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There are decades of conflicting information about
the flammability of native plants. The fear of fire and the
abundance of misinformation about native plants has resulted in
wildlands (and their wildlife) being replaced with more flammable
landscape materials. After 30 years of experience with California
native plants in their natural environment, (and fourteen years as
a firefighter) we have developed a simple method to compare the
flammability of native plants. The experiment is simple, fair, and
repeatable, with relevance for firefighters, designers, and
homeowners.
In a two week period of September of 2005, temperatures were in
the 90's and the humidity was about 30%. Leaves (or clusters as
they were on stem) of various plant species were tested for
ignition times until two numbers were the same within a few
seconds. If after five tries(boring!), numbers were still
divergent, numbers were either listed as a range or averaged if
all over the place. Most plants tested were field grown and had
not been watered all summer (exceptions noted in table below).
Every effort was made to duplicate (or worse) a dry coastal garden
under water rationing.
Garden
watered plants should be considerably harder to ignite if
watered as little as fifteen minutes once every two weeks, BUT,
not always. However, the worst fires I've seen are at the end of a
drought cycle when there is no water to even fight the fire, never
mind water the plants. (For those of you back east, it is similar
to putting the plant in a convection oven set at 130 degrees for a
month.)
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Flame
applied to leaf. Notice it is not bursting into flame.
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If you live in town and have a twenty foot front yard, ignore
this list. This is primarily for those of you in rural residential
areas, at the worst with a poor well, thirty minutes from the
nearest fire engine and are gone a lot. The designers that are
planning an urban interface should find this useful also.
Using a propane torch with a one centimeter length flame (+/-
1mm), the blue tip of flame was placed on to a leaf, if leaves
large, or first leaf cluster if leaves small, until the leaves
ignited and held a flame longer than five seconds. Some leaves
would flash. If they held a flame or carried to other leaves that
was counted. Some blacked and never ignited, some never even
glowed, and others ignited easily. At first the tests were done on
the plants themselves, but that proved too exciting and the
slightest breeze altered the results (and had potential for even
more excitement). I settled on collecting a few stems of a few
plants and testing those in a closed barn within minutes of
collection. Results were not what I'd had heard or read, and often
not what I expected. Generally, (and boy are there
inconsistencies,) the more drought tolerant the plant, the poorer
it burns, the smaller the leaf, the poorer it burns, and the wider
spaced leaves are very hard to ignite. For the most part,
un-watered natives did better than watered non-natives.
Good
mulch is an important component of California's gardens/landscapes
and ecology. The moisture that mulch retains helps keep the
plant material hydrated and a little less flammable. Mulch
(shredded redwood bark or shredded cedar bark) does burn, and
creeps along with a smoldering fire that can be kicked or raked
out. This type of mulch burns with a lot of smoke, little flame. A
pile of dead leaves, twigs and sticks does not burn in the same
way. Think of the comparison like a newspaper laid flat on the
ground versus each page wadded up into a pile. The worst situation
is when you have flashy fuels like dead grass running up into
either taller weeds, dead leaves of garden plants or some of the
native plants.
This experiment really points out that weed control and garden
hygiene are as important, or more important, than plant choice or
irrigation practices.
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Many
of the leaves never even glowed.