Using forest fires to prevent forest fires

Aug 31, 2015

The United States has a basic and intuitive policy when it comes to forest fires: put them out, and put them out as quickly as possible.

This policy of fire suppression is one the US has followed for over a century. Some scientists, however, are beginning to question this strategy. There is a growing consensus of researchers who believe suppressing forest fires might actually be causing more severe fires, and worsening climate change long-term. 

“Continued fire suppression costs us,” says Scott Stephens, professor of fire science at UC Berkeley, “More and more areas being lost, structures lost. So the equivalent is we continue to do this forever or look for different means, a different trajectory.” 

More than 100 years of fire suppression policy means that today’s forests in the western United States are so clogged with debris — kindling essentially — that fire can easily rip through tens of thousands of acres without running out of fuel.

During catastrophic fires like California's Rim Fire in 2013, thousands of acres of trees can be reduced to ash and embers, Stephens says. It’s unclear whether forests can regenerate on those huge swaths of land. Instead, quick-colonizing bushes, often invasives, can be first to return, claiming the open real estate as their own.

Stephens and many other scientists are looking for a way to change the US’s approach to wildfire management.

They have been studying the effects of un-suppressed forest fires in the Illilouette Creek Basin, a wilderness area in Yosemite National Park. Park managers have been allowing forest fires to burn unsuppressed in this Yellowstone wilderness since the 1970s. Now, after some 40 years of a hands-off approach to the vasin, scientists have noticed a surprising effect.

The fires, which occur about once every seven years, are less severe, and tend to burn themselves out without interference. What’s more, the wilderness region, which used to be a continuous canopy of trees, has now turned into a patchwork of diverse vegetation — forest alternating with wetland.

“Since the continuity [of forest] is so low, when the fire moves it doesn't have the chance to really increase its severity, increase its flame lengths. It hits a discontinuity, goes to the ground, goes over here and goes out. We did one study that if an area had burned nine years previously so the interval between fires was nine years or less, in 95 percent of the time the fire went out at the end of the boundary with no human action,” Stephens says. 

The appearance of wetland in the Illilouette Creek Basin has also changed the hydrology in the region — a sign that smart fire management might also have collateral benefits, like increasing the water budget in the Sierra Nevada mountains.

“[The] mosaic of vegetation is phenomenal and I think that's part of the dynamics of why we're seeing maybe changes of hydrology and also increases of forest resiliency. The forest is really resilient today to fire and climate change,” Stevens says.

Sally Thompson, a professor of surface hydrology at UC Berkeley, has been measuring water content in the newly-grown wetlands. 

“This is normally a dry sort of place. We'd go in and we'd measure water content … and by the time we're at this point in the summer, there's no water left in the soil. But these burned areas, we'd go and measure the water content. There's a water table maybe a couple of feet below the soil's surface and even at the surface the soils are still wet,” Thompson says. 

There is a growing consensus of scientists, researchers, and environmental advocates who, after studying some of these effects, would like to change the US’s approach to fire management. They are beginning to pick out more wilderness areas that can be used to study the effects of unsuppressed wildfires. 

“Most environmentalists in the state really would like to see fire begin to work land more,” Stephens says, “We're not getting forest back, [and] we're basically going to have climate change impacts. So I think it is possible that you could actually get more people interested in this and right now with the plans going forward in California, the three national forests that are head of this are the Sequoia, Sierra and the Inyo, and I think they've actually designated over 50 percent of their land base potentially for fire use and managed wildfire.”

There are still concerns about the effect unsupressed fires could have on local wildlife, and on the health and safety of those exposed to fire risks, but many fire scientists are pressing ahead to convince policy makers to change their approach to forest fire management. 

“What we are going to be advocating when we start putting these results before policy makers is to be thinking very strategically about the regions where this is likely to be useful and feasible. So some of the constraints that really come into play are of, course how, isolated an area is, its proximity to some sensitive set of uses who you just don't want to be exposing to a fire risk. But also issues around air quality,” says Thompson.

“And finally we need to think carefully if water is going to be part of our rationale for thinking about fire management. We need to think strategically about where this is going to have the greatest value, and that's likely to be in places where right now forests are chewing up the largest part of the water balance.”

This story first appeared as an interview on Science Friday with Ira Flatow.