Ghost forests are likely not filled with ghosts, but they should probably scare us. A ghost forest is a stand of dead and decaying trees, an eerie sight that serves as a dramatic warning of a growing problem within the global ecosystem. Ghost forests form when the ocean rises and floods coastal lands, a phenomenon generated by rising sea levels or by tsunamis (catastrophic ocean waves caused by seismic activity that can devastate low-lying coasts). When salty ocean water meets and mixes with fresh water, it forms pools of brackish marshy water. The salt content in this water is too high for most trees to tolerate, and it poisons them. Over the course of a few decades, this exposure to seawater can cause hundreds of acres of previously healthy forest to die. A tree can stay standing for a decade or longer after its death, which is part of what lends ghost forests their spooky appearance. In time, however, the marshy land gives way too, and the area becomes part of the open sea.
Because of rising sea levels, some Native communities in Alaska have had to be relocated, and the survival of whole countries like Kiribati are threatened. Kiribati is an island country, and the bulk of its land is just a few feet above sea level. As sea levels rise in response to increased global warming, it could become uninhabitable in this century. As flooding and other natural disasters become more common because of climate change, ghost forests provide striking evidence of how quickly healthy wetlands and upland forests—which are valued economically because of their timber, the agricultural potential of their land, and their use as a protective barrier from storm surges—can be lost. Because of how rapidly they form, ghost forests have become a stark indicator of climate change; some scientists note that it may be the most striking one. The mean sea level has risen almost six inches in the last century, and the rate of sea level rise is escalating.
Ghost forests are emerging in areas that have been forested for hundreds or, in some cases, even thousands of years. One ghost forest that formed recently in North Carolina contained a root system that dated to 1,800 years ago. Since the late 19th century, more than 100,000 acres (about 156 square miles) of forest along the coast of the United States have been lost, and thousands of acres more are at risk today. Ghost forests can occur in any coastal area around the world at or near sea level. In the U.S. they occur primarily on the East Coast and in the Mississippi delta region, because so much of this low-lying land is flat, which makes it more prone to flooding. A few ghost forests have also been reported along the Pacific coast and in Alaska.
The earliest record of the use of the term ghost forest comes from the 1920s, which is when they began to be studied, but ghost forests have existed for far longer. Throughout Earth’s geologic history, the world has passed through various cold periods and warm periods, with large amounts of water freezing and thawing, causing sea levels to both fall and rise, respectively. The number and intensity of extreme weather events—such as drought and tropical cyclones (hurricanes and typhoons)—have risen in several parts of the world during the 21st century. These events have contributed to an increase in the rate of ghost forest formation in the last two decades, with some climate scientists reporting that ghost forest formation tends to be most rapid in areas where a period of drought is followed by a tropical cyclone.
Ghost forest emergence also appears to be contributing to global warming. In coastal landscapes, they replace healthy wetlands, forests, and mangroves, all of which serve as carbon sinks that lock away carbon, preventing it from being released into the atmosphere. When trees and other plants in these ecosystems die, they tend to release the carbon they’ve stored aboveground (that is, in the leaves, trunk, and branches) into the atmosphere, whereas the carbon found in the underground portion (that is, the roots) of the plants tends to remain stored in the soil.
Still, one estimate puts the amount of carbon stored in wetlands at between 20 and 30 percent of all terrestrial carbon. If all of this were released, it would greatly exacerbate the global warming already underway. If ghost forest formation becomes widespread, it could become a notable factor driving climate change. To prevent this from happening, some researchers suggest a series of solutions. They note that adding trees to shorelines can slow erosion, because their root systems can hold the soil in place, especially if these trees can also adapt easily to changes in soil chemistry brought on by seawater. In addition, depositing sediment can raise the bottoms of coastal marshes, which can allow these wetlands to slowly spread to higher elevations out of reach of rising seas. Other tools that address the root cause of ghost forest formation include preventing and controlling wildfires and reducing individual and national carbon footprints—all of which help to avert sea level rise by limiting the amount of carbon that enters the atmosphere in the first place.