Unexpected changes: What happens to boreal forests after fire?

A study from Northern Arizona University has brought to light surprising findings on the effects of fires in North America’s boreal forests. 

The research reveals that the post-fire shift from coniferous to deciduous trees is not permanent, which is contrary to previous beliefs.

Deciduous trees 

Historically, wildfires in the region led to the dominance of deciduous trees over their coniferous counterparts. Deciduous trees, known for their rapid growth, absorb more carbon and reflect more light. This leads to a cooler climate and a reduced likelihood of subsequent fires.

The study’s findings, however, reveal a more complicated picture. While the boreal forests indeed turn more deciduous post-fire, they do not remain in this state. 

Coniferous trees 

Approximately three to four decades after a fire, a shift back toward coniferous trees begins. To reach this conclusion, the experts analyzed satellite imagery from boreal forests spanning three decades.

The researchers also found that there was no overall shift toward deciduous cover. This is because the abrupt loss of coniferous forests to wildfire was offset by the gradual increase in coniferous forests in areas that had not recently burned.

Tremendous dynamics 

“We confirmed that fires clearly shift forests from conifer to deciduous cover, but when we look at those changes over many decades, we find deciduous trees begin to be replaced again by conifer trees three to four decades following fire,” said study co-author Professor Scott Goetz. “There are tremendous dynamics taking place, but when we tally those all up, the net feedbacks to climate were fairly small.”

“This was somewhat surprising because several recent studies suggested there were shifts toward deciduous forests at local to regional scales,” said study co-author Logan Berner, assistant research professor in SICCS. 

“While our study indicates there have not been whole-sale shifts in forest composition during recent decades, we anticipate that continued climate warming and increased wildfire activity could lead to pronounced changes in forest composition over the coming decades.”

Study significance 

The study’s insights hold significant importance, especially in the light of increasing fire disturbances observed in these forests in recent years. With climate changes making the environment warmer and drier, both the pattern of fires and post-fire recovery of the forests could be affected.

Brendan Rogers from the Woodwell Climate Research Center emphasized the importance of these findings. After a summer that witnessed record-breaking fires in Canada, understanding the compositional shifts of these forests in response to fires over time becomes paramount. 

Future research

“As we think about fire management approaches, including efforts to reduce carbon emissions and mitigate fire risk to local communities and infrastructure, this study provides a critical foundation for future research,” said Rogers. 

“Especially after a summer of record-breaking fires in Canada, understanding how the composition of these forests will shift and respond to fire over time is crucial to informing best management practices and protecting people and the planet.”

Arctic Boreal Vulnerability Experiment

Conducted as a part of NASA’s Arctic Boreal Vulnerability Experiment (ABoVE), the team utilized high-resolution satellite imagery captured by the Landsat series of satellites. This allowed them to quantify changes in forest composition and the associated climate feedback effects.

The research was led by Richard Massey, a former postdoctoral scholar at Northern Arizona University. It is published in the journal Nature Climate Change. 

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