Is It True That Oaks Survive Fire, and How?

Ah oaks. Yes, they do usually survive most fires. And thank goodness—they are among
my favorite trees. Oaks are not the oldest, widest, largest, or tallest trees, but wherever they
occur, they tend to dominate both in the forest and in scrub land. Oaks cover 1/3 of California’s
33,000,000 acres of forest. That is a lot of acorns!

The genus for oaks is Quercus and is thought to be of Celtic origin meaning “beautiful tree”.
Agreed! The Romans in Ancient Britain must have incorporated that local name into their Latin
language. About 500 species are widespread throughout the temperate northern regions and
range as far south as the equator. But there are no oaks in the Southern Hemisphere. We have
about 22 species in California and at least 10 in the Bay Area. The common tan bark oak is
closely related to Quercus but falls into a different, more primitive genus, Lithocarpus.
The Spaniards noted the difference between evergreen and deciduous oaks. The former they
called encino and the latter, robles. Both thrive in our Mediterranean climate. Due to our mild
winters, encinos do not require complete dormancy to survive the cold and their evergreen leaves
persist for years. Another main attribute of the Mediterranean climate And then there are the
regularly recurring fires of a Mediterranean climate.

In addition to fires started by lightening, Native Californians have been using fire as a
management tool for perhaps 10,000 years. Fire clears out the undergrowth, creating improved
habitat for deer and it facilitates the gathering of acorns—the most important food source for
most California tribes. The fires also free nutrients into the soil, enhancing growing conditions
for the trees. These anthropogenic fires were usually of low intensity and fairly frequent so that
there was not a huge buildup of combustible material, nor much lasting damage to the trees.
As long as fires are not intense infernos, most oaks will survive. They have very thick barks that
are resistant to heat and safeguards the vital cambium layer. Evidence suggests that fire scars
may even help protect the trees from invasive fungus. How? Some oaks develop tyloses. These
are fast growing cells that effectively block off the damaged parts and isolate them. And even if
all the leaves are burned off in a spring fire, they can totally regrow the leaves by summer’s end.
Occasionally a tree is burned completely to the ground, but with the extensive root system still
intact. The next year multiple trunks emerge like a flock of woody Phoenixes rising from the
ashes.

Scrub jays and western gray squirrels are continually caching acorns throughout my yard in
downtown Santa Rosa. Thanks to these widespread critters there’s always a huge reservoir of
potential oak trees below the surface protected from the heat of fires. Fortunately, they forget to
eat many of them, so the seeds are ready and waiting to sprout when the conditions are ideal. An
extensive study in the Sierra foothills covering the last 200 years, showed a clear correlation
between periodic fires and successful establishment of young blue oak saplings.
The Druids were the priestly class of the ancient Celts. Druid literally means the “knower of the
oaks.” In the last hundred years or so there has been a resurgence of tree huggers, regardless of
class. Count me as one of them, Alma! Count me in as a student and a stewarder of these
beautiful trees.

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Skills

Posted on

June 9, 2021