Plants that kill: Invasive species damaging the local ecosystem

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This story originally appeared in the April 7 edition of the weekly LINK Reader. To get these stories first, subscribe here.

They’re here. They’re green, and they’re taking over. 

While the pop of green can be a welcome promise of warm days to come, it can also be the first sign of trouble ahead, resulting in an artificial beauty that kills natural food sources for wildlife. 

Invasive plants tend to leaf early and can shade and crowd out native plants, which need the sun to grow, according to Jim Benton, chairman of The Campbell Conservancy. 

“Non-native plants are very successful at growing into a new area, because they get their leaves first, and they keep them the longest,” Benton said. “Right now, pretty much anything that you see is green, odds are that it’s a non-native and invasive plant.” 

Many invasive plants are attractive to humans, he said. Many come with lacy flowers that emit pleasant scents, while others appear as a deep rich green blanket on the landscape. They are easy to grow and seem hearty no matter what the conditions. Their attractiveness is a prime reason many of these plants, native to Europe or Asia, are here. 

While the early foliage may seem like a good thing, those invasive plants can actually poison the soil and further harm native plants. In contrast, native plants are adapted to the local climate and will attract pollinators more easily, which is good news for those growing fruit and vegetables. 

Invasive plants today can take root from landscapers seeking pretty and fast-growing trees for new developments, or by homeowners who want flowering bushes to line their property. Other plants can come as stowaways on packaging and products shipped from overseas. Even some government fish and wildlife agencies have brought them in to provide food for animals and to help with soil and water conservation, Benton said. 

The Bradford pear tree is a classic example. 

These trees grow fast and bloom with pretty white lacy flowers and a not-so-pleasant smell. Brought in to decorate new suburban developments, they were initially deemed safe and easy to control. They were even considered sterile. Yet, thanks to the bird population that found them tasty, their seeds spread and mixed with a local variety of the plant. Now the hybrid, known as the Callery pear, is quite prolific, Benton said. It’s crowding out native trees, and can be seen flowering among the greenery now.

While the Bradford pear came to the U.S. in 1963, many invasive plants have been here a much longer time. English ivy likely came with colonial settlers, Benton said. The vine creates a tough thicket and needs to climb trees to propagate.

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Kristopher Stone, director of the Boone County Arboretum, said Spring Grove cemetery used it in the 1840s as a plot cover. 

“So, when people were buried there, they had square plots of English ivy ground cover, and that’s all spread out into their trees,” Stone said.  “[Staff is] at war with it all the time, cutting it out of their trees.” 

Taking over

Not only do these plants smother out native plants, they can poison the ground so that nothing else can grow, Stone said. 

Bush honeysuckle, an early blooming woody bush with small white to yellow flower clusters, is considered enemy No. 1 for this and many other reasons. 

“Honeysuckle is allelopathic, so that means as the foliage on the highest level drops off, and it decomposes, it releases chemicals,” Stone said.  “It creates a chemical barrier that prevents other plants from sprouting underneath it.” 

In fact, it takes additional time, up to two years, after honeysuckle is cut down for the poison to leave the soil and becomes hospitable once again for other plants. 

Bush honeysuckle on a hillside can also contribute to soil erosion and the hillside slides regularly seen in the Northern Kentucky area, according to Brandon Helm. 

Helm is the manager of the Stream Restoration Project for the Northern Kentucky University Center for Environmental Restoration. 

Honeysuckle has a very shallow root system, he explained. Not only does it smother the herbaceous layer of the forest floor, it can inhibit the growth of the native plants that have deeper roots that would fight erosion by keeping the soil in place.

“So you’re looking at, like, an entire watershed,” Helm said. “Where there’s a lot of honeysuckle, you often see lots of erosion going on, because of the fact that the forest floor underneath is barren…The ground is pretty much bare soil. So groundwater, rainwater, stormwater, is able to flow across that and erode that zone underneath the honeysuckle plants.” 

The Kentucky Exotic Pest Plant Council publishes and maintains a list of the most common invasive plants in the state. The list rates plants as either a severe threat, significant threat or lesser threat. 

Callery pear and bush honeysuckle are high on the threat list, and English ivy is considered a significant threat, according to the Exotic Pest Plant Council. 

