Unique field study shows how climate change affects fire-impacted forests

The team during field work in northern Sweden.

ImageGeerte Fälthammar-de Jong

The boreal forests form a single biome that spans the entire Northern Hemisphere. These forests play a key role in the global climate system by absorbing carbon dioxide from the atmosphere. Increasing forest fires, in the wake of climate change, threaten to undermine this ecosystem service.

In the aftermath of the summer 2018 forest fires in Sweden, a team of researchers began the most extensive field campaign ever performed in boreal forests to study how the fires affected 50 forests spread across the country.

“Many studies on wildfires have focused on just one fire, often an unusually severe one. So the approach taken potentially gives a better overview of the natural range in fire impacts in boreal forests,” says Professor Daniel Metcalfe, Umeå University, who supervised the doctoral project.

The researchers found that climate change may reduce the ability of burnt forests to absorb carbon after a fire.

“Many of the old trees remain, but some of their important functions appear to be weakened,” explains Johan Eckdahl, a physical geographer at Lund University.

After a forest fire, root systems are weakened, and trees risk falling.

ImageJulia Iwan

The study shows that regrowth after a fire is influenced by the climate-sensitive partnership between plants and soil microbes. As the climate changes, the carbon storing function of this interaction is weakened because of a mismatch between the adaptive capacities of plants and microbes. Namely, the current northward migration of fast-growing, warmth-adapted plant species might not pace increasing rates of microbial decomposition under escalating growing season temperatures. 

“During global warming, plant species migration is a necessary process to maintain biodiversity and ecosystem services. If it does not keep pace with climate change, the ability of Sweden’s boreal forests to function as effective carbon sinks will be compromised,” says Johan Eckdahl.

The boreal region, also known as the taiga, serves as an immense global carbon reservoir. Research shows that the boreal region may experience greatly reduced carbon storage capacity in the coming century due to climate change and increased wildfire activity, reducing its traditional role as an absorber of greenhouse gases. A better understanding of the response of boreal forests to external influences is essential in predicting their resilience to climate change and the increased frequency of forest fires.