Planet Earth

The Familiar Plants and Animals That Invaded America’s Landscape

Palms in Southern California, tumbleweeds in the desert West, earthworms in rich American soils: These well-known species aren’t what you think they are.

By Jeanne ErdmannMay 20, 2020 10:00 AM
Amur honeysuckle, Lonicera maackii - Shutterstock
Amur honeysuckle, Lonicera maackii (Credit: Nikolay Kurzenko/Shutterstock)

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Growing up, I loved honeysuckle. My friends and I couldn’t wait to pull at the blossoms and inhale their sweet smell. That was childhood life in crowded Midwestern suburbia. But now that I’ve spent the last 20 years surrounded by farmland, I’ve seen the dark side of bush honeysuckle, watching as my childhood favorite reaches across fence lines and chokes out our local woods.

I’ve also come to realize that many of the species I encounter every day are also not-so-friendly intruders. Those fat earthworms wriggling on my garden trowel, the honeybees buzzing in the flowers and the feral cats sheltering in my neighbor’s barn are also aliens among us. (Yep, even those sunny-faced interloping daffodils have escaped the garden gate.)

You probably encounter species every day that are not native to our shores. In general, a species in the U.S. is considered non-native if wasn’t here before European settlers arrived some 400 years ago. Today, every corner of the U.S. harbors impostors to its native ecosystems, regardless of whether they arrived on purpose or accidentally. These non-natives are considered invasive once they start to harm the environment or economy. Here are some of the most surprising offenders.

Photo Gallery:

Photo Credits: ppa/Shutterstock

The invaders among us lurk right under our noses. Kentucky’s beloved bluegrass isn’t from Kentucky at all; rather, it’s native to Europe, northern Asia and parts of Africa. The grass likely arrived with colonists as part of turf grass seeds, and today can be found in all 50 states, most especially as an invader in native grasslands in the northern Great Plains. Sod lawns south of the Mason-Dixon line are almost always non-native, enthusiastically invasive Bermuda grass.

Photo Credits: born_to_travel/Shutterstock

When you think of Los Angeles, you envision palm trees. But only the California fan palm is native to the Western U.S.

In the 18th century, for biblical reasons (think Palm Sunday) Spanish Franciscan missionaries planted foreign palms in Los Angeles. Over the next 100-plus years, city officials imported them from around the world to cultivate an aura of exotic luxury — an image boosted by Hollywood. In the 1930s, a planting craze helped employ people during the Great Depression.

Today, these palms are dying out because they’ve reached their 75- to 100-year lifespans, and they’re falling prey to the South American palm weevil and Fusarium fungus. (By the way, botanists don’t consider palms trees at all; they’re more closely related to grasses and bamboos.)

Photo Credits: yhelfman/Shutterstock

We become strongly attached to the life that’s growing, buzzing and swimming around us. Those beings intertwine with our history. Unfortunately, nostalgic ties can hamper the tough decisions necessary to save local environs, especially when the interlopers are fetching. In California, for example, the eucalyptus tree arrived with European settlers by way of Australia, and became popular during the Gold Rush to help deforestation.

“These trees burn really hot and there have been several fires in the Berkeley, California, area that have destroyed houses and could have killed people — folks who want to keep them from being removed have an indirect role in increasing the likelihood of catastrophic fires in urban areas,” says Elise Gornish, an ecologist at the University of Arizona.

Photo Credits: Dominic Gentilcore PhD/Shutterstock

We end up claiming species like these as our own for two reasons, says Gornish. For starters, time matters. If something has been around for 100 years, we feel ownership. Plus, if it’s useful, it must be “ours” — like the cheatgrass that the government planted all over the Great Basin during the Dust Bowl of the 1930s to prevent soil erosion. The plant had come over in the ballast of ships in the 1600s, and today has long worn out its welcome, covering more than 100,000 acres in the American West, says Gornish, where it robs the native sagebrush habitat of water and nutrients.

