Invasive Plant Species

What is an invasive species?

Most nonnative species, including most of our sources of food and fiber, are not harmful; and many are highly beneficial. A small percentage of nonnative species cause great harm to the environment, the economy or human health. Nonnative species that cause harm are collectively known as invasive species.

An invasive species is a non-native species whose introduction causes or is likely to cause economic harm, environmental harm, or harm to human health. The term "invasive"; is used for the most aggressive species. Those species grow and reproduce rapidly, causing major disturbance to the areas in which they are present.

A plant is deemed to be invasive if it causes negative environmental, economic, or human health effects, which outweigh any beneficial effects.

National Invasive Species Management Plan

See http://www.invasivespecies.gov/index.html

In Maine the list of invasives plants is maintained by the Maine Department of Conservation's Maine Natural Areas Program (MNAP) with many organizations commenting on the risks these plants represent and what can be done to control them, including the following samples:

"Invasive plants degrade habitat quality in a variety of ways. Their fruits are often less nutritious than those of their native counterparts, they host fewer and less diverse insect prey for birds, and their aggressive expansion displaces and reduces native plant diversity. "

Mass Audubon Society: 2017 State of the Birds page 44

"Invasive species are the second greatest threat to global biodiversity, after loss of habitat."

MNAP Bulletin #2536. See below.

"Time is of the Essence - The invasive plant problem at Fort Williams Park is worsening every day. Mackworth Island in Falmouth, Maine is facing a major and costly battle to save its ecosystem due to invasive plant dominance."

Prospectus of the Arboretum at Fort Williams Park

Our analysis points to an overarching conclusion: we need to act immediately to reduce, mitigate, or reverse non-climate threats that are weakening plant communities. ... The key goals can be summarized as save threatened species, control invasive species, and keep common plants common.

New England Wild Flower Society: 2015 State of the Plants in Brief

Recommendations - Urgently Conserve Plant Diversity page 8

Habitats may also suffer degradation from the accumulation of toxic chemicals or the introduction of invasive species. The greatest danger of degraded habitats is that they often still appear to be suitable, both to humans and to birds.

Mass Audubon Society: 2013 State of the Birds

Drivers of Decline - Habit Fragmentation page 14

"..there is 35 times less food (caterpillar biomass) available for birds in habitats that comprise primarily alien plants..."

Tallamy, Douglas W. Bringing Nature Home. Portland, Oregon: Timber Press, Inc., 2009 - page 61.

"An invasive plant is defined as a plant that is not native to a particular ecosystem, whose introduction does or is likely to cause economic or environmental harm or harm to human health. ... OCT will use best practices to manage invasive plants on its properties by actively monitoring for their presence and by proactively managing them when necessary. OCT’s goal will be to minimize the impact of invasive plants on its properties. OCT will also seek to educate abutters and the communities where its properties are located about invasive plants and the importance of identifying and managing invasive plants."

Oceanside Conservation Trust of Casco Bay Invasive Plant Policy

"As Allan and his colleagues report this week in the Proceedings of the National Academy of Sciences, the density of white-tailed deer in honeysuckle-invaded areas was roughly five times that in areas without honeysuckle and the density of nymph life-stage ticks infected with bacteria that cause human disease was roughly 10 times higher."

Science Daily October 12, 2010 http://www.sciencedaily.com/releases/2010/10/101011173245.htm

Abstract at Proceedings of the National Academy of Sciences

Both Chuck Lubelczyk, of MMC Vector Borne Disease Laboratory and Gary Fish from the Maine Board of Pesticides Control, said there are steps which can be taken to reduce tick habitat. Remove leaf litter where ticks hide. Remove shrubby growth, especially invasives such as bittersweet, barberry and honeysuckle. Widen paths through woods and shrubby areas.

