Tennessee is no stranger to invasive species, and many of these plants and animals can cause direct harm to the trees located in Shelby Avenue Arboretum. Clearing invasive species around the arboretum is essential for promoting healthy tree growth. Read on for a rundown of some of the most common invasives in Tennessee and the steps being taken around Shelby Ave. Arboretum to mitigate the harm they can cause.
The United States Department of Agriculture defines an invasive species as one that is “non-native (or alien) to the ecosystem… and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Essentially, this describes any living thing that is introduced to the environment in an unnatural way and will cause damage to other native species or the people living there. The USDA and any arborist will specify, however, that non-native and invasive do not mean the same thing. Many non-native species are not harmful to the environment, including several trees we have planted here in our arboretum. So, while not all non-native species are invasive, the ones that are usually pose a fairly grim threat to native trees, plants, and animals.
There are a variety of invasive plants that have found their way into the United States and Tennessee, so let’s outline a few that pose a threat to the trees here in Shelby Ave. Arboretum.
Not all invasive plants are large. In fact, many of the most dangerous invasive plants are vines that appear to grow alongside a tree. While you might mistake this for symbiosis, many vining plants are actively killing the trees they grow on. Japanese wisteria is a vining plant that was introduced to the United States in the 19th century for its beauty. This is an important thing to consider when asking, “Why are invasive species a problem?” When we note the introduction of invasive plants, you’ll probably notice a trend. Many of these invasive species came into the U.S. prior to the establishment of any concerted conservation efforts. These plants often came in the wild west of agriculture, back when experimentation without forethought was thought of as innovative. And we certainly did introduce a great deal of helpful, non-native species to the nation that helped us find independence and flourish economically.
The beautiful Japanese wisteria is still being planted by people to this day, without considering the damage being done to the ecosystem. Vines are similar to parasites, feeding off of other plants and slowly killing them. Vines often girdle trees — that is, essentially strangle them by boring into the bark and cambium of the trunk, cutting off their access to nutrition. Girdling also can allow disease and insects to enter the tree, accelerating the speed at which the tree dies. While standing dead wood trees are an important part of an ecosystem, fast-spreading vines can quickly decimate entire clusters of trees and rapidly deforest regions in a matter of years.
In Nashville, the most common invasive vine is the euonymus fortunei, or winter creeper vine. Native to China, Japan, and Korea, this invasive plant was introduced as ornamental ground cover. Now, however, winter creeper enters forests quickly. By rapidly spreading across the forest floor, it displaces small plants and seedlings. Additionally, it can climb high into tree canopies and damage the bark. Like many other invasive plants, it’s remarkably tough and resistant to weather and climate, making it durable and capable of outlasting other plants. While this vine is destructive to mature trees by damaging the bark and allowing pests and disease into the tree itself, it also prevents new growth. It often smothers the canopy floor preventing spring flowers and other meadow wildflowers a chance to take root and thrive under its choking vines.
One of the biggest threats to the trees of the arboretum — and trees across the state — is the tree of heaven. Don’t let the name fool you because these trees are anything but heavenly. These plants, native to China and Taiwan, are incredibly hardy and fast-growing deciduous trees that can quickly take over native forests, fields, and other important ecosystems. They are considered clonal trees, which means they rapidly seed and grow similarly to weeds. Unlike troublesome weeds, however, the tree of heaven can grow to a height of 60 – 70 feet quickly. In their early years, saplings can grow 10 – 15 feet in a single year. Their complex and shallow root systems can disrupt growth near them and cause damage to sidewalks and roadways incredibly quickly. This tree was introduced to the U.S. as an ornamental garden plant, and it was mostly popular in cities, making it an especially valid threat to the urban Shelby Ave. Arboretum.
Invasive insects and diseases are another major threat to the trees of Shelby Avenue. How do invasive species affect trees? There are a number of native species of insects and diseases that can kill trees, and these are generally necessary in nature to balance tree populations. What makes invasive species dangerous is that they are not a part of the standard equation. Native plants, animals, and insects have found a balance after thousands of years of cohabitation, but most invasive species have only been here for less than 200 years. As a result, many insects don’t have the same number of natural predators that native species have, making their populations dangerously high and growing at an unchecked rate. Especially in the case of invasive insects, this means there’s an all-you-can-eat buffet in every forest they find themselves in.
