Scientists using fungi to stop an invader
Not everything the U.S. Forest Service does involves protection and conservation.
Sometimes you’ve got to kill something.
In this case, it’s an aggressive, non-native tree that grows fast, spreads quickly and robs native oaks and maples and their undergrowth of the sunlight and space necessary for survival.
In a research project launched recently in Ohio, scientist Joanne Rebbeck is bottling a kryptonite of sorts in hopes of stopping Ailanthus altissima in its tracks.
Rebbeck has injected a native fungus into 40 trees at each of five test sites: the Wilds, a private, nonprofit wildlife-conservation center in Muskingum County; Blue Rock State Park, also in Muskingum County; Tar Hollow State Park in Laurelville; Perry State Forest in New Lexington; and the Wayne National Forest’s Marietta Unit.
The fungus — Verticillium nonalfalfae — can kill mature trees within a growing season. Six months into the program, Rebbeck said, “ things are looking really good. We’re killing them for sure.”
Ailanthus, also called tree of heaven, was introduced into North America from Asia in the late 1700s as an urban landscape tree. It also was used in strip-mine reclamation because it grows so fast.
“I came here, and I was shocked to see the Ailanthus growing out in the forest,” Rebbeck said. “I’m from New Jersey. I’m used to seeing it in more-urban settings.”
The deciduous tree reaches heights of 60 to 80 feet, and its sprouts can grow to 6 to 12 feet in their first year, according to Ohio State University Extension. The female tree can produce 300,000 seeds in fuzzy clusters in one year.
What makes the fungus particularly effective is that it spreads to many trees because Ailanthus roots interconnect with other trees of heaven.
Research suggests that the fungus can move 200 to 400 feet per year, depending on the density of the Ailanthus growth in its path.
Finding the fungus, however, wasn’t easy.
It was first detected in 2002 in south central Pennsylvania, when a U.S. Forest Service forester found thousands of Ailanthus trees dying from a condition later dubbed “ Ailanthus wilt.”
Through extensive research, Verticillium nonalfalfae was isolated and began to successfully be used in controlling the invasive tree in Pennsylvania. Rebbeck decided to bring it to Ohio. But when she inquired about importing the fungus, she was told that she couldn’t transport the spores across state lines because the U.S. Department of Agriculture was concerned it might be an invasive species in Ohio.
So Rebbeck began a quest to find the fungus in Ohio. After three years of searching, a private consulting forester told of Ailanthus wilt in Pike County in 2012. Since then, she has found Verticillium nonalfalfae only in Pike and Monroe counties.
With samples in store, Rebbeck headed to her lab in Delaware County, where she spent two years growing the fungus and inoculating plants in her greenhouse labs. She tested it on more than 70 native species, with little or no effect. Tests and controlled cultivation continue.
“It’s very promising because it’s very specific to this terribly invasive species,” Rebbeck said.
Why is this so important? A recent aerial survey of the Marietta Unit of Wayne National Forest showed at least 3,000 Ailanthus trees growing.
“It’s a relatively small percentage considering the land base of 123,000 acres, but our goal was not to let that change,” said Sierra Patterson, a Wayne National Forest botanist.
Tony Scardina, supervisor of the Wayne, said he hopes this fungus lives up to its potential. Treating each tree with a herbicide would be too large of an undertaking.
“What we are experiencing is the rapid expansion of the tree of heaven replacing our native species,” he said. “This might be our shot at overcoming its expansion.”
Ailanthus trees have been found in about 40 states, though the fungus that makes them wilt has been found only in Ohio, Pennsylvania and Virginia. Indiana is “looking for naturally occurringAilanthus wilt there, Rebbeck said. “We need to find it in as many states as possible."
Tree of Heaven
This native of China was brought to North America in the 1700s as an ornamental tree.
Ailanthus altissimais a rapidly growing tree that reaches as tall as 80 feet. It has large leaf scars on the twigs.
Leaves resemble native sumac and hickory species, but it is easily distinguished by the glandular, notched base on each leaflet.
Flowering occurs in early summer, when large clusters of yellow flowers develop above the foliage.
Fruit produced on female plants is tan to reddish, single-winged and can be dispersed by wind or water.
The trees form dense thickets that displace native species and can rapidly invade fields, meadows and harvested forests.