Photo Credits: Carl Erdmann

“Our woodlands look very different today,” says Scott Woodbury, a horticulturalist at Shaw Nature Reserve, part of the Missouri Botanical Garden. Before colonial visitors, our woodlands were more open. Hot fires would occasionally sweep through, which helped maintain the open ground layer. Now, in Missouri and places east of the Mississippi River, bush honeysuckle and other invasive shrubs have created so much underbrush that the leaf litter stays too moist.

The density of the trees and underbrush blocks the wind from drying out the ground layer, which prevents the hot fires needed to push back the honeysuckle, says Woodbury. Native to Western Asia and Europe and brought to the U.S. in the 1800s as an ornamental, honeysuckle was planted widely in the 1960s to promote soil stability. The shrub has no predators here, and the hardy plant is now cutting down on species diversity in the Northeast and other areas. Birds like the berries, but they’re kind of like junk food, Woodbury says, because they’re not very nutritious. Our feathered friends then poop out the seeds, spreading even more honeysuckle across the landscape.

Photo Credits: Mama Belle and the kids/Shutterstock

Earthworms love the moist soil of the woodland and forest floors, and we might think that love is returned. Not really. Our native earthworms, which burrowed more deeply in the soil, probably disappeared after the Pleistocene Ice Age — making most, if not all, of these squishy subterranean invaders non-native. These larger settlers wriggle in soil’s upper layers. Earthworms help aerate the soil, making for happy gardens, which thrive on aeration; but their love for the upper layers of soil makes them destructive forces in forests, where they consume organic matter that plants and animals rely on.

Photo Credits: Maciej Bledowski/Shutterstock

In the American southwest — Gornish’s territory — the worst invasive plant is the Russian thistle. You know it better as the tumbleweed, the most reliable character in western movies. The plant came to the U.S. by accident in the late 1800s as a stowaway, hitchhiking in shipments of flax seeds bound for South Dakota.

Tumbleweed can grow up to 3 feet tall and earns its name because dead, dried-up plants break off at the stem, rolling and bouncing into the sunset. But here’s the worst part: As they roll along, they spew as many as 10,000 seeds onto the passing ground. And tumblin’ tumbleweed rarely travels alone; hundreds of the thistles can cover roads and cars, clog fence lines, surround homes and make driving dangerous enough as to actually endanger lives.

“Growing up watching westerns, people don’t realize how bad Russian thistle is,” says Gornish.

Photo Credits: Greg Westbrook/Shutterstock

No romantic vision of the Old West would be complete without the galloping freedom of wild mustangs. But these feral horses are descended from the stock brought to the Americas by Spanish explorers 400 years ago. The horses share land with other species and can be as invasive and destructive as tumbleweed or honeysuckle; we’re just more sentimental about them, which makes finding solutions for them much more challenging.

And although they’re not invasive, the same story can be told for those glossy, speeding thoroughbreds that grew up farther east: They’re English imports to colonial Virginia, where they likely munched on imported Kentucky bluegrass. (Before racing fans get too depressed, the bourbon in the traditional mint juleps is distinctly American. But the mint ... maybe not.)

“People have emotional connections to these things, and that’s it,” says Gornish. “The consequences can be vast.”

Photo Credits: Greg Westbrook/Shutterstock

The emotional attachment to the feral horses, says Gornish, is disastrous for both the horses and the environment. These horses are destroying vulnerable habitat very quickly, especially native plant communities.

“However, people really dislike the ideas of killing horses, so they push back against control measures,” she says. 

The result is too many horses in really bad condition, the irreparable destruction of critical native habitat, and the consumption of management resources to capture and then cage the horses.

“Because people are so far removed from the direct experience of seeing native habitat become destroyed from these feral horses — or the terrible condition they, the horses, find themselves in because there are not enough resources to sustain the exploding population — people who emotionally connect with horses cannot get over the idea of their removal. So they make it difficult, if not impossible, for managers — particularly, the government — to do its job, and the environment suffers greatly,” Gornish says.

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