Fire-Safe Landscaping with Kate Frey

By Kate Frey
Special Contributor

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 is 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 to provide nutrients for certain plants. The soft, new growth of native shrubs that grow after a fire provide 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 more dense 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 in 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 gardens 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 structure.

• Remove dead plants and dead grass/weeds.
• Remove any overhanging tree branches over roof or touching 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 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 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 greenwaste.

Choosing and maintaining fire-resistant plants and gardens

All plants can burn!

• 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 ‘fire ladder’ effect. Limb up shrubs so foliage does not touch ground.
• In wildlands thin chaparral shrubs. Base-sprouting plants like coyote brush, chamise and coffeeberry can be cut down every few years in fall to reduce fuel load and keep vegetation young.
• Chose fire-resistant plants for your garden. Fire-resistant plants are open in growth habit, don’t accumulate dead wood/leaves/stems, and are free of flammable resins/oils and turpenes.
• 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 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 greenwaste 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 microsprinklers 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.

Further information:

The Napa Communities Fire Wise Foundation Defensible Space

http://www.napafirewise.org/DS%20Download/defensable-space-live/index.html

Cal Fire

http://www.fire.ca.gov

Home Landscaping for Fire UCANR Publication 8228

http://ucanr.edu/sites/cfro/files/167774.pdf

Defensible Space State Law: Public Resources Code 4291

http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?sectionNum=4291.&lawCode=PRC

The photos are all from Brett Van Paepeghem and are of his beautiful fire-wise garden at the:

College of Western Idaho – Idaho Botanical Garden
2355 Old Penitentiary Rd.
Boise, ID 83712

The Firewise Demonstration Garden at the College of Western Idaho – Idaho Botanical Gardens (IDG) was the first of Firewise demonstration gardens developed in Idaho to show homeowners how they can live on the edge of wildlands more safely and beautifully.

This Firewise Garden was born out of the 2000 fire season, the worst at the time since 1910. Seven million acres burned and fires caused $10 billion in loses – including entire neighborhoods in Los Alamos, NM. Bureau of Land Management (BLM) botanist Roger Rosentreter, now retired, got the idea from a similar garden he saw in San Diego. Many of the plants in the San Diego garden would not grow in Idaho’s climate, so Dr. Rosentreter convinced the BLM to partner with Boise State University, the Idaho Botanical Garden and later the College of Western Idaho and Idaho Firewise, to install and manage this garden in what once was an ugly weed patch.

The garden was opened to the public in 2008 and is currently visited by over 100 thousand people a year.

The BLM Firewise Garden was developed just outside of the Lewis and Clark Native Plant Garden Wetlands area. It is a partnership between the Bureau of Land Management, College of Western Idaho’s Horticulture Program, and the Idaho Botanical Garden. The Garden now supports more than 300 species and cultivars of plants, both native and non-native.

Brett Van Paepeghem is a 4^th generation Idaho native. He holds an AAS in Horticulture and BAS in Biology with specialization in Botany and Ecology from Boise State University. Brett has worked for the USFS on the Payette National Forest as a Range Tech with the Noxious Weed Control Team and 7 years at the Idaho State office BLM as a Plant Biological Tech. In June of 2014 he joined Idaho Firewise as the Southern Idaho Project Manager where he manages the BLM/CWI/IBG Firewise Garden and has collaborated with various agencies on the development of several new Firewise Demo Landscapes throughout Southern Idaho.