Invasive Plants in the United States National Parks

Natural area parks managed by the United States National Park Service were established to protect native species and historical (but living) landscapes and scenery, and to provide public enjoyment of the same, as long as the natural area remained “unimpaired for future generations.” A growing human population, and a 40-fold increase global trade and transportation may provide the most significant challenge to Park Service management: the invasion of alien plants, animals, and diseases into so called ‘protected areas’. General ecological theory suggests that an increase in biological diversity should increase the overall stability of an ecosystem. We provide examples of plant invasions in U.S. National Parks to show that, despite increases in plant diversity, alien plant species are capable of greatly affecting the native species that the parks were established to protect. Furthermore, alien plant species are affecting natural patterns of grazing, disturbance, and nutrient cycling, resulting in decreased habitat quality, perhaps providing less resistance and resilience to natural and anthropogenic stresses such as climate change, land use change, recreation, and future invasions. The primary mission of the National Park Service, protecting native species and ecosystems for present and future generations, may be increasingly difficult due to the continuing invasions of alien organisms. Key elements of an effective invasive plant management programme are identified.