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Invasive species management crucial to forest health

Invasive species management crucial to forest health

Invasive species management crucial to forest health

Published on Nov. 26, 2008

Beneath the woodland canopy at McConnell Springs, Jeff Stringer stands ankle-deep in winter creeper. Bush honeysuckle is within arm's reach. Neither plant in abundance is a sign of a healthy forest. Stringer and other University of Kentucky College of Agriculture researchers are working hard to find management solutions to the pervasive spread of some exotic species throughout the state's woodlands, farmlands and urban landscapes.

"We have a growing list of invasives," said Stringer, an extension professor in the UK Department of Forestry.

On that list, which includes plants, insects and pathogens, are bush honeysuckle, Japanese honeysuckle, winter creeper, tree-of-heaven, multiflora rose, kudzu, musk thistle, poison hemlock, sudden oak death, hemlock woolly adelgid, Johnsongrass, gypsy moth, fire ant and emerald ash borer.

"Ground covers like winter creeper are a particularly bad problem in some parts of the state. Bushes like bush honeysuckle and burning bush, those are significant problems," he said.

Although the term ‘bush honeysuckle' encompasses many different species, all are exotic and invasive in North America. The most common species in Kentucky, Amur honeysuckle, is native to northern China, Korea and parts of Japan. It was first introduced to the United States in 1897 for use in ornamental plantings. In the 1960s and 1970s, it was even recommended for conservation and wildlife use, though now it is recognized that its berries are not as nutritious for wildlife as native fruits are. The plant reproduces through seed; a mature plant can produce approximately one million berries in one season. And according to a story that will appear in the next issue of Kentucky Woodlands Magazine, evidence points toward the fact that Amur honeysuckle produces chemicals detrimental to native plant growth. This is a condition known as allelopathy. All of these factors make it a threat to native woodlands.

Because Amur honeysuckle can grow in a range of habitats and light conditions, the entire state is susceptible to invasion from this species, which is found currently in greatest abundance in north and central Kentucky.

"Ultimately, the biggest effect is these invasive plants squeeze out our native plants to a point where our native woodlands can't regenerate," Stringer said. "We've got an example that we're standing in right here, where we've got winter creeper that's covering the ground and precluding any of our native tree species or even our wildflowers from germinating and successfully developing."

The problem doesn't only include loss of native plant species. It directly affects native wildlife and impacts the state's economy. Stringer said wildlife contributes approximately $2 billion to Kentucky's economy, so the loss of their habitat, and consequently their disappearance, has a big economic impact.

Stringer said that a number of invasive species, plants as well as insects and pathogens, such as the hemlock woolly adelgid and sudden oak death respectively, also are detrimental to timber production in the state, which could negatively impact the state's $8.7 billion wood industry.

A number of college researchers, including Stringer, UK Forestry Assistant Professor Songlin Fei and Extension Forester Billy Thomas have been studying a variety of ways to control invasives. Fei is working with parks in Lexington and Louisville to map the extent of the invasive species using remotely sensed imageries. The U.S. Forest Service National Urban and Community Forestry Advisory Council is funding the project.

He is also working on a project to classify hemlocks in eastern Kentucky as a first step in stopping the progress of the hemlock woolly adelgid, an insect that can kill vast tracts of these trees that are vital to healthy stream systems.

Stringer, Thomas and John Cox, adjunct professor of wildlife and conservation biology, have been researching ways to control invasive plants, including manually removing them, as well as using herbicides to prevent their reproduction.

It's no accident that at the moment Stringer is standing in the middle of a stretch of woodlands submerged in winter creeper and bush honeysuckle. They are two of the species on which the men are concentrating their efforts.

"The work has been pretty successful. We have good recommendations that we can provide to woodland owners and state agencies involved in eradication," Stringer said.

Thomas has been working in partnership with state and local agencies to establish demonstration areas for investigating control techniques for bush honeysuckle.

"What we're finding is there is one treatment that we can recommend most frequently to landowners, and that's going to be the cut stump treatment," he said.

The cut stump treatment combines cutting the plant down at its base and, within an hour, applying an herbicide solution to the stump. Thomas said the treatment must be done from mid-growing season through fall.

"You definitely don't want to do that during the spring as the sap is rising, because it will just end up pushing the herbicide out," he said.

They are also looking at some other techniques, including a manual technique that doesn't involve the use of herbicides, which is important in areas where herbicides cannot be applied.

"We're getting good results with that as well," he said. "The drawback to that technique is it is much more labor intensive, and it's much more time consuming. But it can work. It just requires a little more commitment as far as time and effort."

But that thick mat of winter creeper is a different beast to tame because it has such an extensive root system, Thomas said.

"You can get one little area, but another area can sprout right back up on you, so it's going to take a sustained effort. We've been looking at a few different techniques where we come in and knock it back with a weed eater and then let the leaves sprout just a little bit and apply a herbicide solution to that. We have found that to be quite effective," he said.

UK is not alone in its fight to manage the problem. Stringer and Thomas regularly partner with the Kentucky Division of Forestry, Natural Resources Conservation Service, Lexington-Fayette Urban County Parks and Recreation, Kentucky State Nature Preserves Commission and Kentucky Department of Fish and Wildlife Resources, as well as other research institutions such as Purdue University.

"The issue of invasive species, and particularly plant species, it's a regional, it's a national, it's a global concern," Stringer said.

More information about invasives species work in the College of Agriculture can be found at Kentucky Woodlands Magazine can be found at

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