  
Creating Defensible Space (Part 2) - March 6, 2002
Jeff Schalau, County Director, Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
This column is a continuation of last week's column on creating defensible space to reduce risk to your home and property associated with wildland fire. Last week we outlined Zones 1, 2, and 3. To review, Zone 1 is a 15-foot band around the home and structures that is completely cleared of flammable vegetation. Zone 2 is the area adjacent to Zone 1 that varies in size and shape according to slope steepness and whether it is uphill or downhill from the home or other structures. A graph showing these relationships is illustrated in February 27, 2002 column on the Backyard Gardener web site (ag.arizona.edu/yavapai/anr/hort/byg/). Zone 3 extends from beyond Zone 2 to the edge of your property.
If your home has non-flammable siding (not wood), then perennials and low growing shrubs can be grown in Zone 1. Under no circumstances should trees be planted in Zone 1. Shrubs should be maintained regularly to remove dead wood and keep away from structures.
The entire area of Zone 2 should be flagged or otherwise delineated prior to start of fuel reduction treatments. Here, multiple decisions must be made based on knowledge of fire behavior, energy contained in the fuel, and the continuity/arrangement of the fuels. Most often, Zone 2 treatments will require some knowledge of proper pruning techniques and personal aesthetics. This is a true blending of art and science. The following recommendations should be followed when creating Zone 2:
- Thin trees and large shrubs so there is at least 10 feet between crowns. Crown separation is measured from the furthest branch of one tree to the nearest branch on the next tree. On steep slopes, allow more space between tree crowns. Remove all ladder fuels (shrubs and low limbs) from under these remaining trees. On large, mature trees, carefully prune limbs up to a height of 10 feet above ground.
- Because Zone 2 forms an aesthetic buffer and provides a transition between zones, it is necessary to blend the requirements for Zones 1 and 3. Thin the inner portions of Zone 2 more heavily than the outer portions. Gradually increase tree density as you approach Zone 3.
- Isolated shrubs may remain, provided they are not under tree crowns. Prune and maintain these plants periodically to maintain vigorous growth. Remove dead stems from trees and shrubs annually.
- Limit the number of dead trees (snags) retained in this area. Wildlife need only one or two snags per acre. Be sure any snags left for wildlife cannot fall onto the house or block access roads or driveways.
- Mow grasses (or remove them with a weed trimmer) as needed through the growing season to keep them low, a maximum of 6 to 8 inches. This is extremely critical in the fall when grasses dry out and cure or in the spring after the snow is gone but before the plants green up.
- Stack firewood and woodpiles uphill or on the same elevation as the structure but at least 30 feet away. Clear and keep away flammable vegetation within 10 feet of these woodpiles. Do not stack wood against your house or on or under your deck, even in winter. Many homes have burned from a woodpile that ignited as the fire passed.
- Locate propane tanks at least 30 feet from any structures, preferably on the same elevation as the house. You don't want the LP container below your house -- if it ignites, the fire would tend to burn uphill. On the other hand, if the tank is above your house and it develops a leak, LP gas will flow downhill into your home. Clear and keep away flammable vegetation within 10 feet of these tanks. Do not screen propane tanks with shrubs or vegetation.
- Dispose of slash (limbs, branches and other woody debris) removed from your trees and shrubs through chipping or by piling and burning. Contact your local Fire Department for information about burning slash piles. Only if neither of these alternatives is possible, lop and scatter slash by cutting it into very small pieces and distributing it over the ground. Avoid heavy accumulations of slash. Make it lay close to the ground to speed decomposition. If desired, no more than two or three small, widely spaced brush piles may be left for wildlife purposes. Locate these towards the outer portions of your defensible space.
While pruning generally is not necessary in Zone 3, it may be a good idea from the standpoint of personal safety to prune trees along trails and fire access roads. Or, if you prefer the aesthetics of a well-manicured landscape, you might prune the entire area. In any case, pruning helps reduce ladder fuels, thus enhancing wildfire safety. Mowing is not necessary in Zone 3.
Landscapes change over time. Trees and shrubs continue to grow, plants die or are damaged, new plants begin to grow, and plants drop their leaves and needles. Like other parts of your home, defensible space requires maintenance. Use the following checklist each year to determine if additional work or maintenance is necessary.
Defensible Space Annual Checklist
- Trees and shrubs are properly thinned and pruned within the defensible space. Slash from the thinning is disposed of.
- Roof and gutters are clear of debris.
- Branches overhanging the roof and chimney are removed.
- Chimney screens are in place and in good condition.
- Grass and weeds are mowed to a low height.
- An outdoor water supply is available, complete with a hose and nozzle that can reach all parts of the house.
- Fire extinguishers are checked and in working condition.
- The driveway is wide enough. The clearance of trees and branches is adequate for fire and emergency equipment. (Check with your local fire department.)
- Road signs and your name and house number are posted and easily visible.
- There is an easily accessible tool storage area with rakes, hoes, axes and shovels for use in case of fire.
- Attic, roof, eaves and foundation vents are screened and in good condition. Stilt foundations and decks are enclosed, screened or walled up.
- Trash and debris accumulations are removed from the defensible space.
- A checklist for fire safety needs inside the home also has been completed. This is available from your local fire department.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/.
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