When I joined the effort in the scorching hot summer of 2007, I was paired with two other volunteers: a gentle Egyptian lady in her sixties, and a charming woman in her fifties who loved gardening. We had signed up to help conduct a tree inventory in Harbord Village, a midtown Toronto neighbourhood, and we carted our tools around in a bundle buggy. They included a quadrant and a large measuring tape to calculate tree height; a smaller tape to measure “DBH” (tree diameter at breast height); a copy of John Laird Farrar’s Trees in Canada; shears for making cuttings; masking tape; sealable plastic bags in which to store cuttings; and a Google map for each city block on which to mark trees as the count mounted. Our most precious document was a sheaf of papers on which we recorded 12 attributes of the health of each tree.

We were one of 15 teams of two or three volunteers assessing the approximately 2,000 trees on the streets and in the front yards, backyards and alleys of the neighbourhood. We were surprised at how many non-indigenous trees we found: Siberian elms, Russian-olives and the ever-present but inaptly named tree-of-heaven. Along the way, we got to know our neighbours better, both the human and woody variety. A birch is no longer just a birch, but a weeping black birch from Europe. As one Harbord coordinator said, “I now recognize a beautiful tree that I had seen through my second-floor window but didn’t know” – a bur oak.

After completion of the Harbord Village survey last summer, Puric-Mladenovic delivered her analysis: 129 different species of trees live in our neighbourhood. White cedar and Norway maple together accounted for more than 25 percent of them; the NeighbourWoods protocol, however, recommends that the tree cover of an area contain no more than 5 percent of one species and no more than 10 percent of one genus. Of the total, 13 percent of the trees were either in poor or very poor condition. To offset their probable loss, the committee planted about 60 native trees on residential properties where the homeowners agreed, plus 19 at the local high school.

Still, Harbord Village is fortunate in being a well-treed area, with 25 to 28 trees per acre. Toronto’s Davenport West neighbourhood is not. An industrial area with a giant hydro corridor and crossed by three major rail lines, Davenport West has not only less than half the tree density of Harbord Village, but also less than a quarter of the green space of the average Toronto neighbourhood.

The carbon question

One of the arguments for promoting urban forests is their contribution to offsetting greenhouse gas emissions. Trees absorb carbon dioxide and store it in their leaves, trunk, branches and roots, which is why big trees are more beneficial than small ones. How much impact trees have also depends on their type and age, says Bruno Chicoine, project manager at Tree Canada. “They sequester more when they’re young because they are growing. And in urban areas, [trees’ carbon intake] could be different from one type of park to another.”

But trees can do only so much. While a community forest can store up to 2.6 tonnes of carbon per acre per year, their rate of carbon sequestering cannot keep up with the pollution we produce. A hundred 20-year-old red pines in a city park could store 128 tonnes of carbon dioxide, the equivalent of 46 cars’ worth of emissions in one year. That seems insignificant when you consider that there are about seven million vehicles on Ontario roads. As well, urban tree maintenance involves the use of fossil fuels to run chainsaws, trucks and chippers.

According to The Nature Conservancy, in comparison to rural trees, urban trees are less effective at sequestering carbon, because they grow further apart than rural trees and tend to be smaller and less healthy. For these reasons, the environmental organization suggests that cities consider rural tree planting when developing carbon offset programs.

Still, plants are the only things that are capable of photosynthesis, and trees also curb greenhouse gasses in less direct ways. “Trees provide shade, and shade reduces energy costs” in heating and cooling, says Andrea Dawber of GreenHere, a Toronto non-profit organization dedicated to increasing green space. Moreover, trees’ natural beauty encourages people to walk, rather than drive.

S.G.

This is where GreenHere planted its roots. Andrea Dawber founded the not-for-profit organization when, in 2001, she was struck by the fact that the playground where she took her son was completely unshaded. She started a reforesting project in collaboration with the city, eventually planting 150 trees and getting various amenities for the park. Five years and an Ontario Trillium Foundation grant later, she formed GreenHere, broadening her focus to the entire Davenport West area. Dawber believes that environmental hazards disproportionately affect the health of less affluent communities because they tend to have less green space. “During summer, toxic gases, such as nitrogen oxide, become less stable as the temperature rises,” she says. “There is a volatile mix in the air.” Trees provide the double benefit of cooling the air and filtering particulate matter from it.

