As seawater moves inland, ‘ghost forests’ are spreading. Why that’s so scary

September 29, 2020, 11:00 PM UTC

Rising sea levels have begun to decimate coastal forests, leaving white, dead stumps in their wake as salt water damages ecosystems that previously relied on freshwater ecosystems. Scientists call them “ghost forests.” And they’re growing at an alarming pace, say researchers at North Carolina State University.

A study released this week of the state’s Albemarle-Pamlico Peninsula found these ghost forests had spread across 15% of the land between 2001 and 2014, the years the study tracked. The researchers calculated that devastation equated to 130,000 metric tons of carbon that otherwise would have been captured by the forest.

“Many people think about sea level rise as being more of a long-term threat,” said the study’s lead author, Lindsey Smart, a research associate at the North Carolina State University Center for Geospatial Analytics.

But the researchers saw “significant changes” over shorter time periods, not just because of sea levels rising gradually, but because of extreme weather including hurricanes and droughts, which can bring salt water into regions that previously relied on fresh water. The peninsula lies just inland from the island chain that forms North Carolina’s Outer Banks.

This ecological impact underlies other research showing that while we often think of climate change as bringing gradually rising seas, the coastal flooding that threatens vast swaths of the earth’s ecosystems will be in large part the result of exceptional storm surges from hurricanes and flash floods. Over the years, the expansion of coastal marshes and the retreat of the region’s forests have also upended local communities and livelihoods. In addition, coastal forests provide a vital level of environmental protection as their soil, in good times, stores more carbon than forests further inland.

The ghost forest degradation also puts these ecosystems at greater risk for forest fires. “We think there may be an interaction between salt water and fire that accelerates forest retreat, and facilitates marsh migration into areas that were once healthy coastal forest,” Smart said.

It’s not that frequent, low-level fires don’t serve a role in the local ecosystem, the researchers noted. But after a fire, a period of regeneration must allow new seeds to take root and begin restoring the region’s vegetation. However, young seeds of woody vegetation—like trees—can be damaged by excessive salinity.

There are similar risks to coastal forests that are increasingly hit with drought, the paper noted. Collectively, the creation of ghost forests means those forests are also less able to play their roles not just as carbon sinks, but as storm buffers, to limit the impact of the same storms that are bringing salt water inland.

The intrusion of salt water into forests that were previously fresh water is often an “invisible threat” the researchers said, “because shifts in soil chemistry are difficult to measure at large spatial scales and are not generally perceived by the public,” they write in the paper.

Instead, ghostly white, semi-submerged stumps are a warning sign of what’s happening below.

“Ghost forests provide clear markers of sea level rise’s leading edge,” they wrote.

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