Katsura trees, often found on city boulevards and in private gardens, have a sweet surprise for us every autumn.
By Carol Volkart
Ahhh, ever wonder where the sweetest scent of autumn comes from? It’s like carmelizing sugar, and who, like me, has searched vainly for the source of those tantalizing whiffs in the great outdoors?
The answer, one of the many small mysteries revealed during a recent Dunbar Neighbourhood Café about trees, is that it’s sugars breaking down in leaves. And if you have a lot of Katsura trees in your life – lucky you! They’re especially known for the scent they give off as their heart-shaped leaves turn from yellow to brown in the fall.
Nobody appreciates the benefits of trees more than horticulturalist Allison Luke, frequent speaker, tree-tour guide, and founder of Arborlight Consulting, who brought her enthusiasm and insights to the Sept. 16 Dunbar café.
Allison Luke opened her talk with a joyous description of biking to school with her kids through a tunnel of trees.
In a talk she described at the outset as anthropocentric – it’s all about “me, me, me” – she focused on the many benefits of trees to humans:
The products they give us – wood, fuel, building materials, coffee, tea and linen. “We’re all wearing plants.”
How they regulate our environment – improving air quality, managing storm water, reducing pollution, sequestering carbon, and providing cool relief in hot spells. “For weather events, heat is the leading cause of death, more than tornados, hurricanes – it’s the silent killer,” Luke said. “So trees will be one of the tools in our toolkit to cool our neighbourhoods for extreme weather events.”
Then there are the pleasures and health benefits they provide – both social and personal. Tree-related events, from Salmonberry Days forest walks to the Cherry Blossom Festival, bring people together. And the mental and physical benefits of spending time among the trees is well-documented. Breathe deeply in the woods, for example, and the volatile organic compounds in the forest air help boost immunity.
All these benefits are based on a science that Luke clearly loves – the “scaffolding” that trees depend on for their vibrancy and health. Listen to her enthusiasm: “Where leaves aren’t raked up and allowed to decompose, the shredders, insects and birds come along, break those down, and they’re further broken down into micronutrients, carbon and nitrogen. And then all those nutrients are cycled in the soil.
“And you know we’re a part of these invisible cycles, the carbon cycle, the nitrogen cycle, in the city, it’s all going on around us. Photosynthesis, when you think about leaves and the sun, plants incredibly manufacturing their own food. What an amazing thing!”
The clearly tree-enthralled audience was engaged from the start to the end of Luke’s presentation, peppering her with questions and observations ranging from the city’s tree canopy, to questionable boulevard tree-planting, to techniques for ripping ivy off trees, to the zipline in Queen Elizabeth Park, to keeping space for trees in a densifying city.
The tree canopy – the percentage of tree cover from an aerial point of view – was top of the list, especially when Luke showed a map from a city report revealing the difference between the luscious west-side tree coverage compared to the skimpy coverage in the east. As of 2022, Dunbar-Southlands (35 percent) was second only to Shaughnessy (41 percent) in terms of tree canopy, while Strathcona was at a low of nine percent.
City map shows high tree coverage in many west-side neighbourhoods compared to the east side.
When an audience member commented on the disparity, Luke said the city is now working to balance that. She said the differences are the result of “long, long embedded histories.” Bylaws passed in the 1920s actually contributed to the differences, she said, and much had to do with which parts of the city were developed first.
Vancouver’s overall tree coverage was 25 percent in 2022, and the city’s goal is to reach 30 percent by 2050.
Which raises, as Luke acknowledged, the problem of how to do that along with the city’s other prime goal of building more housing.
“This is the number one thing,” she said. “We need densification. We also need urban forests.” The question, she said, is how to do both: “We’re trying to figure out how we can do this better together.” One of the solutions may be more collaboration between developers and arborists at the planning stage, she suggested.
Residents’ appreciation for trees echoed Luke’s own. She clearly relished one audience member’s anecdote about a friend who’s taken it upon herself to go into forest areas and rip ivy off trees with the help of a 50-foot rope. And she sympathized with the problems one resident has run into in sourcing 100 saplings she plans to give away free to people who will plant them in their gardens.
When another audience member complained about a zipline “disneyfying” Queen Elizabeth Park, Luke said it raised important issues around consultation. “A theme I’m hearing is that you want some agency in the choice and you want some say in our urban forest. I think this is an important topic. We need to be consulted and we need to have a say in the direction of our urban forest, from species selection to usership.”
The choice of trees was at the centre of many questions, including one about how much consideration of fire risk goes into tree selection. Luke said that “foolishly,” it’s not on our radar because we live in Vancouver. That’s not the case elsewhere, she said, noting that on a recent drive to Whistler, she noticed the whole side of the highway being cleared of understory, a change from a year ago.
Another audience member with a bad experience regarding boulevard planting asked how intentional the city is about choosing the right tree for the right place. She said that when a cherry tree died, she asked for a replacement, but was told the city wasn’t planting cherry trees anymore. Instead, workers planted three other trees, way too many for the space, she said. When she asked why those trees were chosen, a worker told her, “I know I’m not supposed to tell you, but these were the last ones left on the truck.”
Luke said that as in all fields, city workers face limitations. “There’s the right way to do things and then sometimes – it’s the last tree on the truck.”
But she rejected the old stereotype that city workers don’t know what they’re doing. “Sometimes it’s species selection. Sometimes landscape architects have a whole planting list and it gets thrown out because they’re not available.” It takes seven years before a city tree is ready to be planted, she said, and it’s hard for nurseries to know what trees will be wanted seven years in advance.
Then there’s the question of why, at a time of high food prices and food insecurity, the city doesn’t plant more fruit trees on boulevards. The answer, said Luke, is that people “just don’t like walking through apples and plums.” The city got rid of fruit trees because people “complained bitterly,” considering them a nuisance and a danger for slipping. “So now we need more strategic planting of that kind in park areas away from bike lanes and roadways. But I think we should have more fruit and nut trees in the city.”
The impact of climate change on trees was a theme of the session, exemplified by one questioner asking, “What trees that we love are expected to permanently disappear?”
Luke said the western red cedar will likely have a hard time in urban areas in the future, but may survive in good locations with water in the summer.
She also had an answer for those wanting to know what kind of trees we should choose for the future: Metro Vancouver has created a list of climate-adaptable species, which can be found here.
Toward the end of the meeting, when the issues of dangers surrounding trees had been raised, Luke noted that her talk had focused on the positives of trees, but there are negatives.
“Do trees cause risk? Yes, absolutely, they fall on houses, they fall on our cars sometimes in wind events, they can disrupt us. They’re not all positives,” she said.
“But I think the overwhelming benefits of the urban forest outweigh our risks and that’s why we need them.”