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Trees & Nature | Urban Forestry

Battling buckthorn to bring back biodiversity

Peter Kuitenbrouwer
April 21, 2021

From the Mississippi River Valley up through Ontario and Quebec, and from Atlantic Canada west to the border of Saskatchewan, municipalities, private landowners, farmers and even hospital groundskeeping staff are fighting a powerful plant invader: buckthorn.

Buckthorn came to North America innocently enough. In the 19th century, landscapers brought the ornamental shrub from Europe, mainly to plant as hedges. The plant’s proponents treasured buckthorn’s glossy green leaves and its ability to thrive in many conditions: from shade to bright sun, from sand to clay. Alas, long ago, this plant escaped from yards and began a steady conquest of the forest. The plant’s hardiness has become a menace.

Buckthorn produces leaves earlier, and they last later than other plants. It can grow to seven metres with a 25 cm diameter trunk, and colonize every environment, from wetlands to conifer plantations. Thanks to its dense canopy, no sunlight can reach, for example, a native oak or maple seedling, struggling to emerge from the earth. Deer and cattle refuse to eat its leaves. However, by late summer buckthorn is “full of berries that the birds love to eat,” notes Michael Petryk, a licensed arborist at Tree Canada. As the birds fly about and let go of their waste, they spread buckthorn seeds far and wide.

The more recent arrival in Canada of another invader, the emerald ash borer beetle, has opened a new front for buckthorn’s onslaught. As ash trees fall to the voracious beetle, buckthorn moves aggressively in to fill the gaps, overtaking native trees and shrubs. With few domestic predators, pathogens or parasites, buckthorn continues its rampage, wiping out biodiversity in its path.

What to do? One technique is to rip out the buckthorn. The City of Winnipeg, for example, loaned vice grips to teams of volunteers to yank buckthorn at its roots to try and remove the plant from Munson Park; recent photos show that with the buckthorn gone, trillium found space to grow and bloom in the park. The Nature Conservancy of Canada has organized events for volunteers to cut and carry away buckthorn growing on its land in the Niagara Peninsula. A problem emerges, however, because buckthorn will grow back from the cut stumps.

Battles to beat back buckthorn can inspire dramatic language. The Nova Scotia report “Monsters in the Marsh!” describes the epic struggle by teams of volunteers, with public and private funding, who banded together to rip buckthorn from the Annapolis Royal Marsh. Children pulled smaller plants by hand; adults used weed wrenches. Volunteers girdled trees with a trunk over 2 cm in diameter.

Others trying to get rid of buckthorn paint glyphosate on the cut stumps; the Nova Scotia crews however chose not to apply this chemical in a marsh habitat, “in fear of the herbicide damaging sensitive ecosystems.” As an alternative, a student at the University of Wisconsin – Madison has invented the “Buckthorn Baggie,” a heavy black plastic bag one zip ties to the severed stump of a buckthorn bush to prevent resprouting.

BioForest, an innovator in advancing tree health in Canada, can also help by offering a bioherbicide. BioForest manufactures LALCIDE CHONDRO, a product whose active ingredient, Chondrostereum purpureum, is a naturally occurring fungal plant pathogen which can readily be found in Canadian forest ecosystems. The fungus releases an enzyme which provokes a foliar reaction known as silver leaf disease in post-harvest sprouts. This disease inhibits the stump sprouts, eventually killing them. The risk to non-target species is very minimal as Chondrostereum purpureum requires a fresh wound for colonization, is a paste (not an airborne application), and is applied directly to the target stem requiring control. The company calls this, “a biological solution that provides a more environmentally sensitive option to vegetation managers who may be limited in the use of chemical herbicides.”

LALCIDE CHONDRO requires only one application per stem and a pesticide applicator’s license is needed to apply the product. The company recommends applying this paste from mid-June to early-July (once buckthorn is fully leafed out), within 30 minutes of cutting or girdling the plant.

Regardless of how one eradicates buckthorn, removal of the invader is only half the job. Having ripped out the buckthorn, the volunteers in the Annapolis Royal Marsh, for example, came back to plant water-loving species, such as elderberry, dogwood, hemlock, red oak, and cranberry. The Friends of the Marsh then placed mulch around the bases of the new native seedlings, to suppress any buckthorn seedlings and give the domestic trees a head start with positive hopes of bringing biodiversity back to the marsh.

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