What Is An Invasive Plant?
What is an invasive plant?
An invasive plant is a species that has become a weed pest that grows rapidly.
It spreads and displaces other plants. Invasive plants typically appear on
disturbed ground. The most invasive ones can actually invade existing
ecosystems. Invasive plants can be very expensive to control and
environmentally harmful.
What is a native plant?
A native plant is one that occurs naturally in a particular place without human
intervention. Species native to North America are generally recognized as those
occurring on the continent prior to European settlement.
Exotic or translocator?
Exotic plants are mostly European or Asian species that have been accidentally
introduced or intentionally imported for their ornamental value or their ability to
provide shade, windbreaks and/or erosion control.
Translocators are native plants that have moved out of their original range into
an area that favors their over-production.
What makes plants invasive?
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Fast growth rate
Grow well in a wide range of soil and growing conditions
Some have high seed production with seeds that easily disperse and
sprout quickly
Some have the ability to reproduce by roots or shoots, called suckering
Why are invasive plants bad?
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Displace and reduce native plant species
Destroy habitats that support native animals
Change ecosystem processes so that they support aggressive and exotic
plants, animals and pathogens
Are difficult to control, can escape from cultivation and can dominate
whole areas
Multiflora Rose
Rosa multiflora
Where did it come from?
Multiflora rose is an exotic species that is native to Japan and Korea and was
introduced to the U.S. in the 1860s. It was originally planted as an ornamental
shrub. In the 1930s conservation agencies began to promote it as a wildlife food
and a cover plant for animal habitats. It was also used for erosion control and
as living fences to confine livestock. Since its introduction, multiflora rose has
spread rapidly from cultivation and readily invades open woodlands, forest
edges, open fields, stream banks and other areas that have been subjected to
land disturbance.
How does it spread?
Multiflora rose is spread by seeds and by suckering. Suckering occurs both when
the tips of arching stems root where they contact the ground and also when
roots sprout new growth. Birds eat and disperse the seeds which is the primary
means by which the shrub moves to new areas. Reproduction by suckering
allows the plant to form dense, impassable thickets. An average plant may
produce a million seeds per year. These seeds may still sprout for up to 20 years.
Multiflora rose has a wide tolerance for soil, moisture and light conditions
allowing it to spread to many habitats.
How can it be controlled?
Regular mowing and repeated cutting in grassy areas inhibits seedling
establishment. However, repeated cutting is often preferred to mowing
because mowing will also damage native plants. Shrubs can be removed by
digging and pulling. This is only effective when all of the roots are removed.
Treatments with certain herbicides have also been effective at controlling the
plant. Repeated treatments are needed because the seeds remain viable in
the soil for many years. Also, two biological controls have been used
successfully to manage the spread of multiflora rose. One is a native fungal
pathogen (rose-rosette disease)
this is spread by a tiny native
mite. The second is a nonnative seed-infesting wasp, the
European rose chalcid.
Native alternatives:
Common blackberry
Flowering raspberry
Pasture rose
Swamp rose
Witch hazel
Tree of Heaven
Ailanthus altissima
Where did it come from?
Tree of heaven is an exotic species that is native to central China. It was
introduced to the U.S. in 1784 by a Philadelphia, PA gardener. By 1840 it was
commonly available from nurseries. Since its introduction, tree of heaven has
sprouted up just about anywhere including alleys, sidewalks, parking lots, streets
as well as in fields, roadsides, fencerows, woodland edges and forest openings.
How does it spread?
Tree of heaven spreads by seeds and suckering. Suckering occurs when cut
stumps and root fragments resprout. A single tree can produce up to 325,000
seeds per year. Once established, it grows dense stands that displace native
plants. Tree of heaven also produces chemicals that kill or prevent other plants
from growing near it.
How can it be controlled?
Seedlings can be pulled or dug up.
Care must be taken to remove the
entire plant including all roots and
fragments to prevent resprouting.
