we don’t do anything intelligent here, we just keep letting this happen, we’re going to lose our coastal wetlands. We’re going to salinize huge areas of agricultural land so that they are no longer viable for that livelihood,” she said.
The salts will deplete nutrients in farm fields and cause massive problems for coastal fisheries and water quality.
Bernhardt and her team worked on a restoration project to convert farmland to forested wetland just east of Columbia in Tyrrell County. The land, at least 3 miles from the nearest coastline, was drained when it was used for agriculture.
As part of the restoration project, the drainage pump station was removed, and “we started to see during these periods of drought, brackish water entering this restoration wetland. A lot of trees that were planted as part of this restoration project died as a result of the drought and salinization,” Bernhardt said.
Part of what makes the coastal plain of North Carolina, and many other flat landscapes, vulnerable to saltwater intrusion is all the connected ditches and canals. “As people — either because of restoration or because of farm abandonment — stop actively maintaining this drainage, it becomes a route for salts to move upland,” Bernhardt said.