To Help Prevent the Next Big Wildfire, Let the Forest Burn

Roughly one-third of the 100 million acres that make up California are covered in forest.

Before Euro-American settlement in the 1800s, fires burned about 1.5 million acres of forest each year, on average, according to an analysis of fire return intervals by Scott Stephens, a professor of fire science at the University of California, Berkeley. Skies were most likely smoky through much of the summer and fall, and most forests in California burned every five to 25 years from wildfires caused by lightning or Native American burning practices, he said.

These small fires benefited the entire forest ecosystem, returning nutrients to the soil by burning old vegetation and encouraging new growth by allowing sunlight to reach the forest floor.

But between 1950 and 1999, fires burned just 57,000 acres on average each year under a sweeping fire-suppression policy. Forests that were once periodically cleared by less intense wildfires are now covered by “thick carpets of forest fuels,” according to a report by the Little Hoover Commission, an independent California oversight agency.

In the past two decades, California has begun to see the consequences. Wildfires are now burning much larger swaths of California each year.

Forests across California have also grown much denser over the past 70 years, partly due to less frequent fires, but also because large, old trees have been harvested by loggers. In their place are numerous young, small trees of species that can tolerate the shade from thicker canopies and are easier to burn because of their thinner bark and slimmer trunks.

Decreasing the amount of fuel available to wildfires requires a combination of practices that remove vegetation, like prescribed fires and the selective removal of smaller trees and mulching.

Stephen Pyne, an environmental historian who studies fire, emphasized that logging would not keep wildfires at bay. “Logging takes the big trunks and leaves the small stuff because there’s no market for it,” he said. “Fire burns the little and leaves the big.”

Making matters more complicated, more than 11 million Californians live in the wildland-urban interface, fire-prone transition zones between unoccupied land and developed areas.

Because the majority of wildfires are caused by human activity, the growth since 1990 of these transition zones is troublesome.

The presence of people in these areas makes it difficult to conduct prescribed burns. It also increases the odds of deadly wildfires starting because of the proximity of buildings and flammable vegetation to ignition sources like sparking power lines, cigarettes and campfires.

Many wildfires in the past decade have occurred in and near the areas where forest meets human development. Approximately 6.9 million acres burned in California wildfires from 2008 to 2017.

Over the same period, there were far fewer prescribed fires, which are intentionally set by fire managers to mimic the natural cycle of wildfire. They burned about 250,000 acres, a conservative estimate according to CalFire, the state agency responsible for fire protection in forests.

Patchwork forest ownership further complicates the application of fire-prevention strategies. State and local governments own only 3 percent of forestland. Federal agencies own 57 percent. Almost 40 percent is owned by private landowners, most of whom own small tracts of land, lack the expertise to conduct prescribed burns and are reluctant to be held liable if the fire gets out of control.

CalFire is seeking to address these challenges by streamlining the permit and planning process and training more personnel to conduct burns.

Researchers like Greg Asner, an ecologist at the Carnegie Institution for Science, are working to understand how the shift toward a hotter, drier climate in California is escalating tinderbox-like conditions and stressing densely packed trees already competing for water.

More than 120 million trees have prematurely died in recent years, according to the Forest Service. Dr. Asner estimated this is a tenth of the state’s trees. The large amount of combustible dead wood increases the risk of severe fire.