GOODWIN ISLANDS — Wetlands scientists William "Willy" Reay and Matt Kirwan hop from their research boat anchored along a western stretch of the Goodwin Islands and splash into the York River.
They wade up to a shoreline that's being chewed up and spit out again by corrosive waves, then slosh through knee-deep salt marsh cordgrass and ankle-deep muck.
They marvel at the resilience of tidal marshes like this one to retreat and rebuild in the face of sea level that's rising at a rate twice the global average.
But that resilience comes at a cost: this string of islands once teemed with forests — unbroken acres of loblolly pine, mostly, but salt-tolerant red cedar and mixed hardwoods, too.
Now the same surging tides and inundation that deposit sediment on the islands over and over again, nourishing new marshland, is killing off those forests, tree by tree.
Aging pine stumps jut like broken teeth through the cordgrass. Towering just beyond are limbless, lifeless, bare tree trunks. And beyond those is a tree line that's been in retreat for decades.
This is what scientists call a "ghost forest."
"A ghost forest is the remnants of a live forest that are now dead — standing dead trees and stumps in the middle of a marsh," said Kirwan, who researches coastal landscapes at the Virginia Institute of Marine Science in Gloucester Point. "Where you have marsh vegetation now, you used to have trees."
Not a new phenomenon, but a growing one, such die-backs are now being observed and studied along the mid-Atlantic coast. Others are cropping up in Canada and the Gulf Coast.
But here in the Chesapeake region, where sea-level rise is coupled with sinking landmass, coastal forests are smack in the crosshairs.
A VIMS analysis shows that some 100,000 acres of coastal forest that once rimmed the Chesapeake Bay and its tributaries have died off since the 1850s — a loss of roughly half the forest that once existed.
"The mechanism in the long-term is sea level rise," Kirwan said. "But it can be punctuated by storms, specific storms, that kill the adult trees. Or it can be insect outbreaks or any number of factors. But storms on top of sea level rise is the main driver of ghost forest formation."
The Goodwin Islands lie at the broad mouth of the York River.
They're owned by the College of William and Mary in Williamsburg and offer habitat for species such as horseshoe crabs and mussels and terrapins, all manner of fish that swim in and out of the rapidly encroaching tidal creeks, periwinkle snails that inch up and down grass blades along with the tides, eagles and great herons, and even deer, raccoons and foxes that swim over from the mainland to escape predators or find food.
The islands also serve as a protected sentinel site for research on the impacts of climate change and rising seas.
This means that Kirwan and Reay — who heads the Chesapeake Bay National Estuarine Research Reserve for VIMS — monitor and measure soils, groundwater, tidal surge, weather, flora, fauna and even sunlight to observe the smallest changes in habitat and what drives them.
"We use Goodwin Islands as a case study to understand the processes that influence ghost forests ... how ghost forests in general operate and how ghost forests in general form across the Chesapeake region," Kirwan said.
The islands are expected to be a living laboratory for decades.
The reserve's other sentinel sites are Sweet Hall Marsh, Taskinas Creek and Catlett Islands, which together represent a range of salinities in the lower bay.
"These kinds of coastal systems and their tidal tributaries rank among the most sensitive to climate change," Reay said.
There are 28 research reserves in the country, managed in partnership between states and the National Oceanic and Atmospheric Administration.
Striking a balance
There's evidence that the rate of sea level rise has been accelerating in this region since the 1950s, said Reay, possibly linked to increasing groundwater withdrawal, which causes land to subside.
In the 1940s, sea level rise was about 3 millimeters a year, or nearly 0.12 inches, he said. Today, it's ticked up to closer to 5 millimeters, or nearly 0.2 inches.
Luckily, what they're finding is that island marsh is growing right along with that rate, which indicates a healthy wetland system.
Because the islands are uninhabited, Mother Nature can simply do as she's done for thousands of years: drown coastal forests and convert them to salt marshes.
Tides and surge carry in sediment, building up the marsh vertically, and also creep deeper into the forest to lay the groundwork for high-marsh plants such as salt grass and saltmeadow hay as well as invasive Phragmites australis reeds to migrate in and thrive.
"Sometimes you'll hear people talk about habitat loss," Reay said. "It's sort of a habitat change — it's going from one habitat to a different habitat, and you could argue the value of that."
In a balanced natural system, there's also opportunity for coastal forests to migrate to higher ground.
But on an island — or on a mainland coast boxed in by development — a forest might not have anywhere to migrate to. And as seas rise at an ever-faster clip, Mother Nature might not be able to keep up.
That's cause for concern, said Kirwan.
"It's happening at a faster rate than it used to be," Kirwan said. "Keep in mind it's not just forests being converted to wetlands, but it's also other types of usable land — people's farms, people's backyards. You have entire communities now that have been displaced by sea level rise."
'A forest no longer'
Maritime forests, where they exist, are key to stabilizing barrier islands that protect mainlands from erosion.
A recent study of dead and dying loblolly pine forests on the barrier Assateague Island on the Eastern Shore found that ghost forests are likely to hasten erosion and increase the impacts of sea level rise on the mainland.
Scientists from Shippensburg, Kutztown and Lehigh universities in Pennsylvania presented their research last year at the annual Geological Society of America conference in Baltimore.
They found that Assateague and neighboring islands were losing nearly 10 to 23 feet of ocean-side shoreline a year.
That storm surge had inundated back shore areas at elevations of up to 8 feet above mean sea level and flattened natural dunes.
And that salty water surge impacted forest soil chemistry for months or even years after recurring storm events.
And as the soil goes, say Reay and Kirwan, so go the trees.
On Goodwin Island, for instance, the forest is shrinking even as adult trees on the uplands that are more tolerant to waterlogging and salts are still hanging on.
But the long-term outlook is grim: There are just no young trees anymore to take their place — saturation and salinity kill them off.
In an experiment a few years ago, Reay and Kirwan planted year-old loblolly seedlings in the ecotone, or transitional area, where the high marsh and forest meet, and more seedlings in plots strung deeper into the forest.
Not only did the seedlings in the ecotone die off within a year, nearly all the seedlings deeper in the forest also died. The handful that remain are so stressed they won't survive long.
Even healthy adult trees are on borrowed time now.
"The soils have already transitioned to a marsh," Kirwan said. "The trees just don't reflect that yet."
Since the 1950s, he said, the rate of forest loss to wetlands on Goodwin has tripled, from about 1 foot a year to 3 feet.
Their analysis of historic maps found that the 365-acre island system had almost 135 acres of forest. Today, it's down to just 45 acres, and decreasing.
"I'm guessing somewhere around the 2080 mark we're looking at potentially a forest no longer being there," said Reay.
"You don't have to go far to see the effects of global warming," Kirwan said. "You can see it right here in our backyard."
Using what they learn from sentinel sites in the bay, the researchers hope to create computer models so other scientists can forecast climate change impacts in other areas.
"We're seeing impacts that the rest of the world will see in 50 years," Kirwan said.
Dietrich can be reached by phone at 757-247-7892.