Mayor seeks to weed out invasive common reed near Stony Brook Harbor

Head of the Harbor Mayor Douglas Dahlgard is weighing action against an invader: phragmites australis, a fast-growing reed producing dense stands around Stony Brook Harbor.

Dahlgard, state environmental officials and a Stony Brook University scientist recently visited several stands on the harbor’s south shoreline near Smithtown’s Cordwood Park, where Dahlgard hopes to win grants and funding for eradication.

"This is an invasive species which has taken over the viewshed, which is an asset of the village," he said. "People come to look at the water, take photos, and we want to restore that — it’s something that is valuable."

The most common strain of the plant in the northeast United States came from Europe in the 18th or 19th century in ship ballast. It spread across much of the eastern half of the United States and across New York State and grows along many Long Island waterways.

In the salt marsh on the harbor’s edge, tufted brown blades of phragmites grew 12 feet high. They grew tallest on the county land, bowllike and fed by runoff from surrounding hills. Stunted specimens grew closer to the harbor’s brackish water.

"This is pure monoculture," said Rob Marsh, Department of Environmental Conservation natural resources manager, pointing to the stand nearest Cordwood Park. Phragmites can be pretty and its roots stabilize the shoreline, but this stand was so dense phragmites appeared to have crowded out plants like spartina grass and groundsel bush, he said.

A healthy marsh supports a variety of birds and wildlife. Not phragmites. "Nothing eats it and only the redwing blackbird nests there," Marsh said.

Dahlgard said he envisions several years of repeated cutting and digging channels to drown the freshwater-loving plant in saltwater from the harbor. He also hopes to replace a metal and plastic culvert under Harbor Road with a more attractive bridge that would allow for more water flow from the harbor to an area, owned by the county, that is thick with phragmites. He did not yet have a cost estimate.

Repeatedly cutting phragmites back has worked on small lots but could take years for larger patches, DEC's Marsh said. Channels worked in the Wertheim National Wildlife Refuge in Brookhaven, he said.

"This is definitely a very doable project," Marsh said. But phragmites have outlasted its human opponents elsewhere. Ward Melville Heritage Organization discontinued a $21,500, 2019 program to hand cut phragmites in Stony Brook Creek that yielded mixed results. In some places, "it looks like it flourished," said the group's president, Gloria Rocchio. State environmental officials said it might take 10 years or more of cutting to produce lasting results, "but we're not in a financial position to do that," she said.

Mike Kaufman, a Suffolk County Planning Commission member who participated in Head of the Harbor tour, said that marsh restoration could be eligible for federal grants and funding through the county’s clean water fund. "This is a significant coastal fish and wildlife habitat," he said. A county spokeswoman did not respond to a request for comment.

Near the culvert, Stony Brook University oceanographer Malcolm Bowman warned that the tidal currents carrying salty Long Island Sound water weaken before they reach this deep into the harbor. "It’s not going to be a straightforward solution," he said.