Research helps California forest managers assess smoke risks from prescribed burns

Across the American West, managers of fire-prone landscapes are increasingly resorting to a practice that seems counterintuitive: starting small fires to prevent larger, more destructive ones. Commonly called “prescribed burns,” these targeted, controlled fires keep forests healthy by reducing the buildup of grasses, leaves, branches and other debris that can fuel larger wildfires and smoke out communities. neighbors.

But smoke from prescribed burns also poses health risks. Today’s forest managers must ask themselves: How excessive is prescribed burning? When do the long-term benefits of fuel reduction no longer outweigh the short-term smoke costs? And how can neighboring communities better prepare for a fire season?

An international team led by University of Washington researchers has developed a framework to help land managers assess the air quality implications of land management scenarios with varying levels of prescribed burning. To apply this framework, researchers linked a series of models that estimate the effects of smoke from different levels of prescribed burning on neighboring ecosystems and communities.

After using these models to estimate smoke produced under six different levels of prescribed burning in California’s Central Sierra range, the researchers found that moderate burning would reduce overall smoke levels. All tested levels of prescribed burns led to an overall decrease in wildfire smoke. But more prescribed burning could pose notable health risks.

The researchers reported their findings, specific to the Central Sierra landscape, in two papers. The first, published on December 27 in Sustainability of nature, estimated the impact of different levels of prescribed burning on the total amount of smoke produced during an average wildfire season. The second, published on January 16 in Environmental Research Lettersanalyzed the impacts on outdoor agricultural workers in the region.

“We haven’t previously had a good way to quantify this trade-off in smoke exposure because of the challenges of integrating data and methods across sectors,” said former PhD student Claire Schollaert. from the UW Department of Environmental and Occupational Health Sciences and lead author on both papers. She is now a postdoctoral researcher at UCLA.

“We know that if we can reduce fuel density, wildfires could be less severe when they start. Emissions may also be lower, and therefore subsequent smoke exposure and health impacts will be less. We also have to consider where and when they occur. Prescribed burns are planned, which is not the case for wildfires. That’s the concept. But I think that communicating to this subject was previously difficult.

“The cool thing about this work is that we were finally able to quantify the trade-off between wildfire risk reduction and its impacts on human health through prescribed burning on a local scale.”

The researchers focused on the Tahoe Central Sierra Initiative, a 2.4 million-acre tract spanning public, private and commercial lands. A consortium of area land managers developed six forest management scenarios with increasing levels of prescribed burning. They ranged from minimal management, with no prescribed burning and limited efforts to reduce excess fuels, to a scenario called Fire++, with approximately 30,000 acres of prescribed burning each year.

These scenarios were fed into a series of models that estimated the amount of smoke generated by wildfires and prescribed burns in each scenario, as well as the health impacts on nearby communities.

Each scenario including prescribed burning under the Tahoe Central Sierra Initiative resulted in a shorter wildfire smoke season, with less overall smoke, than those without prescribed burning. As a result, neighboring communities and outdoor agricultural workers may be exposed to less smoke.

The model predicts that overall smoke levels, measured by concentrations of fine particulate matter (PM_2.5) were lowest with a moderate amount of prescribed burning – a scenario the researchers called simply “Fire.” Scenarios involving larger amounts of combustion (Fire+ and Fire++) produced slightly more total smoke than the moderate scenario.

Schollaert hopes forest managers across the country will replicate these methods to better integrate public health considerations into management planning for their specific landscapes.

“The exact location of that prescribed burning sweet spot is going to vary. But to mitigate extreme wildfire risks, the more you can reduce fire severity, the lower your emissions will generally be,” Schollaert said. “And that sweet spot is also coordination with health agencies, because you can theoretically plan for smoke from prescribed burns. That’s the kind of planning I hope can come from this.”