Non-Native Invasive Plants

Non-native invasive plants are species that reproduce and out-compete native plants in areas where they themselves are not native. They often degrade habitat for wildlife as well.

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How Did Non-Native Invasive Plants Get Here?

Coming from places as far flung as England, Japan, and Iran, most of these plants were brought to the United States in the nursery trade as special new introductions. No one knew they'd be such a problem! (Not all non-native plants sold in nurseries cause headaches in the long-run, but these ones do.)

Most, unfortunately, are still available at plant nurseries and are commonly planted in gardens and backyards.

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Why Do They Do So Well in the Wild?

Characteristics that may make certain non-native plants valuable to gardeners make them aggressive invaders or naturalizers if they make it into the wild, easily thriving and reproducing. Some of their competitive advantages over native plants include the following:

Many Lack Natural Predators in the United States

In their native environment, most plants have natural predators like insects, diseases, hungry animals, and/or enterprising people that keep their growth in check. Non-native plants may lack these specific natural controls in their new environment. Kudzu, known to Americans as “the vine that ate the South,” does not grow out of control in its homeland of Japan.

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Many Have Longer Growing Period

Many non-native invasive plants green up earlier in the spring, remain green longer in the fall, or are green all winter. For example, non-native wildflowers that produce their greenery early in the spring can shade out native wildflowers that get going a bit later.

Evergreen non-natives such as Japanese honeysuckle and English ivy can grow bigger and faster because they benefit from a longer growing season than native deciduous plants. The downside to sporting green leaves in winter instead of going dormant, however, is the possibility of damage by freezing winter storms. This risky trait also puts at greater risk the shrubs or trees on which evergreen vines climb. The weight of ice or snow on the climbers’ leaves can be enough to break the supporting plants.

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Many Are Shade Tolerant

Many non-native invasives (like garlic mustard, porcelain-berry, Japanese barberry, winged burning-bush, privets, linden arrow-wood and other viburnums, and oriental bittersweet) grow not only along trails, where volunteer weed-pullers can more easily find and remove them, but in the shady interior of forests.

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Many Grow Quickly

Non-native plants such as mile-a-minute weed grow quickly, shading out and choking out other plants. Porcelain-berry, Chinese wisteria and kudzu vines can overcome entire forests. Japanese stiltgrass can shade out entire forest floors.

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Many Are Profuse Seeders

Garlic mustard and Japanese stiltgrass each generously reseed themselves, making a dense groundcover in no time. Brilliant red berries of linden arrow-woodattract birds and get dispersed in the woods through their droppings, as do the berries of oriental bittersweet, and of English ivy grown vertically (Ecobit: Don’t Let Your Ivy Climb). The profuse purple blooms of princess-tree promptly turn into pods filled with thousands of tiny wind-borne seeds. All of this spells trouble for nearby woods, unless their berries and flowers are harvested and used for indoor decorations before their seeds are carried away by birds, animals, wind, and streams (or dumped by landscapers into the wild).

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Many Reproduce Aggressively Even Without Seeds

The reproducing bulblets and tubers of lesser celandine multiply underground and dislodge easily with a slight disturbance or flood, re-settling wherever they’re taken. Vines like oriental bittersweet, English ivy, and Japanese honeysuckle can run for great distances on and under the forest floor, putting down new roots at short intervals. Tree-of-heaven sends up a forest of saplings from one original root.

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You Can Make a Difference!

Most parks and natural areas have plenty of opportunities for volunteers to work in the park to help protect the natural communities there. Contact your local park or natural area for more information.

When you’re visiting a park, you can help keep natural communities healthy by being observant and sharing what you see with park staff. Ecobit: An Extra Set of Eyes

Have a smart phone? You can make a difference wherever you go! Get the app, and locate/photograph infestations of non-native plants for (Early Detection & Distribution Mapping System).

You can also help parks and natural areas from the comfort of your own backyard. You can avoid planting non-native plants that tend to be invasive. Ecobit: Go Native Or if you do, you can maintain them to keep them from reproducing and spreading. Ecobit: Don’t Let Your Ivy Climb

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