Fire Wise Plant Spacing Suggestions
Proper placement or replacement of plants is important for any defensible space plan. Through proper plant selection, placement and maintenance, we can diminish the possibility of ignition, lower fire intensity, and reduce how quickly a fire spreads, increasing a home’s survivability.
Recommend separation distances for shrubs:
For areas with dense brush, the recommended separation distance is dependent upon shrub height and steepness of slope.
Note: Separation distances are measured between canopies (outermost branches) and not between trunks.
For example: if your home is located on a 10% slope and the brush is four feet tall, the separation distance would be two times the shrub height or eight feet. The recommended separation distance can be accomplished by removing plants or through pruning that reduces the diameter or height of shrubs (shorter height means less separation is needed.)
Recommended separation distance between tree canopies:
For forested areas, the recommended amount of separation between tree canopies is determined by steepness of slope. If your house is situated on a 30% slope, the separation of tree canopies within your defensible space should be 20 feet. Creating separation between tree canopies can be accomplished through tree removal. Another option is to have a continuous canopy of overstory trees. This approach requires having no understory and adequate pruning of trees.
Fire Wise Plant Choices
All plants – all organic matter – can burn, but the ease of ignition, rate of consumption, and generation of heat is vastly different between species of vegetation. Fuel is variable.
Far more important than the actual species and its flammability is to be able to recognize and dispose of dead wood, which ignites and burns with much greater ease and intensity than living green vegetative material.
What follows is a list of plants used in landscaping around your home that are labeled either good or bad from the standpoint of fire (only). The lists are not all-inclusive, and many species – both bad and good choices – have been added to our landscapes from worldwide sources. Most of the common native plants are mentioned and more fully described.
Pyrophytic Species are “fire-loving” vegetation which is adapted to or which contributes to rapid burning, high heat output, and ember creation.
Many brush species – such as broom, manzanita, coyote bush, and juniper – are highly flammable and burn with an oily heat. Anything that smells when crushed has oils which volatize and burn readily, including bay, fir and eucalyptus trees.
Chaparral species are those brush species which grow in dense, pure or mixed stands and which create impenetrable fields that burn with intense heat and are very difficult to suppress or control.
They include manzanita, coyote brush, buck brush, broom, chamise, mountain mahogany, as well as scrub oaks and other flammable species. Chaparral species are among the hardest to manage and to keep fire safe.
Nevertheless, these can be made fire safe with work. If near structures, all pyrophytic species should be removed, and all dead vegetation removed from the remaining species. What is left should be small trees, and healthy, well-separated selected plants which have had ground fuels removed.
Resprouting may occur and need to be dealt with annually. Proper attention to timing of repeated removal of sprouts may encourage the roots to gradually lose vigor and die.
Conifers are evergreen trees that have needles for leaves, and most of these have resins and pitch in addition to a tendency toward twiggy growth. Coniferous species should be considered pyrophytic near homes. All can be made less flammable by pruning and removal of dead portions, but conifers tend to grow large and overtop other vegetation, making for potentially long flame lengths, if ignited.
At another extreme are the low conifers – juniper in particular – which contribute to rapid fire spread largely by becoming dense with un-maintained dead and dying vegetative materials that lie in wait for an ember to ignite. In addition to the listed and described species, obvious poor choices near homes include cypress, cedar, all pines and firs.
The one native conifer exception is redwood, which tends to exist in more humid environments and does not have abundant pitch. Redwood can burn, however, as it can quickly accumulate large amounts of debris. Even with low flammability, maintenance and removal of dead vegetative material is key in all vegetation management to prevent wildfire.
Hardwood trees, particularly deciduous species, are less flammable than conifers, with the notable exceptions of non-native eucalyptus, native bay laurel, and a few others. Most local oaks are low in flammability except for the live oaks (which appear evergreen).
The live oaks should be kept in the landscape but pruned away from the ground, with dead material removed to avoid ladder fuels. If surrounding brush species are removed, the fire ladders are also removed and fire safety greatly improves.
This is generally the best course to take in the oak woodland portions of the Wildland Urban Interface (WUI). Excellent trees to have nearby that burn poorly (as long as you keep out the dead materials) are alder, ash, buckeye, cottonwood, maple, deciduous oaks, madrone, and willow.
These should all be maintained free of dead materials and pruned high above the ground.
The following plants are further shown with pictures and descriptions due to their ubiquitous nature. For the most difficult plants, recommendations are made for effective removal techniques.
