Invasive FAQ

What is an invasive plant species?

• Native Plant – a species that reached its location without assistance from humans.
• Exotic species – a non-native plant or animal introduced into a new location by human activity, either intentionally or by accident.
• Invasive species – a non-native (adventitious) species that is capable of moving aggressively into a habitat and monopolizing resources such as light, nutrients, water, and space to the detriment of other species

How do invasive species spread?

• Horticultural activity is responsible for about 60% of invasive species introductions (arboretums, gardeners).
• Conservation activities (Soil Conservation Service, Department of Agriculture) introduced about 30% of invasive plants, mostly for screening, windbreak, and erosion control, but also to supply food and cover for wildlife.
• Accidental introductions make up the remaining 10%. For example, purple loosestrife was first brought to the U.S. in the hold of a ship via ballast water, then later introduced for horticultural purposes.
• Some species may be native to certain regions of North America where they are not invasive, but arrive in new regions through assisted range expansion or transportation to other parts of the country for ornamental purposes where they can become invasive.

Why are we concerned?

• According to the North Carolina Botanical Gardens "Biota of North America" study, at least 4,000 species of non-native plants occur outside cultivation in the United States. Most of these escaped species cause few problems, but 79 species cost the U.S. economy more than 97 billion dollars annually in lost crops, failed recovery efforts for endangered species, and control efforts.
• Invasive species have contributed to the decline of 42% of U.S. endangered and threatened species, and for 18% of U.S. endangered or threatened species, invasives are the main cause of their decline.
• Invasive species compete directly with native species for moisture, sunlight, nutrients, and space. Additionally, some studies suggest that the fruit produced by invasives may not be as nutritious for local wildlife, requiring them to eat more frequently. Fruits and seeds of invasive species are the "junk food" of the natural world.

Why are invasive species so successful?

• Most species have predators in their natural range that keep their population numbers in check. When new species are introduced, however, they come without their natural predators.
• Most invasive species produce copious amounts of seed. This seed is often bird- or wind-dispersed, allowing it to cover great distances in a short period of time.
• Some invasives have aggressive root systems that can spread long distances from a single plant. These root systems often grow so densely that they smother the root systems of surrounding vegetation.
• Some species produce chemicals in their leaves or root systems which inhibit the growth of other plants around them.
• Most invasives cast extremely dense shade beneath which native vegetation can not survive.
• Most invasives thrive on disturbed soil, such as that around newly developed land, or along highways.
• As our region becomes more fragmented, through development, local habitats become more vulnerable to invasives.

Adopted from New England Wild Flower Society available at: www.newfs.org/protect/invasive-plants/invasive-plant-faqs.html