A little known alien invasive tree – European buckthorn – is quietly degrading the biodiversity of the Grand River watershed.
Foresters are starting to fight back and they need all the help they can muster. The trouble is that people are attached to their greenery and they find it hard to believe that a tree that has popped up in their yard could possibly be bad for the environment.
Even avid gardeners and environmentalists are often unaware that their cherished buckthorn is detrimental to the environment.
“It is a serious threat; it’s a ticking time bomb and most people don’t even know about it,” said Moritz Sanio, coordinator of Trees for Guelph. “It started on the perimeter of the city and is spreading from there. Now it is erupting in backyards, so it is vitally important for people to take steps to remove it from their own property. This has to be a joint effort.”
The seeds are widely scattered by birds and viable for five years. Buckthorn’s Latin name is Rhamnus cathartica because the small berries it produces move through a bird’s system very quickly and the bird deposits the seed with a nice package of fertilizer in a new location where buckthorn will soon pop up.
Murray Cameron, general manager park maintenance and development for Guelph, also has an intense distaste for buckthorn.
“People think it is a tree, so it must be good habitat and a food source. But it terribly degrades the diversity, air flow, and sight lines. If buckthorn trees are cut off at the ground, it will sucker up quickly. It is backbreaking to remove it,” he says.
Cameron, Sanio, and Martin Neumann, manager of terrestrial resources with the Grand River Conservation Authority, represent organizations that have teamed up in a pilot program to remove buckthorn in Guelph, beginning with its removal in places where trees are being planted through the Trees for Guelph program.
It feels like an uphill battle. They believe Guelph is an epicentre of buckthorn and that it grows more intensively there than elsewhere in Ontario. That makes the challenge of curtailing its exploding population in Guelph even greater than in other communities.
“We aren’t sure why it is so established in Guelph, but it could relate to the Ontario Agricultural College that dates back to 1864. The plants were introduced from Europe because they are a natural green fence that is impassable for animals and ideal as hedgerows. They grow so densely that livestock can’t get through. Native plants don’t thrive in areas that include buckthorn, and, in fact, this is a natural green fence that has run amuck,” said Cameron.
He and other city staff got a nasty browbeating from city residents when they destroyed some buckthorn while removing trees damaged during severe wind storms in June.
Cameron said he sees buckthorn being cared for by landscapers at apartment buildings and even Guelph staff have trimmed around it when it has popped up on city property. It causes the most trouble in newly-planted native areas, and that is where the city and Trees for Guelph are working to remove it.
When they are small, buckthorn plants can be pulled up by their roots. But when they grow bigger, the roots hold tight and it is very challenging to remove them.
The density of buckthorn in urban areas means it is a good place to dump garbage or to hide illegal activity from public view. Police and parents have both helped the city to remove buckthorn at some locations.
Even though it is a small tree, European buckthorn (also called common buckthorn) is one of 24 noxious weeds in Ontario – akin to giant hogweed and ragweed – and is listed on the Weed Control Act.
Those are the plants that a weed inspector can order a property owner in a rural area to remove.
If the buckthorn is not removed, then the inspector can bring in a crew to take it out and present the property owner with a bill for the work.
It is listed because it is an alternate host for a fungus that impacts oats and because its leaves and bark are a strong laxative for humans, not because of its invasive properties.
Despite the legislation, buckthorn thrives. It is seen as an ornamental garden plant, incorporated into hedges, and is often found invading native plant gardens, although it is not sold.
Identifying buckthorn
Common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula) are known to spread aggressively. They grow up to six metres tall and the stems are 25cm or 10 inches in diameter. Buckthorn is among the first trees to come into leaves in the spring and hold onto its leaves late in the fall, so there is no fall colour.
It flowers early in the season and female plants form small, black, berry clusters in July.
It rapidly produces seeds early in the season that germinate quickly.
It has male and female plants, and one strategy to remove plants is to focus first on removing the female plants to stop seed production.
The roots of plants need to be dug up completely, or they will sprout suckers, quickly replacing any tree that is cut down.
Here are a couple of links to more infornatuib to help recognize buckthorn: http://www.omafra.gov.on.ca/english/crops/facts/info_buckthorn.htm and www.ontarioinvasiveplants.ca/files/tedlettersBuckthornFINAL3.pdf.
Janet Baine is a GRCA Communications Specialist
