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Invasive Species

An Invasive Species is non-native to the ecosystem under consideration and whose introduction causes, or is likely to cause, economic or environmental harm, or harm to human health. Invasive species may be plants, animals or pathogens.

Economic Impacts:  Reduced agricultural yield, decreased fisheries health, loss of recreation opportunities, decrease in wood/forest products, disrupted trade, decrease in tourism and rising management costs.

Environmental Impacts:  Decrease in biodiversity and structural diversity, disruption of natural processes, and reduced ecosystem function and services.

Human Health Impacts:  Human injury or illness, decreased soil, air, and water quality, climate and other weather changes, and altered flood regimes.



Native:  Any species that is part of a natural ecosystem or habitat within an ecosystem – often associated with a historical time frame such as prior to European settlement in North America.

Non-Native:  Any species that is not a natural part of a specific ecosystem or habitat.

Exotic:  Most often refers to species from ‘far away’, such as another continent.

Invasive Species:  Non-native species that causes, or is likely to cause, economic or environmental harm, or harm to human health.

Weed and/or Pest:  This subjective term can be used to describe any species, anyone doesn’t like for any reason.


Why are Some Species Invasive?

Species may become established for a number of reasons. Often, this is due to the lack of a natural check on the population, such as a predator, parasite, or pathogen, that allows them to outcompete native species. They may also fill an ecological niche that was vacant before they arrived, such as an ability to take advantage of early or late season growth while native species are dormant. Forms of human disturbance may also alter the habitat in a way that it is no longer suitable for native species, but invasive species may thrive in such conditions.

Invasive species often have a high reproductive rate, reach maturity early, have effective dispersal mechanisms, disperse rapidly, and/or have a broad tolerance range to environmental conditions.


Pathways of Invasion

Pathways of Invasion are the means by which invasive species move from one location to another and become established. These are often distinguished between natural pathways and assisted pathways.

Natural Pathways:  Means of natural dispersion of species such as seed dispersal mechanisms or species specific adaptations for movement. Natural pathways include wind, water/currents, weather events and flight. Once established, a species may effectively use natural pathways to spread.

Assisted (Man-Made) Pathways:  Assisted pathways are enhanced or created by human activity. Such pathways are often how species first become established within a new area. Some examples of assisted pathways include construction, roads and rights-of-way, shipping, nursery and landscape trades, dumping bait, exotic pet releases, forms of disturbance and soil movement, and transportation on vehicles, boats, equipment, clothing and mowers.