Lyme/Tick informational Forum Notes, Long Island Learning Center, Saturday, April 21, 2012

*** Please help with this threat and report ticks you find to the University of Rhode Island at the TickEncounter Resource Center ***

Invasive plant species have become a source of problems that have grown more serious in the past twenty years. The increase of invasive plants in the region has increased risk to ecological systems, public health and public safety. Land stewards in our region are responding to issues with invasives, including the Casco Bay Invasive Species Network (CBISN) that advocates why we should care on their website and Cliff Island Corporation for Athletics, Conservation and Education (ACE) that has published a Guide on Invasive Plants. They and many other Maine organizations are responding to issues that include the following:

Early dense foliage of invasive plants blocks light, preventing any ground cover and crowding out native plants and degrading quality of local ecology with lower plant diversity, lower value food sources and altered cover for wildlife.

Invasive plants will impede regeneration of woodlots by altering soil chemistry, disrupting plant succession, damaging tree structures, and limiting native plant diversity.

While often introduced as part of erosion control programs, invasive plants' shallow roots have proven them to be undesirable for use in soil stabilization.

Invasive plants lower surrounding water quality by increasing soil erosion versus areas with more native plants and shrubs.

Invasive plants degrade habitat for birds by exposing nests to increase predation and by providing food sources of lower value versus native plant species.

Invasive plants support dramatically fewer insects than native plants, lessening the food supply for many birds.

Invasive plants are found to carry many more ticks infected with Lyme Disease (and at least four other serious health risks) than is true with native plants.

Invasive plants can cause undergrowth to die out, creating increased fuel sources for wildfires.

Like CBISN and many other organizations in Maine, CICC is developing a best practice stewardship program to manage invasive plant species. The CICC program is based on the State for Maine Department of Conservation's Maine Natural Areas Program (MNAP) whosemission is "to ensure the maintenance of Maine's natural heritage for the benefit of present and future generations. MNAP facilitates informed decision-making in development planning, conservation, and natural resources management. The Program's success relies upon consistent and objective methods to collect, organize, and interpret information".

CICC focus is on control of four major invasive plant species that dominate certain areas of CICC land.

Asiatic Bittersweet

Shrubby Honeysuckle

Japanese Barberry

Black Swallowwort

Selections from Fact Sheets developed by the Maine Natural Areas Program and University of Maine Cooperative Extension are noted below. For complete descriptions on invasive plants please go to the MNAP link.

Invasive Plants Threaten Maine’s Natural Treasures

Bulletin #2536

What’s the difference between a “weed” and an “invasive plant”?

A weed is simply a plant growing in a place where it’s not wanted. It might be a problem locally, but it generally doesn’t spread to become a large-scale problem in natural areas.

An invasive plant is a non-native plant with very high reproductive potential and the ability to establish across long distances (for example, it might produce seeds that can spread by wind or by animals). An invasive plant can become established in natural areas, and disrupt natural communities by outcompeting native plants.

What problems do invasive plants cause?

Invasive plants outcompete native species and agricultural crops, causing billions of dollars of damage each year. They affect forests, wetlands, lakes, streams, croplands, and pastures, and degrade many of our sensitive natural habitats. They grow rapidly, multiply, and spread to unmanageable levels in short periods of time.

Invasive species are the second greatest threat to global biodiversity, after loss of habitat. Invading plants outcompete native species for sunlight, nutrients, and space. They change animal habitat by eliminating native foods, altering cover, and destroying nesting opportunities. Some invaders are so aggressive that they leave no room for our natives.

Invasive plants threaten Maine’s natural and working landscapes. Their aggressive growth degrades our recreational experiences. Species like Japanese barberry and multiflora rose can form thorny, impenetrable thickets in forests. Other invasive plants choke waterways, limiting their use. Invaders increase the costs of agriculture and affect forest regeneration. And, these species mar the natural beauty of our regionally distinctive landscape.

Asiatic Bittersweet

Bulletin #2506

Threats to Native Habitats

Asiatic bittersweet poses a serious threat to other species and to whole habitats due to its aggressive habit of twining around and growing over other vegetation. This plant has a high reproductive rate, long-range dispersal mechanisms, and the ability to root-sucker. The vines can strangle tree and shrub stems. All types of plants, even entire plant communities, can be over-topped and shaded out by the vine’s rapid growth. Nearly pure stands of this vine are sometimes found in affected areas. Recently it has been discovered colonizing sand dunes in Connecticut and Rhode Island.

