By Kate Frey
Nevermore than now has this topic of creating fire-safe landscaping become relevant to all of us in the Western States of the United States. That is why we thought it important to share. The article states…
The recent fires in the Napa/Sonoma area have touched everyone in Northern California. The physical composition and appearance of our landscapes and our relationship with them are forever changed. From wildlands, rural hillsides, to city streets, what seemed permanent and safe is vulnerable to periodic fire. Not just the built environment, but many of our trees, shrubs, and gardens are gone, living elements that act to soften and aesthetically anchor houses and buildings to the earth and create a sense of place around our homes.
Our homes and businesses are set in and adjacent to wild landscapes. In our leisure time, we walk, bike, or drive through their majestic scenes. People travel from all over the world to enjoy the atmospheric and rugged Napa Valley, and the wine region set in it. Our intense engagement with these environments has created a strong urban-wildland interface that is susceptible to fire, a natural aspect of our summer-dry landscape.
The Larger Context
It helps to understand the larger context of fire in the environment our homes and businesses are set in. Due to our long dry season without rain, low relative humidity, sometimes heat and winds, and with often abundant fuels (vegetation), California is a fire-prone landscape. Ecosystems and plant communities have developed and evolved in this environment. Periodic fires are a natural aspect of most California ecosystems. Some are fire-dependent and require fire for seeds to germinate, renew over-mature vegetation, open forests to sunlight, and provide nutrients for certain plants. The soft, new growth of native shrubs that grow after a fire provides much nutritious browse for animals such as deer. Bare soil and the lack of competition from shrubs and trees allow annual wildflowers to grow. But too frequent fires destroy seedbanks, and young trees and shrubs before they are old enough to set seed, and set in motion a landscape’s conversion to grasslands, a highly flammable vegetation type.
Fire in Plant Communities
Dry conditions, low relative humidity, and winds help create physical conditions conducive to fire. Vegetative fuels with low moisture levels and structural elements like houses feed fires. The golden hills of California, a ubiquitous and inherent aspect of our state’s identity, are now composed of over 90% non-native grasses and forbs. We have both purposely and inadvertently converted our natural understory landscape of perennial grasses and ephemeral annual wildflowers to very flammable non-native grasses. These plants grow quickly with the advent of winter rains, set seed, and die early in the spring. They are highly flammable (often called “flashy), and allow fires to spread extremely rapidly. Dried grasses are dangerous when they invade or are adjacent to shrub or chaparral plant communities as the grasses act as ladders into the flammable shrub overstory. These grasses also dry much earlier in the season than other vegetation, and so extend the fire season greatly.
Chaparral, the most common plant community in the state, is composed of densely growing shrubs such as manzanita, chamise, toyon, scrub oak, and Ceanothus that form a closed stand over time. It is a fire-dependent ecosystem, yet fires historically naturally occur in these systems only about once or twice a century. Fires are often severe, eliminating most standing vegetation. Many shrubs and trees of this ecosystem either sprout from the base after a fire or their seeds are stimulated to grow by fire and the resulting bare soil. Fires rejuvenate these areas. In conifer forests, fires were more frequent, usually patchy, and lighter in intensity, mostly consuming the understory and young trees with branches that reach the ground. With the advent of effective fire suppression, forests are widely considered denser and even-aged than they were naturally, and consequently, fires are now often severe and enter and spread in tree crowns. In oak woodlands, trees and shrubs both grow singly and in clumps. Older hardwood trees such as oaks, madrone, and California bay often have no lower branches due to age. They usually grow in wide expanses of dry grasses that are highly flammable. Winds can act to move flame from ground level into tree canopies.
How do fires start?
Over 90% of fires are started by human activity. Mowing, powerlines, and sparks from cars, cigarettes, and campfires, cause fires far more frequently than do lightning strikes. As we have seen, winds have a great influence on the generation and severity of fires and the catastrophic speed at which they move, and can cause devastation in areas never considered at risk.
We can affect how fire-safe our landscapes are. Choosing appropriate plants for a fire-prone landscape, strategically siting and pruning plants, minimizing dry fuels such as grass, and adequately watering plants can have an effect on how landscapes behave in the event of a fire. Larger landscapes need to have defensible space around structures. Defensible space is defined as space where the vegetation has been designed or modified and maintained to reduce flammability, and where firefighters can defend a structure.