Invasive plants create food deserts for wildlife

Leonard Beck, an adjunct professor at Thomas More University and environmental science teacher at Boone County High School, noted the loss of native species has broad and long-term effects. 

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“Native plants support a lot of wildlife,” Beck said. “If you’re concerned about bees, establishing those native plants is essential. The way things work is you have your native insects and pollinators. And you have these flowers and plants, and they evolve together and are adapted to each other. They have this strong relationship with each other. And so, when you have invasives, that relationship is lost.”

In fact, for pollinators, a yard or forest full of invasive plants becomes a food desert for those important insects. 

“Invasive plants are an issue for a lot of reasons, but they have big impacts all the way through the ecosystem. You lose your insects, that goes all the way through the foodweb, everything else suffers,” Beck said. 

Removing invasives and restoring native plants can be difficult, but the results are dramatic, he said. 

“I would say just plant natives as much as you can,” Beck said. “They’re beautiful. They’re adapted to live here … Everybody doesn’t have to have a nature preserve in their yard. Even if it’s just some native plants, that’s something.” 

Eradication: ‘A one-two punch’ 

Once an invasive plant is identified, what can be done to cull the problem? Local experts advise residents take these steps: 

Educate yourself: Learn all you can about the common invasive plants. Fortunately, there’s a wealth of printed and online resources, organizations devoted to native plant restoration, consultants and free or low-cost training courses.

Take a walk: Do an inventory of your property to identify the invasives and the native plants. Field guides, available on the web or in print, can help.

Be aware: Help stop the spread by checking your clothes and shoes after taking a hike. Many invasive seeds take their own hike on the bottom of your boots. Pets can spread seeds in their paws, so it’s good to wipe their feet after a trip to the dog park. 

Choose an eradication method: You can call in a professional service, but if you decide to tackle the job yourself, get the advice you need, devise a plan of attack and begin. There are different methods, and what you do may depend on the time of year and the tenacity of the plant. Often it’s a combination of eradication methods that works best.

Yanking or digging out shallow-rooted plants is one way. Some plants are easier to pull than others, of course, and you want to be careful to get the roots when you can. 

The smothering/heating method can work. This involves covering the area completely with a black plastic cloth to trap in heat to kill the plant. You may have to leave the cloth on all summer, and you may have to combine the method with pulling.

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Cutting plants and using herbicide on the stumps is probably the most effective even though a lot of people want to avoid using herbicide. For large swaths and stubborn invasives it may be the only way. Glyphosate glycine, also known by the brand name Roundup, can be put directly on the stumps and is absorbed down into the roots. Timing can be important to get the optimal point in the plant’s growth cycle for it to be effective.

Using herbicides is a tradeoff one must weigh carefully, Beck cautioned. 

“You must ask yourself, ‘This will kill all this stuff, but do I want to use it? What are the other effects I will have on the environment? Do I want to expose myself to this chemical? Do I have the physical ability to get rid of this stuff, put in the time and effort?’ You have to weigh all this and make the best decision you can,” he said.

Have patience: “Eradication is a two-step process,” Benton said. “It’s a one-two punch.”

Step one is pulling or cutting the plant, applying herbicide or whatever method you choose for the initial volley. You will have to follow up the next year and possibly the next. Some plants have created a large supply of seeds, their own seedbeds in the soil, and those seeds will germinate in year two and possibly beyond.

Get involved: If you want to do more, consider joining one of the nonprofits devoted to supporting native plants. Most are very open to volunteers and offer events where you can lend a hand clearing parks, roadsides and other public areas. 

Some states have banned the sale of different invasive species. Kentucky does not allow the sale of pear trees. You can work with others to push for legislation that protects native plants.

Plant natives: Fortunately, interest in native plant species has exploded in recent years. Landscapers have picked up on the trend, and now there are native plant nurseries, garden centers and landscapers. Check out native plant sales as well.

A few of some of the more popular natives are spice bush, a pretty and sturdy bush and an excellent alternative to honeysuckle; river cane, the only bamboo species native to North America; native sumacs; native plums; native grasses; wild flowers. The list goes on. Native plants can be ordered online as well.

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