For an existing home, the best way to achieve safety in event of wildfire is to rethink your landscape and to do away with plants in fire-prone locations. However, many times the removal of plants opens gaps in our landscaping that we may not want or did not anticipate. In such cases, replacement plants may be demanded, for erosion control, visual screens, or landscape enhancement. In such cases, it is best to use native materials that are drought and deer resistant, in addition to being fire resistant. This is a tough combination to fulfill, but several choices. which may include some of those attributes, are detailed below.
The Structure Ignition Zone should have only low irrigated or succulent plants. Such non-natives as ice plants and stonecrops (Sedum spp.), and Crassula edulis actually absorb heat and lower the flame temperature as it nears. Good native perennials to use in this space include Yarrow (Achillea tomentosa) which has pretty yellow flowers, Lupines (Lupinus) with multicolored flowers, monkey flower (Mimulus), penstemon (Penstemon) and some sages (Atriplex sonomensis, A. columbariae).
Ground covers are often used in the inner zones, and there are many good nursery choices that might be desirable. There are native species which are part of the chaparral vegetation type, which means they are flammable – but due to the low form may be used sparingly. All need maintenance to remove dead thatch. These include Bearberry (Arctostaphylos uva-ursi) with white flowers and red berries and dwarf coyote bush (Bacharrus pililaris Var. protata) or ‘Twin Peaks’ which can be grown on near-vertical slopes. Since this is the same species which can burn so hot and fast, only a sparse use of the dwarf form should be done. Squaw carpet (Ceanothus cuneatus) is a native low grower which can tolerate drought once established.
Vines can be used to cover a multitude of sins, but be sure to clear out the flammables before planting Jasmine (Jasminium spp.), potato vine (Solanum jasminoides), cape honeysuckle (Tacomeria capensis). Beware the scenic grasses, which have lovely heads and wave in the breeze – but which become both an ember trap and source once they dry.
In the Fuel Reduction Zone, upright plants may be desired. Native species that may already be existing in the landscape that are less flammable than the pyrophytes include toyon (Heteromeles arbutifolia), redbud (Cercis occidentalis), silk tassel (Garrya sp), buckthorn (Rhamnus sp.), and mountain mahogany (Cercocarpus beuloides). Bush anemone (Carpentaria californica) is an evergreen shrub with brilliant white flowers which grows to 4’-6’ tall and wide. It is native California chaparral species which is a good replacement for juniper, coyote brush, manzanita and other pyrophytes. Still flammable, if kept thrifty this attractive evergreen shrub will add to your landscape while replacing known bad actors.
Wild lilac (Ceanothus griseus horizontalis) has beautiful flowers is drought–resistant, but is favored by deer. Well-spaced low-growing saltbush (either Atriplex glauca, or A. semibaccata), Gazania (Gazania spp.) would help to hold a slope in place. Rockrose (Cistus salviolfolius, C.crispus) can be used sparingly in places where erosion control is needed, if cut back after its large white flowers show. Several plants which are drought tolerant and spreading include winter creeper (Euonymos fortunei, E. radicans), and honeysuckle (Lonicera sp.).
For the outer zones, there are many native tree choices when removing pines, firs, cypresses, bays and eucalyptus. Most deciduous species are lower in fire danger, and good choices are maple, walnut, ash, alder, buckeye, and include species in the Prunus genus. Madrone is a native that is having a difficult time with numerous diseases, but periodically cutting out the dying parts should allow you to keep this lovely native in your landscape. While live oak is more flammable than the deciduous oaks (valley, blue, white, black) these are best kept in the environment if limbed up and dead parts are removed. Some non-natives that are low in flammability and somewhat unusual include carob (Ceratonia siliqua), pepper (Schinus Spp.), and strawberry tree (Arbutus unedo). Edible choices would include fruit and citrus trees, all needing irrigation and thus low in flammability.
When planting new vegetation, always keep in mind the ultimate size of the plants and be aware of the maintenance needs to avoid fuel build up. You can grow a fire wise landscape.
General Landscaping Tips
We have discussed the why and the where of defensible space activities, but the what and the when and the how need greater exposition. The homeowner and family may do this work, or work can be contracted.
Defensible space work needs to be planned with recognition of the labor and dangers involved. While a first pass to pick up sticks and dead materials can be done by anyone, this initial step will undoubtedly need to be followed with tools and personnel.
Most people are not used to this type of activity, although it is often an extension of gardening activity, with many of the same tools.
