What’s with the orange and blue flagging tape?

Brian Dewalt

Walkers along the river path south of Strathcona Park may have noticed a number of trees cut off at chest height and marked with orange flagging tape. These are invasive Common Buckthorn, which have infested large stretches of the riverbank.

Over the past two years, local volunteers of the Sandy Hill Green Team have been controlling the spread of this aggressive tree by uprooting seedlings and saplings and removing and destroying berries. For trees that are too large to uproot, we use the “critical period cutting” method developed in Minnesota by the Friends of the Mississippi River. This involves killing the tree in stages. In the first year, the crown of the tree and all side growth is cut and removed, leaving a bare stem. Afterward, at least twice during the growing season, volunteers return to the tree and strip away any green regrowth that sprouts on the trunk. Because the tree cannot photosynthesize, and its energy reserves are depleted constantly putting out new leaves, the tree becomes stressed and its roots are gradually starved of nutrients.

After two to three years of this treatment, the roots and the tree will die. In the meantime, plantings of native trees and shrubs (flagged with blue tape) will have established themselves to outcompete any buckthorn seedlings that remain.