FORT KNOX, Ky. — When folks walk or drive around Central Kentucky, many see the lush forest and fields covered in green grass, trees and bushes with beautiful splashes of color from the flowers that carpet the landscape.
Few see beyond that façade and understand that there is an epic battle being waged in and around Fort Knox, says Mike Brandenburg, chief of the installation’s Natural Resources Branch and a wildlife biologist.
A monarch butterfly sucks the nectar from a native flower in a field devoted for the re-habitat of native Central Kentucky plant and tree species.
Common milkweed and other species of milkweed are critical for the life and reproduction of monarch butterflies.
“It’s like the Matrix for us biologists,” said Brandenburg. “We have studied these species so much that we don’t just see a forest. We see the trees and bushes and plants. We see the good in it, but we also see the bad.”
There are thousands of these bad plants and trees to contend with that are tracked by the Kentucky Invasive Plant Council – what Brandeburg calls “invasives.” The term means they don’t fight fair, they have a leg up on the competition for survival.
An example that might shock many is Kentucky31 tall fescue. The grass seed is sold at virtually all major horticulture and landscaping shops and departments as a favorite sod because of its hardiness under sometimes difficult conditions.
It’s this hardiness that also makes it an invasive, said Brandenburg.
“The reason that makes it a great grass in your yard is exactly what makes it a problem when it’s not in your yard,” said Brandenburg. “It’s a very tough sod grass with a symbiote fungus that gives it a competitive advantage.”
Even more concerning for Brandenburg and his team, though, are what he calls “exotic invasives” – species that are not native to the area.
“With these exotic invasives, especially the ones that pose a severe threat, there is no one-shot treatment and you’re done,” said Brandenburg. “That scenario doesn’t exist.”
Brandenburg explained that the purpose of all this effort to stop the constant assault from invasives onto military lands is rooted in readiness.
“It’s important not only from an economic standpoint because forests are very valuable, but also, if we don’t do something to maintain that ecological value, they’re going to be useless for training, for missions,” said Brandenburg. “The callery pear trees for instance get so thick you can’t walk through them; and if you do walk through them, you’re going to come away bleeding.”
Biologists also have the equally important mission to protect endangered species that live on military land, species that depend on healthy prairies and forests to survive. These include plants like the pollinators, which are needed to help grow crops and reproduce healthy plants and trees, which in turn promote a healthy ecosystem for animals and other species.
“A lot of our pollinators are becoming listed as threatened and endangered,” said Brandenburg. “The reason for it is the habitats are getting degraded by these exotic invasives.”
While the laundry list of invasives is exhaustive, Brandenburg said there are 10 that his team spends a majority of their treatment and management time on.
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Kudzu can be found at several different locations just outside of Fort Knox, especially at the Brandenburg Gate. Biologists have had success in keeping it at bay, but it’s always lurking.
Kudzu can be seen draped over trees and sometimes power lines along the 31W corridor near Fort Knox.
10. Kudzu.
“It takes three treatments just to actually get it under control,” said Brandenburg. “If you don’t keep your eye on it, it’ll run rampant on you.”
Georgia is a daily reminder of the power of kudzu to take over.
According to Wikipedia, this invasive vine was brought to the United States in the 1930s from Asia by the Soil Erosion Service and Civilian Conservation Corps. It was introduced in the southeast as an experimental soil erosion controller and an ornamental to shade homes. Officials who now fight it say it has more than earned the nickname “the vine that ate the South,” with Georgia being the hardest hit.
This sinister plant has been spreading north at an estimated 2,500 acres yearly on a slow crawl to Kentucky and beyond. Its specialty is choking the life out of everything around it, and it’s apparently really good at it. Kudzu has caused utility poles to snap under its weight.
“There are millions and millions of acres in the South and Southeast that are just overrun with kudzu,” said Brandenburg, who explained that they have had success, however, in pushing it back to a manageable state here.
