These price tags are somewhat common practice in Canada, where a type of appraisal is used to determine the monetary value of a tree should it be damaged or killed. But forestry and biology experts say those dollar amounts don’t fully capture the environmental value of trees in an urban landscape — especially as they play an increasingly important role in countering the effects of climate change. “I think monetary assessments are an important tool that we have, but we have to take them with a grain of salt in terms of what they might be capturing and what they might be missing,” said Carly Ziter, assistant professor of biology. at Concordia University in Montreal. Some of the often overlooked benefits, particularly in urban centres, include trees’ cooling effect and potential energy savings, their ability to sequester carbon and their role in maintaining biodiversity. Such aspects need to be evaluated to determine a tree’s true value, experts say, in order to encourage conservation of the current tree population — and 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 usually turn to arborists or other experts for plant appraisals, 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 an amount of money in the event of property loss, as is done in Edmonton. But the formula used by Edmonton and many other municipalities — the Plant Valuation Guide — doesn’t yet include an environmental benefit component, said Jacqueline Butler, an arborist and project leader at the city’s forestry department. These valuations are somewhat common in Canada, where a type of appraisal 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 driver type and other similar assessment methods is because these values are defensible in court when there may be property disputes or other legal challenges, said Michael Petryk, director of operations with Tree Canada, no. – non-profit organization dedicated to the planting and cultivation of trees in rural and urban environments. “THE [courts] he would see that tree as a piece of property,” he said. “Sometimes it’s seen as flawed because it doesn’t always take into account the environmental benefits it would have. It’s often just seen as, ‘How much does this property owner benefit from a tree?’ Cecil Konijnendijk, 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 assess more broadly why trees are important. 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 really 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 that is on public property. (Adrienne Lamb/CBC) Some cities in Canada and elsewhere have already assessed the environmental 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 its urban forest is estimated at about $7 billion, with carbon storage alone at $25 million. That’s on top of the $28.2 million in ecological services — things like air pollution removal, energy savings and carbon sequestration — that the urban forest provides annually, according to the city’s 2021-2022 strategic forest management plan. One of the ways municipalities assess broader environmental value is through the use of i-Tree, a popular software suite evaluated by 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. Nearly 8,000 Canadian organizations and municipalities have used i-Tree, according to its website. Even so, Konijnendijk said, the i-Tree formula only captures part of the picture when it comes to assessing a tree’s value. “We also have things like public health. We have things like biodiversity. Aesthetics. And those aspects are often much harder to quantify.”
Why it is important to give value to trees
There are several ways trees can help cities deal with climate change, said Alison Munson, a professor of forest ecology at Laval University in Quebec City and a member of CRAUM, a research collaboration on urban urban forests. The cooling effect that tree canopies can provide is extremely important and valuable, he said. In some cases, mature trees can cool residential areas by several degrees, compared to streets without a similar tree canopy. A 2019 study led by Ziter found that the right amount of tree cover can reduce summer daytime temperatures by as much as 10 F. There are other benefits, Munson said, particularly in urban areas: sequestering carbon as a tree grows, filtering pollution and particulate matter in the air — even buffering against noise. Realizing these environmental benefits is not only important in the face of climate change, he said, but can also serve as a way for cities to balance density. “There’s a push toward densification that doesn’t always take the value of trees very well,” Munson said. “Cities need to take more responsibility to account for these services that are so important.” Research has shown that mature trees, and the canopy they create, can provide a cooling effect for residential neighborhoods. (Justine Boulin/CBC) Munson, Konijnendijk and Ziter say continued tree monitoring and long-term planning around our urban forests will be critical. “It’s not so much tree planting as keeping trees alive. The average urban tree often doesn’t age much more than 30, 40 years. So if you could double that lifespan, you’d get a lot of ecosystem services,” Konijnendijk said. “That’s where it starts: Managing the existing tree population well and protecting trees as best we can in urban situations.” Ziter said researchers are currently looking at how the environmental value of trees may evolve over the years, and that will 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 warmer or that floods more often,” he said. “Or maybe these trees will no longer be enough to provide that benefit in the future.” How we value our trees cannot be a static approach, he said, noting that such assessments should take into account the changes we expect to see in terms of climate. “Trees take a long time to grow. In terms of practical applications, the trees we plant now are the trees we will benefit from 10, 50, 100 years from now.”
