Invasion from the Himalaya

News release by David Clements, Professor of Biology, Trinity Western University, and member of the Salmon River Enhancement Society Board of Directors clements@twu.ca

Recently a new kind of problem has been increasingly recognized as a significant threat to the global environment: invasion by alien species. These invasions have in fact been occurring ever since people started moving plants and animals with them has they travelled from place to place. One such invasion has found its way to the quiet riverbanks of the Fraser Valley. Known as either Himalayan balsam or Policemen’s helmet, the invader is a tall Impatiens with striking purple flowers that start to appear in early July. It is not known exactly how Himalayan balsam reached our area, but one possible route that is still open is through garden plantings. Impatiens glandulifera is still available in some seed catalogues. Although Himalayan balsam is only moderately common here, other parts of the world, such as Great Britain and Czechoslovakia have been overwhelmed with this invader and its entry is prohibited in New Zealand. It is particularly a problem in riparian areas along riverbanks, where it grows so well that it crowds out native vegetation.

You can see how well Himalayan balsam thrives if you take a casual stroll through Williams Park in Langley, where both the Salmon River and Coghlan Creek are lined with these tall, large-leafed annuals. Its rapid spread is also being documented at the Ecosystem Study Area of Trinity Western University, also located on the Salmon River. Later in the summer, you can get a dramatic picture of how Himalayan balsam spreads if you touch a seed pod that is ready to open. The pods open explosively, potentially releasing seeds several meters from the adult plant. These seeds can survive long periods in water, potentially floating downstream to invade a new area. However, because Himalayan balsam is an annual, if the plants are removed before they are allowed to disperse their seeds, they can be controlled. The Salmon River Enhancement Society is banking on such a strategy to help maintain the natural biodiversity of the banks of the Salmon River.