For the past 15 years, on an 800-acre nature preserve at Pepperdine, Stephen D. Davis, Pepperdine University distinguished professor of biology, has studied native plants — the chaparral shrubs of this area — and the fire cycles that affect them.
Davis terms the increasing fire cycles and their effect on local vegetation “the most profound effect on the Santa Monica Mountains above Malibu.”
“The normal fire frequency for the Santa Monica Mountains is 20 years or more,” he says. “Every 20 years, you would expect to have a fire. If you look at the fire records, there’s a corridor, or path, where the fire frequency is the highest, and Malibu is in that path.”
Until 1985, the fire frequency for Malibu was every 12 years. With the 1993 and 1996 fires, the frequency is obviously increasing. “The reason it’s increasing is because of humans,” Davis says, with arson and accidents the primary cause of these fires.
Outside of his university classes, Davis offers a very quick, very painless lesson in local botany. He describes two basic types of local chaparral – vigorous sprouters after fire and nonsprouting after fire. “The nonsprouters rely on their seeds germinating after fire to re-establish and recover. In fact, these plants need fire to promote germination.” Heat causes the seed coats to crack, allowing water into the developing embryo.
In Malibu, the nonsprouters are called “mountain lilac,” or more correctly “big- pod ceanothus.” These shrubs are drought tolerant, with hearty leaves and shallow roots, able to fill in open, dry areas.
“If the fire frequency goes up,” he explains, “there’s not enough time for the nonsprouters to produce seed before the next fire. So we’re looking at localized, selective extinction of the nonsprouting species.”
As he reminds us, nature abhors a vacuum. “So something is going to take their place,” he warns. That something is weeds, “mainly grasses — highly flammable, flashy fuels.” These include bromegrass, star thistle, black mustard and wild oats — all Eurasian exotics brought here with livestock. Those weeds worsen the fire frequency. “You can have a fire every year or two,” he suggests. “You’re locked in forever.”
Weeds outcompete and displace natives. “They have a high competitive ability, no natural enemies and they love disturbance. And we humans disturb.”
Remember those vigorous resprouters, the other type of local shrub? Called “laurel sumac,” they have replaced the big-pod ceanothus and are now visible in patches on the hillsides above Malibu. And they are vigorous. “Every one resprouted in the last fire,” reports Davis, and did so within two weeks.
And remember the 20-year normal cycle? Those fires burn “hot,” killing all the weed seeds, which leaves the chaparral to grow freely. With fires occurring every three years, says Davis, the fire is “cool” and weed seeds are not killed, which locks Malibu into this “vicious cycle of vegetation conversion.”
The 1985 fire was preceded by a 1982-83 El Nino season. Even with the 1998 fire season nearing and the landscape searing, Davis is looking at fall 1999 for the big fires. “It’s a matter of probability,” he says, “and the probability is higher.”
When Davis arrived at Pepperdine, the hills were “a velvet continuum of chaparral,” he recalls. Now, they burn more frequently and won’t hold back water or soil.
Today, up Malibu Canyon, the future looks greener. The area has not burned since 1972 and is revegetating, providing what Davis calls goods and services: beauty, cover for wild animals, breeding and nesting grounds, watershed, slope stability and erosion deterrent.
The vegetation and soil filter rainwater, then gradually release the water. “If you don’t have a filter, you have a funnel,” he points out. “Malibu doesn’t need a funnel.”
Davis cautions that he is not a landscape architect, and that he has a bias towards native vegetation, but with that proviso he suggests some simple ways to ward off fire. “Try anything that deters arson and accidental fire. Arson watch. Neighborhood watches. Work with a fire marshal on brush clearance. Plant ornamentals that are fire retardant.”
Malibu’s Native Plant Society may recommend plants, as may local fire departments.
Davis also recommends revegetation projects — “to be done with discretion” — including weeding and planting mixtures of natives and nonnatives (which he says is the new Pepperdine policy). Lawns are fine, mainly because we need them for recreation, he says, but natives should be planted a safe distance from the house to allow a natural fire break.
Even the native plants should be thinned, but save their roots for slope control, he says. Encourage growth of coastal live oaks — “Their trunks are like Styrofoam that insulates against high temperatures” — but don’t let branches touch the roof of the house. Let birds and squirrels nab the acorns for natural replanting elsewhere.
Stephen Davis’ writings may be found on the Internet at www.pepperdine.edu/seaver/natsci/faculty/davis.