Aging urban forests under threat
CBC News Online | August 9, 2005
Cities across Canada are in danger of losing their mature trees and urban forestry experts say we need to develop strategies now to stem the loss.
In many older neighbourhoods, trees were planted when subdivisions were first built. That means these urban forests are around the same age and will likely die around the same time.
"We have an age-class imbalance," says Peter Duinker, professor of resource and environmental studies at Dalhousie University in Halifax.
"There was a huge expansion of urban residential areas at the turn of the century and after the Second World War �. In the next 50 years, we're going to see a lot of these trees keel over and that's not a very happy thing."
Urban foresters say that unless we begin to plant saplings soon, some of our leafy neighbourhoods are in danger of looking like clearcut zones.
While Canada has an international reputation as a country of majestic forests, the reality is that about 80 per cent of us live in urban centres. So it's the trees that line our streets and grow in our ravines and parks that provide most of us with our greenery.
Yet it's not just esthetics at stake here.
According to a recent study by University of Toronto forestry professor Andy Kenney, every year, Toronto's seven million trees absorb about 28,000 tonnes of carbon. That cuts back on the amount of greenhouse gas carbon dioxide in the atmosphere.
Toronto's urban forest also stores in its branches, roots and leaf litter nearly a million tonnes of carbon and about 1,500 tonnes of other pollutants, such as nitrogen oxides, sulphur dioxides and particulates, which, when inhaled, aggravate breathing problems.
And urban forests everywhere are energy-savers. They give cooling shade in the summer and cut down on frigid winds in the winter, lessening the need for air conditioning and heating.
"They also have an amenity value," says Duinker. "Who doesn't like driving down a city street where the tree crowns touch?"
Yet despite the significant benefits of city forests, Michel Rheame, urban forestry co-ordinator with the National Forest Strategy Coalition, worries that no one government body is responsible for them.
He says there is too much bickering among the three levels of government over whose job it is to maintain city forests.
"It's a very big concern. We're not receiving the necessary resources to go toward urban forestry," says Rheame.
The coalition, an Ottawa-based non-governmental organization, is working on an inventory of the state of Canada's municipal forests. It hopes to have it completed by the fall of 2005 so it can use it to convince authorities of the need for action.
"The situation is desperate in cities that have a lot of same-age, same-species planting. Fredericton is one. Halifax is not quite that bad," says Duinker. "And some individual streets are going to have a crisis � like mine."
In Vancouver, most of the broadleaf deciduous trees favoured by urban planners after the Second World War will soon need to be replaced.
"The broadleaf trees will be getting close to their lifespan in a lot of places," says Lori Daniels, a professor at the University of British Columbia with an expertise in forest dynamics.
"Out west, we often planted cityscapes with trees like horse chestnuts. These broadleaf trees have a shorter lifespan than our red cedars and Douglas firs."
While deciduous trees grow faster, Daniels says the trade off is that they live only 100 to 120 years. Red cedars, on the other hand, can live to be 1,000 years old.
In Thunder Bay, city forester Shelley Vescio worries that most trees are 40 to 60 years old.
"We probably have 20 years or so left for these trees," predicts Vescio.
"As we start losing the 60-year-old ones, the ones we've been planting will begin to take over. But we've not been planting enough.
"I could line the streets, but there's no point in planting them if someone doesn't water them, especially with global warming. I don't have the [watering] infrastructure for it. It comes down to a lack of resources," she says.
Many foresters are now arguing for a planting strategy that takes into account both public and private land and engages the public in the trees' upkeep. Once we plant trees, they say, we have to safeguard them from modern urban threats, such as road salt and trenching for street construction.
There's nothing like city living for stressing trees.
In fact, look along any tree-lined street and you're likely to see at least one tree with a huge V-shape cut out of its centre.
Hydro workers often prune them back from overhead wires to avoid power outages. Urban foresters say it's an unnatural shape that weakens the tree and makes it more susceptible to broken branches.
And they say that not only must we avoid this kind of damage, we must also ensure we don't repeat the mistakes of the past when replacing urban forests.
"The worst thing we could do is what we did 100 years ago in places like Fredericton and Truro. We planted just American elm and then along came a disease and wiped them out," says Duinker. "It's really important to have a wide variety of trees planted in urban areas."