Alix Rogstad Fire Education Specialist
Arizonas population is growing, its urban areas
and its communities in rural areas are rapidly expanding, and people
are building more homes in what was once natural forest, grass and brush
lands. Thus, it is important people know how to correctly landscape
their property to reduce wildfire hazards. Improper landscaping can
greatly increase the risk of structure and property damage from wildfire.
It is a question of when, not if, a wildfire will strike any particular
Creating defensible space around your home is a primary determinant in helping it to survive a wildfire. Defensible space is an area around a structure where fuels and vegetation are treated, cleared or reduced to slow the spread of wildfire towards the structure. It also reduces the chance of a structure fire moving from the building to the surrounding forest. Defensible space provides room for firefighters to do their jobs. Your house is more likely to withstand a wildfire if grasses, brush, trees and other common forest fuels are managed to reduce a fires intensity. If you have not created defensible space around your home, firefighters may bypass your house, choosing to make their stand at a home where their safety is more assured and the chance to successfully protect the structure is greater.
People often resist creating defensible space because they believe
that it will be unattractive, unnatural and sterile-looking. It doesn't
have to be! Wise landowners carefully plan landscaping within the defensible
space. This effort yields a many-fold return of beauty, enjoyment and
added property value.
Arizona has great diversity in climate, geology and vegetation. Home
and cabin sites can be found from the foothills through 8,000-foot elevations.
Such extremes present a challenge in recommending plants. While native
plant materials generally are best, a wide range of species can be grown
successfully in Arizona.
Many plant species are suitable for landscaping in defensible space.
Use restraint and common sense, and pay attention to plant arrangement
and maintenance. It has often been said that how and where you plant
are more important than what you plant. While this is indeed true, given
a choice among plants, choose those that are more resistant to wildfire.
Consider the following factors when planning, designing and planting
the Firewise landscape within your home's defensible space:
During much of the year, grasses ignite easily and burn rapidly. Tall grass will quickly carry fire to your house. Mow grasses low in the inner zones of the defensible space. Keep them short closest to the house and gradually increase height outward from the house, to a maximum of 8 inches. This is particularly important during fall, winter and before green-up in early spring, when grasses are dry, dormant and in a cured fuel condition. In Arizona wildfires can occur any time of the year. Maintenance of the grassy areas around your home is critical. Mow grasses low around the garage, outbuildings, decks, firewood piles, propane tanks, shrubs, and specimen trees with low-growing branches.
Replace bare, weedy or unsightly patches near your home with ground
covers, rock gardens, vegetable gardens and mulches. Ground cover plants
are a good alternative to grass for parts of your defensible space.
They break up the monotony of grass and enhance the beauty of your landscape.
They provide a variety of textures and color and help reduce soil erosion.
Consider ground cover plants for areas where access for mowing or other
maintenance is difficult, on steep slopes and on hot, dry exposures.
Ground cover plants are usually low growing. They are succulent or
have other Firewise characteristics that make them useful, functional
and attractive. When planted in beds surrounded by walkways and paths,
in raised beds or as part of a rock garden, they become an effective
barrier to fire spread. The ideal groundcover plant is one that will
spread, forming a dense mat of roots and foliage that reduces soil erosion
and excludes weeds.
Mulch helps control erosion, conserve moisture and reduce weed growth.
It can be organic (compost, leaf mold, hardwood bark chips, shredded
leaves) or it can be inorganic (gravel, rock, decomposing granite).
When using organic mulches, use just enough to reduce weed and grass growth. Avoid thick layers. When exposed to fire, they tend to smolder and are difficult to extinguish. Likewise, while your property might yield an abundance of needles from your native pines or other conifers, dont use them as mulch because they can readily catch and spread wildfire. Rake, gather and dispose of them often within your defensible space.
Wildflowers bring variety to a landscape and provide color from May until frost. Wildflower beds give a softer, more natural appearance to the otherwise manicured look often resulting from defensible space development.
A concern with wildflowers is the tall, dense areas of available fuel they can form, especially in dormancy. To reduce fire hazard, plant wildflowers in widely separated beds within the defensible space. Do not plant them next to structures unless the beds are frequently watered and weeded and vegetation is promptly removed after the first hard frost. Use gravel walkways, rock retaining walls or irrigated grass areas mowed to a low height to isolate wildflower beds from each other and from other fuels.
