After nearly a century of fire suppression, it turns out Smokey
the Bear was wrong ““ we should not be preventing forest fire
On the contrary, science advocates fighting fire with fire
““ using intentional, controlled burning as a method of
Controlled burns, also known as “prescribed
burning,” target the dead vegetation, litter and small trees
that clog forest floors and serve as fuel for wildfire.
A preventive measure pioneered by UC Berkeley 50 years ago,
controlled burns are directed at specific areas of over-dense
forest, and at acres of dry, dead chaparral as well.
“Without natural fires, forests get super dense, litter
builds up and causes entire trees to ignite,” said geography
professor Thomas Gillespie. “In healthy forests, fires would
burn along the forest floor like a cigarette; entire trees would
not be destroyed.”
In these overgrown forests that have gone unburned for over 75
years, fires move much faster and burn hotter, destroying whole
trees and their roots below.
Lake Arrowhead, one of California’s densest natural
forests, is particularly at risk. Residential opposition to fire,
whether natural or prescribed, has left the mountain clogged with
excess trees and ground litter.
Bark beetles, native insects which burrow into trees, have
worsened the problem in this area, leaving acres of dead and dying
trees which can ignite quickly and fuel wildfire.
“In order to see change, we need to open the forests. This
will slow down the fires,” said Hartmut Walter, professor of
High intensity crown fires, such as the ones which hit San
Bernardino Mountains last week, can be prevented by reducing ground
fuel and the small trees or “ladders” that lift flames
into the tree canopy.
Prescribed burns, though costly and extensive, seem to be the
most effective method for brush and slash removal.
Controlling a burn is a dangerous process, and a series of
conditions must be met in order to effectively execute and maintain
“In Southern California, there are as few as 50 days a
year that you can even start a burn. You need to involve variables
such as humidity, temperature, wind level and smog level,”
Ideal weather conditions include humidity levels between 25 and
50 percent and a temperature of at least 68 degrees Fahrenheit.
Burns are most frequent during early to late spring.
Burn crews consist of trained firefighters and a burn boss, or
fire leader. Engines, dozers, fire shelters and mobile
communication devices constitute necessary safety and control
Desirable burn sites include natural firebreaks, such as roads
or streams, across which fire cannot pass. Crews further outline
sites, using bulldozers to mow firebreaks, and burning strips of
ground to act as boundary or “back” lines.
Burn teams cross the site in carefully mapped out patterns,
using diesel-filled drip torches that burn with a steady flame,
creating a mosaic of controlled fire.
With a back fire set advancing into the wind, a head fire is
directed towards the burn. When the two fires meet, a lack of fuel
causes them to extinguish each other.
Firefighters are then left to clear the burn unit of any
remaining flames or smoke.
Ideally, controlled burning should be used to create fire
barriers around neighborhoods and structures. Residential
opposition to increased levels of smoke and ash, however, are often
counteractive to this initiative.
Controlled burns are most effective when used in open areas to
combat excessive brush. The fires that destroyed much of Simi
Valley and San Diego County last week are attributed to such an
overgrowth in chaparral, and could have been prevented.
Another method of fire prevention is forest thinning, the
mechanical removal of trees.
Preventive measures such as controlled burning and forest
thinning are supported by institutions such the Healthy Forest
Initiative and the National Fire Plan.