Why This Invasive Plant Has A Shot At Some Redemption
Robert Buchsbaum walks into a salt marsh on Boston’s North Shore. Around him towers a stand of bushy-topped Phragmites australis, an invasive plant commonly known as the common reed. Or, as some call it: the all-too-common reed.
Buchsbaum kneels in the mud and begins to dig. Phragmites is an enemy that this regional scientist with the Massachusetts Audubon Society knows all too well.
The plant, which typically grows about 13 feet high, looms over native marsh plants, blocking out their sunlight. When Phragmites sheds its lower leaves, or dies, it creates a thick layer of wrack that keeps native plants from germinating. Its stalks clog waterways, thwarting fish travel. Salt marsh sparrows avoid them. The roots, or rhizomes, secrete a chemical that prevents other plants from growing, and they grow so deep they are nearly impossible to pull out.
That’s what Buchsbaum is kneeling in the mud at Rough Meadows Wildlife Sanctuary to demonstrate. He grabs a Phragmites root with both hands, leans back and pulls with all his might. Nothing. Phragmites isn’t going anywhere.
“It’s very resilient,” says Buchsbaum. “You need to keep after it, and you’re going to be doing it forever.”
But this stubborn bully of a plant might have a shot at redemption. A recent study from the Smithsonian Environmental Research Center found that the very traits that make Phragmites a tough invader — larger plants, deeper roots, higher density — enable it to store more carbon in marshy peat. And as climate change races forward, carbon storage becomes a bigger part of the ecosystem equation.
“We’re living in a high CO2 world,” says Ian Davidson, lead author on the Smithsonian study. “So it’s become pretty interesting to understand how much carbon is stored in the biosphere, and in particular types of habitats.”
Davidson is quick to say that his research doesn’t advocate removing native plants in favor of Phragmites.
“There’s fairly universal agreement that we should try to reduce and prevent invasions as much as we can. But there’s also the world we have right now,” he says. “[Carbon storage] is one factor that should be considered among many when managers are trying to make decisions about how to help the system function.”
While scientists have long studied carbon sequestration in forests and farmlands, says Davidson, they’ve more recently started to examine “blue carbon,” which is stored in marine habitats like marshes and mangroves. His study is one of the more recent to look at the differences in carbon storage between native and invasive coastal species. And while Davidson’s study is not definitive, its findings on Phragmites were surprising, and gave local ecologists food for thought.
“That paper was very interesting,” says Anne Giblin, a senior scientist and interim director of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole. “[It] did a very nice job talking about the balance between having increased carbon storage, but perhaps having slightly lower ecosystem services for other things, such as biodiversity.”
Giblin says the tradeoffs are complicated. Phragmites gives off methane, a potent greenhouse gas. And the plant only stores carbon permanently when it decomposes into peat, and the peat is left alone. But Phragmites may offer another advantage in the face of climate change — since it builds up so much, it can buffer marshes against sea level rise and storm surges.
“In the mid-Atlantic where they are losing a lot of the marshes really quickly, there [are] discussions about whether or not they should be treating frag because it is one of the few plants that is keeping up with sea level rise,” says Nancy Pau, a biologist at the Parker River National Wildlife Refuge on Plum Island. “So those discussions are happening at kind of localized levels.”
No scientists are advocating for actually planting Phragmites, and Mass. Audubon, the state, the National Park Service and many other groups have active programs to combat it. But where the invader has already won, or has overtaken a mudflat or brownfield, some think it may best be left alone.
Back on the marsh, Mass. Audubon’s Buchsbaum says he bears the invader no ill will. But he doesn’t want to use it to combat climate change.
“Should we be depending on an invasive species, which causes a degradation to the habitat, to make up for our foibles of emitting too much carbon into the atmosphere?” asks Buchsbaum. “Is that the right approach to take, or should we be doing something to reduce our carbon footprint?”
But reducing our carbon footprint quickly enough to avoid the worst consequences of climate change won’t be easy. And it may mean opening our minds to some of our old enemies.
Copyright 2018 WBUR