I volunteered last spring to help GreenHere with its tree inventory. As we wandered the neighbourhood, coordinator Tammy Finnikin, one of the young staffers who accompanied me, explained her “two-knock rule” for giving people the chance to get to the front door and size us up before we moved on to the next house. Some homeowners did not want to be bothered about trees, but others were friendly, telling us about a special specimen we should see up the way.

Counting, identifying and assessing the trees in this area was a repetitive exercise with veteran Norway maples at house after house on the older streets and juvenile Japanese silk lilac already showing sun scars in new townhouse blocks. And there were many cemented front yards and backyards, with perhaps a grape arbour and some laundry to deflect the sun’s glare. We were relieved when we discovered church grounds filled with soft- and hardwoods, or a yard crammed with fruit trees, where the homeowner would welcome us and offer apples or pears.

Most of us take trees for granted, like a great-aunt or -uncle we love, but largely ignore. Once you start paying attention, however, you see the almost absurd abuse meted out. We saw a mature pear tree whose trunk had been wrapped in a string of lights at an early age, resulting in a swirling indentation in the bark. Elsewhere, we came upon an ailing catalpa, its branches hung with dolls and toys like garish earrings. On Old Weston Road, a high-traffic thoroughfare, we found a gigantic Norway maple that had grown up and through the chain-link fence and was completely surrounded by pavement.

The Davenport West project is partially complete, although the project has expanded its area now, and the results so far indicate that 35 percent of the canopy is made up of only three species: Manitoba maple, Norway maple and tree-of-heaven (all invasive alien species to Ontario), an unhealthy proportion. To address this situation, GreenHere now goes door to door, explaining the city’s free front-yard tree program (see “What to plant,” page 34). GreenHere also offers home-owners willing to plant trees on their properties six native, large-canopy species, including slow-growing northern red oaks and white oaks, eastern white pine and broad-leafed basswood, which is ideal for sequestering carbon dioxide and other particulate matter.

Tree biodiversity is essential to promoting resilient, self-sustaining urban forests. Puric-Mladenovic is concerned that municipalities are still overdependent on a few species, such as green ash or honey-locust. “If you lose 2 percent or 3 percent of your trees because of a bug [like the emerald ash borer] or something else, that is not so bad,” she says. “But if you lose 20 percent, 30 percent or 40 percent, you’re in trouble. With biodiversity, you have a buffer as protection against future uncertainties.”

But maintaining existing tree stock is at least as important as planting the new generation, because canopy coverage is the critical issue. As Kenney wrote in a 1999 report, “since big trees have a much greater leaf area than small trees (and also store much more carbon), it is important to retain these big trees as long as possible.” The tree canopy in Toronto is estimated to cover 17 percent of the city’s area, but without increased tree maintenance and stewardship, projections indicate that the cover will decline to 10 percent. In Peterborough, Cathy Dueck, who led an extensive tree-assessment project there, says the city is replacing only approximately one tree for every two lost each year on public land. “And many of the remaining trees now have structural problems that will shorten their lives,” such as poor branch attachment, roots damaged during landscaping and trunk scarring that gives easy access to pests.

Rallying communities to the cause of protecting their trees is a challenge, however. Since private citizens own 80 percent of the trees in Peterborough’s residential neighbourhoods, Dueck knew that public engagement was crucial to the health of her city’s urban forest. Tree care workshops and a tree contest her group held were popular, but the response to a coupon program covering half the cost of specific tree species has been lukewarm at best. “I guess the next step may be knocking on doors,” she says.

Puric-Mladenovic counsels patience. Just as trees take time to reach their full potential as guardians against urban ills, so the campaign for the growth and preservation of the urban canopy is a long-term fight. “The benefits of improving urban forests won’t be felt today or tomorrow,” she says. “You have to look to the future. You have to say to yourself, ‘It will benefit my kids and my grandkids.’”

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Susan Grimbly is a former newspaper editor who now spends her summers working as a volunteer in the community forestry movement.