See also a good summary from the US Forest Service with details to support the below summary at http://www.fs.fed.us/database/feis/plants/vine/celorb/all.html

"Oriental bittersweet presence may alter soil chemistry, plant succession, and stand structure; threaten native plant diversity; and reduce productivity in silvicultural and agricultural systems."

Control

Small patches can be hand-pulled. Take care to remove the entire root to prevent resprouting. Low patches have been successfully removed by cutting the vine and treating the regrowth with a triclopyr herbicide. Control is more successful in taller patches when cut stems are immediately painted with triclopyr or glyphosate. This plant has a substantial seedbank, and complete eradication may depend on repeating control methods for several years.

CICC Preferred Control Method - Mechanical Cutting. Cut with mowers on targeted open areas. With adequate training and supervision paint freshly cut stumps with Roundup.

Field notes: Bittersweet is widespread on CICC land with problem areas noted on the Point and along Calumet Ave near the Swamp where the effects of strangling and over topping are prevalent. Threat area that is a focus is below Battery Foote where we want to protect the forest regeneration process. The preferred time for cutting bittersweet is in late June when the energy in the root system is reportedly at its lowest level. Effort is underway to create a perimeter clearing below Battery Foote to prevent bittersweet from creeping downhill into the woods and to allow us to address the pockets of invasives that have taken hold in the area cleared of storm damage in 2010.

Shrubby Honeysuckle

Bulletin #2507

Threats to Native Habitats

Shrub honeysuckles can rapidly invade and degrade native plant communities. They form a dense layer that shades the ground, interfering with the growth of many native woody and herbaceous species, including rare plants. The ground under a honeysuckle thicket is often void of other vegetation. Shrub honeysuckles leaf out earlier than native species and they retain their leaves longer into the fall, giving them a competitive edge. Their success on high pH, dry, exposed soils has made them a threat to some of the Northeast’s unique limestone plant communities. The fruit of these shrubs is eaten by common birds, which helps spread the seed into new locations and makes the shrub even more difficult to control.

See also a good write up from the Kittery (Maine) Land Trust at http://www.kitterylandtrust.org/honeysuckle1.cfm on the ecological threat from honeysuckle as follows:

"Exotic bush honeysuckles can rapidly invade and overtake a site, forming a dense shrub layer that crowds and shades out native plant species. They alter habitats by decreasing light availability, by depleting soil moisture and nutrients, and possibly by releasing toxic chemicals that prevent other plant species from growing in the vicinity. Exotic bush honeysuckles may compete with native bush honeysuckles for pollinators, resulting in reduced seed set for native species. In addition, the fruits of exotic bush honeysuckles, while abundant and rich in carbohydrates, do not offer migrating birds the high-fat, nutrient-rich food sources needed for long flights, that are supplied by native plant species.

Here is a link to a summary of sources that support removal of honeysuckle.

Control

The best method of control is to prevent non-native shrubby honeysuckles from becoming established. These plants should be removed as soon as possible if they are found colonizing an area. Small infestations can be cleared by hand using a shovel or hoe, provided the entire root is removed. Larger colonies have been controlled by various combinations of repeated treatments of mechanical control, burning, or applying a glyphosate herbicide. If cutting is included as part of a treatment, it should be done in early spring and in late summer or early fall. Cutting of plants results in resprouting, but is effective in temporarily reducing seed production. Seedlings are easily pulled. Treatment by prescribed burning is most effective if conducted during the growing season. Control methods may need to be repeated for three to five years to inhibit resprouting and to exhaust the seedbank.

CICC Preferred Control Method - Mechanical Cutting. Cut with mowers on targeted open areas. With adequate training and supervision paint freshly cut stumps with Roundup.

