Researchers are growing increasingly critical of a common forest management practice, as studies show it may be causing fires to travel farther, faster.

"In 2017 and 2018 here in British Columbia, in both summers, we burned over 1.2 million hectares of forest," says Lori Daniels, a forest ecologist at the University of British Columbia.

"Diversifying the forest ... is a really effective way to create resilience in our landscape and resistance to these major fires we've been witnessing."

Meanwhile, much of the Canadian forestry industry is doing the opposite, spraying thousands of hectares of public forest with glyphosate each year to promote profitable coniferous growth, and eliminate hardwood species like aspen and birch.

The primary ingredient in the Monsanto-made herbicide Roundup, glyphosate has been under scrutiny in both agriculture and forestry for years. It remains widely used, because while softwood species like pine and spruce can tolerate a certain dosage of the chemical, glyphosate can be effective in eliminating the growth of hardwood trees for decades.

It's an efficient way for the forestry industry to streamline cut blocks so they contain the most profitable kinds of trees.

But aspen and birch burn more slowly than the glyphosate-resistant coniferous trees, and some experts say removing them is like quite literally stoking the fires that have plagued the province.

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

Natural fire barrier

"In aspen, birch or broadleaf forests, because of that subtle change in shade, temperature and humidity, they tend to be more resistant to fire," says Daniels. "[The fire] might burn through, but in a less intense way."

It's something she has seen tangibly in the remains of the historic Williams Lake fire that ripped through B.C.'s northern forest in 2017.

University of British Columbia forest ecologist Lori Daniels shows how the 2017 Williams Lake fire changed behaviour when it hit a patch of mixed forest that included aspen. 0:53

"As the fire spread closer into the aspen stand, it stops," she says. "And if we look in the aspen stand, the trees all have survived."

But the B.C. Council of Forest Industries says its practices meet strict criteria that make it a world leader in sustainable forest management.

"Once it has been determined that glyphosate use is appropriate, it is applied either manually or by precise aerial methods to ensure that application is limited to the target area," the council's manager of public affairs, Diamond Isinger, wrote in an email to CBC News. "Our forest sector is - and will continue to be - committed to responsibly managing our forests for the environment, the economy, and the communities that rely on them."

Not a vegetable garden

More than 200 kilometres north of Williams Lake, woodworker James Steidle says he's seen the changes the logging industry — and glyphosate use — have made to the landscape around him.

"We look at forests as some kind of farm, some kind of vegetable garden where you're trying to grow carrots, and if it's not a carrot you get rid of it. And I think it's a lot more complicated than that."

He is part of the Stop the Spray B.C. movement, a group working to raise awareness about the use of herbicide spraying and its consequences for the forest. The group is aggregating research and posting videos that show what the industry is doing, under rules set by the provincial government.

That's because the province of British Columbia mandates that Crown land be nearly all coniferous on cut blocks, but that's not how the forest tends to grow naturally.

"We have a coniferous forest industry and the government saying 'we are going to get rid of these [deciduous] trees, they are no longer part of the forest,'" says Steidle. "That makes me furious."

This forest near Williams Lake was decimated by fire in 2017. (Maxime Corneau/CBC)

Forest ecologist Daniels echos the sentiment, calling for a change in forest management practices.

"I think that some of those concepts are outdated," she says.

"When glyphosate is used to kill aspen and competitive vegetation, the word competitive is crucial. These plants compete with conifers that we want to grow to have a strong forest industry. It means that we put only one value, the financial value, before all the other values."

The value of diverse forests extends to mitigating disease, limiting insect infestations, and sequestering carbon dioxide.

"There as been great research in the last 10 to 15 years that shows that there are tremendous benefits, even to those conifer seedlings, by having other species around them," says Daniels.

Deformed vegetation

University of Northern British Columbia researcher Lisa Wood has been doing controlled experiments with glyphosate to determine how long traces of the herbicide remain in surviving plants. (Maxime Corneau/CBC)

Newer research also indicates glyphosates may have an impact on the plants that survive the sprays.

"Toxicity, the immediate death of plants, these aspects have been studied extensively," says Lisa Wood, a plant biologist at University of Northern British Columbia.

"But the small nuances ... the nuances that you do not see at first glance, these require more time for one to really understand what is happening."

Her team has shown that glyphosate is present in the surviving plants for at least a year after it is sprayed, a finding that surprised the scientific community.

The maximum amount of time the chemical may be present in plants has yet to be determined.

A University of Northern British Columbia researcher examines a plant sprayed by glyphosate. (Maxime Corneau/CBC)

The B.C. Ministry of Forests declined a CBC News request for an interview, saying in writing that the use of glyphosate is declining in the province and that it is used under regulation, as it is in almost every other province.

"B.C.'s reforestation practices are updated when new scientific research and information becomes available," ministry spokesperson Dawn Makarowski wrote. "Aspen and deciduous will not disappear from our regeneration forests."

The only province that has banned glyphosate use in forestry is Quebec.

WATCH | The National's story on glyphosate spraying and its effects on forests: