The National Park Service plans to apply herbicide to Canada thistle infesting critical habitat for the island marble butterfly at American Camp, an area of critical importance to the island marble butterfly, announced San Juan Island National Historical Park Superintendent Lee Taylor.
The treatment will target 1.5 acres east of Pickett’s Lane and one acre south of the Redoubt Road. This step is one part of a broad strategy to restore habitat for the island marble butterfly (Euchloe ausonides insulanus), a federal species of concern.
"The island marble butterfly population is dwindling and American Camp is their final stronghold," Taylor said. "We must take action now to improve and expand habitat for these creatures or they will not survive."
Herbicide use will help combat nonnative, invasive thistles that compete with island marble butterfly host plants for habitat. Island marble butterflies rely on just a few plant species as a source of food and as a location for laying their eggs.
No road closures are anticipated during the treatment, although a few trails in the immediate vicinity may be closed for a short time. Caution signs will be posted along road ways and trails near the project. Park visitors are urged not to stop along the roadway or enter the area while herbicide operations are taking place.
Herbicide use is the only effective method to control certain invasive species. Annual or biennial weeds in low densities can usually be controlled by pulling if the entire root is removed. With perennial species, such as Canada thistle, which reproduce by fragmentation of roots or shoots, herbicides are necessary to ensure death of the entire plant. Manual or mechanical removal exacerbates thistle infestations because new growth occurs from portions of the plant left in the ground.
"We'll be using the safest herbicide possible in a focused way on a small area," Taylor said. "I believe it is worth it to accomplish the goal of saving a species on the brink of extinction."
For questions or comments please contact Chief of Integrated Resources Jerald Weaver at 360-378-2240, ext. 2224 or firstname.lastname@example.org.