Reducing Wildfire Risk
September 27, 2023
  • Firefighter in field with smoke in the background
    Forester Sarah Collamer stands in a patch of land that had been burned a month earlier in a prescribed fire operation.

    “It’s going really well. We’re getting great consumption, and it’s going quickly.” Sarah Collamer is a Forester at CAL FIRE CZU. She’s in charge of the planning and execution of all prescribed fire in CAL FIRE CZU’s San Mateo Division, encompassing all the State Responsibility Area (SRA) within San Mateo County. Collamer is watching two firefighters use a drip torch to light tall grass on fire while another uses a hose attached to a fire engine to spray water on the flames.

    Within the last few years, in a bid to reduce wildfire risk throughout the county, Collamer and firefighters from both our unit and partnering agencies have successfully executed several prescribed fires, including 20-acres on the field between Filoli Historic House and Garden and Cañada Road. The property is on San Francisco Public Utilities Commission Watershed (SFPUC) land.

    On a positive note, less fire activity this year has given us an opportunity to do more prescribed burning in our unit.  We have more resources available, and conditions are not as volatile as in previous years.

    Since 2021 in San Mateo County, CAL FIRE CZU successfully burned 62-acres of privately-owned land at TomKat Ranch in Pescadero, 20-acres of SFPUC watershed land at Sheep Camp Trail, 5-acres on the face of San Andreas Dam and 3-acres on the face of Pilarcitos Dam. Both dams are maintained by SFPUC.

    On June 30, 2023, firefighters conducted two prescribed fires on bayside San Mateo County, clearing grass from San Andreas Dam and 15-acres of grass from the field next to Filoli.  

    This is quite notable since, due to many factors, there had been no prescribed fire for a number of years in San Mateo County. 

    Firefighter sprays water on fire with firefighters, trees in background
    Firefighters burn grass on a field between Cañada Road & Filoli Historic House & Garden on SFPUC watershed land.

    On July 31, 2023, one month after the first prescribed fire on the field next to Filoli, Collamer and the CZU team burned the remaining unburned 5-acres of grass that wasn’t consumed during the initial operation.

    Guests were able to visit the museum and the gardens while both burns were executed.

    Over the years, the field adjacent to Filoli had become overgrown with medusahead. With intense winter rains, this non-native grass had grown very tall, blocking out light to native species like milkweed which serves as an important monarch butterfly habitat.

    Burning medusahead serves several positive functions. First, it cuts down on the flammable flashy fuels that could help wildfire spread quickly. Secondly, a field free of tall grass could give firefighters a clear area to take a stand against oncoming wildfire. Third, giving the milkweed the chance to thrive creates more habitat options for butterflies.

    Fire Consumes Vegetation
    Prescribed fire consumes invasive weeds in San Mateo County

    The goal of any prescribed fire is to get good consumption. Consumption refers to the amount of vegetation that is burned during the operation. Conditions must be near-perfect and within the prescription of the planned fire.  During the field operation, Collamer noted “The relative humidity is supposed to get up to 90% tonight. We’ll be on site until the fog rolls in. After that, we’ll probably check back in every couple of hours. Once you’re getting above 80% humidity, it’s safe. This fire has been in prescription the whole time. We would not be here if it weren’t.”

    The prescription written and approved for the field prescribed fire called for a relative humidity between 30% to 70%, a temperature between 45° and 80°, and a wind speed between 0 to 10 mph. The grass had to be brown and fully cured.  All the boxes were checked, and the prescribed fire was successfully executed.

    Firefighter in Water Tender
    Kings Mountain Volunteer Fire Brigade Firefighter Apparatus Engineer John Curcio stages Water Tender 56 at the field near Filoli Historic House & Garden.

    Collamer says the ecosystem in San Mateo County is fire dependent. She says, “There has been fire exclusion on the bayside of San Mateo County for decades. It used to be a pretty common practice with the farmers when it was more rural, but because it’s become suburban, there’s been a lot of fire suppression. But that’s obviously what we need for the environment.  It needs disturbance, specifically fire disturbance. A lot of these plants and animals are dependent on that. By bringing back that tool we’re going to be benefitting the ecosystem.”

    She adds, “It’s very challenging in San Mateo County. There’s always a reason not to burn. There’s always fire activity in and outside the region which could be a draw on resources. There is air quality which is very restrictive in the Bay Area because we’re competing with all the industrial air quality problems as well, like cars and dry cleaners. This burn is right in front of a historic museum. They (Filoli) had an art and wine walk this weekend so we have to be cognizant of that as well.”

    Milkweed is disturbance-dependent, which means it relies on periodic disturbances to survive, like fires, windstorms, or farming. In the field next to Filoli, several milkweed plants were observed a month after the first prescribed fire with new green growth.

    Milkweed plant in field
    A milkweed plant on July 31, 2023 shows new green growth after having been burned in a prescribed fire a month earlier.

    Collamer says there are many disturbance-dependent species in San Mateo County including some flowering annuals. “Bare mineral soil is very important of a lot of flowering annuals, so to be able to create that naturally without heavy equipment, you can’t beat it.”

    She adds that planning a prescribed fire is no easy feat. “There are a lot of checks and balances in our system. We have to get permission from the local battalion chief, from the unit operations chief, and from CAL FIRE’s Northern Region.” Northern Region is an administrative unit located in Shasta County responsible for wildfire prevention, firefighting, and resource management throughout the SRA of Northern California and including San Mateo County.

    Collamer hopes to build on the strong work that has taken place within the last few years. She says, “My wish 10 years down the road is that we burn 200 acres annually throughout the county, and that people are used to it and it’s just normalized, and that people say ‘Oh that’s just CAL FIRE. They’re just burning on the watershed again.’”