If a tree falls

Jesse Winter – The Globe and Mail 

The city says clearing dead wood from Stanley Park is vital for safety. A local group is challenging their science

High in a tree in Vancouver’s Stanley Park, an arborist dangles from a climbing harness with a chainsaw and lops off the dead crown of a hemlock. It takes more than a full second for it to crash to the forest floor below.

When he’s finished, the debris is removed. Little will be left but a dead standing tree, a towering wooden spire known as a snag. Elsewhere in the park, pockets of whole trees have been removed, leaving large holes in the once-thriving green canopy.

The work is part of a significant – and, to some, distressing – intervention to address a moth outbreak that killed almost a third of the public park’s 600,000 trees between 2020 and 2023. The moths swept through the park and nearby coastal mountain forests, devouring the needles of the park’s famously giant trees.

The city says removing some of the dead trees is necessary to protect people from falling trees and branches, and the area itself from wildfire as debris from dead trees could become fuel in dry conditions. But as the snarl of saws rises above the park’s famous Lover’s Walk trail, a small but vocal group of park devotees challenge the science behind removing the trees, which they say amounts to “logging” a national crown jewel.

Beyond arguments over which trees should be cut or saved, what’s happening in one of Canada’s most iconic urban parks underscores the broader challenges of managing city green spaces in the era of climate change.

Stanley Park is home to 600,000 trees, but not all are living ones. Many were killed by a type of moth that consumed their needles, hence the efforts to cut them down. Removing the crowns of dead hemlock trees is, city planners hope, a step to prevent Stanley Park’s visitors from being injured. Left on their own, the rotting branches could fall on passersby.

Though it’s often described in loving terms as a temperate rain forest, Stanley Park is not the same as the vanishingly rare old-growth forests of Vancouver Island. In the mid-to-late 1800s, much of the park peninsula was logged; the stumps of once-proud giants – some the size of a small living room – still dot the forest in some places.

Today, there are roads and pathways and sewer pipes and fire hydrants. There’s a miniature train railway, a horse riding stable and a sprawling aquarium complex. The park is a managed forest that’s seen nearly 200 years of human interventions.

In 2020, the Hemlock looper, a type of native moth, began one of its once-every-15-years cyclical outbreaks, which typically last around three to four years. This most recent outbreak was particularly significant, the city says. Every summer from 2020 to 2022, the moths in their larval form swarmed over the park, rappelling from the trees on barely visible threads. Runners and cyclists on the park’s narrower trails often finished their workouts covered in silky strands, picking the little green inchworms from their hair.

As the outbreak progressed, the larvae eventually killed around 160,000 trees before subsiding in late 2022 and early 2023. Whole stands of hemlocks and other trees were stripped of their needles, standing like grey phantoms.

The city says those dead trees pose many risks, and the only way to deal with them is with saws. Joe McLeod, the city’s associate director of urban forestry, called it a “risk mitigation project for public safety.”

The most obvious risk, city staff say, is the chance that dead branches or whole trees could fall, risking injury to more than 18 million people who use the park every year.

In high winds, the dead tree crowns have a tendency to snap off and come crashing down. They can also get hung up in the branches of other nearby trees, dangling dangerously and able to fall without warning.

But there is a second, less obvious risk: As all those dead branches and snags come down, they accumulate on the forest floor, in some cases piling up more than a metre high.

Under dry, windy conditions, if an errant marijuana joint landed in one of those piles or a car crash on the park’s causeway threw sparks, that dead brush could go up like a bonfire.

Around 60,000 to 80,000 cars go through Stanley Park every day, over the Lions Gate Bridge, Mr. McLeod said.

“If there was ever a fire in Stanley Park that, God forbid, damaged one of the steel girders on the bridge and resulted in that bridge being closed for weeks or months or longer, that would have just a shocking effect, I think, on the economy of the region,” he said.

To better understand the twin risks of wildfire and falling trees, the city hired veteran wildfire ecologist and forester Bruce Blackwell.

His firm is behind wildfire protection plans for cities across British Columbia. He also contributed to a seminal 2004 report on the devastating 2003 Kelowna wildfires, one that argued for sweeping changes to how cities and towns manage their bordering forests.

Mr. Blackwell’s Stanley Park analysis described a significant rise in the park’s wildfire risk from all that dead tree material – what wildfire experts refer to as fuel. In the early post-moth-outbreak phase, many trees would remain standing with their crowns and upper branches dead.

If a fire were to start in a densely wooded section of the park, it could climb the branches of nearby trees and reach into the canopy, causing one of the most dangerous and fast-moving types of wildfire: a crown fire.

As the dead material began falling to the ground, it would continue to accumulate, his report found. As it dries out, downed woody debris like this can make a surface fire hotter and harder to control.

The other contributing factor is drought. During the looper outbreak, Stanley Park was in a years-long drought that weakened the trees’ natural defences, the city says.