Rewetting severe wildfire-affected peatlands may provide an unexpected climate benefit

Wildfires are typically associated with ecosystem destruction, carbon loss, and significant climate impacts. However, new research suggests that they may also leave an unexpected legacy in peat soils.

Researchers from Aarhus University have shown that severe wildfires fundamentally alter peat chemistry and microbial communities, resulting in much lower methane emissions after rewetting than previously expected. The findings challenge a key assumption in peatland restoration.

Normally, methane emissions increase when drained peatlands are rewetted. However, a new study shows that this does not necessarily apply to peatlands that have previously been exposed to severe wildfires.

The researchers found that rewetting heavily burned peat soils reduced methane emissions by more than 90 percent compared with rewetting similar peatlands that had not been affected by fire. At the same time, carbon dioxide (CO₂) emissions remained relatively low.

The study was conducted by Shihao Cui, Haonan Guo, Lorenzo Pugliese, and Shubiao Wu from the Department of Agroecology at Aarhus University as part of the EU-funded Horizon Europe project WetHorizons. The project develops knowledge and solutions to support wetland and peatland restoration across Europe and globally.

Peatlands cover only about three percent of the Earth's land surface, yet they store roughly one-quarter of all carbon contained in soils worldwide. As a result, they play a crucial role in climate mitigation.

When peat soils are drained for agriculture or other land uses, large amounts of CO₂ are released into the atmosphere. Rewetting has therefore become a key instrument in both Danish and European climate policy.

However, rewetting also presents a challenge. The wet conditions promote methane production, and methane is a far more potent greenhouse gas than CO₂ over shorter timescales.

For this reason, the researchers were particularly intrigued by their results. The experiments showed that severe fires fundamentally alter peat chemistry and microbial composition. Following intense heating, carbon becomes more stable and more difficult for microorganisms to decompose. At the same time, populations of methane-producing microbes decline substantially.

As a result, the surge in methane emissions that typically follows rewetting is almost eliminated.

The study comes at a time when wildfires are increasingly dominating headlines around the world.

From Canada to Southern Europe, Scandinavia, and Russia, many regions are experiencing more frequent and extensive fires as a consequence of prolonged droughts and rising temperatures. Researchers point out that drained peatlands are particularly vulnerable because lowered water tables leave peat drier and more susceptible to burning.

The new findings therefore highlight a paradox. Wildfires are generally destructive for ecosystems, climate, and economies. Yet once the damage has occurred, they may leave behind sites where rewetting delivers greater climate benefits than expected.

The researchers emphasize that their findings should not be interpreted as an argument in favor of wildfires. On the contrary, fires release large amounts of carbon and can severely damage ecosystems and livelihoods. However, the study suggests that peatlands previously affected by severe fires may represent particularly promising candidates for rapid restoration once the fire event has occurred.

Although Denmark has not experienced wildfires on the same scale as Canada, Norway, or Southern Europe, the findings are highly relevant to the national discussion on lowland peat soils.

In recent years, Denmark has intensified efforts to retire carbon-rich agricultural peatlands from production and restore them as wetlands in order to reduce greenhouse gas emissions from agriculture. In this context, methane emissions following rewetting remain a crucial consideration.

The study demonstrates that a site's history may have a much greater influence on restoration outcomes than previously assumed. Future restoration strategies may therefore benefit from taking past disturbances such as drought, wildfire, and other environmental changes into account.

The findings also illustrate how climate change, land management, and wetland restoration are interconnected to a much greater extent than is often recognized.

The researchers combined laboratory experiments with global datasets on peatlands and wildfire-affected areas.

Their analysis indicates that targeted rewetting of wildfire-affected peatlands could reduce methane emissions by up to 0.8 million tonnes of CO₂ equivalents annually worldwide. More than 70 percent of this mitigation potential is located in Asia, although significant opportunities also exist in Europe, North America, and Africa.

The study further shows that wildfires affect millions of hectares of peatlands each year.

The researchers stress that the findings are based on controlled experiments and that more long-term field studies are needed to determine how wildfire-affected peatlands evolve after rewetting under natural conditions.

Nevertheless, the results suggest that previous wildfire exposure may be an important factor to consider when prioritizing and designing future restoration projects.

The study contributes new knowledge about how wetlands and carbon-rich soils can be restored most effectively. As climate change increases the risk of droughts and wildfires in many parts of the world, understanding how these disturbances influence nature's capacity to store carbon becomes increasingly important.

The findings indicate that wildfires leave more than visible marks on the landscape. They can also alter biological processes within the soil and thereby influence greenhouse gas emissions after rewetting. This knowledge may prove crucial for how future peatland restoration initiatives are planned and prioritized.

Collaborating institution:
Department of Agroecology, Aarhus University.

Funding:
This study was supported by the European Union's Horizon Europe Programme (WetHorizons, Grant Agreement No. 101056848) and the China Scholarship Council (No. CXXM20220022).

Conflict of interest:
None declared.

Publication:
"Severe wildfire legacies suppress methane emissions after peatland rewetting", published in Environmental Science and Ecotechnology.

Authors:
Shihao Cui, Haonan Guo, Lorenzo Pugliese, and Shubiao Wu.

Contact:
Camilla Brodam Galacho
Communications Advisor
Department of Agroecology, Aarhus University
Tel.: +45 9352 2136
Email: brodam@agro.au.dk