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Invasive Plants in Maine Forests



Invasive Plants in Maine Forests


22 State House Station, Augusta, ME 04333


Practical advice for your land and trees from the Maine Forest Service


What are Invasive Plants?


Invasive plants are able to grow rapidly and aggressively enough to out-compete and displace

locally adapted native plants. Many species of invasive plants, but not all, have been brought by

people to North America from Europe and Asia.


Why are Invasive Plants a Concern?


Invasive plants can make it difficult to achieve many of the objectives that landowners commonly have for

their woodlands. For example, invasive plants compete for resources with desired tree species,

especially young seedlings. This can make it difficult to establish new seedlings to replace the larger trees

when they die or are harvested. Some invasive plants, particularly species of vines, such as Asiatic

bittersweet, can even kill valuable mature trees by smothering or strangling them. Other species, such

as Japanese barberry, often form dense thorny thickets. These thickets can make it nearly

impossible to access the woods for work or enjoyment. Because invasive plants can out-compete

native species, they can also lead to a reduction in the diversity of species present in the forest.


What Makes a Plant Invasive?


Not all non-native species of plants are invasive; in fact many non-native species never escape from

cultivation. Of the species that do escape into the wild most never become invasive. Botanists use what

is called the “tens” rule to describe how many plant species are likely to become invasive. According to

the tens rule only one in ten non-native species is likely to escape into the wild. Of those that escape,

only one in ten is likely to become invasive. Certain species of plants have characteristics that make

them more likely to become invasive. In general, invasive plants have most of the following



1.  They are habitat generalists, able to invade a range of sites;


2.  Their seeds germinate early and they leaf out before native plants;


3.They out-compete native plants through shading and nutrient competition;


4.  They have few, if any, natural predators here;


5.  They produce both sexually and vegetatively.


6 They have long flowering and fruiting periods and produce many seeds;


7 They are pollinated by wind or by generalist pollinators; and/or,


8.  Their seeds are dispersed over long distances (e.g., by birds, wind, water or people).


What Invasive Plants Species are Causing Problems in Maine Forests?


Although there are many species of plants that are considered invasive in Maine, there are a few species

that are of particular concern in the forest. These species include:


 Japanese barberry (Berberis thunburgii)

 Honeysuckle (Lonicera sp.)

 Asiatic bittersweet (Celastrus orbiculatis)

 Common buckthorn (Rhamnus carthatica)

 Glossy buckthorn (Frangula alnus)

 Autumn olive (Elaeagnus umbellata)


Many of these species already are causing serious problems, particularly in southern and coastal Maine

and the islands. Norway maple (Acer platanoides) is another species of concern. Currently, it is mostly a

problem around cities and towns, but it has the potential to become more widely established. Some

of these invasive species, such as the honeysuckles, Asiatic bittersweet and autumn olive are particularly

problematic along forest edges and in young forest stands. Others such as the buckthorns and Japanese

barberry are able to invade the understories of undisturbed mature forests.


How Can I Keep My Woods From Being Invaded?


Learn to identify invasive plant species. There are many excellent sources available to help you identify

invasive plants. Fact sheets on the species listed in this information sheet, as well as, additional species

of concern are available from the Maine Natural Areas Program website or by phone or mail request:


Maine Natural Areas Program 

157 Hospital Street

State House Station #93

Augusta, Maine 04333

(207) 287-8044


Don’t plant invasive species in your woodlands or near the edges of your yard. Many invasive plants

are still sold legally by nurseries. Know which plants are invasive and don’t plant them near the wild lands.

The University of Maine Cooperative Extension maintains a list of nurseries that sell native

landscaping plants. The list can be accessed by contacting your county extension office:


Get ahead of the invasion. Once invasive plants are well established getting rid of them can be very

difficult and costly. Therefore, prevention and early detection are key to keeping the invaders at bay.

Because invasive plants are so aggressive, they tend to occupy disturbed areas more rapidly than native

species. Therefore, it is particularly important to determine if there are invasive plants present in the

forest understory before creating a disturbance such as a timber harvest. Identifying and removing a few

individuals of an invasive species before a harvest could prevent a full-scale invasion later on.


How Can I Control Invasive Plants in My Woods?


There are two primary methods of controlling invasive plants; mechanical and chemical.


Mechanical control involves cutting and or pulling up the undesirable plants. Mechanical control is most

effective when entire plants, including the roots, are removed. Mechanical control is best suited to

situations with few plants where a thorough job can be done. Before using mechanical control, check on

which method is most effective. Chemical control involves the use of an herbicide to

kill the plants. An advantage of chemical control is the proper herbicide, properly applied, can kill the

entire plant. Some types of herbicide may only be applied by licensed pesticide applicators, but many

are available to the general public. Information on the laws and rules governing pesticide use in Maine can

be obtained from the board of pesticide control:  (207) 287-2731 des/laws/index.htm


The labels on all herbicide containers contain

information on what types of plants they control, how to apply them and the necessary safety precautions

that you must take when using them. ALWAYS READ THE LABEL AND FOLLOW THE DIRECTIONS WHEN

USING ANY HERBICIDE! Different types of herbicide are designed to kill different types of plants, so

reading the label is essential to be sure you are using the correct type. Improper application can harm or kill

desirable native plants along with the targeted invasive species. For controlling woody invasive

species, the mechanical control and chemical control methods can also be combined. The combined

method involves cutting the invasive plants and then applying an herbicide to the cut stumps. This kills the

roots and prevents sprouting.


Can I Get Help Controlling Invasive Plants in My Woodlot?


Contact your nearest Maine Forest Service District Forester for more information on these



For more information, please contact:

Maine Forest Service



22 State House Station

Augusta, ME


(207) 287-2791 or





​Maine Forestry

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