Field notes: Honeysuckle is also widespread on CICC land with problem areas noted on Whitehead, the Point and Cellar Point. Cleared areas near the Point gazebo and along Calumet Ave have allowed native plants to recover, especially noted is the recovery of jack-in-the-pulpit, elderberry and viburnum. Cleared area along Calumet Ave has been seeded with pasture mix grass and wildflowers. Grasses seem to have been established enough to support a maintenance program with a single annual mowing. Threat area that is a focus is on the Point.

Japanese Barberry

Bulletin #2504

Threats to Native Habitats

Japanese barberry has escaped from cultivation and is progressively invading natural areas. It is a particular threat to open and second-growth forests. An established colony can eventually grow thick enough to crowd out native understory plants. Traversing through dense patches of barberry can be difficult and even painful. Birds eat the red berries, thereby spreading the shrub into new areas.

Control

Mechanical removal is recommended because it is effective and may cause the least disturbance. Japanese barberry is one of the first plants to leaf out in spring and is therefore easy to distinguish from other shrubs. Whole shrubs may be removed with a hoe or weed wrench. Use of thick or sturdy gloves is recommended to provide protection from the spines. Plants can resprout from roots, so remove as much of the roots as possible. Regular mowing can prevent barberry from returning once it has been removed. In areas where mechanical removal is not practical, such as rock piles or outcrops, a glyphosate herbicide can be used. Consult a licensed herbicide applicator before applying herbicides over large areas.

CICC Preferred Control Method - Mechanical Cutting. Cut with mowers on targeted open areas. With adequate training and supervision paint freshly cut stumps with Roundup.

Field notes: Barberry problem areas are in the Swamp, on Farm Hill and below the Ottawa House foundations. Use of hand tools and mowing is hopefully going to be an effective way to control this plant. Note: This method is a change from the initial method of pulling out plants with tools like a weed wrench, which has not been effective.

Black Swallowwort

Bulletin #2523

Threats to Native Habitats

Black swallowwort is particularly troublesome in open areas and along edges and banks where it grows over other vegetation, blocking light and creating tangled thickets. It alters and degrades natural habitat by crowding out native plants and is a threat to rare species in some locations in New England.

Control

Mechanical Control: Digging up the root crowns is effective but relatively destructive and the whole crown must be removed. Pulling the plants by hand generally leads to resprouting but can prevent seed production, especially if repeated during the growing season. A less effective method is pod picking, which also limits seed production, but does little damage to the existing population. Mowing is best for preventing seed production. Mow frequently (one to two visits per season) just as the pods are beginning to form.

Chemical Control: Apply a one-percent solution of a triclopyr-based herbicide at an application rate of 2.25–19 L/ha (one to eight quarts per acre). The use of a triclopyr-based herbicide is especially desirable in grassy areas. Repeated herbicide applications will most likely be necessary in vigorous stands. It is best to spray early in the season before viable seeds are produced (before mid-July). Cut-stem applications are recommended for small infestations or if nearby desirable vegetation will be adversely affected. Burning and grazing do not appear to be effective. Use herbicides responsibly and follow manufacturer’s directions. Contact the Maine Department of Agriculture for information on restrictions that apply to the use of herbicides. Consult a licensed herbicide applicator before applying herbicides over large areas.

CICC Preferred Control Method - Mechanical cutting where possible, twice a season - once in late June and again in August, if seed pods are forming.

Field notes: Swallowwort is widespread across the island, especially in the more open areas. The goal is to balance limited mowing with the desire to maintain a pastoral, unmanicured appearance.

What you can do

Input on appropriate stewardship is sought from all CICC members, guests, friends and other interested parties. Stewardship plans are expected to evolve based on actions that become best practice for our land. Those willing to help control invasives with time and/or donations should contact a CICC officer to coordinate on work in any of the existing or new projects. See Projects page.

Report on other invasives plant sightings (See MNAP link) and help CICC avoid a future problem. Examples of this action are the single purple loosestrife plant spotted in 2011 in the Swamp drainage ditch and jimsonweed on Spicers Cove in 2012.

All comments and contributions are welcomed and appreciated.