What is a non-native?
Non-native plant species are those that occur outside their native ranges in a given place as a result of actions by humans. The term non-native can be used interchangeably with the terms alien, exotic, introduced, and non-indigenous (on this web site the term weed refers to non-native plants as well). Therefore, non-native plants can be thought of as those that accompany non-native peoples to a new land.
Native plant species are those that have not been introduced to a given area through the actions of humans. They are naturally adapted to their given area and they have generally existed there for much longer than have humans. The term native is often used interchangeably with indigenous. While some native species grow aggressively and can appear to invade natural areas, they are all in fact naturally adapted, and are valuable members of the ecosystem.
For conservation purposes, a non-native plant species cannot ever become native, even if it persists in an area for hundreds of years. By definition, a non-native plant did not arrive at its new location by natural means, and therefore it can never be considered a native species.
Most of the plant species that humans grow are not native to the areas in which they are grown; such plants include food crops, ornamental plants, roadside weeds, and garden plants. Most of these plant species do not reproduce without the aid of humans. Those that do reproduce and spread on their own are known as naturalized non-native plant species.
Innocuous Non-native Plants
While nearly one in eight plant species in Sequoia and Kings Canyon National Parks are non-native, a great number of them are considered innocuous. Innocuous non-native plants do not appear to threaten native species or ecosystems. For example, swine cress (Coronopus didymus) is a small, non-native, annual mustard that is known only from two locations in the parks, both of which are horse corrals. Swine cress is not known to be a problem species elsewhere and it is not considered to be a threat to Sequoia and Kings Canyon National Parks.
Invasive Non-native Plants
Invasive non-native plants are those that spread, often very quickly, from their original point of introduction into surrounding natural ecosystems. The term invasive non-natives can be used interchangeably with wildland weeds, noxious weeds, or pest plants.
There are numerous non-native plant species in Sequoia and Kings Canyon National Parks that are known to be highly invasive and are actively threatening park resources. These invasive species spread aggressively into pristine areas and displace or disrupt the natural plant communities. Himalayan blackberry (Rubus discolor) takes over moist areas such as stream banks and excludes vast numbers of understory plants. There are several well-entrenched populations of Himalayan blackberry in Sequoia National Park. We are actively controlling many of these species.