Ghost Forests: How Rising Seas Are Killing Southern U.S. Woodlands

by Roger Real Drouin (Yale Environment 360) A steady increase in sea levels is pushing saltwater into U.S. wetlands, killing trees from Florida to as far north as New Jersey. But with sea level projected to rise by as much as six feet this century, the destruction of coastal forests is expected to become a worsening problem worldwide.

Saltwater, flowing into this swampy, freshwater-dependent ecosystem as a result of rising sea levels, is turning these stands of hardwoods into “ghost forests” of dead and dying trees.

A similar transformation is occurring in coastal floodplains across the southeastern and mid-Atlantic regions of the United States, representing what scientists say is the leading edge of climate change in what were once largely freshwater ecosystems. From Florida’s hammock islands to North Carolina’s swamp forests, rising sea levels, often compounded by regional water management practices, continue to push saline water further inland, wiping out swampy woodlands.

In addition to killing off bottomland forests, saltwater intrusion is affecting wetland habitats in places along the U.S. East Coast like the Delaware Bay estuary, where encroaching sea levels are inundating the salt marsh and killing a line of forest fringing the coast — allowing a non-native, invasive strain of reed to colonize.

Before bottomland hardwood forests disappear, the subtle signs of saltwater intrusion take place in the soil. Plant growth halts, trees and plants produce fewer seeds, and the seeds that do drop to the ground have a harder time germinating. “Even with relatively low levels of salinity, trees slow their growth,” Ardón says of swamp trees such as water tupelo and pond pine. Cypress trees are often the last to die, since they are among the most salt-tolerant of coastal forest trees.

Saltwater also begins breaking down peat — partially decomposed vegetation — faster, which can have drastic consequences in places like North Carolina’s Albemarle-Pamlico Peninsula, where elevation on average is only two feet or less above sea level. The loss of peat causes land to subside, enabling saltwater to move farther inland. Forest habitat can then transition to marsh and, eventually, open water.

As part of a National Science Foundation-funded, $1.5 million collaborative project among North Carolina universities, researchers are working on mapping a vulnerability index for ecosystems prone to saltwater intrusion.

Over the past several decades, in places such as Cumberland and Cape May counties in southern New Jersey, encroaching sea levels have been inundating salt marsh and killing forest flora such as tupelo, Atlantic white cedar, and shrubs fringing the coast. In some instances, a non-native, invasive strain of a reed, Phragmites australis, is taking root — thus preventing the marsh from retreating inland, according to a 2013 study. READ MORE and MORE (Globe and Mail) and MORE (Washington Post)