TULSA MASTER GARDENER LEL

Wild Fires and Rural/Suburban Settings
Part 2
Landscape Considerations

Landscaping for Wildfire Control¹

Fire needs three basic elements to burn--oxygen(air), fuel(any material that will burn), and heat(to ignite the fuel). Isolating any one of these elements from the others is the basis for fire prevention.

Preventing ignition is the key to fire prevention. Material that does not reach its ignition point cannot burn.

Creating a defensible space² around your home is one of the most important and effective steps you can take to protect your home from catastrophic wildfire. Defensible space is the area between a structure and an oncoming wildfire (or between a burning structure and wildland vegetation) where nearby vegetation has been modified to reduce a wildfire's intensity.

All vegetation, naturally occurring and otherwise, is potential fuel for fire. There are no truly "fireproof" plant species. Under extreme fire conditions all plants will burn. Plant choice, spacing and maintenance are critical to defensible space landscaping. Where and how you plant can be more important than what species you use. However, given alternatives, choose plant species that tend to be more fire resistant.

Landscape considerations

Landscaping can be aesthetically pleasing while reducing potential wildfire fuel.

• Landscape in defensible space zones.² The plants nearest your home should be more widely spaced and smaller than those farther away.
  • Zone 1--Within 15 feet of structures, house, decks, porches, etc. Only sparse planting of low growing plant material. No planting within 5 feet of combustable (wood) siding or structures.
  • Zone 2--From zone 1 to 75-125 feet. Scattered low growing trees. Crown spacing (not trunk or stem spacing) a minimum of 10 feet, more if on a slope. Shrub spacing is a minimum of 2 1/2 times mature shrub height measured from the outside edges of the clumps. Maximum clump size is 2 times the mature shrub height. For a 6 foot shrub the maximum width of the clump is 12 feet, with a 15 foot clearance between clumps.
  • Keep a clearing of at least 30 feet around your structures for fire fighting equipment.
  • Keep ample turnaround space (100-150 feet) near your house for fire equipment.
  • Zone 3--Depends on the intended usage of this space. Tree spacing is a function of the trunk diameter and height. Area should be cleared of all excess combustible fuel.
  • Mark your driveway and access roads clearly. Provide a minimum of 12 feet horizontal and 15 feet of vertical clearance for fire fighting equipment.
• Plant in small, irregular clusters and islands, not in large masses.
• Do not plant material under trees which will form "ladder fuels", flammable material which will carry fire from the ground to the crown of the tree. There should be a minimum of 6-10 feet from the ground or the nearest combustible material.
• Do not place flammable structures under trees.
• Make trellises of non-flammable metal.
• Break up the continuity of the vegetation(fuel) with decorative rock, gravel and stepping stone pathways and driveways. This will help modify fire behavior and slow its spread across your property.
• Plant a variety of types and species. This will provide a healthier ecosystem by reducing insects and disease.
• In the event of drought and water rationing, prioritize the plants you wish to save. Provide supplemental water to those nearest your home.
• Mulch to conserve moisture and reduce weed growth. Mulch can be organic(wood chips or small park pieces) or inorganic (gravel or rock). Avoid pine bark, thick layers of pine needles or other materials that can easily carry fire.

Landscape maintenance

A landscape is a dynamic, constantly changing system. Plants considered "fire resistant" and that have low fuel volumes can lose these characteristics over time. Your landscape and the plants in it must be maintained to retain their Fire Wise properties.

• Be aware of the growth habits of the plants on your land and the changes that occur seasonally. Stay ahead of the need to reduce fuel volumes and break up fuel continuity.
• Remove "ladder fuels" that link the grasses and the tree tops.
• Prune tree limbs so the lowest is between 6-10 feet from the ground or the nearest combustible material.
• Remove annual, herbaceous plants after they have gone to seed or when the stems dry out.
• Rake up and dispose of litter, cuttings and debris promptly as it builds up over the season, obeying any local regulations for disposal.
• Mow or trim grasses to a low height within your defensible space. Keep grass shortest in the inner part of your defensible space and no more than 6 inches high in the outer portions. This is especially important as they begin to cure and dry.
• Remove plant parts damaged by snow, wind, frost, insect or disease.
• Timely pruning is critical. It not only reduces fuel volume, but also maintains healthier plants with more succulent, vigorous growth.

