New plant invader takes over Eastern forests

A pretty ornamental shrub from Japan found in many people's yards is sprouting wild in an increasing number of parks and forests across the United States.

Now, researchers at the University of Cincinnati warn that the shrub, Siebold's viburnum, is showing up in many public forests across southwest Ohio.

Landscapers plant Siebold's viburnum because it is hardy, grows in sun or shade and doesn't need a lot of water. It has pretty white blooms in the spring and produces colorful berries.

The invasive viburnum is sold and planted in all 50 states and has been identified as an invasive species in 10 so far, including New York. The Lower Hudson Partnership for Regional Invasive Species Management warned that Siebold's viburnum is crowding out native plants in some of its parks.

"A large, quick-growing shade-tolerant shrub with a high reproductive potential, the species is capable of changing both the composition and density of the shrub layer in habitats it invades by outcompeting other vegetation," the environmental group said.

"It's probably going to become a problem in more states eventually," botanist and UC College of Arts and Sciences Professor Denis Conover said. "It spreads pretty easily."

Sprouting in city parks

Conover said the shrub comes from part of Asia that has a similar climate to that found in the Midatlantic and Eastern United States.

"It grows in Japan in a similar latitude to the Midwest, so the plants will do very well here," Conover said.

"Birds like to eat its berries, so it has some ecological value. But it would be better to plant native viburnums instead," he said.

The United States is home to many native species of viburnum. But nonnative, invasive species of viburnum are increasingly showing up growing wild around Cincinnati, said Drew Goebel, a conservation technician with Cincinnati Parks.

"These plants are a problem in other parts of the country," Goebel said. "They're not officially a problem here yet."

Ironically, Goebel said one reason viburnum hasn't overtaken woodlands in Southwest Ohio is because another invasive species beat it here. Goebel said Amur honeysuckle dominates the understory in many local forests.

"They haven't been planted in sufficient numbers here to explode like we've seen other plants do," he said. "And there's a lot of competition from Amur honeysuckle."

But new invasives such as Siebold's viburnum are quick to take root in places where volunteers and city workers have removed honeysuckle, he said.

"We'll see other invasive species creep in like Higan cherry or Amur cork tree. And now viburnum," Goebel said.

The city is working to eliminate the invasive viburnum before it becomes a problem.

"We've killed a lot of viburnum in California Woods and hundreds of them at French Park," he said of two city parks.

Conover said the nonnative viburnum also was found at a third city park, Burnet Woods, next to UC's Uptown campus. Last fall, he and Goebel demonstrated how the plant can be controlled by sawing through the heavy trunk and applying a pesticide to the outer edge of the sawed stump to prevent it from sprouting new growth. The two are collaborating on a new study examining successful ways of controlling the invasive plant.

States like Ohio are taking steps to address the spread of nonnative, invasive species that are causing agricultural or ecological harm. But there are no restrictions on selling or planting nonnative viburnum.

"We have proof that they can escape and reproduce in the wild. But there are no regulations on planting them now," Goebel said. "And there's no public awareness about the potential problems they pose. I feel like we need to get on top of them."