Toronto tree’s canopy is suffering from a pest that’s killing off ash trees and forcing the city to sink money into removing and replacing them.

Toronto has more than 10 million trees of at least 116 different species inside the city limits. As much as 30 per cent of the city’s 190 square kilometres is covered by trees or other shrubbery.

But the emerald ash borer, an invasive bug that cuts off the water supply to the tree, has made its presence known in and around Toronto as well as other areas of Canada and the United States.

Madison Matters-Ash Borer

The emerald ash borer cuts off the water supply after it has infected ash trees, which can then dry out and collapse. (Minnesota Department of Natural Resources/The Associated Press)

According to the city, the emerald ash borer, an insect pest from Asia, has devastated ash trees in southern Ontario and parts of the United States since its discovery in Detroit in 2002.

In 2007, The Canadian Food Inspection Agency confirmed the bug's presence in Toronto, in the vicinity of Sheppard Avenue East and Highway 404. 

All infested trees must have affected parts removed before they dry out and collapse.

The Murphy family in Toronto has already lost multiple trees.

“We've had five ash trees in the back and four in the front, and we have to cut them all down; we have lost the whole canopy, as have our neighbours," said Carol Murphy. "Our neighbours on all sides are losing our ash trees."

More than 20,000 ash trees on city property have already been removed, and city staff say taking out all infected ash trees coupled with the damage to other trees by this past winter’s ice storm have left a mark on the important urban canopy.

Urban forests 'an important investment'

A report by TD Bank in June said Toronto’s tree canopy is worth about $7 billion to the local economy.

"Urban forests do more than beautify the scenery," the bank's chief economist Craig Alexander said. "They represent an important investment in environmental condition, human health and the overall quality of life."

Toronto has more than 10 million trees of at least 116 different species inside the city limits. As much as 30 per cent of the city's 190 square kilometres is covered by trees or other shrubbery.

"It's easy to forget that trees have a monetary value," he said.

The replacement value of the tree cover would be about $7 billion, or $700 per tree.

The emerald ash borer problem has forced the removal of many trees, and more will be cut down in the following year.

“We plan on removing 14,000 trees this year … next year will be the peak,” said Jozef Ric, who's with the City of Toronto.

The city has an ambitious plan to replant trees taken down on its property. Homeowners who lose trees are not as lucky, as there is no plan to cover or subsidize their removal on private property – a cost that can go into the thousands.

The city hopes its replacement work will lead to coverage of as much as 40 per cent of the city in the canopy.