Shrubs lend color and variety to the landscape and provide cover and food for wildlife. However, shrubs can add significantly to total fuel loading around a home. The primary concern with shrubs is they can serve as ladder fuel and carry a relatively easy-to-control ground or grass fire into tree crowns. Once a fire reaches into the tops of trees (the crowns) it is difficult, and sometimes impossible, to control (see Figure 2).
To reduce the fire-spreading potential of shrubs, plant only widely separated, low-growing, nonresinous varieties close to structures. Do not plant them directly beneath windows or vents or where they might spread under wooden decks. Do not plant shrubs under tree crowns or use them to screen propane tanks, firewood piles or other flammable materials. Plant shrubs individually or in small clumps apart from each other and away from any trees within the defensible space.
Mow grasses low around shrubs. Prune dead stems from shrubs annually. Remove the lower branches and suckers sprouts from trees to raise the canopy away from possible surface fires.
Trees provide a large amount of available fuel for a fire and can be a significant source of fire brands stems and branches, carried in the smoke column ahead of the main fire rapidly spreading the fire in a phenomenon known as spotting. Radiant heat from burning trees can also ignite nearby shrubs, trees and structures.
Arizonas elevation and temperature extremes limit tree selection. The best species to plant generally are those already growing on or near the site. Others may be planted with careful selection and common sense.
If your site receives enough moisture, plant deciduous trees such as aspen or narrow-leaf cottonwood. These species, even when planted in dense clumps, generally do not burn well, if at all. The greatest problem with these trees is the accumulation of dead leaves in the fall. Remove accumulations close to structures as soon as possible after leaf drop.
When site or available moisture limits recommended species to evergreens, carefully plan their placement. Do not plant trees near structures. Leave plenty of room between trees to allow for their growth. Spacing within the defensible space should be at least 10 feet between the edges of tree crowns. On steep ground, allow even more space between crowns. Plant smaller trees initially on a 20- to 25-foot spacing to allow for tree growth. At some point, you will have to thin your trees to retain proper spacing.
As the trees grow, prune branches to a height of 10 feet above the ground. Do not overprune the crowns. A good rule of thumb is to remove no more than one-third of the live crown of the tree when pruning. Prune existing trees as well as ones you planted.
Some trees tend to keep a full crown. Other trees grown in the open may also exhibit a full growth habit. Limit the number of trees of this type within the defensible space. Prune others as described above and mow grasses around such specimen trees.
When building a deck or patio, use concrete, flagstone or rock instead of wood. These materials do not burn and do not collect flammable debris like the space between planks in wooden decking.
Where appropriate on steeper ground, use retaining walls to reduce the steepness of the slope. This, in turn, reduces the rate of fire spread. Retaining walls also act as physical barriers to fire spread and help deflect heat from the fire upwards and away from structures.
Rock or masonry walls are best, but even wooden tie walls constructed of heavy timbers will work. Put out any fires burning on tie walls after the main fire front passes.
On steep slopes, consider building steps and walkways around structures. This makes access easier for home maintenance and enjoyment. It also serves as a physical barrier to fire spread and increases firefighters speed and safety as they work to defend your home.
A landscape is a dynamic system that constantly grows and changes. Plants considered fire resistant and which have low fuel volumes can lose these characteristics over time. Your landscape, and the plants in it, must be maintained to retain their Firewise properties.
Landscape maintenance is a critical part of your homes defense system. Even the best defensible space can be compromised through lack of maintenance. The old adage An ounce of prevention is worth a pound of cure applies here.
This fact sheet is based on and draws heavily from a publication titled Fire-Resistant Landscaping written by F.C. Dennis and produced by the Colorado State Forest Service. FIREWISE is a multi-agency program that encourages the development of defensible space and the prevention of catastrophic wildfire.
Arizona FIREWISE Communities Cooperators
University of Arizona, Northern Arizona University, Arizona State Land Department, Arizona Fire Chiefs Association, Arizona Community Tree Council, Arizona Fire Districts Association, Arizona Emergency Services Association, Arizona Planning Association, Bureau of Indian Affairs, Bureau of Land Management, Bureau of Reclamation, Inter-Tribal Council of Arizona, National Park Service, USDA Forest Service, USDA Natural Resources Conservation Service, U.S. Fish and Wildlife Service
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.
The University of Arizona College of Agriculture and
Life Sciences is an equal opportunity employer authorized to provide
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and institutions that function without regard to sex, religion, color,
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Any products, services, or organizations that are mentioned, shown, or indirectly implied in this publication do not imply endorsement by The University of Arizona.Document located http://ag.arizona.edu/pubs/natresources/az1291/
Published July 2002
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