Non-native or “exotic” species of plants that are introduced into new ecosystems, i.e. to regions of the world where they have not lived before, may or may not become invasive. Some scientists estimate that about 25-30% of the non-native species that have been introduced to the United States have now become invasive.
Invasive plants, essentially, are species that grow very rapidly and out of control. Away from the diseases and predators that helped to keep them in check in their home environments, they are able to grow and reproduce so aggressively that they quickly out-compete native species—damaging the ecosystem because their dominance reduces biodiversity—eliminating many of the plants and animals that used to live there. Often, they spread extensively enough to form “monocultures,” or areas where they literally are the only plant growing.
Just as not all native plants have the same range, a particular exotic or introduced species might be invasive in one part of the United States but not another. Or it may take some time for that species to get established in different regions, so it may already be invasive in one area or state, but not yet have had the same impact elsewhere. Because our study of invasiveness is relatively new, and plants constantly continue to colonize new areas, it is quite likely that the range within which any given introduced plant species is recognized as being “invasive” will grow over time.
SO BAD, that they are Now Illegal
Currently, in Massachusetts, approximately 140 species of plants are legally designated as noxious or invasive in the Commonwealth. These plants are considered so damaging to both our environment and our economy that it is now illegal to import, propagate, or sell any of these plants in the state. Regulated by the Department of Agricultural Resources, the plants that were chosen for this notable status were drawn from the Federal Noxious Weed List as well as through the work of the Massachusetts Invasive Plant Advisory Group— a collaborative group representing federal and state governments, private land trusts and conservation organizations, the nursery and landscaping industries, the scientific community and academia. So take a good look at the Massachusetts Prohibited Plant List and get to know the species considered to be the most harmful of all.
Yet, even though the propagation, sale, and distribution of these species is now illegal, most are growing prolifically and running rampant in various parts of our state and in our neighborhoods here in Cambridge. They are doing, and will continue to do, a fantastic job of increasing their numbers all on their own. That is, unless we all learn to recognize them and to take corrective action-- concerted steps to control them and minimize their numbers.
And finally, note that many ecological gardeners and landscapers consider additional non-native species to be invasive, even though they might not to have made it into the status of illegality. The best advice for all of us who garden and steward land is:
If you don’t know it, don’t grow it.
Get to know the plants you garden with. Find out if they are native or non-native. Learn a little bit about their history and growing characteristics. Emphasize natives in your planting for the health of our common ecosystem. And when you decide to plant a non-native, be sure it isn’t known or suspected of being invasive. You will love the results—more songbirds, butterflies, and lots of beauty all around.
Find resource materials to learn more about invasive plants.