A new study by researchers at Stanford University has found that expanding the use of prescribed fires in California’s conifer forests could significantly reduce harmful wildfire smoke pollution over the long term. According to the research published in the journal Science treating around 500,000 acres of forest annually with controlled burns could lower dangerous smoke pollution by approximately 10% over a decade and by as much as 20–25% during the state’s worst wildfire years.
The findings come as California continues to battle increasingly severe wildfire seasons fueled by climate change prolonged droughts and decades of fire suppression policies. Researchers Ivan Higuera Mendieta and Marshall Burke analyzed two decades of wildfire and smoke data and discovered that low severity fires dramatically reduce the likelihood of future extreme wildfires.
Controlled Burns Reduce Future Fire Risk for Up to a Decade
The study found that areas affected by low-severity fires experienced an immediate 92% reduction in the risk of very severe wildfires. These benefits lasted for as long as ten years and extended up to five kilometers beyond the areas directly treated.
Scientists explained that prescribed fires mimic the natural fire cycles that historically maintained healthier forests. By removing accumulated vegetation and combustible materials under controlled conditions, these burns can prevent the development of catastrophic wildfires later.
Researchers noted that smoke pollution from prescribed burns initially increases air pollution levels. However, the long term benefits outweigh the short term impacts. Their modeling suggests that after about four years the reduction in wildfire smoke begins to offset the smoke generated by prescribed burns leading to a net improvement in air quality.
Air Quality Benefits Outweigh Costs of Prescribed Fire
The researchers estimated that prescribed burning 500,000 acres annually would initially increase fine particulate matter (PM2.5) pollution by roughly 50% during years with relatively little wildfire activity. However, sustained treatment would reduce cumulative smoke exposure over time particularly during severe wildfire seasons such as those experienced in 2020 and 2021.
According to the study, every acre treated through prescribed burning delivers air quality benefits that are about five times greater than the pollution costs generated by the controlled burn itself over a ten year period.
The analysis also revealed that conifer forests which cover much of California Sierra Nevada region, showed the greatest benefits. In contrast shrubland ecosystems experienced only short term reductions in wildfire risk.
Researchers acknowledged that the study did not directly calculate health outcomes such as reductions in asthma attacks heart disease or premature deaths. It also did not compare prescribed burns with other forest management approaches, such as mechanical thinning.
The team is now working to link smoke reduction estimates with public health data and identify the most effective locations for future prescribed burning programs. They emphasize that large scale implementation will be necessary if California hopes to substantially reduce wildfire smoke pollution and improve long-term forest resilience.