When a species is invasive...

A large snake in the grass
There is perhaps no better example of an invasive species than the Burmese python, which has taken over much of the Everglades, even competing with the alligator for the spot as top predator in the ecosystem.

NPS Photo.

The National Park Service defines a invasive species as non-native species that causes harm to the environment, economy, or human, animal, or plant health (Executive Order 13751). Learn more about invasive species by visiting our About page.

It is often thought that the terms 'invasive' and 'non-native' can be used interchangeably, but this is not always true. For a plant or animal to be invasive, it must do harm. Simply being non-native is not cause for concern. The National Park Service actively manages those non-native species that do harm.

Understanding the difference between invasive and non-native species and when a species is managed is crucial.


...and when a species is non-native

A pepper garden in a wood planting box with a sign in front that says "Peppers - Jalafuego"
Fruits, vegetables, and herbs grow along the path through the White House Kitchen Garden in President's Park.

NPS Photo.

Non-native species are organisms that do not occur naturally in an area, but are introduced as the result of deliberate or accidental human activities.

Unlike invasive species, non-native species may not hinder or prevent the survival of others within the ecosystem. They simply exist where they have not naturally occurred. Other terms used for non-native species include 'exotic' or 'alien' species, but these are often discouraged terms, as they may imply another meaning.

You might even recognize some non-native species of plants in your own backyard or on your dinner table. Non-native species such as petunias and tomatoes, present no threat to native plants and have been cultivated by humans for centuries.


Location, location, location...

In some cases, it is not correct to call an entire species native, non-native, or invasive to the U.S. In fact, a species may be considered native in one park, but invasive in another if it had not been historically found there. Rainbow trout provide an interesting example of a species for which management is complex. Rainbow trout are native to only a few states in the Western U.S., and non-native throughout much of the rest of the U.S. However, this species is considered invasive in some lakes and streams due to its effects on those native ecosystems.

A rainbow trout held in the hand of a person above water. The pink, iridescent sheen obvious down the fish's side
Rainbow trout in Yellowstone National Park.

NPS Photo.


More information about invasive species from the NPS and our partners can be found on the Resources page.

Last updated: December 3, 2020