Wildfire impacts are evolving due to climate change, but in what ways?

As the peak summer fire season of 2023 progressed from June through August, Canadian wildfires had already consumed over 25 million acres of land, affecting millions of lives. The fires extended beyond the typical boundaries of western Canada, spreading as far as Nova Scotia in the east. 

This development garnered renewed attention as the smoke reached densely populated areas, casting an orange hue over the New York City skyline and even drifting across the Atlantic to Europe by late June.

Although wildfires have been a longstanding natural force shaping the environment, their frequency, range, and intensity have recently increased due to climate change. 

At the Oak Ridge National Laboratory of the Department of Energy (ORNL), scientists are actively engaged in multiple initiatives aimed at comprehending and forecasting wildfire impacts, along with their implications for the carbon cycle and biodiversity. 

The role of forest thinning in controlling wildfires

In one of these projects, Henriette “Yetta” Jager, a scientist at ORNL working at the intersection of energy and ecology, has delved into the potential of selective forest thinning. This practice not only reduces fuel for wildfires but also yields plant material suitable for conversion into biofuels.

“It’s a multifaceted subject,” Jager explained. “Research indicates that although removing undergrowth and thinning trees might be challenging in certain roadless zones, allowing untouched old-growth forests to remain untouched could lead to more harm than good. Allowing fuel buildup in such areas could result in larger, more extensive fires with greater long-term consequences, especially for vulnerable species like spotted owls.”

Jager and her colleagues have developed a framework to support decision-making related to forest-thinning strategies, landscape patterns, and even spatial firefighting approaches. The outcomes of their work could play a pivotal role in safeguarding terrestrial and aquatic species that require safe passage away from wildfires and subsequent return.

While wildfires are a natural part of ecosystems, their impact is evolving due to climate change. “Wildfire disturbance is inherent to nature, and species have adapted to it. However, our current situation is different due to climate change. There will be significant shifts in the timing, size, and severity of these fires, leading to corresponding alterations in vegetation and new impacts on animal species. By continuing our research, we can aid forest managers in preparing for these changes.”

Insights from the carbon-rich Arctic tundra

Another ORNL scientist, Fernanda Santos, an expert in Fire Ecology, has recently examined not only individual fire events but also repeated wildfires spanning decades to clarify the implications of these fires for the land’s capacity to sequester carbon. 

Moreover, since the world’s soils house over three gigatons of carbon – three times the amount in the atmosphere – and around 70 percent of the uppermost soil layer has encountered fire at some point, Santos has also investigated how fires can contribute to carbon emissions, potentially exacerbating the warming cycle.

Her recent research – including a study published in the journal Functional Ecology – sheds new light on the emerging transformations of the landscape as it evolves in response to fire. 

“Many associate evolution with changes occurring over centuries,” Santos noted. “However, the concept of rapid evolution, including the swift adaptation of plants and soil microbiomes to increased fires, is relatively recent. Will repeated fires lead to higher or lower biodiversity? Ultimately, we seek to understand how fire influences these environments, including below the surface.”

Wildfire impacts on plant diversity 

Wildfires impact plant traits, as well as the diversity and function of microorganisms in and around the soil. These factors can alter plant and soil quality. For instance, changes in wildfire patterns due to a warmer climate, such as increased recurrence and severity, have been shown to expedite the transition from tree-dominated to shrub-dominated ecosystems. 

Moreover, fire-driven evolutionary forces manifest in the selection of plants with traits like thicker bark, rapid germination, and resprouting, leading to reduced plant diversity.

According to the scientists, further research on how fires impact plant-fungal interactions in forests are needed, since more severe and frequent wildfires might also disrupt the sensory cues that animals, including insects, pollinators, and herbivores, typically rely on to evade fire, potentially introducing additional consequences for biodiversity in a changing climate.

Within ORNL, Santos is engaged in projects such as the DOE Next-Generation Ecosystem Experiments Arctic (NGEE Arctic). Through experiments and data collection, she aims to enhance our understanding of the changes unfolding in Arctic ecosystems.

Santos focuses on disturbance ecology, investigating the implications of events such as wildfires and pest outbreaks for the environment and future climate feedback loops by analyzing the organic and inorganic chemistry of the Arctic topsoil, which acts as insulation for the carbon-rich permafrost layer.

Enhancing large-scale climate simulations

In addition, Santos is also contributing to the refinement of large-scale simulations of Earth’s climate, such as the DOE’s Energy Exascale Earth System Model (E3SM). Her efforts involve ensuring that these simulations accurately represent various forms of carbon resulting from wildfires, including charred biomass like soot and charcoal. 

E3SM, supported by the DOE Office of Science’s Biological and Environmental Research Program and spanning multiple national labs, including ORNL, operates on some of the world’s most powerful supercomputers and delivers advanced simulations to better predict environmental shifts that could impact the energy sector.

The success of all these endeavors hinges on the quality and quantity of observational and experimental data. To enhance datasets related to wildfires, Santos and her ORNL colleague Jiafu Mao have initiated a Fire Community Database Network.

This initiative encourages scientists and land managers to contribute environmental data from fire-affected areas to a centralized repository. As the scientists emphasized, sharing such information not only advances research but also informs land management strategies.

Finally, wildfires not only consume plant and tree biomass but can also release carbon that has been sequestered in soils for extended periods, even centuries. 

“Our work in the Arctic focuses on gaining a deeper understanding of what might transpire in these carbon-rich soils of higher latitudes, such as Alaska and Canada. We model and predict the land carbon cycle, and my focus is on reducing uncertainty in these models through historical fire data collected from the field,” Santos concluded.

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