The trees are considered a noxious weed in some U.S. states
LACOMBE, Alta. — The Russian olive should be banned from Alberta before it becomes an invasive species, clogging rivers and choking out native trees and fish, says an Agriculture Canada research assistant.
Governments across North America once promoted the beautiful silver-leafed tree as an ideal shelter belt and ornamental tree for dry areas, but it is now considered a weed that should be banned.
“I think it is the beginning of the invasion and could potentially get worse,” Liana Collette said during the Alberta Invasive Species Council conference.
“I think it is a serious issue. Right now, people don’t see it on their radar.”
The Russian olive was originally imported from Europe in the 1800s by homesick settlers. It was one of the few trees that thrived in poor soil and dry conditions.
The Prairie Farm Rehabilitation Administration distributed more than one million Russian olive trees across the Prairies between 1948 and 2002, mostly in Saskatchewan, as part of its shelter belt program.
Collette doesn’t know how many of those trees are still alive, but they are the source for the naturalized Russian olive trees that are taking over wetlands and riparian areas.
Russian olive trees are considered noxious weeds in California and New Mexico and are banned in Connecticut.
Little research has been done on the invasiveness of Russian olives on the Prairies, but pockets of the trees are creating problems in the Lethbridge, Taber and Brooks area of Alberta, along the Okanagan region in British Columbia, near Moose Jaw and Belle Plaine in Saskatchewan and throughout the greater Toronto area.
“We’re just seeing the beginning of the invasion,” she said.
Russian olive is on Jason Bullock’s radar. The agriculture fieldman for the Municipal District of Taber said the trees are slowly spreading across the municipality into roadside ditches, irrigation ditches and coulees.
“The biggest problem is in the irrigation ditches,” Bullock said.
The municipality cuts down trees that are growing in ditches but has no jurisdiction to do so on private property and under power lines or fences.
“It’s a great tree for this area, but after the birds and the deer spread the seeds, it’s become a fairly significant nuisance,” said Bullock.
“It’s not a problem in our area yet, but I could see in another 10 or 15 years it could become a serious issue.”
The trees’ suckering root system allows them to regrow after they’re cut down, especially in moist, shady areas.
A lack of natural controls means they have started to push out native cottonwood trees along streams and rivers.
Rivers in heavily infested areas will slowly dry up as the trees suck up moisture and spread their roots. The leaves are high in nitrogen and add to the nitrogen loading of streams when they fall into the river.
Cottonwood trees need the natural flooding of riverbanks to grow and thrive. They have started to decline on rivers where dams control water flow, which has allowed Russian olives to take over.
The number of cottonwood trees downstream from the St. Mary Dam in southern Alberta has already declined, and Russian olive trees have crept in.
Russian olive leaves in the Okanagan Valley have become food for common carp, an invasive fish, while some birds in the United States are on the list of threatened species as the Russian olive replaces their native trees.
Bob Battiste, former director of the Alberta Invasive Plants Council, started to notice the spread of Russian olive trees about five years ago, especially in southern Alberta and Saskatchewan and parts of Toronto.
The trees have taken over coulees and wetlands east of Moose Jaw, Sask., and east of the Trans-Canada Highway overpass near Belle Plaine, Sask.
“They were probably planted by the government shelter belt system years ago, but they have almost filled the whole area of marsh,” said Battiste.
“I think it is a real concern.”
Collette said Russian olive trees require ideal conditions to thrive and naturalize.
“If the conditions are right, if the temperature is right and within one kilometre of a water body, that is the prime range for it to become an invasive species,” she said.
The trees are not considered a weed or an invasive plant and are still sold in greenhouses and nurseries as a showy landscape plant.
“These are outstanding trees,” Battiste said.
“If you go into a tree nursery and see a nice Russian olive, people just go gaga over it. They love it and take it home and plant it, but sooner or later it will be a problem.”
He said the nursery industry needs to develop a replacement for the silver-leafed plant.
“It is a real problem for the landscape industry in Saskatchewan and Alberta because they don’t have any good alternatives for a nice silver colour.”
Collette said banning the sale of Russian olive would start with awareness of the problem and the development of an alternative tree.
“I don’t think we can convince people to give up their Russian olives. People are very attached to their plants and trees because it beautifies their property,” she said.
“In the U.S., they were told by government to plant all these trees. Now they’re told by the government to cut them all down and they’re not happy.”
Researchers in some parts of the United States are developing mites and moths to eat the trees’ flowers and seedlings, to prevent their spread, but not harm the tree.