It is best to plan the work in stages, with each step gaining more open conditions. One can mark the vegetation to be cut or to be left, either in the mind or physically with some flagging. Often this stage allows one to step back to see the next steps more clearly before you commit to action.
After assessing the needs and difficulties, starting with a lopping tool allows one to get rid of the small stems that inhibit movement through the wildland. Cutting at the base (but out of the dirt) will allow for the entire plant to be removed at once, and allow for easy future management of the stump, if needed. Of course, a worker should be able to recognize poison oak as well as the pyrophytes you want to remove.
As the ground begins to get more open, it becomes easier to see what is needed next. Once the space is opened up, a weed whacker may allow for easier movement.
At each stage, the preparation and use of each tool should be done to ensure safe and efficient operation. Debris should not be left in the way, but pulled out in readiness for the next step.
Once the undergrowth is either removed or trimmed to remove all dead branches, the trees can become the focus. Trees to be retained may need pruning with a handsaw. Other trees may need to be cut using a chainsaw.
Preparing for chipping means getting the material to a location next to access and “indexing” the ends. This means stacking the brush to be chipped in a parallel manner, with large end toward the access road, and relatively flush for easy grabbing.
Piles can be as large as 20 feet long and 6 feet high. For additional information about chipping, visit the Napa Firewise Web site at www.napafirewise.org.
Pruning will need to be done on trees that have branches reaching below head height (or so). Breaking the fuel ladders is an essential part of defensible space.
Pruning can be done with hand saws, shears, and/or loppers. Most branches can be cut off with one cut, and larger branches may need three cuts (see inset).
Every pruning cut on live wood is a wound. A branch needs to be cut so to not damage the tree and also to leave no stub. This does not mean making a cut flush with the bark, but instead cutting just outside the branch collar. Cutting in this way minimizes the impact, since branches compartmentalize decay and keep rot away from the main stem.
Many large trees can be disfigured or killed by improper pruning, so be sure of yourself or call a certified arborist before work begins.
The branches to remove are those which are either dead or which have parts which reach below eight feet (or so) from the ground surface. Steeper slopes often need higher pruning. For tree health, never prune more than ½ the height of the tree.
Branches which provide a screen or which are particularly useful or attractive may be left, if the area of the lower tree crown is open and has no flammable vegetation for 10 feet around the area.
Overhead pruning work can be and dangerous. Head and arm protection are essential, while face and neck covering will make falling sawdust a great deal easier to endure.
Pruning done in the spring and summer can attract bark beetles to conifers, while pruning oaks in areas of sudden oak death should be done during the dry months. Constraints and hard dirty work make it easy to ignore the need for pruning, but remember that fuel ladders promote crown fires – the worst of wildfires. The good news is that once done, pruning needs only occasional attention, since the removed fuel will not return. back to top …
Stumps should be cut as low as possible for both aesthetic and for sprouting reasons. If sprouts quickly return and grow, they can be cut almost as quickly.
While managing vegetation to make your situation more fire safe, you are also altering the habitat for what lives there.
Many times, removing debris piles also reduces the rat population. You also may uncover snakes, squirrels, birds of all types, and certainly arthropods and other small life forms. For the most part, whatever is disturbed will quickly find a new home further away from your areas of highest value.
Remember that removing dead vegetation more than 1/2 inch in diameter is a key to preventing the passage of a hot wildfire.
The forest floor has a life of its own, and generally should be left undisturbed. The duff and litter will turn into mulch with vital nutrients to nourish the forest over time. When chipping, casting the chips on the surface to a depth of 4 inches is a good way to retain soil moisture while also inhibiting weed growth. Deeper piles may build heat as vegetation decomposes and should be spread out to avoid potential ignition.
Workers removing trees and shrubs should be alert to what is living there. If active nests are encountered in trees planned for removal, it is best to cut from August to March to avoid impact to young birds.
Another consideration regarding when to cut may be the activity of insects and diseases. With the threat of bark beetles, the disease Sudden Oak Death (SOD), and many other pests, it may be difficult to find the right time to best fulfill your plan by doing the actual cutting and pruning. All host material for SOD is best left on site where it is.
This is not a time to delay! If concerned, call the Master Gardeners and they can usually answer your specific questions over the phone. They are available M-W-F from 9am-12pm at 707-253-4221 or toll free at 1-877-279-3065.
If working in a drainage where water sometimes flows, it is best to tread lightly and remove only pyrophytes and small dead materials, leaving in place any big wood (more than 12 inches in diameter or more than 4 feet long). The canopy should not be reduced in such places, which usually have higher humidity and lower tendency to burn.
