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The Snakeheads of Trees

Taking the chain saw to invasives along Route 50 and Interstate 97

Tree of heaven was originally brought to America by Chinese immigrants who prized its straight-growing trunk. Prettier to the eye but just as invasive is callery pear.

Pretty is as pretty does, or so the old saying goes. When it comes to the vegetation lining the roadsides of Bay Country highways, the State Highway Administration couldn’t agree more.
    Take the callery pear.
    Almost anywhere you drive in Maryland in springtime, you’ll be greeted by beautiful clouds of white flowers tinged with green. But the impact of this native of China and Vietnam on our native woodland is far from lovely.
    The invasive callery crowds out native species.
    “It is top-heavy and has brittle wood,” says Bay Gardener Dr. Francis Gouin. Fallen limbs from storms often pose safety hazards to motorists.
    The callery pear is the focal point of a State Highway Administration project to remove invasive plant species from segments of Route 50 and Interstate 97 in Anne Arundel County. The project will cover 540 acres on 26 miles of roadsides. Initial removal will be completed by fall 2017, weather permitting, with a further 18 months to eliminate regeneration.
    So, while you’re on the road, keep your eyes peeled for removal crews. You may see bucket trucks extended 50 feet in the air as workers in yellow-green fluorescent safety vests wielding chain saws rip heavy limbs from tall trees. You may also spot the powerful jaws of wood chippers tearing into large branches, and dump trucks hauling away debris. Slow down and give them a wide berth.
    Crews are working alongside the northbound lanes of I-97 between Crownsville Road and the Route 3 interchange. Over the course of the project, they will cover seven miles of Route 50 from the Anne Arundel/Prince George’s County line to I-97, and six miles of I-97 from Route 50 to Route 3.
    Last month, crews were working at the I-97/Route 50 interchange.
    “This interchange exemplifies the invasives problem. Sixty-five to 70 percent of vegetation here was invasive,” says Pam Milby of the Highway Administration’s Landscape Operations Division. Most of the invasive vegetation here was callery pear, with Ailanthus altissima, or tree of heaven, a second species of concern.
    Some may have sentimental memories of this tree featured in A Tree Grows in Brooklyn. Others say it is more like the forest equivalent of the snakehead fish.
    “Ailanthus was brought in by Chinese workers on the railroad. It was used by them for many purposes. In gardening, it produced straight stems for bean poles,” says Dr. Gouin.
    Here, it’s proved a dominator.
    “Tree of heaven has its own enzyme system like black locust,” Dr. Gouin explained. “It prevents grasses and other plants growing near its roots, which promotes monoculture.”
    It spreads rapidly by seed, growing tall and thick. In dense stands, tree of heaven — aka stinkweed tree — can have a weak root system that makes it liable to topple during storms, creating a safety risk on the highway.
    As the project moves from initial removal of invasive plants to control of regeneration, the latter might be just as challenging if not more so.
    “Callery pear is going to be hard to eradicate,” says Dr. Gouin. “The seeds stay in the ground for many years.”
    Perhaps because of the beauty of the callery pear in the springtime, removal can be touchy.
    “The reaction is more positive than negative,” says Milby. “Some people have seen the progressive takeover of invasives, and they are thrilled that finally something is being done.”
    For those who react more negatively, the agency has put together educational material. “Outreach seems to be helpful,” Milby says. “People are happy to hear about replanting.”
    Indeed, the invasives removal program on Route 50 and I-97 will be followed by a two-year program of replanting and re-creation of native habitat starting in June 2019. This effort will feature development of pollinator habitat where appropriate, including planting of pollinator-friendly trees and seeding of roadside meadows.
    The Highway Administration hopes that, after replanting, the native plants and habitats will keep the invasives at bay and Mother Nature will manage herself.
    “We are trying to do the right thing,” Milby says. “We want to create something that can be maintained fiscally, that is sustainable. Something that will use less herbicides, something that will take care of itself.”