Boreal carbon might enter atmosphere
SASKATOON, Sask. — The boreal forests that blanket northern Canada could become a significant source of carbon emissions if wildfires keep getting larger and more frequent, according to recently published research looking at the effects of a heavy 2014 wildfire season in the Northwest Territories.
Adjunct Professor Jill Johnstone from the University of Saskatchewan was part of a team of researchers that looked at how much carbon stored in the forest soils was emitted during the fires.
Their findings, recently published in the journal Nature, show wildfires were getting at the “legacy carbon” in soil where the forest had burned within the last 60 years prior to burning again in 2014.
“That means that those forest stands were actually emitting more carbon than they had accumulated during the past fire-free interval,” Johnstone said.
Johnstone explained that boreal forests trap carbon as plant matter becomes compacted in the soil over decades and centuries. She said the planet’s boreal forests currently store some 30 to 40 per cent of all the carbon trapped in the Earth’s soils.
For now, she said most of that carbon remains relatively safe from fires, as the younger growth found to be a net emitter usually only accounts for about five to 10 per cent of a burn area.
But, she said the findings are alarming when taken in the context of increases in both the number of heavy fire years per decade and the average area burned by wildfires each year.
“If fires become more frequent, and right now that appears to be the trend, then more young stands are going to burn and so that makes those legacy carbon stores from previous fire cycles really vulnerable to getting emitted.”
Johnstone said the research presents a “scary story” of the potential for legacy carbon released by boreal forest fires to contribute to further global warming.
“It really suggests that even if we slowly reduce our emissions over the coming century, that there may be natural feedbacks between the Earth’s systems and the atmosphere that could continue to exacerbate warming caused by increased carbon in the atmosphere.”
Johnstone said it was difficult to gauge how fast those feedbacks could take hold –– as such, she said she remained hopeful action could be taken to reduce human-made carbon emissions and stall the worst effects of climate change.
She said the team soon hoped to publish further data from its study of the 2015 wildfire season in Saskatchewan, but said early results suggest a similar pattern when it comes to emissions from young tree stands.