Predicting Wildfires : CHAPARRAL STUDIES MAY HOLD THE KEY TO PREVENTION

Wildfires may occur without warning, but by monitoring the growth of Southern California’s distinct chaparral plant community, firefighters attempt to predict how (and possibly when) an area will burn. The Los Angeles County Fire Department’s Vegetation Management Program in Pacoima uses vegetation sampling and maps to assess the area’s abundance of chaparral.

Specialists closely watch areas with low moisture readings and sometimes plan prescribed burns to clear dead material.

There are other plant communities in Southern California--including coastal sage scrub, oak woodlands and riparian woodlands--but chaparral dominates.

The area’s unique topography and climate contribute to hazardous fire conditions. Its steep, brushy slopes and narrow canyons make the area a tinderbox when combined with dry weather and hot Santa Ana winds.

Monitoring Fuel Moisture

Plant samples are collected from 17 sites every two weeks, year-round. A single sampler collects the cuttings over three days.

1. Garden clippers are used to cut three-inch stalks.

2. Cuttings are placed in cans. Two cans of cuttings are collected at each site, for a total of 25 to 30 grams--this comes to 75 cuttings of chamise, 25 of ceanothus.

3. Data on cuttings and weather is transferred to charts, to be later used for fuel moisture calculations.

4. Each can is first weighed, and results entered on a chart as “gross weight wet.” A can is put into an oven, and contents are dried at 110-120 degrees Fahrenheit for 16 hours. As foliage bakes, moisture escapes through a hole in the top of the oven. When done, the can is removed and weighed again, and entered on a chart as “gross weight dry.” The sampler also notes the weather condition at each site. A weather kit contains a psychrometer (thermometer for measuring air temperature), a humidity calculator, a wind-measuring tool and compass.

Moisture in Chaparral

The moisture content of chaparral follows a cycle, which roughly coincides with the seasons. Moisture content is highest in the spring, when plants’ growth begins. It remains high as long as there is adequate moisture. By summer and fall, moisture content decreases and remains low until growth occurs again in the spring. Fire danger is highest when fuel moisture is low.

Fire Frequency

The L.A. County Fire Department has been mapping fires since 1919. These maps are used to determine the age of chaparral and estimate when a deadly blaze may occur again. Maps are also used in fighting fires. Burned areas can be used as natural barriers to prevent the spread of fire.

The Chaparral Family

The following are common chaparral plants in Los Angeles-area mountains:

Chamise (Adenostoma fascicula tum)

Has needle-like leaves and white flowers that bloom from April to June.

* Habitat: Dry ridges and brushy slopes below 5,000 feet.

* Fire behavior: Highly flammable. Burns fast due to its high resin content.

Ceanothus (Ceanothus)

Tree-like shrubs with oval leaves and pale blue flowers that bloom from February to May.

* Habitat: Dry slopes of the Santa Monica Mountains below 3,000 feet.

* Fire behavior: Heavier fuel type, slower burning.

Laurel sumac (Rhus laurina)

A tall, leafy evergreen shrub with flowers that remain on the plant when dry.

* Habitat: Dry slopes below 3,000 feet.

* Fire behavior: Contains a greasy substance, igniting quickly.

Black sage (Salvia mellifera)

* Habitat: Dry slopes and grassy hillsides below 2,000 feet.

* Fire behavior: Fast-burning fuel.

Toyon (Heteromeles arbutifolia)

A tree-like evergreen shrub with white flowers that develop into red berries in December.

* Habitat: Common below 4,000 feet.

* Fire behavior: A slower-burning species.

Manzanita (Arctostaphylos)

Two to four feet high, its thick, leathery leaves and reddish bark that peels off are trademark characteristics.

* Habitat: Brushy slopes at medium and low elevations.

* Fire behavior: Slower-burning, ignites after finer fuel.

An Efficient Ecosystem

A. Main Stem

* Roots extend deep into ground--a length about equal to the height of the plant above ground (for example, a five-foot shrub has five-foot-long roots). Roots draw water through cracks in the bedrock.

B. Roots

* Main stem carries nutrients to plant and then back into ground. Plant contains dead material toward the middle, while foliage outside remains green and alive (plant feeds just portion it needs to stay alive).

C. Soil

The deep root system of chaparral stabilizes slopes, controlling erosion and allowing plants to thrive in Southern California’s dry climate. Soil ranges from gravelly to heavy and rocky.

Sources: Los Angeles County Fire Department; “Flowering Plants of the Santa Monica Mountains”; “Roadside Plants of Southern California.”

Researched by JULIE SHEER / Los Angeles Times