Pulling out to my research sites near the Alligator River National Wildlife Refuge in North Carolina, I hit through knee-deep water on a section of the trail that is completely underwater. Permanent flooding has become commonplace on this low-lying peninsula, located behind the outer shores of North Carolina. The trees that grow in the water are small and sluggish. Many are dead.
Across the coast of North Carolina, there is evidence of forest deaths everywhere. Nearly every ditch along the road I pass as I drive through the region is lined with dead or dying trees.
As an ecologist studying the response of wetlands to sea level rise, I know that these floods are proof that climate change is changing landscapes along the Atlantic coast. It is indicative of environmental changes that also threaten wildlife, ecosystems and local farms and forestry businesses.
Like all living organisms, trees die. But what is happening here is not normal. Large patches of trees die at the same time and trees do not grow to take their place. And this is not just a local problem: Seawater raises salt levels in the coastal forest along the Atlantic coast, from Maine to Florida. Large parts of adjacent forest die. They are now known in the scientific community as ‘ghost forests’.
Deer photographed by a remote camera in a climate-changing forest in North Carolina. Emily Ury, CC BY-ND
The treacherous role of salt
Rising sea levels driven by climate change are making wetlands wetter in many parts of the world. It also makes them saltier.
In 2016, I started working in a wooded wetland in North Carolina to study the effect of salt on its plants and soils. Every few months, I dress in heavy rubber runners and a mesh shirt for protection against biting insects, and pick up more than 100 pounds of salt and other equipment along the flooded track to my research site. We salt an area as large as a tennis court to mimic the effects of sea level rise.
After two years of effort, the salt did not affect the plants or soil processes we watched. I realized that instead of waiting for our experimental salt to slowly kill these trees, the question I had to answer was how many trees had already died, and how many more wetland areas were vulnerable. To get answers, I had to go to places where the trees were already dead.
Rising seas are flooding North Carolina’s coast, and salt water is leaking into wetland soils. Salts move through groundwater during phases when fresh water is depleted, such as during droughts. Salt water also moves through canals and ditches and penetrates the interior with wind and high tide. Dead trees with light trunks, without leaves and limbs, are a sign of high salt levels in the soil. In a 2019 report, they are called ‘wooden tombstones’.
As the trees die, more salt tolerant shrubs and grasses move in to take their place. In a recently published study I co-authored with Emily Bernhardt and Justin Wright at Duke University and Xi Yang at the University of Virginia, we show that this shift in North Carolina was dramatic.
The coastal region of the state suffered a rapid and widespread forest loss, with an enormous impact on wildlife, including the endangered red wolf and impala cape. Wetland forests hold up and store large amounts of carbon, so that forest deaths also contribute to further climate change.
Researcher Emily Ury measures salinity in a ghost forest. Emily Bernhardt, CC BY-ND
Assessment of ghost forests from space
To understand where and how fast these forests are changing, I needed a bird-eye perspective. This perspective comes from satellites like NASA’s Earth Observing System, which are important sources of scientific and environmental data.
Since 1972, Landsat satellites, operated jointly by NASA and the US Geological Survey, have captured continuous images of the earth’s land surface that reveal both natural and human changes. We have been using Landsat images to quantify changes in coastal vegetation since 1984 and refer to high resolution Google Earth images to detect ghost forests. Computer analysis helped identify similar patches of dead trees throughout the landscape.
A 2016 Landsat8 image of the Albemarle Pamlico Peninsula off the coast of North Carolina. USGS
Google Earth image of a healthy forest on the right and a ghost forest with many dead trees on the left. Photo courtesy of Emily Ury
The results were shocking. We have found that more than 10% of the wooded wetland in the Alligator River National Wildlife Refuge has been lost over the past 35 years. It is federally protected country, with no other human activity that could kill the forest.
The rapid rise in sea level seems to exceed the ability of these forests to adapt to wetter, saltier conditions. Extreme weather conditions, fueled by climate change, cause further damage due to severe storms, more frequent hurricanes and droughts.
We found that the largest annual loss of forest cover in our study area occurred in 2012 after a period of extreme drought, forest fires and hurricanes from Hurricane Irene in August 2011. This was a turning point of the triple blow that caused mass tree deaths across the region.
Habitat maps we created for the Alligator River National Wildlife Refuge showing the change over time and the appearance of ghost forests. Ury et al, 2021., CC BY-ND
Should scientists fight the transition or does it help?
As global sea levels continue to rise, coastal forests from the Gulf of Mexico to the Chesapeake Bay and elsewhere around the world can also suffer heavy losses due to the intrusion of salt water. Many people in the conservation community are reconsidering land management approaches and exploring more flexible strategies, such as facilitating the inevitable transition from forests to salt marshes or other coastal landscapes.
In North Carolina, for example, the Nature Conservancy is implementing some adaptive management approaches, such as creating ‘living coastlines’ made of plants, sand and rock to provide natural buffering of storm surges.
A more radical approach would be to introduce marsh plants that are salt resistant in endangered areas. This strategy is controversial because it contradicts the desire to try to preserve ecosystems as they are.
But if forests die anyway, it’s a better result if you have to have a salt than to have a wetland reduced to open water. Although open water is not bad by nature, it does not offer the many ecological benefits that a salt marsh offers. Proactive management can extend the lifespan of wetlands along the coast, enabling them to continue storing carbon, providing habitat, improving water quality and protecting productive farm and forest land in coastal regions.
This article was published from The Conversation under a Creative Commons license. Read the original article.