NPS Photo
Though pretty, purple loosestrife has the ability to overrun native plants
Nonnative species are also referred to as introduced, exotic, or alien species. The National Park Service defines nonnative as species that occur in a given place as a result of direct, indirect, deliberate, or accidental actions by humans. Plant species that are brought into an area as food, fiber, or ornamental landscape plantings can "jump the fence" and become established in the wild. Likewise, nonnative animal species can be introduced into an area deliberately, for agricultural use or fish stocking; or by "hitching a ride" on objects like boat hulls and outboard motors. Many species find their way to new locations in crop seed, soil or nursery stock. Although many introduced species have had a negative impact on our society, primarily in agriculture, these species would not have evolved with the native species and therefore are not a natural component of the ecological system. In extreme cases, invasive nonnative species can displace native species, thereby degrading the integrity and diversity of native communities. Alien species can also become pests, such as Asian lady beetles and zebra mussels.
There are currently about 8 nonnative plant species being targeted for action in the "rec river" that are of high management concern. Purple loosestrife, salt cedar, Russian olive, Canada thistle, and leafy spurge are among the park's invasive plants. Purple loosestrife, although beautiful, is a noxious weed, well known for its capacity rapidly to invade wetlands, replace native vegetation and dominate those habitats at the expense of turtles, birds and other animals. Salt cedar or Tamarisk is a deciduous shrub or small tree. It can absorb 200 gallons of water per day, giving heavy infestations the ability to dry up creeks and small lakes. Leafy spurge is a noxious weed that has driven out and taken over from native species.
