Invasive honeysuckle threatens Kentucky woodlands

Published 2:39 pm Tuesday, March 7, 2023


The Kentucky Lantern

From late fall to early spring, volunteers fan out across Kentucky woodlands to battle an aggressive invader they know they can’t defeat but hope to hold at bay: Lonicera maackii aka Amur honeysuckle aka bush honeysuckle.

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They pull it, dig it, spray it and cut it (then spray again) in an effort to protect ecosystems that have nurtured plants, insects and animals for millenia.

The Lantern could find no estimates of how many tens of thousands of acres of Kentucky woodlands — not to mention pastures and highway rights of way — are in peril because of bush honeysuckle.

A small study in 2011 gives some idea of the magnitude of the challenge. At Locust Grove National Historic Landmark in Jefferson County, students surveyed at 60 points in 27.5 forested acres, finding about 31,000 honeysuckle plants.

“The days of being able to not do anything are past us,” said Ellen Crocker, who teaches at the University of Kentucky’s Department of Forestry and Natural Resources.

A benign-seeming honeysuckle can start in a fence row or roadside then move on to “wreak havoc” in natural areas, she said. Once established it can outcompete native plants and help starve native animal species of the nourishment they need to survive and thrive.

How did this happen?

Like almost all invasive species, bush honeysuckle — the most common species in Kentucky is Amur honeysuckle or Lonicera maackii — came from somewhere else, in this case the region where China and Korea meet. Also, as often but not always happens, it was invited here, arriving as an ornamental planting in the late 19th century. And like kudzu and some other invasives, it was promoted for conservation use because, well, it’s good at covering bare ground quickly.

Too good. Once honeysuckle gains a toehold in an area, “if you don’t do anything it will be a honeysuckle field,” Crocker said.

Bush honeysuckle, like most invasive species, has particular qualities that allow it to “out-compete” native species. It can thrive in many soils and produces a vast number of seeds — as many as a million on a mature, 20-foot tall plant per season — which birds eat (more on that later) and then distribute through their droppings.

Plus, it is allelopathic, meaning the roots emit a chemical that can hinder growth in other, native plants. (Some native species, like the black walnut, also use this characteristic to their advantage.)

And, it leafs out earlier in the spring and stays green later in the fall than most native species, meaning it claims an early share of sun and water that plants need to emerge.

This last characteristic, though, is one that foresters, natural land managers and homeowners can use to their advantage in fighting bush honeysuckle. As the only green plant in the landscape early and late, honeysuckle is easy to spot. Small plants can easily be pulled up, especially if the soil is damp, while larger ones might require a tool to get the roots out of the soil.

Large plants can be cut down and then the stump treated with herbicide to prevent re-sprouting. For huge infestations, herbicide sprays can be effective when honeysuckle is the only green thing around and the poison is less likely to damage other, dormant plants.

This all sounds time-consuming and expensive, and it is. That’s why natural areas often rely heavily on volunteers to manage invasive species.

At Floracliff Nature Sanctuary in southeastern Fayette County “volunteers come out once a week almost every week of the year working on invasive species,” said Josie Miller, the stewardship director there.

Annually, volunteers put in about 3,000 hours at Floracliff. They do other things, like guide hikes and work on trails, but a large portion of that time is spent on fighting invasive species. “It would be a huge barrier if we were doing this with paid staff,” Miller said.

Given that it’s impossible to remove all the honeysuckle and other invasive species and keep them out, land managers like Miller have to make choices. At Floracliff the choice is to focus on the areas that have the most native species to help them survive and thrive. That’s typically the ravines, which were never farmed and were lightly disturbed for logging, if at all. In those areas native trees can drop seeds and some of them will sprout to become replacement trees, if they aren’t crowded out by honeysuckle.

Promoting a diverse forest of native species isn’t just an academic or aesthetic preference. All species use sun, soil and water to grow and produce food that other species consume, and so on through the food chain.

Honeysuckle berries “are like junk food,” Miller explained, high in carbs but low in the fats — provided by native species like viburnum and dogwood — that birds need to survive the winter. Plus, they “can cause diarrhea in birds.”

But it goes beyond that. “Insects convert plants to food for birds,” Miller explained. Honeysuckle “is not much of a host plant to caterpillars and insects” whereas an oak tree hosts 400 to 500 different varieties of caterpillars, providing lots of protein for birds in the spring when they need it.

Vigilance advised

So, when an invasive species like honeysuckle gains hold of an area it begins a downward cascade that affects the entire ecosystem and can potentially disrupt it for decades.

Research at Northern Kentucky University has recently found that bush honeysuckle can endanger stream health because its leaves decompose rapidly, sucking up oxygen in the water that aquatic species need to survive.

When the invasives are dominant “our native communities are no longer functioning well,” Miller said.

This is what Jessica Slade found in the woods at the University of Kentucky Arboretum when she became the Native Plants Collection manager and curator there last year.

The 15 acres of woodland in a corner of the Arboretum is a remnant of forests once found throughout the Bluegrass. Some trees there are as much as 300 years old but the woods had become “pretty degraded” through the onslaught of invasive species, including honeysuckle and winter creeper, an evergreen groundcover that can climb up tree trunks and is still sold in many nurseries.

“You could spend all of your time on” trying to eradicate them, she said. At the Arboretum, like Floracliff, volunteers “are pretty passionate about” removing the invasive species and know them very, very well. Slade and Miller quickly ticked off a list of invasive species, some of which are still being planted along highways, around shopping malls and in private yards: Lesser Celadine, Miscanthus, Porcelain berry, Autumn Olive, privet, Johnson grass, garlic mustard, callery or Bradford pear, Tree of Heaven, Burning Bush. “They all have different strategies that make them more successful,” Slade said.

What to do? “Be vigilant,” recommended Billy Thomas, an Extension Forester with the UK Department of Forestry.

Learn to identify the invasive species and pull them up before they get big enough to spread elsewhere. There are resources to help people who own larger tracts of land — most forest in Kentucky is in private hands — manage the expense of controlling invasive species. He said that, rather than try to eradicate them from an entire tract, “just pick an area” and work to control non-native species there.

But, all the experts said, it’s important to recognize that it’s an ongoing thing. Invasive species spread through bird droppings, on the wind, through the water and in other ways so they will always return.

If nothing else, Thomas said, just take it as “a great excuse to get out into your woods, scouting for invasives.”

Happy hunting.