Perhaps the most notable of all invasive insects in the United States is the emerald ash borer beetle. These insects, native to Asia, have been in the U.S. just 21 years and have already caused a massive decline in ash trees across the country. They have only been in Tennessee for 13 years, and in that time have covered 65 counties. With an estimated 271 million ash trees in the state, these insects have a huge selection of trees to infest and kill. They damage a tree by laying eggs in the bark of ash trees. Larvae then develop and feed for up to two years within the same tree, then emerge as adults to reproduce and create their own offspring, thus spreading.
The spongy moth, formerly known as the gypsy moth, is a European species of moth that is beginning to spread in Eastern Tennessee. This moth species poses a major problem for trees in the arboretum and across the state, and they are spreading at an unanticipated rate. Originally not expected to arrive for several years, they’ve already been detected in the state. These moths breed and feed on the foliage of a variety of trees, but they especially favor oak trees. By defoliating trees, spongy moths put a great deal of strain on their health. Trees affected by the moth populations are then susceptible to disease and other native insects like the two-lined chestnut borer. While these insects don’t often kill oak trees on their own, those already weakened by the spongy moth are then killed by two-lined chestnut borer invasions.
The tree of heaven mentioned earlier brings a unique threat along with it. The spotted lantern fly, an invasive insect that is decimating trees across the U.S., favors these trees. Where there are trees of heaven, the lanternfly is sure to follow. This invasive insect breeds on and consumes the tree of heaven, quickly moving onto other native trees in the area. These insects aren’t picky; they’ll consume many species of tree, and their threat is imminent. Removing any trees of heaven is a crucial way to prevent the spread of the spotted lanternfly, and the effort is ongoing. Given their nature of spreading quickly, they are not easy to contain, but with vigilant tree removal, it can be done.
So, why is it important to remove invasive species? And how exactly is it done? There are a few ways the Tennessee state government has gone about mitigating the spread of invasive plants and insects. Likewise, invasive clearing around the Shelby Avenue area is essential for healthy tree growth. Many of the large-scale methods for clearing invasive species have been applied on a more local level here, so let’s get down to what we can do to protect our trees.
The emerald ash borer is actually so destructive that the best way to prevent its spread in the arboretum was to remove all ash trees in an area. Fortunately, Shelby Avenue did not have any mature ash trees growing in the grass strips so no removals needed to happen. Unfortunately, the Emerald Ash Borer’s presence in Nashville, means we won’t be planting this beloved native tree in the project.
On a larger scale, efforts to trap and kill the emerald ash borer beetle have proven effective in slowing — but not stopping — their spread. Likewise, as with other insects like the spongy moth, pheromone treatments can help to ward off the spread of insects. These pheromones are spread across wide areas and discourage populations from developing in unaffected areas. This natural, non-pesticide method is preferred, though much harder to enact on a grand scale that would halt the spread of any invasive insect.
Stopping the spread of invasive plant species like the tree of heaven and vines is a bit trickier because these plants are hardy and can live where other trees may not. Fully removing trees of heaven and halting the planting of any more Japanese wisteria in the city are two effective methods for stopping their spread. But these two methods rely in part on the community as a whole to recognize and remove these invasive species from their own property. Because of how fast tree of heaven can spread, even one year of seeding can lead hundreds of trees to grow the following year. Knowing what to look for and how to remove the trees can be challenging, as they do resemble other native species that aren’t harmful to the ecosystem. If you suspect you have an invasive plant on your property, you can contact local arborists to have them removed. By doing this, you can support Shelby Avenue Arboretum directly and aid in the conservation of Tennessee’s native plants and animals.
Invasive species are a real threat to trees both in and out of Shelby Ave. Arboretum. If you’re interested in learning more about the arboretum project and its efforts to clear invasive species, don’t hesitate to reach out online.
The Shelby Avenue Arboretum is a community-grown project led by Nashville Tree Conservation Corps and is in partnership with NTCC and Metro Nashville.
Nashville Tree Conservation Corps
PO BOX 60683
Nashville, TN 37206