Working on steep slopes (more than 60%) should be avoided, and surface litter should be left to protect against erosion.
It is often recommended to leave big wood on these slopes, removing the smaller dead wood only (1/2 inch to 12 inches in diameter) .
Aspect: The direction of the slope. Generally, a south or southwesterly aspect presents the greatest hazards from wildfire. The aspect determines the intensity of solar heating and rate at which wildland fire fuels might be expected to dry out during the fire day. Aspect also affects what grows naturally on a slope.
Canopy: Woody upper layer of a forest formed by mature tree crowns.
Conifers: Woody plants. Typical conifers include cedars, Douglas-fir, cypresses, junipers, redwood and pines. There are over 600 living species within the conifer family.
Crown Fuels: Crown fuels are what are above the stem of the plant – the branches, twigs, needles, and leaves, often called the overstory. Separating crowns from each other gives each plant its own piece of the sky. Cleaning the crown of dead and dying vegetation is important in keeping potential flame height and ignitability low.
Deciduous: Shedding or losing leaves annually – the opposite of evergreen.
Dominant Vegetation: Vegetation type determines fire behavior – the flame length, intensity, and rate of spread – and can be predicted through measurement of fuel type.
Ground Fuels: The low ground fuels are grasses, dead branches on the ground, shrubs and brush. This is often referred to as the understory. Removing ground fuels cools a fire and disallows its spread.
Hardscaping is the use of rock and other non-combustible hard surfaces such as concrete sidewalks, brick patios and asphalt driveways.
Home Ignition: There are three forms of ignition:
- Direct flame impingement (convection), in which flames overwhelm a structure. This results from having no defensible space.
- Radiant heat, when objects nearby are so hot that they provide sufficient heat for the home to burst into flames. This possibility is greatly reduced as space between fuels is increased.
- Embers, which can come as a blizzard and ignite any available light fuels such as needles or dry vegetation.
Ignition-Resistant Construction (fire hardening): These construction methods or components increase exterior building ignition resistance to a wildfire. Non-combustible roofing materials, double window glazing, vents with minimum openings, fire-resistant siding, and other materials will help to reduce structural flammability. Building or remodeling with these materials adds to overall survivability when done in combination with vegetation management measures for defensible space.
Ladder Fuels: Fuels that provide vertical continuity between layers of vegetation, thereby allowing fire to travel from surface fuels into the crowns of shrubs and thence into trees. Ladder fuels initiate and assure the continuation of crowning (crown fire) during wildland fires.
Overstory: The upper crowns or canopy of a forest.
Prevailing Wind: Many wildland fires are wind-driven. Knowing the direction of prevailing winds and how they might behave is crucial for wildland fire protection planning. Typically, in the late summer and fall, hot, dry northeasterly winds occur. Northeast winds have been a major factor in virtually every California firestorm.
Pyrophytic Species: Literally, “fire loving” vegetation which is adapted to or which contributes to rapid burning, high heat output, and ember creation. Many brush species – such broom, manzanita, coyote bush, and juniper – are highly flammable and burn with an oily heat. Anything that smells when crushed has oils which volatize and burn readily, including bay, fir and eucalyptus trees.
Shrubs: Woody plants. Distinguished from a tree by its multiple stems or lower height, usually less than 15-20 feet tall.
Slope: The steeper the slope, the greater the rate of fire spread. The critical slopes are those downhill of the structure because these pose the greatest threat. Slope is measured as rise over run. Thus a 20 foot vertical drop in 100 feet of horizontal distance is a 20% slope.
Understory: The area of a forest that grows in the shade of the forest canopy.
Wildlife Urban Interface (WUI): The wildland/urban interface is any location where a fire can spread from vegetation (wildland fuels) to buildings (urban fuels), resulting in multiple house fires that overwhelm fire protection efforts.
ACACIA is a non-native tree or shrub that comes in many forms. Species commonly planted in Napa are often highly flammable, seed profusely, and also sprout. They can be beautiful yellow in springtime, and many have large pods in the autumn. It must have full sun to live, and will grow quickly, producing many offspring.
Acacia can be removed by cutting and then removing sprouts and seedlings in subsequent years, but roots can be very deep (acacia came from dry climates). Many acacias can be managed as single stem trees, and kept with a crown well off the ground, which would lower flammability as long as sprouts are controlled.
