Smokey Bear. Photo credit: National Agricultural Library.

What’s the first thing that comes to mind when you think of fire prevention? For many, it may be the stern face of Smokey Bear, one paw pointed at the viewer: ONLY YOU CAN PREVENT FOREST FIRES. Smokey’s right: 90% of wildfires are started by humans, and the most damaging ones often spark by accident, so yes, simply preventing  fires from starting is crucial.

What Smokey doesn’t tell you, though, is that forests are not naturally fire-free. The most powerful tool we have to prevent destructive fire is… fire.

But not all fire is the same.  The wildfires that make the news are high-intensity fires, which reach the crowns of tall trees and burn hot enough that they sear right through to a tree’s core. Old, strong trees – the pillars of the forest ecosystem – often die, which leads to a serious, long-term reduction in biodiversity and ecosystem health.

Low-intensity fires, on the other hand, burn near the ground and maintain a moderate temperature. They often only burn low grasses, shrubs, and deadwood, sparing older trees that are protected by their thick outer bark.

A low-intensity controlled burn in vs. the aftermath of a high-severity burn. Top image: a controlled burn in Coconino National Forest, AZ, 2014. Photo credit: Coconino National Forest. Bottom image: flyover of the Delta Fire in Shasta-Trinity National Park, CA, 2018. Photo credit: Julie Nelson.

Across the Western US, high-intensity wildfires are on the rise. They are occurring more often and burning more land. Additionally, many forests are now suffering drought and accumulating large amounts of fire fuels like deadwood and low vegetation, which add to the risk of severe fires.

Why have carefully managed public forests ended up in such a dire situation, and how can they be better? A recent study by Cansler et al. used mapping and statistical analysis to measure the effectiveness of different fire prevention treatments.

As Cansler et al. explain, the main method of fire prevention in the Western U.S. since European colonization has been “fire exclusion.” They thought that total prevention of forest fire was the best way to conserve forests. What foresters didn’t realize is that “pristine” low- and mid-elevation forests actually burned regularly for millennia: indigenous peoples all over the Americas have used controlled burns to actively manage forests for thousands of years, and continue to do so today. Controlled burns are carefully managed to reduce future fire risk. These forests, made up of a mix of pines and firs, once burned very frequently – just at a much lower severity than they do now.

But when settlers arrived in the West, the practice of controlled burning was outlawed. Native Americans were displaced from their land by force or legal enclosure, religious ceremonies were banned, and Native people were arrested for attempting to practice cultural burning in areas where they had historically maintained plant health. In some areas, bounties were even placed on Native peoples who were living in their ancestral territory.

As this 2020 article explains, many indigenous tribes still practice intentional burning – not only for the purpose of fire management, but to maintain the health of plants such as the three-leaf sumac, which is used by the Mono people to make baskets and grows longer and stronger branches after being burnt, and to keep cultural practices alive. Keith Turner of the North Fork Mono explains, “A cultural burn is very spiritual. . .  I used to fight fire for the Forest Service. And it was all about fighting fire.”

A firefighter builds a controlled burn in Kings Canyon National Park, CA. Photo credit: National Park Service.

Western foresters are finally catching up to the value of controlled burns. Cansler et al.’s research shows that the ability of controlled burns to prevent high-intensity fire is unmatched.

What the researchers found was this: for sixteen years after the last fire, the risk of a reburn is much lower, because the forest composition changes to include more fire-resistant species and more open canopy structure.

In mixed-conifer forests that historically experienced low severity fires, performing prescribed burns regularly, roughly every fifteen years, can prevent more severe wildfires.

Because of the vegetation change and fuel buildup that has occurred since colonization, however, they can be hard to control. They can also worsen drought conditions and temporarily decrease the biodiversity of a forest. In addition, burning over and over again takes a lot of money, manpower, and time.

Many forests throughout the US are already involving controlled fire in their fire-management  plans. The USDA released a 10-year plan for wildfire management, in which controlled burning plays a central role. The key now is to increase the scale and funding of burning programs, so that they can be done more regularly and effectively.

Osceola National Forest, in Florida, has ramped up its use of prescribed burns over the past 20 years.  Now, some areas are re-burned every year.  It has seen native species thrive and ecosystems return to their historical composition and the prevalence of severe fires go down as a result.

New technology is also helping improve fire prevention: a supercomputing lab at the University of California, San Diego recently built a program called WIFIRE that it can use to predict fire behavior by modeling an area’s topography, wind patterns, and vegetation.

Though US land managers have historically feared to use fire as a tool, current research proves that it’s not something to fear; rather, it is the single most powerful tool to prevent fire. With the implementation of increased funding, modeling of fire behavior and forest health, and leadership by indigenous people, prescribed burning has the potential to return long-unburned forests to a sustainable equilibrium and protect their future.