Along an Edmonton street, mature trees sit protected by a green fence near the construction of a new light rail transit line. Signs posted on the fence indicate the value of the foliage: a rosewood tree is worth $1,389, while a nearby spruce is valued at $2,185.
These price tags are somewhat common practice in Canada, where a valuation formula is used to determine the monetary value of a tree in the event it is damaged or killed.
But forestry and biology experts say those dollar amounts don’t fully reflect the ecological value of trees in the urban landscape — especially as they play an increasingly important role in helping to address the effects of climate change.
“I think monetary estimates are an important tool that we have, but we have to take them with a grain of salt in terms of what they might capture and what they might miss,” said Carly Zitter, an assistant professor of biology at Concordia University in Montreal. .
Some of the benefits that are often overlooked, especially in urban centers, include trees’ cooling effect and potential energy savings, their ability to sequester carbon and their role in maintaining biodiversity.
Such aspects must be evaluated to determine a tree’s true value, experts say, to encourage the preservation of the current tree population — and to better protect the next generation of growth.
What is a tree worth?
Determining the economic value of a tree is not a new practice; municipalities and property owners typically call upon arborists or other experts to appraise plants, and value is determined based on several factors, including height, species, health, and location.
These factors are then used as part of a formula to determine a monetary amount in the event of an asset loss, as is done in Edmonton.
But the formula Edmonton and many other municipalities use — the Plant Assessment Guide — still doesn’t include an element of environmental benefit, said Jacqueline Butler, an arborist and project manager for the city’s forestry department.
These assessments are somewhat common in Canada, where an assessment formula is used to determine the monetary value of a tree in the event of damage. (Stephanie Dubois/CBC)
One of the reasons Canadian municipalities use the guidance formula and other similar assessment methods is that those values are defensible in court when there may be property disputes or other legal challenges, said Michael Petrick, director of operations with Tree Canada, a not-for-profit organization dedicated to planting and growing trees in rural and urban environments.
“The [courts] will look at that tree as part of the property,” he said.
“It’s sometimes seen as flawed because it doesn’t always take into account the environmental benefits it would have. It’s often seen simply as, ‘How much does this property owner benefit from one tree?'”
Cecil Koneenendijk, a professor of urban forestry at the University of British Columbia in Vancouver, said it’s time for more municipalities to look beyond the dollar amount and take the time to more broadly appreciate why trees matter.
Many smaller communities in Canada “often struggle to put good value on their trees,” he said, suggesting that finding some easy-to-use methods “that actually show the true value of trees” will be key going forward .
Edmonton’s tree bylaw requires a permit to work within five meters of a tree located on public property. (Adrienne Lamb/CBC)
Some cities in Canada and elsewhere have already assessed the ecological value of their urban forests — taking into account things like how much oxygen a tree processes or how it helps with pollution, Konijnendijk said.
In Toronto, for example, the structural value of the urban forest is estimated at about $7 billion, with carbon storage alone estimated at $25 million. That’s in addition to the $28.2 million in environmental services — things like air pollution removal, energy savings and carbon sequestration — that the city forest provides annually, according to the city’s 2021-2022 strategic forest management plan .
One way municipalities assess this broader ecological value is through the use of i-Tree, a popular, peer-reviewed software package from the USDA Forest Service. It helps organizations and city leaders understand how much a tree or urban forest removes carbon dioxide and air pollution, how it can help with stormwater runoff and other benefits.
Almost 8,000 Canadian organizations and municipalities have used i-Tree, according to its website.
However, Konijnendijk said, the i-Tree formula captures only part of the picture when it comes to estimating the value of a tree.
“We also have things like public health. We have things like biodiversity. Aesthetics. And these aspects are often much more difficult to quantify.”
Why valuing trees matters
There are several ways trees can help cities deal with climate change, said Alison Munson, a professor of forest ecology at Université Laval in Quebec City and a member of CRAUM, the city’s urban forest research partnership.
The cooling effect that treetops can provide is extremely important and valuable, she said. In some cases, mature trees can cool residential areas by several degrees compared to streets without similar tree canopy.
A 2019 study led by Ziter found that the right amount of tree cover can lower summer daytime temperatures by up to 10 F.
There are other benefits, Munson said, especially in urban settings: sequestering carbon as the tree grows, filtering pollution and airborne particles — and even buffering against noise.
Realizing these environmental benefits isn’t just important in the face of climate change, she said, but can also serve as a way for cities to balance densification.
“There’s a push toward compaction that doesn’t always account well for tree value,” Munson said. “Cities need to take more responsibility for addressing these services, which are so important.”
Research shows that mature trees and the canopy they create can offer a cooling effect to residential neighborhoods. (Justin Boulin/CBC)
Munson, Konijnendijk and Ziter say ongoing tree monitoring and long-term planning around our urban forests will be critical.
“It’s not so much about planting trees as it is about keeping the trees alive. The average urban tree often doesn’t age much more than 30, 40 years. So if you can double that life, you get a lot of ecosystem services,” Konijnendijk said.
“It starts here: managing the existing tree population well and protecting trees as best as possible in urban settings.”
Zitter said the researchers are currently looking at how the ecological value of trees may evolve over the years, as this will also be important for both current and future urban trees.
“For example, if we think about the benefits of a tree in terms of temperature regulation or flooding today, those trees may be even more important in a future that is hotter or that floods more often,” she said. “Or perhaps these trees will no longer be sufficient to provide that benefit in the future.”
The way we value our trees cannot be a static approach, she said, noting that such valuations must take into account the changes we expect to see when it comes to climate.
“Trees take a long time to grow. In terms of practical application, the trees we plant now are the trees we will benefit from in 10, 50, 100 years.”
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