Fires: Do What We're Told?

Questions Remain about the Efficacy of Plant Removal

December 9, 2008

By Russ L. Hudson

Darren Sandquist

The recent Triangle wild fire that stretched from Corona to Brea showed why energetic debate continues in scientific, firefighting and environmental circles over the landscaping vegetation that best protects homes during a fire. Some homes burned in spite of cleared areas and low-growing, water-fat landscaping around them, while others with trees and shrubs nearby were spared.

Many firefighting agencies' recommend fire prevention strategies that include the use of nonnative, high water-content plantings, and removal of native chaparral from hillsides. On the other hand, many environmental groups strongly caution against wholesale removal of chaparral, arguing that California chaparral plants are needed at property perimeters to block invasion bye non-native species.

Darren Sandquist, associate professor of biological science, questions some of the “common wisdom” on fire retardant landscaping, and cautions against lumping all chaparral species together. For more than 20 years, Sandquist, who holds a doctorate in biology from the University of Utah, has studied native and non-native vegetation in the Southwest and in the drier areas of Hawaii, where the vegetation and fire hazards are similar.

Q: Why do you say there is controversy over the best way to protect structures via landscaping?

A: Well, first, not everything is controversial. Everyone agrees that palm trees are the worst, hands down. The dead fronds catch fire and can sail on the winds for long distances like flying blow torches, spreading the fire very quickly. Fountain grass, popular as landscaping, is also easily ignited and burns hot. And fountain grass is doubly evil because it is highly invasive and can overwhelm native species.

Q: Then what is controversial?

A: Many recommendations for protecting homes stem from techniques that work well in forested areas. Forest fires tend to burn slowly, closer to the ground and with a continuous fire line. And because most forest fires occur at higher elevations, they burn under cooler conditions, usually without winds. A brush fire is a completely different beast. But most of our Southern California fires are brush fires, usually starting at the wildlands-urban interface, where a single mistake — or an arsonist — in a high wind can start a holocaust.

And our most common, and most dangerous, fires are in chaparral and sage-scrub areas, where they burn very differently, and don't act like forest fires at all. The fire line is unpredictable, since flying embers can move the fire hundreds of yards beyond its fireline border in an instant.

Q: What about removing trees and planting succulents within several feet of a home? Won’t that help?

A: A cleared, defensible area of at least 30 feet is recommended around structures, and firefighters do need that when they arrive to be able to do their job. But we’re talking about what helps to protect houses passively, in the absence of firefighters, and there is no single answer.

As we saw in the recent Triangle Fire, embers fly a long way with the winds. Even 10-lane highways were no barrier to the fire's movement. Succulents and other water-rich plants are good at resisting fire, but they are not the fix-all some say. They are certainly better than dry grasses and weeds, but embers can fly right over an agave hedgerow.

Tree removal is one of the issues being debated, and I'd like to see some serious research on that. All trees may not be equally flammable. In fact, Rick Halsey , founder of the California Chaparral Institute, has suggested that some trees might actually help by intercepting flying embers before they reach the house and ignite the eaves. This is still unproven, but it seems reasonable that well-hydrated, fire-resistant trees with dead foliage removed could screen embers. And, if the lower branches are removed, they won't catch fire from burning grasses or weeds below them.

Q: We have been warned to keep native species away from houses because they have flammable resins. Do you agree with that?

A: Well, I have seen "My succulent garden saved my house" articles in the newspaper, and I've seen well-hydrated native plants being trimmed back or cut down because they are considered fire prone. Both of these conclusions are naive.

Some chaparral species are more flammable than others, but each species is different, so making the wholesale statement that "natives are bad, get rid of them" ignores their individual ecology. If chaparral and scrub are universally flammable, then why is it nearly impossible to ignite them in spring in normal years with average rainfall? There are no firestorms in a normal spring, even though there are still sparks, burning cars and downed power lines.

When native plants are removed, nonnative species, especially grasses and weeds, invade. Nonnative species die and dry out every year as part of their natural cycle, providing plenty of ignitable fuel for a fire to start and spread to scrublands. Fire-resistant native species at the outer perimeters of the defensible spaces can help prevent nonnative invasions and the annual fuel deposits they create. If kept healthy and appropriately hydrated, some native species like toyon or sugar bush are not easily ignited. So, although we would all love a simple, one-size-fits-all solution, it's just not realistic.

Q: What would you recommend?

A: I like the suggestion of ring-like landscaping. For example, an outer ring of fire-resistant native plants, which would have the added benefit of keeping nonnative species from invading. Then maybe the taller fire-resistant native shrubs or trees would be next, if there is proof they would do well as ember screens. Then succulents, and a lawn or low-growing, water-rich species like wild strawberry for the cleared defensible space. And be sure to throw the flammable patio furniture into the pool! Residents were asked to do this during the recent fires, and it sounds prudent to me!