03.2020 | THE SCIENTIST 31
T
hey look like the skeletons of giants
reaching for the s ky. Tall and ashen,
stripped of their leaves and most
of their branches, the trees stand
in uneven rows that extend as far as the eye
can see, grave markers of a forest that once
thrived near this North Carolina coastline.
“These ghost forests are the leading edge
of climate change,” Emily Bernhardt, an eco-
system ecologist and biogeochemist at Duke
University, tells The Scientist. They suc-
cumbed in slow motion to salty water making
its way inland as sea levels rose, and serve as
a reminder that global warming isn’t some-
thing just affecting polar bears in remote
locations, or something that will happen
in the distant future, she says. “It is already
happening, and happening really fast on the
coastal plain of North Carolina.”
In the decade that Bernhardt has worked
on the Albemarle-Pamlico Peninsula, a few
dozen miles west of the Outer Banks barrier
islands, she’s watched “acres and acres” of the
state’s wetland forest die. Cedars, maples,
pines, and elms are drying up, becoming too
stressed by salt to produce the chlorophyll
they need to survive. While the loss is devas-
tating, Bernhardt says, she and her colleagues
are acutely aware of the opportunity they now
have to study what’s going on. They want to
identify exactly how salt kills, understand
what happens to the ecosystem as the trees
die, and determine whether there’s any way
to intervene and preserve the habitat.
Inland forests aren’t the only eco-
systems threatened by the rising seas. All
along the Atlantic coast, from Canada to
northern Mexico, saltwater is inundating
freshwater marshes, cypress swamps, and
even farm fields. “Ghost forests are per-
haps the most iconic and easy-to-photo-
graph example of a much larger problem,”
Bernhardt says. “Basically, if you’re on the
coast and on flat land, saltwater intrusion
is going to be an issue.”
As salty water floods and then recedes
from these freshwater environments after
storm surges or record-breaking high tides,
the periodic inundation may increase the
emission of greenhouse gases such as meth-
ane from the soil. Because of this, scientists
are concerned about the environmental effect
of saltwater’s inland intrusion, while farmers
and residents, who are starting to see their
fields and yards affected by salt and flooding,
are bracing for the likelihood that they may
soon be forced to move.
Such concerns have led researchers to get
creative in their search for solutions, includ-
ing envisioning how ecosystems and land use
will change as sea levels rise. The goal of this
predictive exercise, says Matt Whitbeck, a
wildlife biologist with the US Fish and Wild-
life Service working at a station on the Ches-
apeake B ay, is to figure out how to shape the
land into a system that is not only resilient to
climate change but also best supports biodi-
versity, minimizes greenhouse gas emissions,
and provides for human needs. And it’s a safe
bet, he says, that such an ideally adapted hab-
itat won’t be farmland or forest, but probably
something more like marsh.
Droughts and storm surges bring
the salt
On the peninsula known as Maryland’s
Eastern Shore, off historic Route 50, thou-
sands of acres of forest and marsh sit rel-
atively untouched. The land is part of the
Blackwater National Wildlife Refuge, a
28,000-acre sanctuary established in 1933
for birds migrating along what’s called the
Atlantic Flyway. Despite nearly 90 years of
preservation, the area hasn’t escaped the
scars of human activity. From an observa-
tion deck at the edge of Blackwater Pond,
which sits at the center of the refuge, tree
skeletons shoot from the ground in every
direction. Only in the distance can one see
leafy trees dotting the landscape.
“Blackwater is really a place where people
can see the impacts of sea level rise with their
own eyes,” Whitbeck says.
Some of the earliest aerial images of the
refuge date to 1938. Several years ago, Whit-
beck and his colleagues compared those pic-
tures to photos taken in 2006 and estimated
that more than 5,000 acres of tidal marsh in
the refuge had turned to open water, and that
some 3,000 acres of forest had turned into
marsh. The forests and marshes are moving,
retreating farther and farther inland as sea
levels rise. “That [migration] was something
that really didn’t come to our attention until
2010 or 2011,” Whitbeck says.
It was around that time that Bernhardt
and her colleagues started tracking a habitat
that is similarly becoming much wetter—in
this case, partly as a result of human inter-
vention. It’s the Timberlake Observatory
for Wetland Restoration, a stretch of for-
mer farmland that sits off Highway 64 on
North Carolina’s Albemarle-Pamlico Penin-
sula. Developers started converting it back
to its original wetland ecosystem in the early
2000s, lowering the fields, filling in the drain-
age ditches, and planting 750,000 live sap-
lings of wetland tree species including bald
cypress (Taxodium distichum), cottongum
(Nyssa aquatica), and water oak (Quercus
nigra). A few years later, the developers cut
off the pumps that drained the land, flooding
the area with freshwater, and they asked Ber-
nhardt and Marcelo Ardón, then a postdoc in
Bernhardt’s lab, to help monitor how residual
compounds from farming fertilizer affected
the soil and plants growing there.
“We were very interested in this inter-
play—what happens when you have nutri-
ents coming from upstream and salt coming
from downstream where they mix, which
seems to happen a lot in these areas,” says
Ardón, now an ecologist at North Carolina
State University.
The newly flooded area didn’t stay wet
for long. Severe droughts across the state
in the summers of 2007 and 2008 dried
out the soil, which Ardón and Bernhardt
noticed was becoming extremely salty. The
wetland sits more than 30 miles from the
Atlantic coast, but the Albemarle-Pamlico
Peninsula is flat—so flat that the water that
Ghost forests are perhaps the most iconic and easy-
to-photograph example of a much larger problem.
—Emily Bernhardt, Duke University
