Toronto and its city-owned hydro utility plan to examine their tree-maintenance practices to determine whether more can be done to prevent branches from severing and tearing down power lines in bad weather.

The number of trees affected by last week's ice storm is not yet clear. Richard Ubbens, the city's director of parks, said rain, ice and winds damaged a variety of trees throughout the city.

"Young trees, old trees, healthy trees, dead trees, this storm took everything down," Mr. Ubbens said. "It depends on where the ice built up the most."

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There are about 10.2 million trees in Toronto, their canopy covering about 28 per cent of the city. About 600,000 of those trees are city-owned street trees, 3.5 million are in city parks and natural areas, and 6.1 million are on private land.

While the city, businesses and homeowners are responsible for maintaining trees on their properties, Toronto Hydro oversees trimming branches that pose a risk to power lines.

Toronto Hydro spokeswoman Tanya Bruckmueller said the utility has forestry crews and contractors who look for problematic trees to prune. They also respond to concerns from property owners.

The utility's tree program will be reviewed in the wake of the ice storm. However, Ms. Bruckmueller noted a large amount of tree canopy would have to be removed to prevent such damage from occurring again – a measure that would run contrary to the city's goal of increasing tree cover to as much as 40 per cent of Toronto.

Two local arborists see room for improvement in how trees are maintained. Karmatree owner Ryan Kuz and Craig Southwell of Bartlett Tree Experts have spent the past week assessing damaged trees on residential properties, advising owners on whether their trees can still thrive.

Some species, including Siberian elms, silver and Manitoba maples, did not fare well in the storm and their growth needs to be better managed, Mr. Kuz said.

Mr. Southwell noted some trees broke apart because of defects, such as twin stems or twin branches, which could have been dealt with beforehand through pruning or cabling. Other trees were simply too old or too weak.

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"A lot of the trees that are failing now in the city are beyond their useful life expectancy and the city should be replanting," Mr. Southwell said.

In February, city council approved a new forest-management plan that is seeing the city shift to a proactive tree maintenance approach versus its previous model of chiefly reacting to complaints about overgrown or dying trees. A budget increase is being requested for the city's urban-forestry section in 2014.

Overall, 81 per cent of Toronto's tree population was in good condition in 2012, but only 49 per cent of city-owned street trees met this mark, the city's forest-management plan noted.