Landscape plant characteristics

In general, plants that are more resistant to wildfire have one or more of the following characteristics:

• A high moisture content (the most important factor governing its volatility). For example, succulents and some herbaceous plants. Conifers and some other species tend to be flammable due to their oil and pitch content, regardless of water status.
• Usually deciduous. Deciduous plants tend to be more fire resistant, because their leaves have higher moisture content and their basic chemistry is less flammable. Also, when deciduous trees are dormant, there is less fuel to carry fire through their canopies.
• Drought tolerant.
  • "Drought deciduous" plants drop their leaves or needles in extreme drought.
  • Some drought-adapted species have smaller leaves or very succulent leaves that store moisture.
• They grow without accumulating large amounts of combustible dead branches, needles or leaves.
• They have open, loose branches with a low volume of total vegetation.
• They have low sap or resin content.
• They grow slowly and need little maintenance (pruning).
• They are short and grow close to the ground.
• They can reestablish following a fire, reducing the relandscaping costs.

Landscape material considerations

• Not all plants are equally fire resistant.
1. Cactii and succulents-very low flammability.
2. High water content herbaceous-low flammability.
3. Then, the broader leaf vines and shrubs-medium to low flammability.
4. Needle leaf plants, conifers, etc.-high flammability.
• Group plants with similar water and environmental needs into beds.
• Use "drip" irrigations systems.
• Use approximately 3 inches of plant based mulch to reduce soil surface evaporation and cool the plant's roots.

Trees³

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.

• Trees provide a large amount of available fuel for a fire.
• Can be a significant source of fire brands if they do burn.
• Radiant heat from burning trees can ignite nearby shrubs, trees and structures.
• Plant deciduous trees and avoid conifers.
• These species generally do not burn well.
• Requires removal of dead leaves in the fall.
• Carefully plan their placement.
• Do not plant trees near structures.
• Leave room between trees to allow for their growth.
• Use correct spacing within the defensible space.(at least 10 feet between the edges of tree crowns, more if on a slope)
• Thin trees to retain proper spacing.
• Do not plant shrubs, vines or other type of "ladder fuel" beneath a tree.
• Require regular maintenance.
• Prune branches as the trees grow.
• Mow the grass around each specimen tree.

Shrubs³

• Shrubs can add significantly to the amount of available fuel for a fire.
• Can be a significant source of fire brands when they burn.
• They are a "ladder fuel".
• Plant only widely separated, low-growing, nonresinous varieties close to structures.
• Do not plant them directly beneath windows or vents or wooden decks.
• Do not plant shrubs under tree crowns
• Do not use them to screen propane tanks, firewood piles or other flammable materials.
• Plant shrubs individually, as specimens, or in small clumps apart from each other and away from any trees within the defensible space.
• Require regular maintenance.
• Mow grasses low around shrubs.
• Prune dead stems from shrubs annually. Remove the lower branches and suckers to raise the canopy away from possible surface fires.

Ground covering material³

Ground covering material can break up the monotony of grass, replace bare, weedy or unsightly patches and enhance the beauty of your landscape.

• Generally, can be used near your home.
• May be living plants or mulch.
• Living plants
• Ideal ground covering plants.
• Usually low growing.
• They are succulent or have other fire-resistant characteristics.
• Provide a variety of textures and color.
• Will spread, forming a dense mat of roots and foliage.
• Excludes weeds.
• Must be kept free of dead twigs and leaves.
• Effective barrier to fire spread.
• Used in beds surrounded by walkways and paths.
• Used in raised beds
• Used as part of a rock Garden.
• Help reduce soil erosion.
• Useful in areas where access for mowing or other maintenance is difficult, on steep slopes and on hot, dry exposures.
• Mulches.
• Organic
• Compost, leaf mold, bark chips, shredded leaves.
• Avoid thick layers. When exposed to fire, they tend to smolder and are difficult to extinguish.
• Inorganic
• Gravel, rock, decomposing granite.
• Mulch helps control erosion, conserve moisture and reduce weed growth.