Barbarea vulgaris (yellow rocket) is another common introduced species of agricultural areas and roadsides. I mentioned in a previous post that some plants become so cosmopolitan or seemingly innocuous that people forget that they have pushed out other native species in order to become prevalent. Last Saturday, I was out perusing the garage sales. At one house, I stopped by a box of tree seedlings because I noticed that it contained Manitoba Maple (Acer negundo), an invasive plant. After noticing me looking at them, the owner came up and asked if I was interested in the plants for sale. I explained that the tree he was selling is an invasive species and that by selling it they were helping it spread. The owner snapped back defensively, “Well, it’s on the front lawn and makes a great shade tree”. Plants are a tough sell to get people to understand that they can be problematic too, just like the Emerald Ash Borer or rats.
Just because plants can’t move on their own doesn’t mean they can’t get around. Human behavior mediates a lot of invasive species spread, through gardening or container shipping or spreading urbanization. Japanese knotweed is considered by some to be a great ornamental plant but it is one of the worst invaders on the planet. You wouldn’t want to plant Phragmites (common reed) on your property, trust me. I have sampled areas with over 100 stems per square meter. Measuring over 10 feet tall, you can easily lose small children or short botanists (ahem) in their colonies. So what to do? For gardeners and landscapers, watch what you plant. Garden centers are not always sensitive to which species are problematic. Unfortunately, Quebec and Canada has very lax or almost nonexistent nuisance species laws. Most controls are done when species cross national boundaries but a lot can and should be done at municipal or provincial levels.