Heidi Toth

Aug. 22, 2019

Pools of old carbon in the soil of boreal forests historically safe from combustion are being released by more frequent and larger wildfires, a team led by researchers at Northern Arizona University announced in Nature this week. As the climate of these forests in the Northwest Territories of Canada becomes warmer, drier and prone to more frequent fires, the combustion of “legacy carbon,” as the research team calls it, has the potential to shift the global carbon cycle, as boreal forests that have acted as carbon sinks for millennia become sources of atmospheric carbon.

The research team, which included collaborators from NAU, the government of the Northwest Territories (NWT), four Canadian universities, University of Alaska-Fairbanks and Woods Hole Research Center, found that legacy carbon remained protected from combustion in older stands where the historical fire return interval persisted. But in stands younger than 60 years old, legacy carbon burned.

“In older stands that burn, this carbon is protected by thick organic soils,” said Xanthe Walker, lead author and postdoctoral researcher at the Center for Ecosystem Science and Society (Ecoss) at Northern Arizona University. “But in younger stands that burn, the soil does not have time to re-accumulate after the previous fire, making legacy carbon vulnerable to burning. This pattern could shift boreal forests into a new domain of carbon cycling, where they become a carbon source instead of a sink.”

For Walker and senior author Michelle Mack, who first identified these protected pools of carbon in fire scars in Alaska, a series of mega-fires in the Northwest Territories in 2014 offered an opportunity to ask whether legacy carbon was being combusted, and where.

“These were large and severe fires, and we thought: This is when and where it would burn,” Walker said.

“We know that there is really old carbon in these soils—carbon that is hundreds to thousands of years old, carbon that is irreplaceable,” said Mack, who worked with Walker and NAU collaborators Chris Ebert, Scott Goetz and Ted Schuur on the study. “As high-intensity fires begin to burn these stores, we think of this as ‘mining’ soil carbon. Globally, boreal forests store about one-third of terrestrial carbon, primarily in soils, so transferring that carbon from soil to the atmosphere could be a powerful accelerating feedback to climate warming.”

To ensure they sampled a full spectrum of burned areas, Steve Cumming of Laval University in Quebec identified plots in the burn area with maps derived from remote sensing of forest composition. Then Walker and a large field campaign of researchers and students from Canadian universities hiked into the burn areas to sample the soil at 211 of these plots.

“Carbon accumulates in these soils like tree rings, with the newest carbon at the surface and the oldest carbon at the bottom,” Mack said. “We thought we could use this layering to see how far back in time, in the history of the forest, fires were burning.”

To estimate the age of the carbon in the soil, the team used radiocarbon dating, which measures the abundance of 14C carbon isotope in a sample of soil. Carbon dating allows researchers to measure the amount of 14C and gather clues about how long certain carbon stores have been in the soil. This technique requires a high-precision measurement made by relatively few labs in the world; in early 2020, Ecoss will install a Mini Carbon Dating System at NAU.

In nearly half (45 percent) of the young stands the researchers sampled, legacy carbon burned. And while the amount of legacy C didn’t alter total carbon emitted from these fires, the pattern the researchers identified has global implications for future climate scenarios.

“The frequency of boreal forest fires is projected to increase even more with expected climate warming and drying, and as a result total burned area is expected to increase 130-350 percent by mid-century,” the authors write, expanding the proportion of young forests vulnerable to burning and loss of legacy carbon.

“By defining and analyzing ‘legacy carbon,’ this paper offers a new way to think about long-sequestered carbon stocks in boreal forests and how vulnerable they are to being burned during increasingly frequent and severe wildfires,” said Brendan Rogers, a scientist at Woods Hole Research Center who co-authored the Nature study. “This tool helps us understand when burning goes ‘outside the norm’ from a historical perspective and begins to combust carbon stocks that survived past fires.

“Second, this study further emphasizes why more frequent burning in the boreal forest is bad from a climate perspective.”

“The 2014 wildfires were unlike anything the Northwest Territories had experienced, and after them, the Government of the NWT sought to understand the impacts of extreme wildfire on the lands and people of the NWT so they could better plan and adapt,” said Jennifer Baltzer, a researcher at Wilfrid Laurier University in Ontario and co-author of the Nature study. “This research, with their help and partnership, has really advanced our understanding of these fires and the tremendous impact extreme wildfire years have on globally critical stores of carbon.”

“The good news here is that this landscape in the Northwest Territories is comprised primarily of old forests, and legacy carbon stayed protected there,” said Walker, who earned her PhD. with biologist and co-author Jill Johnstone at the University of Saskatchewan. “Young stands lack accumulated fuel and acted as a kind of fire break. But as the climate continues to warm and grow drier, we may see that change, and young stands may begin to carry fire and threaten legacy carbon.”

