This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Emily Ury, Ph.D. Candidate at Duke University
To get to my research sites in North Carolina's Alligator River National Wildlife Refuge I had to walk through knee-deep water on a trail that was completely submerged. This low-lying peninsula is nestled behind North Carolina’s Outer Banks. Permanent flooding is a common occurrence. The trees that grow in the water are tiny and stunted. Many of them are dead.
Evidence of forest death is evident all over coastal North Carolina. Nearly every roadside ditch that I see as I drive around the region is lined by dead or dying trees.
As an ecologist who studies the wetland response of sea level rise, this flooding is proof that climate change is altering landscapes along Atlantic coast. This is a sign of environmental changes that are also threatening wildlife, ecosystems, local farms, and forestry businesses.
Trees die, just like all living organisms. This isn't normal. Large areas of trees are simultaneously dying, and the saplings aren't growing to replace them. It's not a local problem: Seawater is increasing salt levels in coastal forests along the entire Atlantic Coastal Plain from Maine to Florida. Large swathes of contiguous forests are in danger of disappearing. These forests are now called "ghost forests" by the scientific community.
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Salt's insidious and dangerous role
Climate change is making many parts of the globe's wetlands more wetter due to sea level rise. They are also becoming saltier.
In 2016, I started working in a North Carolina forest wetland to study salt's effects on the soils and plants. For protection against biting insects and heavy rubber waders, I wear a mesh shirt and pull over 100 pounds of salt along the trail to my research location. Salting an area the size of a tennis court is our goal to replicate the effects of rising sea levels.
A remote camera captured a deer in North Carolina's climate-altered forest. (Image credit to Emily Ury, CC BY -ND
Two years of hard work paid off, the salt did not seem to have any effect on the soil or plants we were watching. Instead of waiting for the salt to slowly kill the trees, I realized I had to ask how many trees had already been killed and how much wetland was still at risk. To get answers, I needed to visit sites where trees had already died.
Rising sea levels are flooding North Carolina's coast and saltwater is seeping into the soils of wetland areas. Salts can move through groundwater in phases where freshwater is low, such as droughts. With the help of wind and high tides, saltwater can also move through ditches and canals. High salt levels in soil can be identified by dead trees with pale trunks and devoid of leaves or limbs. They were called "wooden tombstones" in a 2019 report.
Salt-tolerant grasses and shrubs replace the trees as they die. We show this dramatic shift in North Carolina in a study I co-authored along Justin Wright from Duke University and Emily Bernhardt at Duke University.
The state's coast has seen a rapid, widespread loss of forests, which has had a devastating impact on wildlife such as the endangered red wolf, and red-cockaded woodenpecker. Forest die-offs can also cause climate change as large amounts of carbon are sequestered and stored in wetlands forests.
Emily Ury, a researcher, measures soil salinity within a ghost forest. (Image credit to Emily Bernhardt. CC BY ND).
Space-based assessment of ghost forests
A 2016 Landsat8 photo of the Albemarle Pamlico Peninsula, North Carolina. Image credit: USGS
A bird's eye view was necessary to understand the changing landscape of these forests. This perspective is derived from satellites such as NASA's Earth Observing System. These satellites are valuable sources of environmental and scientific data.
Landsat satellites have been continuously taking images of Earth's surface since 1972. They are jointly operated by NASA, the U.S. Geological Survey and NASA. These images reveal both natural and man-made changes. To quantify coastal vegetation changes since 1984, we used Landsat images and referred to high-resolution Google Earth photos to identify ghost forests. Computer analysis was used to identify similar areas of dead trees throughout the landscape.
Google Earth image showing a healthy forest to the right and a ghost forest of many dead trees to the left. Image credit to Emily Ury
These results were shocking. Over the past 35 year, more than 10% of the forested habitat within the Alligator River National Wildlife Refuge had been lost. This land is federally protected and there are no human activities that could harm the forest.
The rapid rise in sea levels seems to be outpacing the forests' ability to adapt to saltier, wetter conditions. Climate change is causing extreme weather events like drought, frequent hurricanes, and heavy storms.
Our study area saw the greatest annual loss in forest cover in 2012. This was after a period of extreme drought and forest fires, as well as storm surges caused by Hurricane Irene in 2008. This triple whammy seems to have been the tipping point that led to mass tree deaths across the region.
We created Habitat Maps for the Alligator River National Wildlife Refuge to show the changes over time and the presence of ghost forests. (Image credit: Ury et al, 2021., CC BY-ND)
Scientists should help or hinder the transition?
Global sea levels are rising and coastal forests from the Gulf of Mexico to Chesapeake Bay, as well as other areas around the globe could be affected by saltwater intrusion. Conservationists are constantly rethinking their land management strategies and looking for more adaptive strategies. For example, facilitating forests' inevitable transition to salt marshes or other coastal landscapes.
The Nature Conservancy in North Carolina is one example of adaptive management. They have created "living shorelines" out of plants, sand, and rock to protect against storm surges.
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Another radical option is to plant salt-tolerant marsh plants in areas that are threatened. This is controversial as it does not support the preservation of ecosystems exactly how they are.
If forests are already dying, a salt marsh would be a better solution than reducing a wetland to open water. Open water is not necessarily bad. However, it doesn't offer the ecological benefits of a salt marsh. Proactive management can prolong the life expectancy of coastal wetlands. This will allow them to store carbon, provide habitat, enhance water quality, and protect productive farmland and forest land along the coast.
This article was republished by The Conversation under Creative Commons. You can read the original article.
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