Princess trees can grow up to 80-plus feet tall with large heart shaped leaves that blot out the sun for more native species of trees and plants. They are the giants in a forest of native and invasive species.
9. Princess tree.
With other names that include empress tree and foxglove-tree, this deciduous hardwood is native to China. The species, according to Wikipedia, is “an extremely fast-growing tree with seed that disperse readily and is a persistent exotic invasive species of North America.”
Trees generally grow up to 80-plus feet tall with large heart shaped leaves that blot out the sun for more native species of trees and plants. The seeds come from an egg-shaped fruit that contains loads of tiny, winged seeds that are carried by the wind and water. These trees are known to survive virtually any kind of natural disaster, including fires.
This deciduous tree of heaven has the ability to propagate itself in a multitude of ways, including through sucker roots and a tremendous number of seeds that germinate and grow quickly.
8. Tree of heaven
Also known as ailanthus altissima, varnish tree, copal tree and stinking sumac, this deciduous tree has the ability to propagate itself in a multitude of ways. Like many others on this list, it originates from Asia, specifically Northeast and Central China.
The tree can not only clone itself through suckers, but it also produces tons of seeds and grows rapidly, according to Wikipedia – up to heights of 50 feet in only 25 years. While the consolation is that trees rarely live more than 50 years, this brings little comfort to biologists like Brandenburg since the trees can produce so many offspring rapidly.
Honeysuckle is often a favorite bush in the South because of its pretty, sweet-smelling flowers. However, the bush honeysuckle is not native to the South nor does it like to share space with other plant species.
7. Bush honeysuckle.
This great smelling sweet vine carries with it a lot of wonderful memories for folks who grew up near in the country near them. So, what’s harmful about honeysuckle?
Like a lot of vines, it has the ability to overrun an area when left unmanaged. However, not all honeysuckles are apparently like bush honeysuckle.
These species are sometimes also called Japanese honeysuckle, Chinese honeysuckle or Hall’s honesuckle, introduced in the late 1800s as ornamentals. Later, the government experimented with them for erosion control and wildlife cover.
They’re biggest problem is, once again, rapid growth, which leads to them choking out other plant species underneath. Like kudzu, these species also climb trees and have been known to pull them down by girdling them.
The flowerhead of the milk thistle rises above the landscape. Few plants, animals and humans who encounter thistles become fans of these invasive species. The allergic reactions alone are enough to thwart their growth.
6. Thistle species.
“There’s a whole species there that we battle here,” said Brandenburg.
Most invasive thistles originated in Europe during the 1600s. Why were they brought over? Unlike many of the other exotics on the list, this answer remains a mystery, according to Purdue University’s College of Agriculture, although some speculate the seeds found their way into bags of farm seeds shipped over to the American colonies.
This makes sense when we consider that a lot of thistles show up in crop and farm fields. They are included in the invasives because they reduce crop yields and restrict the foraging habits of animals. Like the others on the list, they do this by growing faster than native plants and stunting their growth.
Anybody who has been in the forests of Central Kentucky is probably familiar with Japanese stiltgrass. It is very good at providing ground cover. It is not very good at sharing the ground with other plant species.
5. Japanese stiltgrass.
This is another quick spreader. According to Wikipedia, it was first introduced to the United States in 1919 as porcelain packing material from China, landing in Tennessee. While its lifecycle lasts from spring to fall each before “dying off” for the winter, it comes back with a vengeance.
“The problem with it is that it has a super-fine seed that just like dust,” said Brandenburg. “That’s how it gets transported, by wind; and it sticks in the fur of deer legs, sticks on your pantlegs and gets on the wheels of machines in the woods. Then where it forms thick mats, it precludes regeneration of the forest.”
The stiltgrass is lovely to look at for those who have found it but insanely hard to get rid of, and it smothers the growth of any and all other ground cover in the area: detrimental to forests and pastures. Deer and other grazers avoid it over much more suitable grasses and leaves, which encourages its spread.
