Exotic, Invasive Species

Exotic, invasive species are organisms that arrive in an area far from their home and then succeed in surviving, reproducing, and spreading.

Exotic, invasive species bring turmoil to a natural system; they can out compete native species and reproduce vastly, taking over a significant swathe of the ecosystem in a short time, changing the structure and composition of wildlife habitat, reducing diversity of species, and even changing the availability and make-up of water resources.

NepRWA’s Projects

Over the years, the Neponset River Watershed Association has taken on several exotic, invasive species control projects, and no doubt will continue to take on more.

In late 2012, the Watershed Association completed a five-year project to release two species of beetles to help reduce and control exotic, invasive Purple loosestrife plants in our watershed’s wetlands.In 2002, we physically removed exotic, invasive Water chestnut plants from Ellis Pond.

Read more about the Purple Loosestrife Project.

Learn More About Exotic, Invasive Species

Plant, animal, insect, and fungi species can be categorized as “native,” “exotic,” a hybrid of the two, “naturalized,” or “invasive.” As such, they have different effects on the surrounding environment.


Species that have been present in a region of the USA for thousands of years are considered “native” to that region because of their long residence. During that time, native species have adapted to their presence and come to rely on them for food, shelter, and/or other needs. It’s possible to learn which species lived in an area thousands of years prior, by taking a core sample of the soil and identifying the species present in that core sample  (i.e., pollen, plant segments, etc.).


Viceroy on willow in Fowl Meadow.

Viceroy on willow in Fowl Meadow.

Because exotic, invasive species can alter Neponset natural landscapes and even reduce local biodiversity, we work to prevent both the spread of these species and their presence in the landscape.

Exotic species are those that arrived more recently, having traveled from elsewhere in North America or even from other parts of the world. Native species have not yet fully adapted to making use of these species.

Commonly, what we consider to be exotic species here in New England are species that were transported to North America since the European colonists arrived. Some of these species were transported accidentally, while others were brought on purpose.

Exotic plant seeds can hitch a ride on a person’s clothes when s/he visits another region or even country, then remain attached while the person travels back home, and later fall off outdoors, at home, during the person’s daily routines. The seeds then have the opportunity to grow into new plants and reproduce in their new home. Such accidental introductions occur all over the world, ever increasingly, because of global trade and travel.

Likewise, aquatic organisms can flow into a ship with the water that is taken on as ballast while the ship is docked in one port. The ship then leaves, and when it arrives at another port, that life-form-filled ballast water is dumped into the harbor to lighten the ship for new cargo. Now, these aquatic organisms have an opportunity to live and reproduce in this new home.

Some people also purposefully transport species from other countries and distribute these, or propagate and sell them (e.g., ornamental outdoor plants or aquarium plants and fish). Then, the species can reproduce and spread on their own.

An exotic species that is reproducing on its own in the new, regional landscape is considered a “naturalized” species.


These species are very successful at spreading through areas, via reproducing and outcompeting other species. Both native and exotic species can be invasive. Often, species that do well in disturbed ecosystems and are considered “pioneer” species because of it, are considered invasive. Such species might include grasses, algae, lichen, wildflowers, birch trees, and mosses.

Exotic, invasive Purple loosestrife, in bloomExotic, invasive

Fortunately, it is only a very small proportion of exotic species that becomes invasive. However, that small segment delivers a big punch.

Naturalized exotic species that spread in the landscape and displace native species or threaten environmental, agricultural or personal resources by the damage they cause are considered invasive. Note that not all exotic, invasive plants are equally invasive. While some only colonize small areas, others may dominate large areas in a short time.

Exotic, invasive species are of special ecological concern because they alter and degrade habitat for native species and also compete forresources, reducing native species biodiversity. Because of this, environmental stewards and land managers attempt to control and reduce exotic, invasive species.

They are successful in their new homes because the growth of their populations is not controlled by the predators and competitors with which they evolved in their old home territory. And, although some native species may begin to prey on the exotics, it is not sufficient to provide control.

After working in a wetland covered in the exotic, invasive species Purple loosestrife, a volunteer cleans her shoes to avoid spreading the plants' seeds elsewhere.What You Can Do

  • After you go for a walk, drive, bike or boat ride through areas infested with exotic, invasive species, make an effort to clean your clothing (including shoes) and equipment before entering other areas. Avoid spreading the seeds of exotic, invasive plants.
  • Plant native plants in your yard, and encourage your neighbors, friends and family to do the same. These plants will provide habitat and food for native species. They also will grow easily, as these species adapted to local conditions over many thousands of years.
  • Learn to identify and control exotic, invasive plants, and then remove and properly dispose of any you find growing in your yard or neighborhood. Your efforts will help to prevent these plants from spreading elsewhere.
  • Learn about and participate in exotic, invasive species control projects and ecological restoration projects around the region. Contact your local conservation group, conservation commission, conservation agent, or land trust to get involved.

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