2014 was the largest fire season in N.W.T. history (File photo/battlefordsNOW).

By Keaton Brown

Depleting Soil Carbons

Forest fires can contribute to depletion of soil carbon, increase global climate: UofS study

Aug 23, 2019 | 2:19 PM

A new study on how forest fires contribute to depleting soil carbon in the boreal forest was published in the prestigious Nature scientific journal.

The research team included University of Saskatchewan (USask) adjunct researcher Jill Johnstone and recent USask PhD graduate Xanthe Walker. The study revealed why more frequent burning in the boreal forest due to wildfires is bad from a climate change perspective.

The research was launched in the aftermath of the severe 2014 fires in the Northwest Territories (N.W.T.), the largest fire season in the region`s recorded history. The N.W.T. government, along with other agencies such as NSERC and NASA funded the project with aims at better understanding of what happened to the boreal forest soils during these fires.

This knowledge could help improve forest fire management and help northerners plan and adapt.

“We know that there is really old carbon in these soils – carbon that is hundreds to thousands of years old, carbon that is irreplaceable” said Michelle Mack of Northern Arizona University (NAU), senior author on the paper.

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Carbon is critical to soil function and productivity. The boreal forest’s soils accumulate carbon and are a globally significant carbon sink. Boreal forests store about one-third of the world’s terrestrial carbon primarily in the soils.

These pools of carbon have historically been safe from combustion but with warming of the forest climate and larger and more frequent wildfires, more of this sequestered carbon is being combusted and released.

“The combustion of this ‘legacy carbon’ in the soil has the potential to shift the global carbon cycle, as boreal forests that have acted as carbon sinks for millennia become sources of atmospheric carbon,” said Johnstone. “This could potentially accelerate climate warming.” she added.

Legacy carbon in danger of burning with more frequent forest fires (supplied photo/USask)

The research team hiked into the N.W.T. burn areas and sampled the soil at more than 200 burned areas that were identified by Laval University researchers.

“These were large and severe fires, and we thought: this is when and where it would burn,” said Walker, referring to old pools of legacy carbon.

In nearly half (45 per cent) of the young stands the researchers sampled, legacy carbon burned. And while the amount of legacy carbon did not alter total carbon emitted from these fires, the pattern the researchers identified has global implications for future climate scenarios.

Johnstone said that the carbon emitted from the forest fires contributes towards Canada’s overall total carbon produced in accordance with the Paris agreement. As more carbon is released by the fires it contributes to warmer global temperatures, which in turn results in more fires. There is the potential for this to snowball into a fairly severe carbon source. It will be important for Canada to design policy around keeping these boreal forests acting as a carbon sink instead of it transitioning to a carbon source.

Saskatchewan also had a significant wildfire problem in 2015, the year after the N.W.T fires. Johnstone said that they have started to develop the same type of research, with a similar research team, studying the effects on the boreal forest in northern Saskatchewan and will be releasing their findings in the future.

Jennifer Baltzer, Wilfrid Laurier University researcher and a co-author of the study, said, “This research, with the help and partnership of the N.W.T. government, has really advanced our understanding of these fires and the tremendous impact extreme wildfire years have on globally critical stores of carbon.”

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Keaton.brown@jpbg.ca

On Twitter: @battlefordsnow