Buckthorn: an invasive plant and one of the “worst botanical plagues of the hour”

A shrub described as a “ticking time bomb” in our woods is currently invading southern Quebec to the point where several areas are out of control.

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“In certain wastelands of Parc national d’Oka, we will never get to the end of it. The best strategy is to limit invasion,” explains biologist Marc-André Villard. He was hired by the Society of Outdoor Establishments of Quebec in 2020 to tackle common buckthorn (see below).

After several attempts at eradication, he concentrated his efforts around areas where populations of rare or fragile plants were spotted. From these points, he tries to slow down the progression of the undesirable. For him, buckthorn is a “ticking time bomb” in many ecosystems in southern Quebec.

Seemingly harmless, the plant destroys everything in its path to settle on the edge of the forest, reducing biodiversity in these places. But no one knows exactly what the long-term effects of buckthorn “forests” will be or where their conquest will stop, because they are too recent to be well documented.

Slim hope: the mature forests seem to be spared, because the buckthorn needs light to settle.

A botanical plague

Common buckthorn and its cousin Glossy buckthorn, which thrives in wetlands, are not new to Quebec, but they are currently experiencing a population explosion, particularly in Estrie and Montérégie.

“Global warming plays a role in this phenomenon, but the species has mainly benefited from the decline of ash, elm and beech. The diseases and parasites (such as the emerald ash borer) that have affected these trees have left a lot of space for buckthorns to conquer,” explains botanist Claude Lavoie.

The professor of land use planning at Laval University, who is nicknamed “Mr. invasive plants” because of his expertise on the subject, places buckthorn in the “top 5” of the worst botanical scourges of the hour. His books list more than 90 species of concern.

Always starting over

This shrub, which grows very quickly in dense groves, has conquered many wastelands, in particular the old agricultural fields that we want to see become forests again. The problem is that the invasive plant takes hold before the first maple or birch stems can take root.

the Log participated in a buckthorn uprooting activity at Mount Royal on October 2. Twenty volunteers cut thousands of stems in an area west of Beaver Lake to “give a chance” to planting native species. In two hours, just two meters of forest had been cleared along a beat of about twenty meters.

“You have to start over every year; many areas have been invaded”, sighs Benjamin Pilon, who orchestrates the activities for the Friends of the Mountain.

Solution: glyphosate

“The common buckthorn represents a major threat to Montreal ecosystems,” admits the spokesperson for the City of Montreal, Kim Nantais. She points out that the fight against buckthorn “has intensified in recent years.”

Botanist Stéphanie Pellerin, who supervised the work of a master’s student on buckthorn control, adds that one of the only recognized strategies for dealing with stands, apart from the pure and simple elimination of roots at using heavy machinery, involves coating the feet with glyphosate, a product banned in Montreal since the beginning of 2022.

“Buckthorn is extremely resilient. And it is one of the rare invasive exotic plants that adapt to forest environments. In Montreal, no more nature park is spared. In some places, it is the dominant species.

Cutting the base of the shrub for six years, as some experts recommend, is it the right solution? M^me Pellerin hardly believes in it. “Faced with this problem, we tell ourselves that we will exhaust our volunteers before exhausting the plant!”

A plant introduced for its pseudo-medicinal qualities

• Common buckthorn was introduced to New England in the late 18^e century for its healing qualities (hence the term “cathartic” in the sense of purifier). An effect that has not been demonstrated, even if the fruit has a purgative effect.
• In 1809, in Massachusetts, then in 1839 in Wisconsin, it was used in landscape architecture to form hedges.
• A century later, the species becomes invasive in these two states.
• The species was sold in nurseries in Toronto for its aesthetic qualities in 1864.
• Even if it had been present for more than a century in Canada, we had to wait until the 2000s to see it proliferate in a worrying way. The exact causes of this sudden invasion are unknown.

Source: Claude Lavoie, 50 invasive plants – protect nature and agricultureQuebec Publications, 2019.