Non-Native Species

two volunteers kneel on the side of the road to pull invasive dandelions
Denali counts on volunteers to help eradicate invasive plants that are found along the park road corridor.

NPS Photo / Claire Abendroth

The National Park Service (NPS) defines non-native or exotic species as those occurring in a given place as a result of actions of humans. Compared to parks in the rest of the United States, the NPS units in Alaska are relatively clear of exotic plants. Most exotic plant species are confined to areas that have been disturbed by humans.

Several factors have protected Alaskan parks from the widespread invasion of exotic plants:
  1. Past and current climates: Past climates have produced a flora low in diversity but adapted to a wide range of ecological conditions. For example, many of Denali’s shrubs and herbs are circumpolar or circumboreal in distribution. They are adapted to thrive in the harsh subarctic conditions. Most exotic taxa are not adapted to the current climate of interior Alaska.
  2. Undisturbed ecosystems: For the most part, Alaskan parks’ ecosystems and processes have all the pieces. This includes key predators, herbivores, and a relatively natural wildfire regime. Ecosystems of parks in other states, by comparison, are altered by livestock grazing, wildfire suppression, altered hydrology, and other factors that ease the entry of exotic species.
  3. Big country: Most parks in Alaska are large enough to include all the ecosystem pieces, and are surrounded by undeveloped lands. In comparison, parks in other states are islands in a sea of altered ecosystems heavily influenced by highly invasive exotic plants
In spite of these protective factors, the threat to parks in Alaska from exotic plants is increasing and Denali is no exception. New exotic plants are appearing, and some of those already present are spreading. For example, Melilotus alba (white sweet clover) has invaded naturally open riparian areas elsewhere in Alaska, but is still confined to areas of human disturbance in Denali. Vicia cracca (bird vetch) is also of concern. It can invade stands of shrubs and tree saplings by climbing and spreading over the native plants. Although bird vetch is not yet a problem in Denali or other Alaskan parks, it is a threat in the urban-wildland interface of Alaska and many parks nationwide.

To ensure that Denali’s native vegetation remains pristine, park staff and volunteers work every summer to keep populations of non-native plants low and away from areas of established native vegetation. So while you may see ‘weeds’ along the Park Road, know that beyond the boundary of human disturbance lies millions of acres of native plant life.

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    Last updated: January 12, 2017

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