New "Ghost Forests” Are a Sign of Climate Change

Now, at the end of August, you may think that it’s about two months too early to talk about “ghost forests.” But, in fact, they have nothing to do with Halloween—and everything to do with rising sea levels.

Along vast stretches of North America’s East Coast, rising sea levels are killing trees by inundating them in saltwater. Researchers are calling these dead trees in what used to be thriving freshwater environments “ghost forests.” Although this is occurring around the world, new ghost forests are particularly apparent in the United States, with hundreds of thousands of acres of salt-killed trees spreading from Canada down to Florida and over to Texas.

They’re also calling them something else: one of the most visible markers of climate change. While the process that creates ghost forests has been going on naturally for thousands of years, it has greatly accelerated in recent decades as polar ice rapidly melts and raises seas, pushing saltwater farther inland.

In some Maryland and Virginia forests, for example, marshes with stumps and dead trees now stand where dry land was just 50 years ago. In many of North Carolina’s maritime forests, ghost forests have taken over where leafy groves once stood.

Watery remains

The National Oceanic and Atmospheric Administration (NOAA) defines ghost forests as the “watery remains of once verdant woodlands”; areas of dead trees in former forests, typically in coastal regions where rising sea levels (or tectonic shifts) have altered the height of a landmass.

As sea level rises, more and more saltwater creeps across the land. Along coasts and estuaries, invading seawater advances and overtakes the freshwater that deciduous trees rely upon for nourishment. The salty water slowly poisons the living trees, leaving only dead and dying timber. Bare, pale trunks line areas where once-healthy, coastal forests thrived. If they should manage to keep standing, the decaying trees soon begin to resemble gray pillars, protruding out of the brackish water.

Sea-level rise is one more stressor on forests worldwide—forests that are already threatened by disease, fires, invasive species and land clearing. Combined, these perils are diminishing the ability of plants to fight climate change.

Plants absorb and sequester carbon dioxide, providing clean air for humans and wildlife to breathe. A decline in the number of plants reduces the amount of carbon dioxide that is removed from the atmosphere, which can exacerbate climate change and its negative impacts. And the death of the trees makes soil microbes release nitrogen—adding to the nitrogen already coming from other sources, including agricultural runoff—contributing to algae blooms and sick or dying fish.

In southern New Jersey, the Atlantic white cedar, which was a mainstay of the shipbuilding industry because of its resistance to rot, is disappearing. Farther south, cypresses, loblolly pines and Eastern red cedars are dying. The retreat of forests eliminates the buffer against storms and storm surges, exposing interior areas that were previously protected. It also fragments—and in some cases even erases—important wildlife habitats.

Fortunate fish

Some scientists, however, note that what harms one species or ecosystem might benefit another one. While migratory birds that rely on coastal forests may have less habitat, the conversion of forest into marshland produces extremely productive wetlands that feed and shelter fish and shellfish. The Atlantic croaker fish, for instance, was rare 15 years ago in southern New Jersey waters but now is abundant.

They suggest that ghost forests actually offer evidence that the natural world is responding to climate change and sea-level rise. By sacrificing a strand of trees along a coastline, the newly formed marshland can protect the forest and other land farther inland, since salt marshes are also effective buffers. And some studies show that carbon sequestration rates may be higher in ghost forests than in the original forests because the wet soil and healthy marsh ecology replaces the dry forest floor.

On the other hand, it’s unclear if marshes will be able to create enough sediment to keep up with further sea-level rise. It’s possible that new marshland would be able to modulate some sea-level rise but may not be able to keep it up for long. Other research has shown that among the most likely plant species to colonize marshlands are the phragmites, a group of perennial grasses. Phragmites sequester less carbon than trees, meaning coastal deforestation will, instead, lead to more carbon dioxide in the atmosphere.

Shocking specters

It’s true that saltwater intrusion has been occurring since the end of the last Ice Age many thousands of years ago when the oceans began rising due to melting ice sheets. But it is the rate at which this is now taking place that has many scientists concerned.

Efforts are currently underway worldwide to determine exactly how quickly ghost forests are now making their appearance. Some scientists say the increase began around the time of the Industrial Revolution, while others say the speedup began more recently than that.

For example, in the past 100 years, 100,000 acres of forest in the Chesapeake Bay has converted to marshland. Photographs show the rate of coastal forest loss is four times greater now that it was during the 1930s. Seas off the East Coast have risen by 1.3 feet over the last 100 years. That is a faster pace than for the past 2,000 years combined.

In the past, when large storms drove saltwater farther inland, the flooded areas would dry out before the saltwater killed most of the trees. If a storm such as 2012’s Superstorm Sandy happened 100 years ago, it would have killed some trees, but the land they stood on wouldn’t have been so wet that new trees couldn’t get established and replace the dead ones. Today’s problem is that our coastal forests just can’t keep pace with the saltwater that is rapidly seeping into the soil and surface waters of the coastal plains.

One thing that scientists do agree upon, though, is that the startling sight of dead trees in once-healthy areas aren’t specters, but easy-to-grasp signs of the consequences of climate change.

Here’s to finding your true places and natural habitats,

Candy