One of the biggest threats to a new riparian restoration project is invasive species. Non-native vegetation can outcompete recently installed native species. This problem can persist for years.

Blackberry – Who hasn’t seen blackberry canes intertwined with a cedar? Blackberries can overtop desirable vegetation and shade it out. Preventing photosynthesis is one way invasive species eliminate competition from native species. Knotweed is especially adept at this survival strategy. Blackberry canes are also capable of overtopping 10 foot tall trees then pulling them down and shading them out.

Blackberry

English Ivy – Most people are familiar with English Ivy and think that it adds a classic look when it climbs buildings and trees. This extra weight and bulk causes trouble for native trees because the ivy leaves act as a sail and can catch more wind during storm events. Native trees are not accustomed to this extra stressor and can breakoff and fall under the extra weight and pressure.

English Ivy

English Holly – Another invasive species from England that thrives in the Pacific northwest are holly trees. This species brings to mind Christmas. It is also one of the few species that is capable of growing and reproducing in an established, mature forest. Typically invasive species prefer disturbed sites to become established, think abandoned lots, clearcuts, agricultural fields, etc. Established forests, especially ones with dense conifers, are one of the best defenses against invasive species establishment. English Holly is capable of becoming established in these habitat.

English Holly

It can get overwhelming when one thinks of all the invasive species across the landscape (and we have only touched in plants, there’s a whole other category of invasive animals). While some invasive species will never be eliminated, it is possible to achieve local control. If you’re interested in more information, contact your local Noxious Weed Control Board.