If a tree falls in an urban forest, and it doesn't make a sound, does it have any value?

According to the folks at one of Canada's largest banks, the answer is a resounding "yes."

Beyond more nebulous social and environmental impacts, Toronto's lush canopy of trees are worth about $7 billion to the local economy, TD Bank suggests in a report released Monday.

"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."

The report lays out a number of ways in which the city's trees are paying dividends to residents.

Although it's not intuitive to think of a city of almost three million people being anything like a forest, Alexander notes that there are more than 10 million trees of at least 116 different species crammed inside the city limits. A bird's eye view of the city shows as much as 30 per cent of Toronto's space — more than 190 square kilometres — is covered by trees or shrubbery.

"When you look at an individual tree, the impact that it is having is very modest, but when you add it up in the entire canopy of trees in the city of Toronto and when you think that trees cover 30 per cent of all the square kilometres in the city...., their effects really add up," Alexander said in an interview with CBC's The Lang & O'Leary Exchange.

$700 per tree

There are about 16,000 trees in the city limits for every square kilometre of space, or about four trees for every person. And all that greenery is worth a lot of green, Alexander said.

"It's easy to forget that trees have a monetary value," he said. The replacement value of the city's tree cover is about $7 billion, or $700 per tree.

Alexander came up with that number by adding up both what it would cost to physically replace each of Toronto's 10 million trees, but also by factoring in the economic benefits those trees are quietly performing behind the scenes.

Trees help ease the burden of managing snow and rain, the reports notes. Every year, Toronto's tree cover intercepts about 25 million cubic metres of precipitation. If they weren't there to do that, that's an extra $53 million the city would have to pay out to perform the same task.

"When it rains the water is going to go into the ground, but the trees help the ground absorb the water and it actually takes pressure off the foundations of homes," Alexander said.

They also remove about 25 per cent of all emissions expelled by the city's various industries — that's about 19 million tons of air pollution a year. For context, that means Toronto's trees soak up the pollution created by one million cars, or 100,000 homes, per year.

700,000 cars offset

It's also well known that trees help manage temperature, both by blocking cold winds in winter, but also keeping the city cool in summer. Alexander said the net cooling effect on the city of a young, healthy tree is equivalent to 10 room-sized air conditioners, running 20 hours a day.

"On their own, these effects might seem small, but over the long term, these benefits make a significant contribution to environmental well-being," Alexander said.

Alexander said his study proves the millions the city spends on maintaining trees is money well spent.

"The investment that`s being done in this area, actually saves the city a lot of money. Not just air pollution and water redirection, but it also has an impact on cooling the city," he said.

Using the city's own budget documents as a reference point, Alexander calculates that the city spends about $4.20 a year to maintain every tree in Toronto. But "for every dollar spent on maintenance in Toronto's urban parks, trees return $3.20 to the community," he said.

Beyond mitigating the need to belch out any more air pollution to cool the city, trees also provide an important role in storing pollutants already out there. The total amount of carbon currently stored in Toronto's urban forest is estimated at 1.1 million tonnes — roughly the amount emitted by 700,000 cars a year.

"Every year, the City of Toronto's urban forest sequesters over 46,000 tonnes of carbon, which is equivalent to the annual carbon emissions from 31,000 automobiles or 16,000 single-family homes," Alexander said.

Trees boost land values

But trees boost the city's bottom line in still more tangible ways, such as boosting property taxes. In some locations, rental rates are about about seven per cent higher on sites that offer trees. "A study of New York City also reported that having trees on, or near, property generates an additional $90 US in property taxes," Alexander said.

While smaller plants also appear to be doing good things for the city, when it comes to the economic impact of trees — bigger is better, Alexander said.

Large, healthy trees absorb 10 times more air pollutants, 90 times more carbon, and 100 times more leaf area to the city's canopy, Alexander said.

"I think the ice storm we had last December certainly increased appreciation for trees, because we take them for granted until a tree that is on your property gets damaged or gets sick and then we realize... we don`t want to lose this tree," he added.