WHAT ARE INVASIVE TREES?
Non-native plants have been introduced to this continent since colonial times. Some were brought here purposely, as agricultural or ornamental plants. Others arrived accidentally, e.g. as seeds or root fragments mixed in with soil or animal feed.
The vast majority of introduced plants have stayed within the confines of the farm or garden in which they were planted. Other plants, like Queen Anne’s lace and dandelions, have naturalized and become a part of our landscapes.
A third group of plants, those that have become invasive in their new environment or have the potential to do so, are a major concern. Usually, invasive plants get a foothold in areas that have been disturbed by human activity, and then move out into natural areas, where they overrun and displace the native vegetation.
The Norway maple is an example of an invasive tree. It was introduced into this country from Europe in 1756, and has been widely planted as a tough shade and street tree. It wasn’t until the early 1900s that its invasive potential was beginning to be recognized. Norway maples produce a large amount of seeds, which are able to germinate and grow strongly even in the shade under an established tree canopy. Norway maples have a shallow, very dense root system and cast a very deep shade. They also leaf out early in the year and lose their leaves later than native trees, resulting in a longer growing season. Many native wildflowers, as well as shrubs and trees, can’t flourish in the changed environment that Norway maples create, and so get crowded out.
WHY ARE INVASIVE PLANTS “BAD”?
Natural communities, or ecosystems, whether they be local ones or larger, are a complex web of life in which plant and animal species have evolved together, function together as a whole, and depend on one another.
Invasive plants disrupt healthy ecosystems by crowding out and causing the loss of native plant and animal species. The resulting loss of biodiversity compromises the health of the ecosystem.
CHARACTERISTICS OF INVASIVE TREES AND OTHER INVASIVE PLANTS
Given the harm that invasive plants can cause, it is important to be able to gauge whether an introduced plant might become invasive in its new environment. There can no prediction with absolute certainty, but there are characteristics that point to a plant’s invasive potential.
The United States National Arboretum lists the following characteristics:
Invasive Plants:
- Produce large numbers of new plants each season.
- Tolerate many soil types and weather conditions.
- Spread easily and efficiently, usually by wind, water, or animals.
- Grow rapidly, allowing them to displace slower growing plants.
- Spread rampantly when they are free of the natural checks and balances found in their native range.
INVASIVE TREES IN MASSACHUSETTS
The Commonwealth of Massachusetts has recognized the need to control invasive plants. According to the web site of the Massachusetts Department of Agricultural Resources:
“On January 1st, 2006, the Department began a two-step ban on the importation and sale of more than 140 plants identified as either noxious and/or invasive in the Commonwealth. The list of plants was developed in collaboration with the Massachusetts Invasive Plants Advisory Group (MIPAG). MIPAG members represent research institutions, non-profit organizations, green industry businesses and associations, and state and federal agencies. The MIPAG list is a product of scientific analysis, and represents the scientific consensus of groups and individuals with a broad range of perspectives on the subject of invasive plants.
Effective January 1, 2009, all plants on the prohibited list are banned from importation, propagation or sale within the state of Massachusetts.
The ban is limited to the importation, sale, trade, distribution and related activities of these plants, and does not impact any existing plantings.”
The Prohibited Plant List for Massachusetts, effective January 1, 2009, includes the following invasive tree species:
Amur cork-tree (Phellodendron amurense)
Black locust (Robinia pseudoacacia)
Common buckthorn (Rhamnus cathartica)
European buckthorn, glossy buckthorn (Frangula alnus)
Norway maple (Acer platanoides)
Sycamore maple (Acer pseudoplatanus)
Tree of heaven (Ailanthus altissima)
HOW CAN I LEARN MORE?
Information on the Web:
Center for Invasive Species and Ecosystem Health
Plant Conservation Alliance’s Alien Plant Working Group
Invasive Plant Atlas of New England
New England Wildflower Society
MA Prohibited Plant List, effective January 1, 2009
Information in Print:
Randall, John M., and Janet Marinelli. Invasive Plants: Weeds of the Global Garden. Brooklyn, NY: Brooklyn Botanic Garden, 1996.