Several herbicides have also proven to
be effective in controlling tree of
heaven. Targeting the removal of large
female trees is the best way to control
the spread. Female trees are
responsible for the seed production.
Before any control measures are used, it
is important to correctly identify the
plant because some native species are
often confused with tree of heaven.
Native alternatives:
Box elder
Smooth sumac
Staghorn sumac
Black walnut
White ash
Tulip tree
Princess Tree
Paulownia tomentosa
Where did it come from?
Princess tree is an exotic species that is native to China. The Dutch East India
Company introduced it to Europe in the 1830’s and North America in the 1840’s,
both times as an ornamental. It is currently grown in plantations for wood to
export to Japan and as a quick growing ornamental. It has escaped from both
uses and grows in forests, fields, and along roadsides.
How does it spread?
Princess tree spreads by seed or suckering. One tree can produce 20 million
seeds per year. Seeds are lightweight and winged so they are spread easily by
wind and water. Suckering occurs from buds or roots after fires, cutting, or even
bulldozing.
How can it be controlled?
Small seedlings can be hand pulled or dug out. Make sure to remove all of the
root system to prevent sprouting. Large trees can be cut and then the sprouts
will have to cut repeatedly. Large trees can be cut and the fresh stump can be
painted with a herbicide to prevent sprouting. Small trees may be sprayed with
a herbicide.
Native alternatives:
Serviceberry
Catalpa
Redbud
Flowering dogwood
Sassafras
Spicebush
Red mulberry
Paper Mulberry
Broussonetia papyrifera
Where did it come from?
Paper mulberry is an exotic species that is native to Japan and Taiwan. It was
brought to the United States as an ornamental and escaped.
How does it spread?
Paper mulberry spreads by seed and suckering. Animals eat the berries and the
seed passes through the digestive system unharmed. Generally the animals
have moved far from the site where they ate the berries before the seeds are
dropped. Suckering from root sprouts occurs abundantly after the tree is injured
in some way.
How can it be controlled?
Seedlings can be pulled when the ground is moist if care is taken so that all of
the roots are removed. Small trees can be cut to the ground followed by
cutting of the root sprouts until they stop appearing. The trees can be cut and
black plastic can be used to cover
any new sprouts. The plastic creates
unsuitable growing conditions, such as
not enough sunshine, not enough
moisture, and too much heat. Large
trees can be cut and the fresh stump
may be painted with a herbicide to
suppress spouting.
Native alternatives:
Basswood
Sassafras
Red maple
Hackberry
Black gum
Norway Maple
Acer platanoides
Where did it come from?
Norway maple is an exotic species that is native to Eurasia from southern
Scandinavia to Iran. It was introduced in Philadelphia in 1776 by John Bartram,
a botanist. It was planted frequently in the 1950’s to replace American elms
planted in neighborhoods that Dutch elm disease killed.
How does it spread?
It spreads mostly by wind. The seeds (samaras) are spread by the wind. Norway
maple out competes native maples even in shady conditions.
How can it be controlled?
Seedlings can be hand pulled when
the ground is wet or dug. Larger
trees can be cut close to the ground.
Native alternatives
Red maple
American beech
Sweet gum
Black gum
Black Locust
Robinia pseudoacacia
Where did it come from?
Black locust is a translocator that is native to eastern North America. Its native
range is Pennsylvania to southern Indiana south to Georgia and Louisiana and
west to Iowa, Missouri, and Oklahoma. Outside of its range it is planted for mine
reclamation projects, afforestation projects, and erosion control windbreaks.
How does it spread?
Suckering from roots and stumps occurs after the tree is cut. Seeds are spread
by wind.
How can it be controlled?
Continuous cutting of trees, root sprouts, and tree sprouts will eventually kill the
tree. It is also recommended to paint a freshly cut stump with a herbicide to
reduce root and stump sprouts.
Native alternatives
Honey locust
White ash
Sassafras
Quaking or bigtooth aspen