Weeding Out the Worst

Enlarged images of carpet burweed collected from Beacon Hill Park, Victoria, April 10, 2006.

W E E D I N G O U T T H E W O R S T

How the Royal BC Museum Herbarium Fights Invasive Species

By Dr. Ken Marr, Curator of Botany

Accidentally or deliberately, humans move plants around the planet. We call them “weeds” if they grow where we don’t want them and “invasive” if they spread, their numbers unchecked by the herbivores and diseases that keep them in control where they originate. Many cannot survive or spread in their new homes without human care—think of pansies and petunias. But a few, the invasives, spread into landscapes disturbed by human activity, like urban areas, roadsides and agricultural fields. Others invade natural habitats, altering ecosystems simply by occupying the spaces in which native species occur, in turn impacting the birds, insects and mammals that depend on those native species for food. Millions of dollars are spent to control agricultural weeds, although ironically, the crops we grow are not native to BC and could be considered “invasive” themselves.

There are about 2,400 native plant species in BC. About 900 are non- native, and of these a few dozen are invasive. Invasive species arrive by various means, intentionally or unintentionally: as contaminants in grains, with the nursery trade, as livestock forage or as ornamentals. A surprising source is commercial wildflower seed mixes. These certainly contain wildflowers, but most are from Europe or Asia, not British Columbia.

Two herbarium specimens of common reed: the introduced genetic type on the left, and the native genetic type on the right.

Himalayan balsam (Impatiens glandulifera) forms dense patches in wet meadows and ditches. Despite its beauty, famed British botanist Sir Joseph Dalton Hooker described it as “a terror to botanists, deceitful above all plants, and desperately wicked”!

The 225,000-specimen herbarium at the Royal BC Museum contributes to the management of invasive species in BC. Invasive species managers at all levels of government (and members of the Invasive Species Council of BC, an NGO) use the herbarium collection to help evaluate which species are of greatest concern. We receive many specimens that are sent either to document new occurrences or to be identified. With funds generously provided by the Ministry of Forests, Lands, Natural Resource Operations and Rural Development (FLNRORD), we hired a temporary collections manager to process a backlog of these specimens, add them to the collection and make their associated collection information widely available.

The negative impacts of invasive species are not always related to their size. For example, a tiny plant from Chile, carpet burweed (Soliva sessilis), has been in North America since at least 1884, but it was first collected in BC only in 1996, on Salt Spring Island. It has since spread to more than 10 coastal BC locations. Carpet burweed fruits bear a sharp spine that makes lawns unusable for picnics and bare feet; it is suspected that this sharp spine embeds the fruit into vehicle tires, contributing to its spread. Several parks in the Victoria area have had to close off areas due to the presence of this species.

At the other end of the size spectrum is a tall grass known as the common reed (Phragmites australis), which grows primarily in wetlands. This species is especially challenging to manage because there are two genetic types, but they are not readily distinguished based on easily observed features. One is native to North America (ssp. americanus) and does not spread to the exclusion of other species. The other genetic type (ssp. australis) is from Europe and is extremely invasive in wetlands and agricultural fields, especially in eastern Canada. In 2001, a biologist at Yale University discovered that the two types can be distinguished using DNA markers. Using this approach, a collaborative effort involving the University of Victoria, FLRNRORD and the Royal BC Museum analyzed 203 plants from southern BC and discovered nine plants of the invasive genetic type.

Early detection and rapid removal is critical to controlling the spread of invasive species, and everyone can assist this effort. If you want learn more, or if you encounter a plant that you suspect is invasive, you can report it to Report-a-Weed at reportaweedbc.ca.

Coral Forbes, temporary collections manager, gluing a specimen of knapweed, one of the province’s worst weeds, to acid-free herbarium mounting paper.