This project was a collaborative effort primarily supported by funding awarded to Michelle Mack by the NASA Arctic Boreal Vulnerability Experiment (ABoVE) and a National Science Foundation (NSF) Division of Environmental Biology (DEB) Rapid grant. Additional funding was provided by: Natural Sciences and Engineering Research Council (NSERC) Discovery Grants awarded to Jill Johnstone and Merritt Turetsky; the Northwest Territories Cumulative Impacts Monitoring Program awarded to Jennifer Baltzer; an NSERC postdoctoral fellowship awarded to Nicola Day; and Polar Knowledge, Canada’s Northern Science Training Program awarded to Canadian field assistants. Logistical support was provided by the Government of the Northwest Territories–Wilfrid Laurier University Partnership Agreement.

Above graphic by Victor O. Leshyk, Ecoss

Aug. 15, 2019

When Jaime Yazzie began planning her research for her forestry thesis, her adviser asked her what species of trees she wanted to save. They would use a computer simulation to measure the effects of a warming, drying environment, and she needed to select which trees to preserve.

“I was a little shocked,” Yazzie said. “In my mind, they’re one big family. To lose one would be like losing a sibling.”

Yazzie, who is Diné, took a different approach with her research. Instead of looking at which trees they could keep or lose, she applied her experiences and priorities as a Native American researcher and asked what society could change so the whole forest, in all its interconnectedness of species, land and people, could adapt as their environment changed. It was born out of the Navajo concept of K’é, or kinship, and the belief that people’s relationship to the forest ecosystem was as powerful and necessary to preserve as people’s relationships to each other.

What stemmed from that “light bulb moment” was a research project that combined western science and modeling tools with Indigenous knowledge and bringing voices into a conversation that haven’t always been considered. Yazzie’s research, “Dine kinship as a framework for conserving native tree species in climate change,” was published in July in Ecological Applications. The other authors are forestry professors Peter Fulé, Yeon-Su Kim and Andrew Sánchez Meador.

The idea for this type of study began several years ago when Fulé approached tribes in the Southwest looking for collaborative research efforts. The Navajo (Diné) Nation was one of the interested tribes, and they worked with Fulé to apply for an agroforestry grant from the U.S. Department of Agriculture. Fulé then recruited Native students to lead the research. Yazzie, then a master’s student in the School of Forestry, jumped at the opportunity.

Looking at the scientific methodology, this study looked much like other studies: The team used the Climate-Forest Vegetation Simulator and input data from the most recent Intergovernmental Panel on Climate Change (IPCC) report to determine how forests could be affected based on different climate events and the effects of specific human-led activities to mitigate the effects of those events. But behind the data and simulations, the entire process centered on Indigenous knowledge and beliefs about the forest, such as how the ecosystem affected society, the spiritual value of the forest to the people and what the people owed the forest in terms of responsibility and reciprocity for what the forest had given. It shifted the entire conversation.

“We found that substantial forest loss was inevitable under the warming climate scenarios,” the authors wrote. “The Indigenous principle of respecting nature does promote adaptive management, rather than complacency. The modeling framework allowed us to evaluate the management treatments, including planting, for conserving multiple tree species in mixed conifer forests, thus providing an anchor for biodiversity.”

While the team was doing this climate study, Yazzie and Kim were concurrently running a related project that focused on outreach and education to the tribes. They hosted local meetings with community members living in the Navajo Nation to discuss priorities, share what they were learning and listen to concerns from the tribes, which changed the way they modeled.

That also meant telling the tribal members what they learned. That was a rough day for Yazzie.

“These results are devastating,” she said. “For the tribes, this is devastating. In workshops I held with community members, the response was silence. We had just gone through how valuable this forest is, how meaningful it is; it’s not just that they have a connection to the land now, but the land connected them to their ancestors. It connected them to the next generation, their children, their grandchildren, and many more that are to come. These results just left them shocked.”

They were quiet for a moment, digesting. Then her community members spoke.

“Right away they said, ‘OK, what can we do? What is being done? What is the tribe doing, what are the forest managers doing, what are other tribes doing, what is the Forest Service doing? They were thinking about how we can take this information and use it in order to ensure that there’s something for the next generation.

“That’s one of the amazing things about my community. There are a lot of concerns about changing ecosystems, but all of our teachings, all of our knowledge has principles and concepts for us to apply to teach us how to be adaptable.”

Kim said incorporating these different ideas is critical in science, which scientists are increasingly recognizing. Getting buy-in and being able to make changes will be much easier if these groups are working together, with the same priorities and same information.

“One of the most urgent problems we face with climate change is the disconnect between what we know from science and what we actually do about it,” Kim said. “It is imperative to produce and communicate relevant information with stakeholders—tribal members, in this case—so they can act on it.”

What Yazzie, who is now an NAU employee, is doing is continuing to work with her community to effect positive change on the forest but also to promote the use of Indigenous knowledge in the scientific community. This project showed her how infrequently Indigenous voices are considered in western science and the importance of including those voices.

“My grandpa used to talk about knowledge as a crystal—you can see it from one side, then you turn it and there’s another side. That’s what knowledge is,” she said. “That’s how you learn, that’s how you teach is that we have these multiple sides. I think predominantly western academia places a lot of weight into western science and puts other knowledges at the opposite end. Really, it’s western science and all these other ways of knowing.

“I think there’s just a lack of incorporation of other knowledges. When we’re discussing a huge issue like changing ecosystems, it’s important to see it from all sides.”