Plant Invaders: Non-Native Invasive Plants in the United States
One topic that has been pervasive in the news lately, especially as we approach important elections in 2014, is the issue
of illegal immigration into this country. Hopeful politicians will no doubt be campaigning on the issue, state and local
goverments are trying to deal with the strains placed on their services and many people are understandably angered
by a massive influx of people who have entered the country without going through the proper channels.
But Did You Know...
Another invasion is taking place in plain sight all across our country? Non-native invasive plant species are
quietly invading this country displacing native species, disrupting entire ecosystems, contributing to loss of diversity, instroducing non-native pathogens,
damaging private and public land (including our National Parks), causing agricultural losses,
perhaps even threatening our food supply and costing the U.S. taxpayers hundreds of billions of dollars each year!
While the particular invasive plant species may differ across the country depending upon the climate and habitat, the
problem exists in all 50 states as well as Canada and Mexico. In fact, the problem of non-native invasive plant species is worldwide.
While many thousands of wonderful different plants have been intentionally imported into this country over the last
200 years and many new ones enter each year, we've unfortunately imported (intentionally or accidentally) some
horticultural problem children that should have been left in their native lands. These invasive plants do well by one or more mechanisms: 1) They have no natural enemies or pathogens in their new habitats;
2) They are able to alter the soil chemistry to inhibit competition (known as allelopathy); 3) They introduce a pathogen to which they are resistant yet our natives are susceptible; and 4) They reproduce
|Invasive Plants of the Southern United States
|Chinese Privet and Japanese Honeysuckle||A native trillium being overrun by Japanese Honeysuckle|
The most familiar invasive plant to those living in the South is Kudzu which is from Japan, but did you know it is not our
worst invader? Chinese Privet (Ligustrum sinense) now covers more ground than Kudzu, but is still sold as a durable and drought tolerant
landscape shrub. Despite cries from the U.S. Department of Agriculture, The U.S. Forest Service, The National Park Service,
The Environmental Protection Agency and multiple private organizations, wholesale growers and nurseries continue to sell this plant because it
is very popular among landscapers and homeowners. Nurseries will be quick to point out that privet is a major source of revenue and profit.
As for profits, the destruction caused by non-native invasive species (plants, animals and pathogens) in this country costs taxpayers $137 Billion
each year1 in damage to agriculture, ecosystems and the costs of control programs. This equals $457.00 for every man, woman
and child in this country or $1,828.00 for an average family of four. Remember that figure when you file your taxes
Below are some of the South's worst invasive plants - some of which are still sold in nurseries. These should not be planted, period.
|Chinese Privet choking a wetland||Autum Olive invading a forest|
Chinese Privet is sold as a variegated evergreen shrub for hedges, but it produces a blue-black berry that produces solid green seedlings.
These are easily seen in forests and wetlands in the winter. Autum Olive (Elaeagnus spp.) is also sold as an evergreen hedge plant.
It produces a pink/orange fruit which seeds into forests.
|Chinese and Japanese Wisteria killing a pine||Mimosa seeding everywhere|
Japanese and Chinese Wisteria (Wisteria floribunda, W. sinensis) can kill anything they climb. If you must have wisteria,
plant Wisteria frutescens 'Amethyst Falls,' which is native to the Southeastern U.S. Mimosa (Albizia julibrissin) seeds so prolifically that it will have hundreds
of offspring very quickly. Mimosas also are susceptible to a root-rot fungus which could eventually jump species and infect other plants, especially those in the same family (Fabaceae) which
consists of most legumes.
|English Ivy everywhere||Japanese Climbing Fern in a tree|
English Ivy (Hedera helix) is often referred to as English Kudzu. This evergreen vine will climb and cover anything in its path.
Because it tolerates almost total shade, it can destroy a forest quickly. Japanese Climbing Fern (Lygodium japonicum) is so invasive
in Florida and South Georgia that it can outrun Kudzu!
|Japanese Honeysuckle choking trees||Princess Tree crowding out natives|
Japanese Honeysuckle (Lonicera japonica) is an evergreen vine sold for its white fragrant flowers. However, this thug will twine
its way around anything in its path, choking it. Princess Tree (Paulownia tomentosa) is sold as a fast-growing, flowering shade tree.
It has upright stalks of purple flowers. Yes, it grows fast and can produce upwards of 20,000 seeds each year.
Unfortunately, it is a short-lived and unstable tree with a hollow trunk and branches. The princess tree is a major threat to ecosystems in much of the Appalachians.
|Nandina berries||Mahonia invading a woodland|
Often our wildlife can exacerbate the problem of invasive plants by consuming the fruit and seeds produced and carrying them
off to infest other areas. Plants such as Nandina domestica and Mahonia bealei are planted for the attractive
fruit which "set the seeds of destruction" for nearby natural areas.
What angers me so much about these plants is that the "Green Industry" (those that collect, research, propagate, promote and sell plants)
refuses to face up to the issue that they are unleashing plants to the unsuspecting public that will result in billions and billions of dollars
in losses that we will all have to pay. When questioned about this, they will reply with a list of excuses. I've heard them all.
If they don't come around
and act responsibly, they will eventually find themselves under government regulations
requiring them to do so. In other states, regulations are already in place, so it's just a matter of time in Georgia.
|Invasive Plants of the Western United States
Since I now live and own rural property in Montana, I'm also keenly interested in the non-native
invasive plants found in that part of the country. While there are some invasives that we share in common with
the West, in certain regions they have an entirely different set of plant problems. Houndstongue (Cynoglossum officinale)
is a biennial listed as invasive in almost 2/3 of the country, although it seems particularly prevalent in parts of Montana and
Wyoming. Cheatgrass (Bromus tectorum) is a serious problem
in much of the West as it invades grasslands and pastures where it displaces native pasture grasses. It can ruin
grazing land for both livestock and wildlife because it is a cool-season annual grass that crowds out perennial
grasses better suited to provide summer and fall grazing. Also of note is that this plant seems to increase the
frequency and intensity of wildfires. Unfortunately, my property contains both houndstongue and cheatgrass (along with several others)
which threaten to thwart my efforts of restoring this area to a natural sagebrush steppe and mixed grass prairie.
Effects of Climate Change
As the worldwide climate is growing warmer, we are already seeing the effects on plant populations. In the United States, native and non-native plant species are able to grow further north. The result is they
displace their colder-natured bretheren and bring with them associated species of insects and diseases for which the local native species may have little defense. Warmer and shorter winters may prevent
many plant species from successfully setting flower buds and producing fruits and seeds. This is already becoming evident in some species of blueberry. Warming temperatures also have an effect on
precipitation patterns which may make it too dry or too wet for native species and crops in areas that once supported them.
What Can You Do?
- Monitor your property. Even a small landscape can contain one or more species of non-native invasive plants which can
serve as a "source of infestation" for surrounding areas. Remove these plants whenever they are discovered.
- Educate your neighbors. Discuss with them the potential problems and possible solutions for dealing with non-native
- Refuse to buy invasive plants listed for your area. Advise the nuseries where you shop that you will not buy them and that
you would like to see these plants
removed from the market and replaced with alternatives that are known to be non-invasive.
- Give preference to plants native to your area. This country is rich in beautiful native plants
that can be used in a variety of garden settings. Contact your local Native Plant Society for assistance.
1Government Report: Invasive Species (PDF)
Invasive Plants of the Thirteen Southern States
Non-Native Invasive Plants of the Southeast
Non-Native Invasive Plants in Georgia
Non-Native Invasive Plants of the Western U.S.
Non-Native Invasive Plants in Montana
USDA Invasive Plants Database
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