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Toronto The emerald infestation: The high costs of removing decaying ash and planting new trees

urban forests

The emerald infestation

Tiny, invasive wood-boring beetles are not only destroying city greenery, but are also leaving a path of blown budgets as cash-strapped metropolises face the high costs of removing decaying ash and planting new trees

In Etobicoke on Friday, July 29 City of Toronto arborists perform maintenance to a tree by cutting off dead and dangerously hanging tree limbs and branches in an effort to increase the tree's lifespan and reduce the hazard of falling and dead branches. The branches, limbs and leaves are then processed through a large woodchipper, and the site is cleaned.

In Etobicoke on Friday, July 29 City of Toronto arborists perform maintenance to a tree by cutting off dead and dangerously hanging tree limbs and branches in an effort to increase the tree’s lifespan and reduce the hazard of falling and dead branches. The branches, limbs and leaves are then processed through a large woodchipper, and the site is cleaned.

Christopher Katsarov for The Globe and Mail

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The tiny emerald ash borer is doggedly chomping through the Greater Toronto Area's ash population, turning once leafy trees into ghostly wooden skeletons.

The infestation of the invasive, wood-boring beetles is currently around its peak, depending on location. The insects are expected to destroy nearly all the region's ash, killing about 3.2 million public and privately owned trees representing 10 per cent of the overall population.

"We're losing the trees. We're losing the canopy height. We're losing the diversity of species. So this is a real challenge," arborist Philip van Wassenaer says, standing near a few dozen dead ash trees in a Mississauga park. "In one generation, things are changing very quickly."

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The iridescent beetles, which can kill healthy trees within a year or two, are also leaving a path of blown budgets as already cash-strapped cities and towns face the high costs of removing decaying ash and planting new trees.

So far, more than 140,000 publicly owned ash trees in the GTA have been chopped down, costing millions of dollars, according to the municipalities that responded to a Globe and Mail survey. For example, Toronto, which has removed 49,000 ash trees, expects to spend more than $74-million on the crisis. Oakville, which has cut down 14,000 ash trees, has already spent $4.2-million. For its part, Whitby has removed about 3,800 ash trees and spent $736,000 out of a projected $2.36-million.

MURAT YUKSELIR/THE GLOBE AND MAIL

"It's a massive problem and it's one that comes whether you want it or not," says Mr. van Wassenaer, a consultant and founder of Urban Forest Innovations, whose clients include several GTA municipalities. "Emerald ash borer comes to every community on top of whatever issues they had before and whatever budget they had before. They have no choice."

At its heart, the infestation is an issue of public safety for cities and towns, which are responsible for maintaining trees on their lands. Once they die, ash trees become extremely dry and brittle and are prone to shedding branches and toppling over, posing a threat to people and property.

However, few communities have the full complement of staff, equipment and resources to properly remove their dying ash – which can cost upwards of $1,000 for each mature tree and stump – Mr. van Wassenaer says, adding that some smaller ones haven't developed tree inventories or urban forest management plans.

"If you don't know where your trees are, what your trees are, what kind of condition those trees might be in, what kind of risk factors they may be posing, it's very difficult to be effectively managing those trees," he says.

Depending on a tree's health and the extent of the infestation, the beetles can kill an individual ash within one to three years and move through the majority of a community's ash trees in about a decade before tapering off after roughly 15 years. Given the rate of destruction, Mr. van Wassenaer recommends inspecting trees every two years.

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But not every ash tree needs to be chopped down. Many are located deep in ravines or natural areas far from so-called targets and can be left to decay and regenerate the soil. "It's nutrient recycling. They'll benefit the natural ecosystem, by falling and rotting and doing their thing the way they should," says Jason Doyle, Toronto's director of urban forestry.

Toronto's infestation peaked last year, he says, and reduced the city's forest cover by about 2 per cent.

In addition, some municipalities are targeting high-value ash trees with an injectable insecticide called TreeAzin that can stave off the beetles. It is unknown whether the treatments, which cost about $150 and should be repeated every two years, will save trees in the long run.

The emerald ash borer, which is native to Asia, was first detected in the GTA in 2007, after crossing into Ontario from Detroit, most likely in wood-packaging materials, in 2002. Large swaths of Ontario and Quebec, along with several American states, are struggling with infestations, after turning to ash in the 1980s and '90s to replace elm trees ravaged by Dutch elm disease.

The first sign of an emerald ash borer infestation is a thinned upper canopy as the adult insects feed and mate in treetops. In the summertime, females lay between 60 and 90 eggs each in bark crevices. After hatching, the larvae feast on the cell-generating layer of tissue just below the bark, creating "feeding galleries" and leaving a serpentine pattern that widens as the fattened insects move through the tree. As they travel, they girdle the tree, preventing the flow of water and food and eventually killing it. The larvae, which survive mild winters, exit trees once they mature in the spring, leaving telltale tiny D-shaped holes in the bark.

In addition to decimating ash trees, the beetles also disturb local ecosystems, allowing other invasive species such as buckthorn to dominate, which chokes off native plants and trees.

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Despite the damage the emerald beetles have wrought, some observers see a silver lining in the epidemic.

"I think it might have been one of the good things that happened," says Sandy Smith, a professor of forest health at the University of Toronto, "because it's raised this awareness and given budgets to forestry that wouldn't have had it otherwise."


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