Fighting Wildfires with Brush Clearance? You’re Doing It Wrong

We’re losing homes in wildfires because wind-blown flames from miles away are landing on flammable rooftops, not because of over-grown vegetation. We need to stop blaming fires on plants.

Every spring as birds and wildlife are nesting, Angelenos living in beautiful hillside communities receive notices from the Los Angeles Fire Department (LAFD) with stringent landscape-clearing instructions that were put in place in 1961. Hillside homeowners have to keep clear 200-feet of property around them, referred to as “defensible space”.  Angelenos have not been clearing defensible space of incendiary brush so much as they have been over-cutting, over-pruning or removing landscape plants and trees that would keep the ground cool and moist. This destruction needlessly harms nature and only escalates wildfires, scientists say.  Instead, the focus should shift to securing homes, as well as applying new research that overturns long-standing conventional tactics for outdated fire defense.

Thanks to work by researchers, we now know wiping bare urban landscapes won’t help Angelenos battling the wind-driven wildfires of today:


Clearing Vegetation is Destructive and Increases Fire

When fire management policies commonly used in forests—such as vegetation clearing—are applied to urban landscapes, the results are destructive to the ecosystem and can actually increase fire. Too much landscape clearance in hillside communities only increases the threat to native ecosystem’s continued existence by converting landscapes to invasive grasses that bring more incendiary fuel for fires. Furthermore, brush clearance is typically conducted in the late spring when the ecosystem is the most vulnerable to damage: the plants are growing, the soil is still moist, and many animal species are breeding. Therefore, clearing can cause significant damage to plant growth tissues, destroy native plants and harm wildlife.

Trees help keep the surface cool when their canopy is green. Green understory plants slow down the spread of flames because fire has to drive off the moisture before it will ignite. Time after time, in infernos created by Santa Ana winds, thousands of homes with defensible space burst into flames. In the July 2006 Sawtooth Fire north of Palm Springs, homes with more than 100 feet (30 m) of bare dirt clearance burst into flames (Syphard et al. 2014). 


Focus on Homes and Their Immediate Surroundings to Make Fire-Safe Communities

The most effective way to keep homes from igniting during wildfires is to focus on fire-safety features for homes and the zone right around them, rather than vegetation alteration of the entire landscape. In a comprehensive study of the 2007 Witch Creek Fire in San Diego County, researchers found, “Windblown embers, which can travel one mile or more, were the biggest threat to homes in the Witch Creek Wildfire. There were few, if any, reports of homes burned as a result of direct contact with flames” from plants (IBHS 2008).

In a study examining 700,000 addresses in the Santa Monica Mountains and part of San Diego County, researchers mapped the structures that had burned in those areas between 2001 and 2010, a time of devastating wildfires in the region (Syphard et al. 2012). Nearby vegetation was not a big factor in home destruction. Looking at vegetation growing within roughly half a mile of structures, the authors concluded that the exotic grasses that often sprout in areas cleared of native habitat like chaparral could be more of a fire hazard than the shrubs. “We ironically found that homes that were surrounded mostly by grass actually ended up burning more than homes with trees and shrubs,” Syphard said.

Working only on defensible space is not sufficient. Many homes with adequate defensible space have still burned to the ground because embers have entered through attic vents, ignited flammable materials around the home (litter in the gutter, wood stacks, wood fencing), or found their way under roofing materials (Maranghides and Mell 2009). The solution is to reduce the flammability of the home as much as possible: install ember resistant vents, Class A roofing, exterior sprinklers operated by an independent system, and remove flammable materials 100 feet from around the structure.