FireWise Plant Materials

by F.C. Dennis

Creating a "defensible space" around your home is one of the most important and effective steps you can take to protect you, your family and your home from catastrophic wildfire. Defensible space is the area between a structure and an oncoming wildfire where nearby vegetation has been modified to reduce a wildfire's intensity. (See fact sheet 6.302, Creating Wildfire-Defensible Zones.)

Many people resist creating defensible space around their homes because they believe these areas will be unattractive and unnatural. This is far from true. With careful planning, FireWise landscaping can be aesthetically pleasing while reducing potential wildfire fuel. It can actually enhance beauty and property values, as well as personal safety.

Fire Resistance

Many native plants are highly flammable during different seasons of the year. At such times, left unmanaged, they can accelerate the spread of a wildfire through your neighborhood, threatening homes, property and lives.

All vegetation, naturally occurring and otherwise, is potential fuel for fire. Its type, amount and arrangement has a dramatic effect on fire behavior. There are no truly "fireproof" plant species, so plant choice, spacing and maintenance are critical to defensible space landscaping. In fact, where and how you plant may be more important than what you plant. However, given alternatives, choose plant species that tend to be more resistant to wildfire.

General concepts to keep in mind when choosing and planting FireWise species are:

• A plant's moisture content is the single most important factor governing its volatility. (However, resin content and other factors in some species render them flammable even when the plant is well-watered.) Conifers tend to be flammable due to their oil and pitch content, regardless of their water content.
• 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.

In some cases, there is a strong correlation between drought tolerance and fire resistance. For example, a plant may shed its leaves or needles during extreme drought. Other drought-tolerant species may have smaller leaves or thick, succulent leaves. These plants offer less fuel or have a higher moisture content, both of which help reduce fire hazard.

There also appears to be a correlation between a plant's salt tolerance and natural fire resistance. Plants adapted to salty conditions, and actually growing in salty situations, may better resist burning.

Conifers

In Colorado, conifers make up much of our natural forest. Because of their high resin content, they are more susceptible to fire.

Even though conifers are flammable, you do not need to remove all of them from around your home. Wildfire hazards usually can be effectively reduced through proper thinning and pruning of existing trees and shrubs.

When choosing conifers for your defensible space, consider those with characteristics that make them better able to survive fire:

• thick bark,
• long needles, or
• self-pruning. (Self-pruning trees lose lower branches naturally, leaving a greater distance between ground and canopy.)

Plants for a FireWise Landscape

Plants that are more resistant to wildfire have one or more of the following characteristics:

• They grow without accumulating large amounts of combustible dead branches, needles or leaves (example: aspen).
• They have open, loose branches with a low volume of total vegetation (examples: currant and mountain mahogany).
• They have low sap or resin content (examples: many deciduous species).
• They have high moisture content (examples: succulents and some herbaceous species).
• They grow slowly and need little maintenance (do not need frequent pruning).
• They are short and grow close to the ground (examples: wildflowers and groundcovers).
• They can re-sprout following fire, thus reducing re-landscaping costs (example: aspen).

Additional FireWise Guidelines

Some additional tips to follow when planning a FireWise landscape include:

• Landscape according to the recommended defensible-space zones. The plants nearest your home should be more widely spaced and smaller than those farther away.
• Plant in small, irregular clusters and islands, not in large masses.
• Break up the continuity of the vegetation (fuel) with decorative rock, gravel and stepping stone pathways. This will help modify fire behavior and slow its spread across your property.
• Plant a variety of types and species. Besides being aesthetically pleasing, this will help ensure a healthier forest by reducing Insects and diseases. Healthy, vigorous, thinned forests can better resist catastrophic fires than unhealthy ones with insect and disease problems.
• In the event of drought and water rationing, prioritize the plants you wish to save. Provide supplemental water to those nearest your home, perhaps using "gray water."
• Mulch to conserve moisture and reduce weed growth. Mulch can be organic (wood chips or small bark pieces) or inorganic (gravel or rock). Avoid pine bark, thick layers of pine needles or other materials that can easily carry fire.

Don't Forget 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 FireWise properties.

Be aware of the growth habits of the plants on your land and of the changes that occur seasonally. Keep a watchful eye for the need to reduce fuel volumes and fuel continuity.

• Remove annual, herbaceous plants after they have gone to seed or when the stems become overly dry.
• Rake up and dispose of litter as it builds up over the season.
• Mow or trim grasses to a low height within your defensible space. This is especially important as they begin to cure and dry.
• Remove plant parts damaged by snow, wind, frost or other agents.
• Timely pruning is critical. It not only reduces fuel volume but also maintains healthier plants with more succulent, vigorous growth.

Additional FireWise Publications

Cooperative Extension

The following publications are available from The Other Bookstore, Colorado State University Cooperative Extension, 115 General Services Bldg., Fort Collins, CO 80523-4061; (970) 491-6198; cerc@vines.colostate.edu. Printed copies cost $1.00; they are available free on our Web site.

• 6.302, Creating Wildfire-Defensible Zones
• 6.303, Fire-Resistant Landscaping
• 6.304, Fire Safety, Evacuation and Home Defense
• 6.306, Grass Seed Mixes for the Reduction of Wildfire Hazard
• 7.205, Pruning Evergreens
• 7.206, Pruning Shrubs
• 7.207, Pruning Deciduous Trees
• 7.402, Protecting Trees During Construction

Colorado State Forest Service

The following publication is available from the Colorado State Forest Service, Colorado State University, Fort Collins, CO 80523-5060; (970) 491-6303:

• Home Fire Protection in the Wildland Urban Interface, CSFS #142-399

FireWise Plant List

The following list was prepared by Phil Hoefer, Colorado State Forest Service. It was reviewed by Jim Knopf, a landscape architect in Boulder, and two landscape architects on Colorado's Western Slope. Bloom time is approximate (observed in Boulder at 5,600 feet).