Ecologist Michelle Mack Advocates For Forest-Based Solutions to Curb Wildfire Emissions

Targeted firefighting and planting fewer flammable trees could help slow a cycle of warming and worsening wildfires in North America’s boreal forest, Northern Arizona University ecologist Michelle Mack said at a Thursday talk.

Mack said high northern latitudes are warming three to four times faster than the rest of the planet, bringing more lightning and drought that dry out fuels. When those fuels burn, they release carbon into the atmosphere, which drives further warming.

Mack leads the Bonanza Creek Long-Term Ecological Research Program in interior Alaska. She delivered this year’s Charles Bullard Lecture, an annual series on forests and climate change hosted in partnership with the Harvard University Center for the Environment at the Salata Institute for Climate and Sustainability.

Fires in the western North American boreal are burning about 0.3 million more hectares each year, Mack said, a faster pace than in the first half of the 20th century. The trend peaked in 2023 with the biggest fire year on record for boreal North America, when fires burned an area comparable to all of New England.

“This is a direct positive feedback to warming, because it increases the concentration of greenhouse gases,” Mack said.

Most of the carbon at stake is underground. Mack said about 90 percent of combustion emissions in the forests she studies come from the thick organic soil layer. Permafrost soils hold roughly 10 times as much carbon as boreal trees.

As fires burn deeper, they are reaching “legacy carbon,” older soil carbon that survived previous fires. Mack’s research found that forests reburning within about 60 years were losing that old carbon.

“Combustion of legacy carbon indicates that ecosystems are experiencing more severe disturbance than they’ve experienced in the past,” she said.

But Mack warned that despite their immediate effects, wildfires can sometimes be a net positive towards reducing carbon emissions. They can create space for deciduous trees to grow in place of the trees originally inhabiting the environment.

“We found that that early movement towards deciduous dominance and higher productivity trees persisted throughout the season,” Mack said. “Even though the sites that transitioned to deciduous dominance lost more carbon during fire, they accumulated more carbon after fire.”

Mack said scientists could use what they have learned about how forests recover from fire to design forests better suited to a warming climate.

“We could harvest these ecological characteristics of deciduous trees to create living fuel breaks, low flammability forests that protect carbon, but also provide the ecosystem services of the forest,” Mack said. “These forests could support co-evolved benefits beyond wildfire risk reduction. They could support subsistence food, areas, moose habitat, recreational spaces.”

Still, Mack emphasized that the most effective way to keep wildfire carbon out of the atmosphere is to stop fires early, before they can spread.

“The best approach is keeping carbon in the ground to target fire suppression. It’s probably the most ready application,” Mack said. “It keeps carbon out of the atmosphere longer.”