Vancouver trees dry out as heat wave continues to take its toll

British Columbia's unprecedented heat wave and drought-like conditions may be what is causing some Vancouver trees to shed their leaves this week, a scientist says.

Social media was filled with pictures of trees drying out on Vancouver's streets last week.

Leaves on trees turn brown and drop off as a defence mechanism plants use to conserve water under dry conditions, according to the director of parks for the City of Vancouver.

While June saw an initial bit of rainfall, the province's record-shattering heat wave meant no rain on the South Coast for most of the month and into the first week of July.

Stephen Sheppard, a professor of forestry at the University of B.C., says cities should be proactive about watering their urban trees and refilling tree water bags.

"We probably need some better co-ordination and, frankly, support from local citizens, just to keep this number of trees going," he said.

"It's a huge task for any city to water all the street trees over a period of two or three weeks of drought."

Joe McLeod, city arborist and supervisor of urban forestry for Vancouver, says some of his staff may have to work overtime to increase watering frequencies.

"These climate impacts are happening a lot faster than, I think, the City of Vancouver has been prepared for," he said. "These temperatures are a lot higher than we've ever seen." 

Forest management plans need to adapt

Sheppard says municipalities need to account for more heat waves in the coming years as part of their urban tree management plans.

Typically, municipalities expect to water new plants and saplings regularly. However, Sheppard says that older and more mature trees have been particularly affected by recent drought conditions.

"I think what we're seeing with these trends in cities like Vancouver, Surrey, and others that are looking very hard at getting ready for greater urban heat, is that they are going to need larger budgets in the future," said Sheppard.

McLeod says he is looking to work with Vancouver's engineering department and its equipment to help water more trees, but he says they are "spread thin" as well.

"Part of that adapting [for climate change] is ... in the future, we'll be looking to modify watering programs," he said. "But I think one of the biggest pieces is ensuring that trees have adequate soil volumes."

McLeod says that trees with larger soil volumes, a larger space to grow, typically fare better than those with minimal soil volumes.

The City of Vancouver's Urban Forest Strategy says that Vancouver's trees, whether planted along the road or in parks, highlight the role of tree canopies in cooling down parts of the city. It aims to increase canopy cover to 30 per cent of the city by 2050.

"Those increases in canopy cover are going to be increasingly important as we move forward and see increasingly hot summers," said McLeod. 

During the peak of the heat wave in Vancouver last week, this aspect of tree cover was highlighted as Vancouver's poorest neighborhood had far fewer trees and experienced a "heat island" effect as a result. 

"Trees are nature's sort of air conditioning and the cheapest way of cooling neighbourhoods," said Sheppard.

Vancouver's urban forest strategy also notes that cherry and maple trees are "not expected to do well" as the weather warms due to climate change.

Sheppard shares this concern, saying that in his anecdotal experience, maple trees have been dropping more leaves than usual this year.

The maple is Vancouver's most common tree, accounting for nearly 25 per cent of all trees in the city. Cherry trees are the second-most common at around 20 per cent.

Sheppard says species that are not used to hot climates, such as the province experienced during the peak of the heat wave, might see particular "damage" during the coming years.

Vancouver and Surrey have both committed to planting more diverse species as part of their urban tree plans.

For now, Sheppard says residents should not hesitate to water trees and plants that look particularly dry.

"We need to save them so that they can save us from the heat waves," Sheppard said.

McLeod says residents should try to water dry trees up to twice a week, for up to a 10-minute period.

"It's best to water the the trees under the entire canopy of the trees. So within the entire drip line," he said. "It's basically the extent between the [...] stem and the farthest branch."

Watering should be done early in the morning or in the evening to avoid water losses from evaporation, according to McLeod.

He says he is working to get notices out to the public to augment the city watering strategy in this way. 

Residents in Vancouver can also call 311 or use the VanConnect app to report trees in need of water to the park board. 

To listen to Stephen Sheppard's interview on CBC's On The Coast, tap the play button: