Science

Opinion | An Invasive Insect Threatens Delmarva Westlands

On the Delmarva Peninsula, the low-lying expanse of coastal plain that bulges east from the Chesapeake Bay, some of the last remaining sizable green and wild spaces are wetland forests that shroud tidal rivers and creeks on their languid journeys toward the bay: the Nanticoke , the Marshyhope, the Choptank, the Tuckahoe, the Pocomoke.

As hard as it may be to believe in this long-settled part of the world, made up of Delaware and the Eastern Shore counties of Maryland and Virginia, many of these forests remain virtually unexplored natural wonders. They are home to an explosive diversity of trees, shrubs and understory plants shaped by the rhythmic undulations of the tides, including rare and threatened species such as red turtlehead and seaside alder. They are havens for salamanders, lizards, woodpeckers, herons and more. The distinctive hill-and-hummock topography creates shallow pools where small fish shelter and forage; these fish feed bigger ones sought by fishermen and women.

One tree makes these wetlands possible: The ash. But now these trees face a formidable adversary. A few years ago, a small beetle showed up and started to change everything: the emerald ash borer, originally from Asia, was most likely a stowaway on a container ship and was first discovered in Michigan in 2002. It is now found in 35 states and was confirmed on Maryland’s Eastern Shore in 2015. This invasive insect has killed tens of millions of ash trees in the United States and threatens millions more in its continuing path of destruction. On the Delmarva, it could end entire ecosystems.

Unlike most trees, the ash tolerates the twice-daily surges of water in the Delmarva’s wetland forests. Its roots accumulate soil and build islands of life that stay above the high tide line. Scientists have a term for such species: “ecosystem engineers.” But resilient as they are, the trees die quickly once infested by the ash borer. The larvae tunnel under the bark and eat their way around the trunk until water and nutrients can no longer flow to keep the trees alive. A mature ash will probably be dead within a few years of becoming infested.

Nobody knows quite how long these tidal freshwater swamps have been here, but it is most likely several thousand years. They may have been logged, but most have never been drained, farmed or developed. Few people have entered these places on foot, because without boardwalks, they are nearly impenetrable. Even scientists have mostly ignored them, favoring other ecosystems like salt marshes.

“These are probably among the least studied coastal wetlands,” Andrew Baldwin, a University of Maryland ecologist who is studying whether they can be kept intact, told me. “Laying out the boardwalk, I was crawling through the mud. It was brutal. But it was also great, being somewhere where no one has been in a long time.”

These swamps may not invite humans in, but they are examples of intact, fully functioning ecosystems in one of the most densely populated and developed regions of the United States. These forests store carbon in the wood and in the soils that accumulated as sea level rose over centuries. They filter and scrub the water, providing one of the last natural protections for the beleaguered Chesapeake, which is undergoing an incredibly expensive, decades-long cleanup.

Not only do these places lock away carbon, slowing climate change, they also protect the surrounding coastal area by absorbing the brunt of the ever-more-powerful storms that our warming planet is tossing at us.

Now, with the arrival of the invasive ash borer, some of these wetland forests are starting to undergo profound transformations. As trees die and decompose, their stored carbon will be released to the atmosphere, and their roots may no longer hold on to soil.

People who own land along tidal rivers face mass tree death and could even lose some of their land to rising water. In one of Maryland’s popular reserves, Pocomoke River State Park, home to perhaps the largest expanse of green and pumpkin ash in this part of the world, the forest could be hollowed out.

At a time when high-level climate and biodiversity conferences are front-page news, and the plights of the rainforests of the Amazon basin and the Tongass of Southeast Alaska are well known, it’s been distressing to see these wetland forests — the Mid-Atlantic’s own version of those far away expands — fall apart with little public recognition.

A local photographer, Leslie Brice, and I have for the past two years documented the work of a small group of scientists who are planting other tree species to test whether they can replace the dying ashes, and whether chemical treatments or selected species of wasps imported from Asia can bring ash borer populations under control. These efforts can be near heroic, requiring scientists and others with the state of Maryland, University of Maryland and The Nature Conservancy to wade through thigh-deep muck in sometimes terrible weather to plant and treat trees and take measurements.

But at present, they are just Band-Aids that can at most save a few small areas. To really protect these forests would require a much larger program of tree treatments and biological controls, probably combined with long-term restoration solutions such as the breeding of a regionally adapted ash tree with genetic resistance to the borer. Because many of these wetlands are on private land, experts must also help landowners adapt. certainly, not every tree can be saved. But perhaps enough can be protected so that the wetlands remain forested and the ecosystem survives.

Gabriel Popkin is an independent journalist who writes about science and the environment. He has written extensively about threats to trees and forests. Leslie Brice is a Maryland-based photographer whose work focuses on the people and natural places of the Mid-Atlantic, Midwest, Latin America and Haiti.

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