Another ground cover nuisance, sericea lespedeza does not share space with other plant species. As well, it’s not a sought-after form of food by foraging animals like deer, which promotes its spread virtually unchallenged.
4. Sericea lespedeza.
This flowering legume is native to Asia and Australia and is also commonly referred to as Chinese bushclover. The stems stand straight up to 2 ½ feet tall.
Its origins in the United States date back to 1896, when it was first planted in North Carolina to combat soil erosion and revegetate abandoned mine sites. Farmers discovered it was also good for vegetation for their livestock.
“It was a plant that was touted by the Soil Conservation Service back in the day, just like Kentucky31 tall, for erosion control,” said Brandenburg. “There was little thought back in those times about the invasive nature of them.”
Its biggest critics say the plant reduces abundance and diversity of plant life in fields and prairies by releasing a toxin that discourages growth of other species, which in turn forces wildlife to look elsewhere for food sources.
An autumn olive stands to the left of the railroad tracks, waiting for deer and other foragers to eat its fruit and deposit its seeds in other locations.
Thousands of flowers from the autumn olive will turn to sweet fruit, which makes eradicating the bush extremely difficult.
3. Autumn olive.
This shrub, also known as Japanese silverberry and spreading oleaster, came from Eastern Asia, ranging from the Himalayas to Japan. It was considered beneficial in the beginning because of its production of huge quantities of edible red drupes – as much as 20,000 per plant – which are juicy and sweet, according to Sarah Coffey of the Lewis Ginter Botanical Garden.
Like its cousin the Russian olive, the deciduous autumn olive can grow up to 20 feet tall. and spread out 30 feet wide. It showed up in America in 1830 to feed wildlife, restore damaged and degraded ground around mines and control erosion. The U.S. Soil Conservation Service mass-planted it in the 1950s for the same reasons.
Today, the Midwest and Eastern states are riddled with this invasive. It gets the label “invasive” for its substantial seed production and ability to germinate virtually anywhere, even after burning or cutting. It also has the ability to change the soil composition through the release of nitrogen, which can favor some plant species while killing off others, especially natives.
The unassuming multiflora rose can grow virtually anywhere, says Mike Brandenburg. It's ability to adapt makes it one of the worst invasives to remove from the landscape.
2. Multiflora rose.
“Multiflora rose grows anywhere – it grows in shade, it grows in sun; it’s terrible,” said Brandenburg.
The multiflora rose is a species of rose that is native to – you guess it, Asia; specifically China, Japan and Korea. According to Wikipedia, this plant “is a scrambling shrub climbing over other plants,” which explains why it is listed as an invasive. It reaches a height of about 16 feet with stems that have recurved prickles.
The multiflora rose was introduced as a natural hedge for grazing lands, and to attract wildlife. It is now often used as an ornamental and, because of its stout rootstock, it becomes the base for grafted ornamentals.
While most animal species actually don’t like the plant for food, it apparently is a favorite among goats.
A callery pear threatens a power line at Fort Knox. Mike Brandenburg's office has submitted several contracts to rid the post of all the callery pears, which has made a big difference in the landscape already.
Callery pears grow sharp thorns all over their branches, which when added to the dense growth patterns of the tree, make many areas impassable in a very short amount of time due to the trees’ rapid growth.
1. Callery pear.
Brandenburg says the “callery pear” is the king of invasives here. Stores market them as the Bradford pear, a lovely tree covered in white blooms in the springtime that look really pretty to motorists driving by.
Brandenburg disagrees about their beauty.
“If we could get 10 people not to plant those trees out in the landscape, we’d be doing a lot better,” said Brandenburg. “Anywhere you drive and you see white flowers in early April, those are calleries, and it’s unbelievable how bad they are.”
Brandenburg explained that having a monoculture of any species like the callery pear is detrimental to an ecosystem. What makes the callery pear so devastating is how quickly they grow, even when cut down. In fact, biologists at Fort Knox quickly learned that cutting down the callery and grinding the stumps to the ground only causes them to come back 12-fold or more.
