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While wildfires happen every season in California, this year’s toll is particularly devastating. According to a briefing Monday by CA Governor Gavin Newsom, this time last year, CA had 4,292 wildfires burning across 56,000 acres. This year, there are 7,002 fires burning across more than 1.4 million acres. There have been seven deaths and over 12,000 structures destroyed. Two of the “lightning complex” fires burning around the San Francisco area are now recorded as the second and third largest in CA history.

Unfortunately, there are no ways to fireproof a property, but the University of California’s Division of Agriculture and Natural Resources offers strategies to design and maintain landscapes for reduced vulnerability. A key component of this protection is the proper placement and maintenance of plants around the home. While many in CA now seek plants with a label assuring some level of fire resistance, it’s important to recognize that any plant will burn under the right conditions.

During a wildfire, structures are threatened not only by the flaming front of the fire, but also by embers that are lofted ahead of the fire front and can come into contact with receptive fuels (e.g vegetation or mulch next to the house), igniting new fires. Traditional “defensible space” tactics are designed to mitigate threats from the front of the fire but do little to address vulnerabilities to wafting embers. Without attention to ember-related risks, defensible space efforts only address a portion of the threat—especially during wind-driven fires.

A Three Zone Strategy

To be able to reduce ember, radiant heat, and direct flame exposure to a structure, develop and implement a three-zone strategy whereby the highest priorities and most restrictive measures are incorporated in the area closest to the building. Treating potential “fuels” within the first five feet of structures is one of the most important aspects of wildfire hazard mitigation.

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While these strategies require some adjustment from methods of the past, it is possible to have both a beautiful landscape and a home that is more resilient to wildfire. Work from the house outward to make sure the structure itself is hardened against fire, then implement the guidelines here in concentric circles moving away from your structures. Here are some tips to think about:

Create Defensible Space

  • Create fuel breaks (essentially spaces) surrounding the house and within the yard.
  • Place plants with ample space both vertically and horizontally.
  • Use hardscape and noncombustible materials around structures and to separate individual plants and groups of plants.
  • Use the right plants in the right places with fire, climate, and irrigation needs in mind.
  • Create plant islands that have similar sun, nutrient, and water needs.
  • Replace combustible (such as wood) gates that attach to the house with materials that will not burn.
  • Decorative Features such as fencing and gazebos, as well as firewood, can be combustible materials that should be considered in a landscape layout. Use appropriate clearance or modify positioning for these features to reduce the threat from burning embers.

Maintain The Landscape

  • Keep the garden free of dead wood, dry grasses, and leaf litter, especially near any structures.
  • Prune plants to maintain horizontal and vertical space throughout the property and surrounding structures.
  • Eliminate “fire ladders.” For instance, a grass fire can move up into shrubs and then further into trees.
  • Hydrate plants with a water-wise irrigation system. Use non combustible mulches near the house.

This defensible space is only part of a larger landscape management strategy, designed to protect a home and property. The general surroundings leading up to a  home or building must also be considered as part of wildfire preparedness planning.

Steep Slopes & Wind

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Source: East Bay Municipal Utility District (ebmud.com)

If the home is located on a steep slope, or in a drainage area, windy area, or an area surrounded by unusually dense, tall, or combustible vegetation, thinning recommendations increase. Additionally, if the property is surrounded by vegetation especially prone to wildfire or has an active fire history, the greater the clearance and separation between plants and plant groupings should be. When a home is at the top of a slope, keep in mind that fire and heat rise, allowing for pre-heating of upslope fuels and resulting in the potential for more intense fire behavior. In these cases, greater effort should be directed at the downslope of the home with even higher levels of spacing given to the area below a deck. Recommendations based on the judgement of fire professionals are:

  • Under 20% slope:  Space shrubs 2 x the height
  • 20-40% slope: Space shrubs 4 x the height
  • Greater than 40%: Space shrubs 6 x the height

Wind is another factor to consider alongside aspect and slope. A south-facing slope with southerly winds can easily span the 30 foot “lean and clean” recommendation. Work with a local resource experts to install adequate measures if a property is at great risk.

Helping client properties achieve greater wildfire resiliency will take a coupled approach and greater awareness of ember protection. Homes survive wildfire through a combination of 1) careful design and maintenance of landscaping; 2) awareness and management of combustible materials on the property (e.g., leaf litter, wood piles, and lawn furniture); and 3) incorporation of fire- and ember-resistant construction materials with appropriate installation and maintenance.

This article was adapted from “Preparing Your Landscape” from the Division of Agriculture and Natural Resources at the University of California. Visit their Fire resources and information pages here.