Invasive Plant Council of British Columbia Carpet Burweed
Carpet Burweed
 
Invasive Plant Carpet Burweed

Carpet Burweed
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Soliva sessilis (Carpet Burweed) in British Columbia

by S.E.T. John

Soliva sessilis, or carpet burweed, is an invasive plant that threatens open areas in parks and golf courses; it has infested thousands of hectares in the US, Australia and New Zealand. Soliva was first
found in Canada in Ruckle Provincial Park on Salt Spring Island, BC in 1996. In 2005, naturalists identified four additional occurrences in BC: one on D’Arcy Island in the Gulf Islands National Park Reserve, two in provincial parks on Vancouver Island and one in a Victoria city park.

This small winter annual in the Asteraceae is native to South America, and is well adapted to areas with mild temperatures, abundant light and moist winter soil. Small (3-4 mm long) spine-tipped seed (achenes) are produced in abundance. Distribution patterns clearly suggest that short-distance spread is primarily through seed embedded in feet and paws, while longer distance “jumps” also
result from seedy hitchhikers on campers’ tents. Seed will germinate wherever light and moisture permit, including hardpacked areas in the middle of hiking trails, shallow soils over mosscovered
rocky outcrops, and wildflower-filled meadows.

As soon as soliva was recognized in 1996, BC Parks moved rapidly to eradicate it, and attempts have continued almost annually. However soliva’s extent within Ruckle Park has increased steadily over the 10 years since discovery. This increase is probably due to two factors: the plant’s phenomenally
effective seed dispersal, and inadequate knowledge of its biology in its new habitat.

In the winter of 2003/04, BC Parks contracted the Island Stream and Salmon Enhancement Society to attempt to control the spread of soliva in Ruckle Park. Hand picking and burning resulted in a dramatic reduction in density. The society again worked to remove soliva in 2004/05, and Friends of Saltspring Parks provided an education and outreach program involving islanders and other agencies
(e.g., National Parks) in early identification and control.

Friends of Saltspring Parks also conducted research into species biology. One key finding is that
germination is continuous through the fall, winter and spring; germination continued from fall
2004 through mid-May, 2005. Similarly, flowering and seedset appear to be prolonged over
several months; flowers were observed from March through to July. Incorporation of newly-acquired knowledge into management strategies provides some optimism for future control, although eradication seems unlikely.