Protecting Residences From Wildfires
Landscaping
The proximity of a structure to native vegetation is a
direct measure of the probability of its destruction by
conflagration sooner or later. Flammable roofs and
inadequate brush clearance are by far the most
significant contributors to hazard and their elimination
would provide the most cost-effective prescription
available (table 3 and, fig. 7).
Nonflammable roofs and
brush clearance are not the only protective measures
needed; however, they are the most critical and, if resources are limited, should receive top priority (Alger
1971, Los Angeles County Fire Dep. 1970, Los Angeles
City-County Fire Bd. Inquiry 1971, County Sup. Assoc. Calif. 1966, Howard and others 1973, Wilson 1962).
Total removal of all vegetation for a specified distance from a house is impractical for several reasons.
Not only would the resulting denudation be unsightly
but it would create several other problems (e.g., dust,
erosion). The obvious alternative is suitable landscaping. In its simplest and least expensive form, such landscaping would be essentially the type of treatment given
areas chosen for fuelbreaks in the wildlands. In its most
advanced form it might take the shape of an irrigated
and shaded lawn or an intricately designed planting of
carefully selected fire-resistant or low fuel-volume
plants. In any event, the purpose is the same: to reduce
heavy loadings of vegetative fuels sufficiently far from
the structure to avoid ignition of the building by radiated
heat or direct impingement of flames and to allow
firefighters a place in which to work when it becomes
necessary to save the house 3l (Alger 1971, Los Angeles
County Fire Dep. 1970, Los Angeles County 1973,
Pacific Southwest For. and Range Exp. Stn. 1963, Wilson 1962).
Native Vegetation
The first step in landscaping for fire protection is to
remove flammable native vegetation, which includes
naturalized introduced species (e.g., eucalyptus), for
some distance in all directions from the structure.
California State Law (Section 4291, Public Resources
Code) and ordinances of several local jurisdictions require clearance for 30 feet. A few local ordinances require it for 100 feet, but these laws and ordinances generally do not mean complete denudation of the land.
The key word is "flammable, " usually interpreted to
mean all dead vegetative matter and enough live crowns
to avoid the direct spread of fire from one tree or bush to
another. To complete the job properly, remaining
crowns should be pruned enough to avoid their ignition
by a ground fire
(fig. 8) (Alger 1971, County Sup. Assoc. Calif. 1966, Los Angeles County 1973, Pacific
Southwest For. and Range Exp. Stn. 1963, Green
1977).
Seldom is a 30-foot brush clearance adequate to protect a home from wildfire. California State law recognizes this fact by providing for an extension to 100 feet
upon a finding of necessity by the Director of Forestry.
Likewise several local ordinances in southern California require a minimum clearing of 100 feet. Even these
distances may not be enough. Several fuelbreak planning and design studies on intensity of radiated heat and
on flame lengths under high wind conditions indicate
that 200 feet may be more appropriate under conflagration conditions. Actual brush clearance needs on the
ground cannot be legislated. They are determined by
native fuel loading, slope, expected wind velocity, and
types of building materials to be protected. In certain
situations, a 400-foot clearance may be barely
adequate 3m (County Sup. Assoc. Calif. 1966, Los
Angeles County 1973, Pacific Southwest For. and
Range Exp. Stn. 1963, Natl. Fire Prot. Assoc. 1974,
Task Force on California's Wildland Fire Probl. 1972).
Adequate brush clearance is purely a matter of fire
physics, and has nothing to do with property ownership
or boundaries. Within limits it can be made easier by
positioning the building with adequate set-back from all
property lines. In most subdivisions, even the so-called
ranch subdivisions, however, lot sizes are too small to
allow for up to 400-foot clearance without some of it
being on a neighbor's property. Some local ordinances
take care of this problem up to 100 feet from the building
by declaring any and all flammable native vegetation
within that distance to be a public nuisance and requiring its abatement regardless of ownership. This approach could be extended both in distance and to other
jurisdictions 3n (Los Angeles City-County Fire Bd. inquiry 1971, Task Force on California's Wildland Fire
Probl. 1972, Howard and others 1973).
Any of several methods of vegetation removal maybe
used, depending on cost, timing, final result desired,
topography, and rock outcropping and would include
hand chopping, bulldozing, discing, and burning. Killing
with herbicides does not, in itself, accomplish the purpose. In fact, if the dead plants are not removed, the fire
hazard is increased rather than reduced. Removal by
one of the other methods while the plants are still live is
usually easier (Pacific Southwest For. and Range Exp.
Stn. 1963, Green 1977).
Proposed Standards: Require native vegetation
clearance and thinning, regardless of property ownership, for the following distances from structures:
Direction from Fire hazard severity class
structure:
Moderate High Extreme
feet
Upslope-25 pct + 30 60 100
Across slope or O-25 pct 60 100 200
Downslope-25 pct + 100 200 400
Plantings
In replacing the removed vegetation, keep and augment the benefits of the removal. Planted, as well as
retained, native trees and bushes should be spaced far
enough apart that their crowns will still be separated
when full-grown. They should not overhang the house.
The space between these trees and bushes should be
covered with relatively low-growing and fire-retardant
plants, a greater variety of which exist than is commonly known. On the other hand some common landscape plants are highly flammable and should not be
used. One of the best and easiest to maintain is lawn.