This miniature grove of callery pear sprouts sprang up within a couple of weeks from one tree that was cut down and its stump ground. Biologists now take advantage of these sprouts to spray them directly, which so far has ensured they "take a dirt bath," as Brandenburg puts it.
This field near Fire Station #2 was once filled with callery pear trees. Some sprouts have already returned two weeks later.
One tree that recently was cut and ground down within a few short weeks had about a dozen shoots springing up from the original stump. Within a few months, the callery grows into a bush and then rapidly into a tree with nasty thorns on it, said Brandenburg.
It also produces fruit that gets eaten by birds that then defecate the seeds at other locations.
“Invasive species like the callery pear can be detrimental to a lot of species because it even causes reductions in species that live on the landscape which other species rely upon,” said Brandenburg. “It’s just this growing, rolling problem.”
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Most exotic invasives are not only fast growing, they are also first growing.
“What you see with a lot of these exotics is that they are the first species to wake up in the spring,” said Brandenburg. “Fescue greens up early. Multiflora rose leafs out early. The privet [hedge] leafs out early; so those get a start on everything.”
A privet hedge will spring to life more quickly than native species, giving the privet an advantage on growth and spread. This also allows it to get its berries out first.
Brandenburg said they took advantage of this early awakening to rid a field near Brandenburg Gate of invasive fescue while the native species slept. They did this by hitting the grass with targeted herbicides and then a prescribed burn.
“The response that we got was dramatic with all the native species that existed here,” said Brandenburg. “To have this suite of species here, some of them very important and uncommon in this setting, returning is a good representation of what Kentucky looked like 250 years ago.”
Great things are happening at Fort Knox these days, says Brandenburg. For instance, when they cleared out an area near the motorcycle training site of invasives, they were greeted with a welcome surprise when the native compass plant returned. Other areas are showing similar signs of growth and ecological health.
Brandenburg said a lot of government mismanagement from the past and a lack of understanding of how habitats naturally form led to the introduction of these exotic invasive species. He lists the repopulation of a forest as an example of this misunderstanding.
“A lot of people think when you go and cut a forest, you’ve got to replant it — not in a deciduous forest,” said Brandenburg. “What you are relying on is natural regeneration from the seeds. That oak tree or that poplar tree that gets cut, 99% of the time it grew from a seed.
“Regeneration in the forest is there, waiting for light, so it can grow.”
A favorite place for invasives to take root and thrive is under rights-of-way that have been cut in the forest for power lines. The reason, according to Mike Brandenburg, is because sunlight now shines down onto the floor and birds eat the fruit of some invasives and then deposit those seeds from the powerlines. Several exotic invasives can been seen in this image.
However, when invasives are introduced, Brandenburg said they typically win out: “If you’ve got one of these exotics there also waiting, they’ll outcompete it, and it precludes you getting any regeneration of the good species.”
Brandenburg said his team has gotten very good at controlling all of these invasive species, starting with a solid plan that includes tackling exotic invasives from the outer perimeter of the cantonment area and working inward to systematically remove them.
“This is a big problem within the ecological community,” said Brandenburg. “It’s actually one of the top priorities in the Department of Defense Natural Resources Program.”
He said this active push to protect land to the tune of about 27 million acres sets the Defense Department apart from many other federal government agencies.
“The DOD is one of the smaller federal landholders, but has the highest density of rare, threatened, and endangered species of any of the federal landholders,” said Brandenburg. “You’d think it would be the Park Service, or Forest Service, or somebody like that, but nah, it’s the DOD.”
Despite all the work biologists do to combat the invasives, he said the public’s help is still needed, such as resisting the urge to purchase and cultivate these exotic invasives, as charming as they may seem.
“It’s all like sticking your finger in the dike,” Brandenburg said. “After a while, you run out of fingers.”
DOD funds environmental efforts to the tune of $5 million annually for natural and cultural resources. The department protects over 500 species on military bases, 55 of which are listed under the Endangered Species Act and that exist on no other federal lands.
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