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Why teaching people about invasive plants can get a little thorny

A blond man smiles while surrounded by big green Japanese knotweed leaves. The plants are taller then him.
Carnegie Museum of Natural History
Mason Heberling, the Carnegie Museum of Natural History's Assistant Curator of Botany, stands in Japanese knotweed, an invasive plant that was originally planted in gardens. Now, it is taking over riverbanks and forests.

Forests and other natural areas in Pennsylvania look a lot different today than just a few decades ago, and that’s largely because of people and how they’ve used plants. The Carnegie Museum of Natural History in Pittsburgh is looking for ways to educate people about how their plant choices affect the natural world.

In the museum’s Botany Hall, a diorama of the Allegheny National Forest in Northwestern Pennsylvania shows a beech-hemlock forest with a floor of native plants. The display was created around 1970.

A diorama of the Allegheny National Forest behind glass, featuring several tree trunks, a big rock with a chipmunk sitting on it, and ferns, small plants and moss on a bed of orange leaves.
Julie Grant
The Allegheny Front
A diorama of Allegheny National Forest behind glass at Carnegie Museum of Natural History in Pittsburgh.

“The herbaceous layer is super-rich. We see ferns, we see flowers of all different colors,” said associate curator of botany Mason Herbling. “We see tree saplings. We see an orchid there, and we see the leaf litter under the dense canopy.”

That is not how a display of the forest would look today, because of all the invasive plants in Pennsylvania. Heberling said if you visit a forest now, “I don’t think you’d have to walk too, too far to find a plant, for instance, like multiflora rose or many other introduced plants.”

He said over time, there has been an exchange of non-native plants for the native varieties, some of which are invasive and have spread and taken over. Thorny multiflora rose and fast-growing Japanese knotweed were originally planted as ornamentals in gardens or flower beds. Japanese stilt grass got here because it was used as packing material.

A green, thick-stock and broad-leafed Japanese knotweed plant towers over a white trillium wildflower.
Carnegie Museum of Natural History
Japanese knotweed, on the left, can muscle out native plants like this trillium wildflower.

Non-native plants can become invasive when their seeds are picked up by birds, wind and water.

“An invasive is a species that causes either economic or environmental harm in some way or another,” said Rachel Reeb, a postdoctoral fellow at the museum.

She said invasives can crowd out native species in woodlands or along creeks and rivers.

Sheets of pressed and labeled invasive plants spread out on a table.
Julie Grant
The Allegheny Front
Examples of invasive plants at the herbarium in the Carnegie Museum of Natural History.

Another common invasive is garlic mustard, a plant native to parts of Europe and Asia.

“People brought it into their kitchen gardens because it was great for cooking,” Reeb said. “Now it’s one of the most common invasive species you see in the forests of Pittsburgh.” 

Garlic mustard starts to grow early in spring, and its leaves shade native wildflowers that emerge later in the season, stunting their growth. Research shows that it also releases chemicals that inhibit the growth of other plants.

Four people stand around a table covered in pressed and labeled sheets of invasive plants.
Julie Grant
The Allegheny Front
From left, Rachel Reeb, post doctoral fellow, Mason Herberling, associate curator for botany, Laurie Giarratani, director of learning and community, and Sarah Crawford, director of exhibitions and design, at the Carnegie Museum of Natural History.

The perils of talking about invasive plants

The museum was recently awarded a $225,000 grant from the Richard King Mellon Foundation (which also provides funding to The Allegheny Front). It is collaborating with the Audubon Society of Western Pennsylvania, Phipps Conservatory and Botanical Gardens, Pittsburgh Botanic Garden, and other institutions to educate the public about invasive plants.

Heberling learned the hard way how tricky it can be to talk about non-natives and invasives. A couple of years ago, he put up a sign in the Botany Hall with information about Japanese knotweed.

“It wasn’t exactly this, but it was like, ‘We hate Japanese knotweed. Remove it,’ you know?” he said.

Then he heard from colleagues who were concerned the sign could be perceived as anti-Asian and anti-immigration.

“We didn’t want visitors to accidentally take home that we are xenophobic or that we’re making comments on immigration or that some people are not wanted,” Heberling said. “So, we changed that text.”

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With this new grant money, the museum and its partners are trying to find new ways to talk about these subjects with visitors.

“It’s not these plants’ fault, so to speak, they’re just doing their thing,” Heberling said. “It really is humans bringing these plants here and ultimately affecting ecosystem function and causing a lot of impacts in our local environment.”

He and his colleagues are looking to create an exhibition, which may include digital resources, an online database, videos, and pamphlets. Their goal is to bring awareness to the problem, but they don’t want people to leave feeling overwhelmed.

“I really hope that we’re not driving home to visitors like, ‘feel guilty.’ I hope the message is more empowering and exciting,” said Sarah Crawford, director of exhibitions at the museum.

Some invasive plants like Callery pear, burning bush and privet are still sold in Pennsylvania, but are being phased out. Crawford thinks it’s important to teach people what they can do, like learn about native plants, and how to foster them.

“It’s exciting to feel like, ‘I know more now, and I can do something.’ That feels good. And that’s kind of what I’d love to see visitors walk away from this with,” Crawford said.

The museum plans to open the exhibit with educational resources late next year.

Read more from our partners, The Allegheny Front.

Julie Grant is senior reporter with The Allegheny Front, covering food and agriculture, pollution, and energy development in Pennsylvania and Ohio. Throughout her career, she has traveled as far as Egypt and India for stories, trawled for mussels in the Allegheny River, and got sick in a small aircraft while viewing a gas well pad explosion in rural Ohio. Julie graduated from Miami University of Ohio and studied land ethics at Kent State University. She can be reached at