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Alaska's national parks are not immune to invasive plants. With more than 54 million acres of Alaska managed by the National Park Service, entire landscapes and the fish, wildlife, and recreational activities they support are at risk. To combat the onslaught of exotic plant invasions, the NPS has Exotic Plant Management Teams, and the Alaska EPMT is wrapping up its sixth season.

The NPS mission directs parks to "preserve unimpaired the natural and cultural resources and values of the national park system for the enjoyment, education and inspiration of this and future generations."

Vast areas of remote wilderness in Alaska's National Parks might seem resistant, but invasive plants first gain footholds in disturbed areas like roadsides, trampled areas and construction sites. What Alaska parks lack in human disturbance, however, they more than make up for in natural disturbances, providing massive avenues for invasive plant dispersal.

Receding glaciers in Glacier Bay leave barren land vulnerable to invasions that can affect the historic successional patterns. Volcanic activity in Katmai's Valley of 10,000 Smokes alters the landscape. Shifting rivers and streams, such as the Copper River of Wrangell-St. Elias, result in disturbed floodplains. Wildfires in Denali and Yukon-Charley Rivers leave land barren and ripe for colonization.

Wildlife trample the ground or graze the vegetation to facilitate invasive plant growth. Global climate change may favor adaptable species, such as invasive plants.

Since inception, the Alaska EPMT has surveyed more than 5,600 acres to document the presence of more than 100 non-native plant species covering more than 1,900 acres in and around the Alaska National Parks.

Team members are stationed at the most vulnerable parks - the three Southeast parks (Glacier Bay, Klondike Gold Rush, and Sitka) and the three parks on the interior road system (Denali, Kenai Fjords, and Wrangell-St. Elias). Other park units receive periodic inventory and control work. Federal employees, interns, volunteers, and youth crews, particularly Southeast Alaska Guidance Association, perform the work.

Initially, the objective of the EPMT was to locate invasive plant populations - a daunting needle in the haystack quest. Some species have been insidiously spreading since before the parks were established. Other species are newcomers to both the state and the parks. Although new species and occurrences continue to be documented each summer, the program's focus has expanded to controlling invasive plants. Prioritization of control work is multi-faceted. Factors taken into consideration include the risk the species poses to natural areas, the current distribution of the species, and the vulnerability of the invaded land.

All control activities to date in Alaska's National Parks have only involved manual and mechanical methods. These methods are very labor intensive. In some cases, invasive plants have been greatly reduced in distribution using these methods. Manual control has not been effective in other situations, such as reed canary grass in Glacier Bay, Japanese knotweed in Sitka, and narrowleaf hawksbeard in Denali. Consequently, the Alaska Region of the NPS has released an Invasive Plant Management Plan Environmental Assessment for public review to enable extremely limited herbicide use when other control techniques prove ineffective.

By far, the most abundant invasive species in Alaska's National Parks is the common dandelion that was likely introduced to North America with the first colonists arriving from Europe. Although it blankets more than 1,200 acres of the parks, it has not yet penetrated into many remote areas, including all of the five Arctic parks.

By contrast, the EPMT program's vigilance has resulted in early detection of and rapid response to several species when they first began to colonize, such as hairy cat's ear, common burdock, and oxeye daisy. Most of the invasive species arriving in Alaska originated in Europe and Asia. Other species, such as the bigleaf lupine, are native to other areas of North America but have proven adept at outcompeting our native Alaskan flora.

The vigilant monitoring and control work focused on invasive plants by the EPMT will continue to protect some of America's greatest treasures. Since invasive species are the second greatest threat to biodiversity after habitat loss and a conservative estimate of the economic costs of biotic invasions in the United States is $137 billion annually, it is hoped that the EPMT will have the resources to proactively prevent in Alaska what has become a costly and seemingly irreversible process elsewhere in the United States and abroad.

With the increased awareness of invasive species issues, Alaskans and visitors can be part of the solution by not transporting invasive plant seeds on their vehicles or gear into natural areas and by planting only species that are known not to be invasive.

To learn more about the Alaska EPMT or invasive plant issues in Alaska's National Parks, visit http://www.nps.gov/akso/NatRes/EPMT/Pages/EPMT_Home.html. To review and comment on the NPS Invasive Plant Management Plant, visit http://parkplanning.nps.gov/document.cfm?parkId=1&projectId=15850&documentID=24597.

• Whitney Rapp is invasive species coordinator at Glacier Bay National Park and Preserve and data manager for the Alaska Exotic Plant Management Team. She lives in Gustavus.