As they arrive in new areas people both intentionally and unintentionally contribute to the spread of non-native species. Some of these highly adaptable plant and animal species (often called "invasives") can reproduce rapidly and compete with native species for valuable resources or sometimes prey on them directly. Invasive species can wreak havoc on ecosystems and are a major threat to native biodiversity.
Combating non-native, invasive plants is a priority for the National Park Service. Non-native plants can destroy the ecological balance of plants, animals, soil, and water. They can quickly take over native landscapes, competing with native plants and robbing wildlife of food and shelter.
Some of the most troublesome non-native plants in Whiskeytown include tree of heaven, Himalayan blackberry, mullein, yellow star thistle, and Scotch, French, and Spanish brooms. Biological, chemical, manual, and mechanical techniques are all used to control the spread of these invaders in the park. As non-native plants are removed, park staff begin restore the natural landscape by planting native plants.
The threat of invasion into aquatic communities is of special interest to Whiskeytown staff. Invasive fish are a factor in the declines of several species of amphibians in the West, and reservoirs (like Whiskeytown Lake) serve as source areas for invasive warm water species such as bass, sunfish, and catfish. Bullfrogs, originating in eastern North America, are also common in Whiskeytown Lake. With their large bodies, voracious diets, and high numbers, bullfrogs can easily outcompete or prey on native aquatic species.