Mapping Species Distributions

NATURE NOTES

Purple Loosestrife (Lythrum salicaria), photo by Brian Klinkenberg

Purple Plague

by Hugh Griffith

There is a standard university dorm prank: Collect as much newspaper as possible, and when a dorm-mate is away, pack his room floor-to-ceiling with crumpled paper. It takes hours, but hey, think of his expression when he opens his door!

Nature has a version of this prank, not amusing in the least, although it is aesthetically pleasing. It is called purple loosestrife. It is the poster child for wetland invasive plants in North America.

Purple loosestrife grows to a metre or more, and has dense spikes of magenta flowers. Its stem is square or hexagonal. Growing against a background of fresh green cattail leaves, it is a visually pleasing accent plant. Within a short time, however, it will replace the cattails and other native plants, and grow so densely that the wetland will no longer provide shelter or food for waterfowl and other animals.

It arrived in North America from Europe early in the nineteenth century, inadvertently, as seeds in ship’s ballast, or intentionally, as a garden ornamental.It has long been an environmental problem in eastern and central North America, and more recently has gained a strong foothold here. Burnaby Lake is clogged with it, the ditches and sloughs of Richmond are becoming purple ribbons, and the habitat-rich marshes of the Sturgeon Banks are under attack.

It is incredibly fecund. A single plant can produce more that two million seeds, which are dispersed by water, wind, or animals. It also grows anew from root fragments, or cut plant parts. On top of that, it is a tough plant, resistant to pulling, and is a perennial, so once there, unless the roots are removed, it remains.

It does so well over here because its natural controls are over there, in Europe. There have been experiments to see if European beetles could be introduced to devour it, but results have been variable and somewhat unpredictable from site to site. There is also a reluctance on the part of ecologists to release yet another non-native species into our increasingly confused ecosystems.

As you read this, Purple Loosestrife seed heads are maturing, readying to bombard local waterways. What to do? If you have a small infestation on your property, dig it out, fast. (It can fill a small pond almost as quickly as a dorm room can be papered.) As for the Sturgeon Banks, do as I do: stand on the dike, enjoy the pretty purple flowers, and wring your hands.

Hugh Griffith is a BC biologist and science writer.