Fuel, not weather, determines wildfire carbon emissions: study

While scientists largely rely on weather conditions to determine how much carbon a wildfire will burn, a new study suggests available fuel is actually more important. 

The Arctic-Boreal Vulnerability Experiment examined 417 boreal forest burn sites across Canada and Alaska between 2004 and 2015, including more than 200 sites affected by the NWT’s 2014 megafires.

Researchers found that drought conditions, temperature, and rain were poor indicators of carbon combustion, compared to how much fuel was available on and in the ground.

The amount of carbon stored in the soil – rather than the trees that burned – accounted for up to 90 percent of boreal carbon emissions, the study found.

The findings were recently published in scientific journal Nature Climate Change. 

“What this study really showed is that the fuels on the ground are important,” said lead author Xanthe Walker at Northern Arizona University’s Centre for Ecosystem Science and Society.

“We need to understand those more and understand how they’re likely going to change with continued warming.” 

According to the study, scientists and forest managers currently rely on a system that analyzes “fire weather” – the Canadian Forest Fire Weather Index System – to predict wildfire activity and carbon emissions in the boreal forest.

Walker said this study’s findings suggest they should also look at other factors. 

She explained that boreal forests are diverse across the North. In some areas there are black spruce forests, which usually have thick, organic soils, while deciduous trees and jack pines grow in more shallow soils. While drier landscapes with jack pine trees are prone to more frequent fires, carbon emissions from those fires tend to be lower. 

Soil moisture and the composition and age of forests are also important for predicting wildfire carbon emissions. 

As for how climate change could affect carbon emissions in the future, Walker said “it’s complicated.”

While warmer and drier summers have led to more severe wildfires and longer fire seasons, the type of fuel being burned can also change over time.

That could include a switch from black spruce to jack pine-dominant forests, changing the amount of carbon emitted.

Meanwhile, with less time between fires, there is also less time for organic soils – and carbon in the soil – to re-accumulate.

Permafrost degradation and the drying of soils, however, could increase the amount of carbon underground that’s available.