Protecting Residences From Wildfires


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 
                        Moderate    High     Extreme 
Upslope-25 pct +           30        60       100 
Across slope or O-25 pct   60       100       200 
Downslope-25 pct +        100       200       400 


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.

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.


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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