Others include both introduced and native ground covers and small flowering plants. 9
Much research has been done recently on so-called
fire-resistant plants for home, fuelbreak, and roadside
plantings. The research has included both native plants
and introduced ones, the latter coming primarily from
areas of the world with Mediterranean climates (e.g..
Australia, Chile, South Africa, Caucasus Mountains).
Although some plants burn more slowly than others because of high salt, ash, or moisture content, the difference is generally not worth the time and expense of
propagating them. In recent years the focus has, therefore, been on finding plants with low volume and height,
and therefore,, with low heat output, as well as some
degree of fire retardance (Los Angeles County 1973,
Green 1977, Nerd and Countryman 1972, Wilson 1974).
Several plants have desirable attributes of fire retardance, low maintenance requirements, availability and
range of successful plantings. These include white trailing iceplant (Delosperma alba), dwarf aloe (Aloe aristata), shortleaf aloe (Aloe brevifolia), croceum iceplant
(Malephora crocea), crocea (Malephora crocea var purpureo) , creeping Australian saltbush (Atriplex semibaccata), Lippia (Lippia canescens var repens),
and quaking aspen (Populus tremuloides). At least as
many others are equally effective but only in limited
climatic zones. Two others show a good deal of promise
in test plantings but are not yet available on the commercial market: creeping sage (Salvia sonomensis), and
Castlevalley saltbush (Atriplex cuneata). A decorative
plant to be avoided is any species of juniper, even the
prostrate variety, as all species contain a high volatile
oil content and are unusually flammable (Alger 1971,
Los Angeles County 1973, Green 1977, Nerd and
Countryman 1972).
The initial choice and planting of the landscaping
plants does not complete the job. All require a certain
amount of maintenance, both to retain their fire protection effectiveness and to keep them healthy and attractive. Various plants have differing water requirements.
All need weeding, at least until they get well established. Most, including the iceplants, need to have dead
branches and leaves removed periodically. Lawns need
to be mowed (Alger 1971, Los Angeles Times 1978, Los
Angeles County 1973, Pacific Southwest For. and
Range Exp. Stn. 1963, Green 1977).
Proposed Standards: Use only those plants that have
been tested and proved to have significant fire protection qualities.
Irrigation and Sprinkling
Almost any landscape planting for fire protection
purposes will require some irrigation-at least while it
is getting established. The installation of pipes, hose
bibs, and sprinklers should be part of the job. Different
types of plants have different water needs, however,
and thus general area-wide sprinkling should be
avoided. Many of the best plants are similar to chaparral in their low water requirements and can be damaged
or even killed by too much water. Other plants have
fairly high water requirements. The different types
should be separated and each provided with its own
water source (Alger 1971, Orange County Bd. Sup.
1976, Los Angeles County 1973).
It has been suggested that rather than removing the
native vegetation, it be made fireproof by sprinkling or
other form of irrigation. The limited research so far
conducted indicates that this approach will not solve the
home fire protection problem. Large quantities of water
are required to raise significantly the moisture content
of the soil and the live fuels in the summer and fall. And
watering would stimulate growth rates, thereby increasing the quantity of vegetative fuels that then increase
the heat energy released in a fire (Orange County Bd.
Sup. 1976, Los Angeles County 1973, Younger 1974).
Proposed Standards: Design and install irrigation
systems so that plants with differing water requirements
can be irrigated separately on different schedules.
Herbicides
Many chaparral species and some other native
plants are sprouters. Unless the root crowns are removed in the initial clearing process, which may not be
desirable for soil erosion reasons, they will resprout
quickly and profusely. If not controlled they will recapture the site within 2 to 5 years, negating both the clearing and the landscaping. The control of weeds and wild
grasses among plantings must also be considered. Properly prescribed and applied herbicides are often the
most effective and economical means of achieving both
of these objectives (Los Angeles County 1973, Pacific
Southwest For. and Range Exp. Stn. 1963, Green 1977,
Harvey 1974).
Although herbicides are not useful for the initial
clearance of native vegetation, they can help prevent
regrowth and maintain desirable landscaping. They
must, however, be used with considerable caution in
order not to produce undesirable results, i.e., killing
plants which have been planted at much expense in
time, labor, and money. The advice, if not the services,
of farm advisors, agricultural commissioners, and
licensed herbicide applicators should be obtained. In
some cases, alternate means of control may be better,
and might include grazing and browsing by livestock
(horses, sheep, goats), hand chopping or grubbing, and
prescribed burning (Orange County Bd. Sup. 1976,
Pacific Southwest For. and Range Exp. Stn. 1963, Task
Force on California's Wildland Fire Probl. 1972, Green
1977).
Proposed Standards: Use herbicides only as prescribed by persons knowledgeable and qualified in their
use and application.
Fire-Retardant Chemicals
The feasibility of applying fire-retardant chemicals for
conflagration protection purposes to vegetation surrounding a home has not yet been explored thoroughly.
These chemicals, used extensively in wildfire control,
are known to have a fire suppressant effect. They do,
however, have some qualities which make their use for
home fire protection questionable. They are quite expensive. Although they retain their fire retardant qualities after drying, they wash off readily with light
amounts of rain or sprinkling. The old ones are soil
sterilants. The new ones are fertilizers which would
probably promote undesirable as well as desirable
growth. Arguments in their favor are that they would
reduce considerably the heat energy emitted by the
burning of either native or planted vegetation. Used
without the dye included for aerial firefighting, they are
almost colorless when dry and their application would
not alter the appearance of any vegetation significantly.
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