San Diegans know that wildfires can spark out of nowhere. That’s why Cal Fire has an investigative team dedicated to assessing fire vulnerability in the backcountry.
Twice a month from May to October firefighters in Cal Fire’s Pre-Fire/Resource Management Office go out into backcountry areas and report on moisture conditions to try and locate fire fuel.
They look for two types of fuels, live and dead. Live fuels are portions of vegetation that are naturally dry or that have dried out excessively due to heat and drought conditions, but are still alive. The moisture content of live fuel can depend on the plant species, time of year and rainfall, and is one of the biggest factors in the flammability of vegetation.
Once plants get below 65 percent of fuel moisture in the live part of the plant, they are considered “critical” and more likely to catch on fire. Vegetation in San Diego is currently holding in the high 40s to low 50s range, which is 10 percent below its average.
Dead fuels are vegetation that has died over the years but remain in the wild. The moisture content of dead fuels, which is also dependent on weather and rainfall, ranges between 1 and 20 percent.
“Five years of below average rainfall is definitely increasing die-off of our shrubs in the foothills and mountains,” said Eric Just, a Cal Fire forester. “When you have dead fuels, it will give us more of a fire issue.”
According to Just, dead fuels are the primary culprit that carry a fire from one place to another.
In order to get an idea of moisture content in different areas, Just and other members of the investigative team search for a plant called chamise that is found throughout the state. They clip the plant samples and run them through a live fuel moisture analyzer machine.
The machine first weighs the sample and then uses high heat to evaporate the moisture within the sample before weighing it again. The difference in weight equals the percentage of moisture that was in the sample. The results are then logged into a national database allowing firefighters to compare regions and develop a regional understanding of fire threats.
Just says that San Diego County forestland is still recovering from the catastrophic fires of 2003 and 2007, but dead trees do still pose a fire threat. Some Oak trees in the region have come under attack of beetle infestations, which throws another wrinkle in researchers’ efforts to manage fire danger.
Swarms of goldspotted oak borers have engulfed an estimated 75,000 to 95,000 acres of trees in areas surrounding Julian and Ramona.
“As far as affecting fire behavior, whenever you have dead trees, fires are going to burn much hotter and more intensely in those particular areas,” Just said. “When we are fighting a fire, oak woodlands are actually seen as a place where you can expect fire behavior to moderate because oaks are resistant to burning, humidity is higher and there’s not a lot of surface growth, just grass. But if you remove a woodland area and replace it with brush, then you completely alter the fire ecology of that area.”
So whether dead trees are left in the ground or removed, fire threat remains. But according to Just, removing the dead trees can create more danger.
Just says that the shade from the trees keeps vegetation from growing beneath, and if a dead tree is removed it opens space for more brush to grow making an area more susceptible to fire.
On the other side of all the different fire threats, there will always be one constant: preparedness. Property owners should do their best to manage live and dead vegetation on their land and create a defensible space. Other members of the community should stay ready and have a family evacuation plan at all times.