Powerful wind and rain that swept the Vancouver region on the weekend highlighted the vulnerability of trees weakened by a summer drought – and the challenges cities will face keeping their tree canopies healthy as climate change brings more severe weather.
Saturday's windstorm left hundreds of thousands of people without electricity after trees fell on power lines, punched through roofs and smashed cars. By Monday, the City of Vancouver alone had received about 650 service requests for damaged trees.
The tree carnage, while not as severe as the damage from a 2006 windstorm that ripped through Stanley Park, comes as cities around the globe try to build healthy urban tree canopies – which have been proven to be beneficial for everything from stormwater management to human health – in the face of increasingly severe weather.
"I think it is definitely related to climate change and it should be a wake-up call," Stephen Sheppard, a professor in the urban forestry program at the University of British Columbia, said on Monday of the weekend storm.
"We often hear about the 'new normal.' The reality with climate change is that we are never going to know what the new normal is."
Vancouver is debating how best to manage its tree cover after a hot, dry summer caused drought conditions in most of the province. The two events are related, experts say: The dry soil was less able to hold trees in place and branches became more brittle.
Urban forestry planners should take a long-term approach that focuses on maintaining existing trees and nurturing new ones to ensure the benefits of a healthy urban tree canopy, Prof. Sheppard said.
In general, such a strategy boils down to planting the right tree in the right place, taking variables such as soil conditions into account.
"For many kinds of trees, the root ball should be about as wide as the tree," Prof. Sheppard said. "And yet you walk down a lot of streets and you see [trees] in narrow little settings – so we are asking a lot of these trees in very confined settings."
City staff are looking at standards for tree management that would specify, for example, the optimum amount of soil for a tree to thrive.
The city is also considering establishing a tree canopy requirement for developers. This would go beyond existing regulations that call for a street tree every 10 metres, Vancouver Park Board planner Katherine Isaac said on Monday.
"What we would like to do is evolve those standards to actually have a canopy requirement so that sites are ensuring they are providing a certain amount of canopy and that the canopy that was lost on that site is somehow compensated for," she said, adding that staff are still working out the details.
The potential changes are expected to go before council before the end of the year.
Vancouver adopted its first urban forest management strategy in 2014. The city mapped its urban forest, finding that canopy cover ranged from a low of 5.9 per cent in Strathcona to 28.9 per cent in West Point Grey. Mapping also determined the urban canopy had declined over the past two decades.
Vancouver's tree canopy is 18 per cent of land area, on par with Seattle and Victoria.
With climate change in mind, researchers are hunting for hardy, drought-resistant species and tree-friendly technology.
Deep Root Canada sells underground, cage-like systems that provide uncompacted soil in which trees can grow.
On Monday, Deep Root general manager Mike James was at Olympic Village to check on about 100 trees, mostly maples, planted using a Deep Root system before the 2010 Games.
None fell in the storm, and most of the trees – now about 20 centimetres around – had not even dropped any branches.
Mr. James could not say whether soil volume played a role in the tree failures on the weekend, but he suspects it might have been a contributing factor in at least some.
Property owners concerned about trees on private land should have a qualified arborist check to ensure they are properly trimmed and free from rot or other problems that could make them vulnerable to wind, tree experts said.
While many power outages result from trees on lines, B.C. Hydro has not made burying the lines a priority.
"We have 77,000 kilometres of power lines in B.C., so it's not realistic to bury all lines," spokeswoman Simi Heer said in an e-mail.
An underground system typically takes longer to repair than overhead lines, and would be more challenging to fix after a major seismic event, she added.