Aspen tree line. Photo: Wikipedia
03 Nov 2019

"Natural fuel breaks": Could aspen trees help solve the wildfire crisis?


Aspen trees and birch naturally flourish after a wildfire, but they're also less vulnerable to flames than coniferous trees. In an article from 2018, Bethany Lindsay, CBC News, looks into various studies showing how modern forestry practices, rather than climate change alone, may be to blame for the recent "wildfire epidemic" in North America and around the world.

In 2017, 12,812 hectares of British Columbia´s forest were sprayed with the herbicide glyphosate. Every year, this mass extermination of broadleaf trees are forced upon foresters by the Canadian provincial government though the current forestry legislation.


Naturally fire resistant trees killed off to maximize lumber profits - but is it economical as a whole?

The eradication of trees like aspen and birch on regenerating forest stands is meant to make room for more commercially valuable conifer species like pine and Douglas fir - trees with "needles" instead of leafs, thought to make better and faster growing timber than leafy trees.

But experts say removing the broad leaf trees also removes one of the best natural defences we have against wildfire, at a time when our warming climate is helping make large, destructive fires more and more common.

When fast growing pine forests burn down on a large scale, insurance companies, private land owners and tax payers are often left paying for the damages - meanwhile, the forest industry to a large extent, writes off their losses - or bills them to the government.

"It blows my mind that nobody is talking about this," said James Steidle, a member of the anti-glyphosate group Stop the Spray B.C.

"The experts know this stuff. They've known about this stuff for decades, but it's just not being translated into reality."

Trees like aspen naturally have a higher water content and do not usually contain the volatile chemical compounds that can make trees like pine so flammable. They also provide more shade, which creates a cooler, more humid environment in the under brush, according to experts.


Aspen fire at Shovel Lake

During a visit to the area of northern B.C. burned by the Shovel Lake wildfire the summer of 2018, James Steidle documented aspen trees that were left standing even though surrounding conifers were incinerated. (Photo: James Steidle)


Broadleaf trees said to form natural fuel breaks

When aspen and other broadleaf tree are allowed to flourish, they form "natural fuel breaks" if their leaves are out, according to Lori Daniels, a professor of forest ecology at the University of B.C. That's why aspen stands are often referred to as "asbestos forests" in wildfire science circles.

A Canadian forests ministry spokesperson said the government recognizes that aspen and other deciduous trees can help reduce the wildfire threat to communities, and that in the future, more thought will be put into planting broadleaf trees near homes and businesses.

Nonetheless, the rules about aspen in managed forest stands remain largely unchanged, both in Canada and in many US states.

If there's too much aspen, the block must be sprayed with glyphosate, a chemical known more familiarly as the active ingredient in the weed killer commercially sold as Roundup. Over the last three years, 42,531 hectares of B.C. forest have been treated with the herbicide.


'That's just nuts'

"At the end of the day, we have rules that make fire-resistant trees illegal in our forests. That's just nuts," Steidle said.

Aspen naturally thrives after a forest has been cleared by logging or wildfire. Their root systems can survive for thousands of years underground, and they're capable of sprouting new clone trees as soon as there's enough sunshine and moisture.

Glyphosate doesn't just kill aspen trees — it can also destroy the root system.

Trees like aspen naturally have a higher water content and do not usually contain the volatile chemical compounds that can make trees like pine so flammable. They also provide more shade, which creates a cooler, more humid environment in the under brush,  Daniels explained.

Often, a "candling" wildfire that's engulfed the crowns of a conifer forest will fall back down to ground level when it hits a clump of aspen.

"If a fire is spreading toward a community and we know that there's a band of aspen trees that it's going to have to cross before it approaches that community, the firefighters can use that band of aspen trees to make a stand and try to stop the fire," Daniels said.

The research backs that up: 

One 2010 study conducted by a fire behaviour specialist with the Canadian federal government tested the fire-resistance of aspen by doing experimental burns of a forest that was split between conifers and trembling aspen.

Even when there was a "high-intensity flame front" in the conifers — with flames leaping into the crowns of the trees — the fire "failed to sustain itself upon entering the leafed-out hardwood portion of the plot," the study says.


Aspen trees test burn


Four Photo Collage: A test burn conducted by a federal fire behaviour specialist shows, at bottom right, how aspen can resist a wildfire spreading through jack pine and black spruce. (The Forestry Chronicle)

Cover Photo: An aspen tree line in the forest. Photo: Wikipedia