At the Beechwood Farms Nature Reserve at Fox Chapel, a Pittsburgh suburb, environmental botanist Roxanne Swann waters plants on a steamy summer day. She looks around the nursery, where she raises more than a hundred species of native plants.
“I think just about every day, I have a new favorite,” she said.
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Swann points out a cluster of purple blazing star, and tassel rue, with its small white flowers, that especially have her interest today. One of her favorites is the fragrant spicebush, where caterpillars of the spicebush swallowtail butterfly have been sheltering. “They look like a cartoon, they’re so cute,” she smiles. “They mimic a snake to sort of frighten their predators.”
Some of the leaves are curled in half, and she peaks inside them looking for caterpillars. No luck there, but then she notices two swallowtail chrysalises attached to a nearby door. “So, they’re on their way to becoming butterflies,” she explained.
This 134-acre nature reserve is headquarters of the Audubon Society of Western Pennsylvania, which is usually associated with protecting birds. “Native plants support native insect species, and birds eat insects,” explained conservation director Sarah Koenig.
A Cornell University study last year that found North America has lost nearly 3 billion birds in the past 50 years, almost 30 percent. Koenig says increasing the population of native plants in the region can help.
“Native plants are the foundation of our ecosystem. It’s [native plant habitat] supporting insects, which are critical bird food. It also provides nuts, berries, and cover for birds,” she said.
Koenig compares an oak tree, with a gingko, “which is a beautiful tree, but it’s not native to the U.S.,” she explained. “So that [gingko tree] supports about three species of caterpillars, but the native oaks support over 500 species of caterpillars.”
According to another Cornell study, a single pair of chickadees must catch 6,000-9,000 caterpillars to rear one clutch of babies.
The Peony Predicament
But what if you want to plant something that’s not native to the region, like some pretty peonies? As poet Mary Oliver describes them, “with their honeyed heaviness, their lush trembling, their eagerness.”
“I think that’s fine,” said Ryan Gott, associate director of integrated pest management at Phipps Conservatory and Botanical Gardens in Pittsburgh.
“Peonies fall in that nonnative category, but they don’t fall in the invasive category,” he said. “They don’t escape and cause any kind of harm. They add aesthetic benefit to your yard.”
The Language Defining Plants in Our Environment
Researchers have been trying to clarify the meaning of these terms. In a paper published this summer in the Journal of Extension, researchers at the University of Florida define nonnative plants, like the peony, which hails from Asia, Europe and western North America, as “a species that does not occur naturally in a specified geographic area.” The definition of an invasive plant goes further, to include plants introduced by humans, and that “does or can cause environmental or economic harm or harm to humans,” according to the paper.
In Pennsylvania, the Department of Conservation and Natural Resources lists 133 plants as invasive, including 42 that are considered “severe threats.”
“The more native species you have, the more life you have in your garden.”
Still, nonnative plants can provide ecological benefits, Gott said. They might bloom at times when no native plants are providing nectar and pollen. “Like certain nonnative Asian species of dogwood [that] mix in with our native species of dogwoods,” he explained. “They do have slightly different flowering times, and the beetles that visit them, you see move between dogwoods. So it’s kind of extending the time that there’s resources available.”
Some researchers even see benefits in some invasive plants. Take Japanese knotweed, which coats the side of many roadways. It also provides clusters of white flowers that can be seen covered in bees and other pollinators, according to Gott.
What Happens When Garden Plants Spread
Native plant enthusiast Nancy Lawson doesn’t trust that nonnative species will stay where they’re planted.
“There were some quote-unquote tame garden plants that were around for a century almost, that suddenly started taking over the forests,” she said. She gives the example of lesser celandine, also called fig buttercup.
If you’ve gone hiking in spring, you’ve probably seen its bright yellow flowers and thick mat of dark green leaves. Lesser celandine, which was brought to the U.S. from Europe and West Asia as a garden ornamental, is now considered invasive in the U.S. It blankets the forest floor in early spring, shading out native wildflowers, which provide nectar and pollen for insects.
Yet, some garden stores still sell lesser celandine, and other invasive plants like Japanese barberry.
Lawson, who wrote The Humane Gardener: Nurturing a Backyard Habitat for Wildlife, encourages people to look for native alternatives for the ornamental plants they love.
For example, instead of invasive Japanese honeysuckle she suggests the native coral honeysuckle vine, “which is a red-flowered beautiful hummingbird plant,” she said. “Also the chipmunks eat the berries, the eastern comma butterflies go to the berries as they ripen, hummingbird moths, their caterpillars eat the leaves. Every part of that plant is used.”
“I mean the more native species you have, the more life you have in your garden and in your habitat,” Lawson said.
At Beechwood Farms, Audubon’s Sarah Koenig envisions a growing movement of homeowners creating habitat for native plants, insects and birds.
“One yard makes a difference, one patio makes a difference,” she said. “A neighborhood or a cluster of gardens using native plants, all of a sudden you’re creating like a distributed nature reserve… really transforming the region together yard by yard,” Koenig said.
Resources for Native Plants
This story is part of our series, Wild Pennsylvania. Check out all of our stories here.
Top Photo by Ron Frazier / Flickr