Invasion of the Knotweed

The Delaware River Basin is under attack from a foreign enemy: Japanese knotweed (Fallopia japonica), a non-native invasive species, has been covering a lot of ground, and water, and wreaking havoc on its environment.

Though the bamboo-like plant seems harmless with its heart-shaped leaves and small white flowers, Japanese knotweed is known as the “Attila the Hun” of the plant world because once it invades, it’s capable of much damage. The plant grows quickly and densely, crowding out native streamside vegetation and worsening erosion and sedimentation. It’s incredibly hard for humans to limit its growth, let alone get rid of the plant altogether.

“A lot of money is spent on stream bank restoration, which often includes removal of invasive plant species, but Japanese knotweed is very difficult to eradicate. It reproduces quickly from seeds or roots, and only a small root fragment is enough to regrow a population or travel downstream and colonize a new area,” says Kathryn Christopher, an Academy staff scientist researching the invasive plant.

In January, the team deployed leaf packs, or mesh bags stuffed with leaves, into several area streams. The packs were collected over several weeks through February and early March for the researchers to examine the insect communities that have colonized the leaves.

“We are looking to see if the insects show a difference in preference between native leaves and knotweed,” she says. “We are trying to better understand the effects of knotweed on stream ecosystems so that management plans can be better tailored for specific sites, with hopefully better results.”

This article originally was published in Drexel University’s 2015 Exel magazine.