Urban and rural areas have different laws and concerns about their properties and gardens. In rural areas existing fire ordinances govern how landscapes are managed. Most break down areas of concern into defensible space zones corresponding to distance from houses or structures. In an urban or suburban setting, where houses are closely spaced, and lot sizes are small, houses themselves form the vast majority of combustible fuels. In these spaces, we can still work to minimize our garden’s possible contribution to further ignition of homes. Minimizing the use of highly flammable trees such as Monterey pines, junipers, and eucalyptus, irrigating our plants well, maintaining plants (trees, vines, shrubs, and groundcovers) free of dead leaves and stems, and thinning dense vegetation will all contribute to a more fire-safe environment.
Defensible Space Zones for Wildfire:
Zone 1: 1-30 feet from a structure.
- Remove dead plants and dead grass/weeds.
- Remove any overhanging tree branches over the roof or touching the house.
- Trees should have a 10-foot space between them.
- Use low flammability shrubs under windows and around decks.
- Use gravel mulches. Compost can be placed around plants.
- Water plants well.
Zone 2: 30-100 feet from a structure.
- Dead grasses mowed to four inches.
- Fallen leaves/needles/small branches and plant debris can be no more than three inches deep.
- Eliminate ladder fuels to trees. Limb up trees to six-foot from the ground.
- Create horizontal space between trees and shrubs. Space trees and shrubs widely. (See CalFire website for details). Create non-contiguous plantings.
- Create vertical space in between trees and shrubs. Remove shrubs under trees that could act as ladder fuels. (See CalFire website for details).
- Use low flammability mulches such as decomposed woodchips or composted green waste.”
This is all really good information. One that we should all take to heart. Read on for more tips for fire-safe landscaping…
Choosing and maintaining fire-resistant plants and gardens
The thing to know about fire-safe landscaping: All plants can burn! Especially here in California stricken with drought conditions.
- Irrigate your plants adequately. A high-moisture content acts to buffer flammability. Well-irrigated plants require more energy to ignite and sustain combustion.
- Maintain plants free of deadwood/twigs/stems.
- Thin dense tree and shrub canopies to reduce fuels.
- Limb up trees 6-10 feet from ground level to minimize the ‘fire ladder’ effect. Limb up shrubs so foliage does not touch the ground.
- In wildlands thin chaparral shrubs. Base-sprouting plants like coyote brush, chamise, and coffeeberry can be cut down every few years in the fall to reduce fuel load and keep vegetation young.
- Chose fire-resistant plants for your garden. Fire-resistant plants are open in growth habits, don’t accumulate dead wood/leaves/stems, and are free of flammable resins/oils and terpenes.
- Use more low-growing plants (less than two feet in height) than upright shrubs or trees.
- Space plants adequately for each fire zone and around structures. On large lots and properties, the immediate critical 30-foot area around houses should have just widely spaced, well-irrigated specimen trees and low plantings free of mulch. Sprinkle compost around plants for soil fertility. From 30-100 feet from houses, space trees 20-40 feet apart. Space shrubs widely. Low plantings should not be contiguous.
- Thin or remove highly flammable plants- such as many conifers, especially near structures. Deciduous trees are less flammable.
- Have adequate numbers of plants with deep and extensive roots (such as native plants), to hold and protect the soil during winter rains- especially on slopes.
- Use mulches with low flammability. Mulches that have large air spaces between particles or pieces are more flammable. Shredded barks can be highly combustible. A two-inch layer of woodchips, and even better, composted woodchips or composted green waste have low flammability and tend to smolder rather than flame. Compost has less flammability still as particles are very small and closer in composition to that of soil. Consider installing micro-sprinklers in mulched areas so mulch can be moistened during times of red-flag fire warnings. Red-flag warnings are when humidity is less than 19% and winds over 25 mph. Intersperse mulch with non-combustible materials such as pavers, decomposed granite, gravel, or rock.
- Mow annual grasses and weeds in a 100 feet perimeter around structures to 3 inches in height before they are completely dry to minimize any fire spread and fire ladder effect.
We hope that this information regarding fire-safe landscaping was useful to you. There is one more thing that you can do however if your property is surrounded by grassland or woody areas. Call us and let us mow down tall grasses, brush, briars, and anything else that can pose a danger of catching fire with our specialized equipment.