Prescribed fire isn't a smoke solution—but it's still essential

Across the Western U.S., communities are increasingly feeling the impacts of extreme wildfire. A century of fire suppression, combined with hotter and drier summers, has left many forests overloaded with fuel and primed for severe burns. These wildfires can cause major damage to communities, both from the flames and from smoke up to thousands of miles away.

Restoring forests to the fire-adapted conditions they once had — where frequent, low-intensity surface fires cleared fuels while many mature trees survived — is a shared goal of public land managers, conservationists, and tribes.

Prescribed fire is an essential tool to achieve that vision. Ecological forest restoration — often involving thinning to reduce fuels followed by prescribed fire — makes forests more resilient to wildfire and other disturbances. When wildfire does move through these restored areas, it typically burns less severely, and firefighters can manage it more safely, helping protect nearby communities.

But fire affects communities in another way: smoke. Fine particulate matter (PM2.5) from fires is linked to increased mortality, worsened respiratory conditions, and increased rates of heart attacks, even at low concentrations.

As smoke seasons worsen, prescribed fire has increasingly been promoted as a strategy to reduce these future smoke impacts. The idea seems straightforward — accept a little smoke now to avoid much more smoke later — especially given prescribed fire’s other well-documented ecological and cultural benefits.

When I began studying the problem as a fire ecologist, I assumed the prevailing wisdom: that prescribed fire would avoid more wildfire smoke than it creates itself. But we’re finding something different.

The issue is that even though wildfires are becoming more extreme, they remain rare at any given place. Only about 15% of prescribed fire treatments ever encounter a subsequent wildfire, and we can’t reliably predict where those encounters will occur. As a result, to get some treatments that interact with wildfire, we inevitably must treat much more area that will never be used in a wildfire.

This doesn’t diminish the value of prescribed fire. Many of its benefits — increasing biodiversity, improving resistance to drought and disease, and providing “insurance” against extreme wildfire — occur whether or not a treatment later burns. Smoke benefits are the exception: the benefits only occur if a treatment later interacts with wildfire, but the costs — smoke from the prescribed fire itself — happen every time.

We analyzed the conditions under which prescribed fire could produce a net smoke benefit, focusing on the chance a treatment is hit by wildfire, the reduction in wildfire smoke when treated areas burn, and the likelihood that treatments help stop or slow wildfire.

What we found is that in most places in the U.S. and globally, prescribed fire emits more smoke than it avoids. Even though treated areas that later burn certainly have reduced wildfire smoke, this reduction is generally far offset by smoke from the prescribed burns themselves. On average, every ton of prescribed fire smoke only avoids ~0.1 tons of wildfire smoke. 

Prescribed fire increases total emissions but reduces the risk of extreme smoke events. It’s like car insurance: the premiums (prescribed fires) are certain, while the claims (reduced wildfire smoke) only pay out if a wildfire hits a treated area. Like insurance, prescribed fire is essential, but we shouldn’t expect to get back more in claims than we pay in premiums.

This metaphor also clarifies why some earlier studies concluded that prescribed fire could reduce overall smoke. Many studies effectively left out the premiums by not counting the guaranteed smoke from prescribed burns, or assumed every car would crash by treating every prescribed fire as if it would later encounter a wildfire. Both assumptions inflate the expected smoke benefit of prescribed fire.

Some places do have the right combination of factors for net smoke reductions: areas with high encounter rates, where prescribed burns emit very little smoke relative to a wildfire, or where treatments are unusually effective at reducing subsequent wildfire emissions. Highly fire-frequent savannas in Australia and Brazil are examples. A key next step is to identify which locations in the U.S. and globally have the greatest potential for net smoke reductions from prescribed fire. For most forested landscapes, however, our results suggest that earlier claims of net reductions are likely overstated.

While prescribed fires generally add more smoke than they avoid, it’s possible they can still reduce the human health impacts from smoke. Wildfire smoke tends to rise higher, travel farther, and more often reach large population centers. Prescribed fires, by contrast, produce smoke under controlled and predictable conditions. When communities know a prescribed burn is planned, they can take proactive steps to reduce smoke exposure, for example by investing in portable air cleaners or creating community clean air spaces.

These differences suggest that prescribed fire smoke may have a lower health impact per unit of emissions than wildfire smoke — an important uncertainty that future research must resolve. If that proves true, prescribed fire could reduce health risk even while increasing total smoke emissions.

Our findings don’t argue against prescribed fire. Instead, they suggest that using it for smoke-reduction benefits may be justifying it for the wrong reason. Prescribed fire provides many well-established cultural and ecological benefits, including reducing fuel, ensuring firefighter safety, helping keep communities safe from severe wildfire, and increasing biodiversity. Our research shows that although prescribed fire remains a critical tool, it’s not a silver bullet.

Regardless of the smoke tradeoffs, prescribed fire remains essential for forest and fire management. The question may no longer be whether prescribed fire reduces smoke overall, but how can we maximize the other proven benefits of prescribed fire while minimizing its risks. Finding the answer to that question will be ever more important in an increasingly fire-prone world.

Dive into the nuances and data at the article here: https://www.pnas.org/cgi/doi/10.1073/pnas.2613722123