A dramatic change in the makeup of North American boreal forests could reduce the amount of carbon released during forest fires, according to new research published by Northern Arizona University. As climate change drives larger and more severe fires across Alaska and northwestern Canada, scientists say the rise of birch‑ and aspen‑dominated forests may offer an unexpected buffer against escalating carbon emissions.
The new findings, Increased deciduous tree dominance reduces wildfire carbon losses in boreal forests, published in Nature Climate Change, show that when boreal forests shift from conifer species such as black spruce to deciduous species like birch and aspen, they lose less than half as much carbon per unit area burned. The study, led by researchers at the Center for Ecosystem Science and Society (ECOSS), suggests that this transition could slow one of the most dangerous climate feedback loops in the northern hemisphere.
“This work shows that not all boreal forests burn the same way,” said Betsy Black, who led the study as part of her master’s thesis research at NAU. “As deciduous trees become more common after fire, they can fundamentally change how much carbon is lost to the atmosphere during future wildfires.”
Boreal forests store a vast share of the world’s terrestrial carbon, much of it locked in deep organic soils that have accumulated over centuries. Historically, these forests have acted as a carbon sink. But warming temperatures have intensified fire seasons, raising concerns that boreal ecosystems could shift from carbon storage to carbon release — accelerating global climate change.
“Our previous research shows that deciduous forests can accumulate much more carbon after fire than spruce forests,” said Michelle Mack, ECOSS professor and senior author on the study. “But we were curious about what happens to that carbon when these forests burn. No one had measured that before.”
To answer that question, the team analysed carbon pools and combustion losses across nearly a dozen large fire scars in Alaska and Yukon. They found that deciduous forests store more carbon in combustion‑resistant tree stems and less in deep organic soils that readily burn, resulting in significantly lower emissions during wildfire.
The study also revealed sharp differences in the drivers of carbon loss across forest types. In conifer forests, for example, emissions were controlled by bottom‑up factors such as fuel availability and soil moisture. Meanwhile, in deciduous and mixed forests, carbon losses were more sensitive to fire weather conditions. “Seeing weather play such a strong role in deciduous forests was surprising, and it suggests that as climate change drives more extreme fire weather, these forests could become more vulnerable in the future,” according to Xanthe Walker, ECOSS professor and corresponding author in the research.
For more information: Black, B., Mack, M., Walker, X., & colleagues. (2026). Increased deciduous tree dominance reduces wildfire carbon losses in boreal forests. Nature Climate Change. https://doi.org/10.1038/s41558-025-02539-z
