Invasive alien plants can bring about significant changes in park ecosystems by changing structural attributes of native plant communities and the processes that support them. A recent USGS report documents nonnative plant surveys at Sequoia-Kings Canyon and Yosemite national parks, and provides a useful template for prioritizing alien species problems in these and other national parks and reserves.

In 1998, the U.S. Geological Survey initiated a survey to describe the distribution and abundance of nonnative plants in disturbed areas of Yosemite, Sequoia, and Kings Canyon national parks. This study built on over a year’s worth of prior work done in Sequoia-Kings Canyon National Park to assess the invadedness of sites having short- and long-term disturbance, both natural and human-caused. Methods were standardized among the parks, thereby laying the groundwork for providing managers with information to assist in managing invasive nonnative plants in the Sierra Nevada national parks. Nonnative plants were mapped, site characteristics described, and permanent records created for evaluating the current status of nonnative plant species in the parks to provide a basis for managers to decide on appropriate direction and levels of response. Disturbed areas were targeted for inventory because plant surveys in undisturbed sites discovered few of the nonnatives encountered during casual observations of heavy use areas. These disturbed areas included campgrounds, corrals, developments, roads, trails, and pastures.

A comprehensive literature review was done for each species encountered during surveys to derive detailed information on biological characteristics (seed produc-tion and viability, mode of reproduction, dispersal habits, etc.), on distributional patterns and known invasiveness, and on control methods (effectiveness of mechanical, chemical or other treatments). The process of ranking exotic species for management took into account many of the biological and control factors recommended for the invasive species. It empirically blended those factors with local and regional information concerning the invasiveness and ecological impacts of each exotic species. This less-than-quantitative approach was necessary because of the lack of published data concerning the biological and ecological characteristics of many of the exotic species and because the parks encompass a wide range of habitats across an elevational gradient from under 600 m (1,970 ft) to over 4,300 m (14,120 ft). Inventories of the current distribution of alien species address the need of managers to have information on all potential invaders so that priorities can be established for the monitoring and control of these species.

Management Implications

• The ranking of the alien plant species into 4 management categories provides general guidance for setting management priorities in Sequoia-Kings Canyon and Yosemite national parks.
• The process of researching life histories and then prioritizing plant species serves as a model for all resource management agencies in dealing with alien species.

J. D. Gerlach, Jr., P. E. Moore, B. Johnson, D. G. Roy, P. Whitmarsh, D. M. Lubin, D. M. Graber, S. Haultain, A. Pfaff, and J. E. Keeley. 2003. Alien Plant Species Threat Assessment and Management Prioritization for Sequoia-Kings Canyon and Yosemite National Parks. U.S. Geological Survey Open-File Report 02-170. Carson City, Nev. 149 p.

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