BAY also known as Laurel, Pepperwood, or Oregon myrtle, is a native tree that grows in generally moist places on the west coast. Its leaves are aromatic and used in cooking. Because of the high oil content, the leaves are very flammable, particularly if dried out. The tree has high protein content and is a preferred deer feed in some locations, which helps to keep the plant under control. The leaves are allelopathic (want to be left alone) and will inhibit the growth of other plant species.
Older tall stands of bay trees often have little understory, and also low flammability if there are no dead ground fuels underneath the canopy. Once cut, the stumps sprout profusely and the low branches and leaves are very flammable, often torching if ignited. Management of sprout clumps requires either periodic removal of
sprouting clumps or cutting and management to a single stem while also removing surrounding ground fuels. In a few years with both natural and human pruning, the bay can grow into a tall shade tree with relatively lower flammability. Seeding of large trees is prolific, but repeated pulling of seedlings will deplete the viable supply quickly if the overstory trees have been removed.
BROOM plants – Scotch, French, Spanish, etc. – came to America from Europe and are invasive perennials that spread easily and grow six to ten feet tall. They are extremely flammable due to oil content. Often beautiful in the springtime with golden flowers, they are abundant seed producers and should be removed prior to seeding. Broom readily colonizes open grasslands, coastal plains, mountain slopes, and disturbed areas such road cuts and managed land. Seeds mature June through July.
One approach for removal is to annually pull the plants prior to seeding or flowering. Do not allow these plants to seed as they have a persistent seed bank that will require ongoing removal. The entire plant with root system must be pulled since it readily resprouts. This is a plant that will need continual revisiting until the seed bank is exhausted, but will get easier with time as the roots decrease in ability to support the plant.
CHAMISE is a native shrub that grows on shallow soils and forms extensive fields, often mixed with other brush species. It both sprouts and seeds prolifically and is aggressive in establishment. It needs full sun in order to grow. Young plants are palatable to deer and goats, but older stems tend to get woody and have low value as food, and these older plants create a very hot fire when ignited.
Chamise removal is best done by cutting off the above-ground portions. The plant has a deep root and will re-sprout, necessitating a re-cutting the following spring. If done at the right time, the roots will be starved of nutrients and will die. It may take two such cuttings to be successful in complete removal of the plant.
CHAPARRAL is a native plant community well-suited to our Mediterranean climate. It consists of many species of low shrubby plants (manzanita, coyote brush, and numerous brush species) that can grow very dense. It houses numerous bird species but can become impenetrable to mammals. Chaparral is perhaps the most fire-prone vegetation to be found, and burns with a fearsome intensity. Chaparral can return very quickly after fire, through both prodigious seeds and sprouting. It should be kept far from any buildings, since it can generate tremendous heat very quickly if ignited.
COYOTE BRUSH, also called greasewood, is a dense multi-stemmed native shrub that is aggressive in colonizing open sites. Its white flowers are welcome in January, but by July the plant is dry, oily, and ready to burn. Older plants tend to develop dead material within the crown of the plant. This plant both seeds and sprouts readily, and growing in the open can easily become a ten foot tall shrub within ten years.
Coyote Brush is deep rooted, and repeated cutting of the plants will be necessary. It is palatable to goats but resprouts with vigor. Timing pruning in spring to rob the roots of carbohydrates may make it easier to kill permanently. Those plants that seed in and grow during the fall can be pulled out (with a weed wrench) before they become established, particularly easily done when soil moisture is high very early in the season (i.e., by January).
EUCALYPTUS comes from Australia and is among the worst of the pyrophytes, having shaggy bark, oily leaves and branches, with very rapid growth and development of debris. In addition, the leaf can lift easily into the wind, and cast burning embers for great distances. It both seeds and sprouts prolifically and is very difficult to remove. Its flowers contribute to allergies and its roots are allelopathic, disallowing all other species in the vicinity (except for poison oak).
Eucalyptus produces hot-burning firewood, one of its few beneficial effects. Because of its rapid sprouting and tall growth, it has fueled many wildland fires and made many more difficult to suppress. It should be kept well away from structures as it can toss embers for hundreds or thousands of feet. If it is to be kept, it requires extensive cleaning at least annually to remove excessive peeling bark, dense litter of leaves, twigs and seeding pods. Removals of big trees are expensive and need follow-up for years to keep sprouts under control. Both keeping and cutting this flaming invader require annual diligence (the author is still cutting sprouts from trees initially cut three decades ago).
FIR Douglas fir grows extensively in the higher areas of Napa, particularly on east- and north-facing slopes. It is an ecological climax species, and promotes itself through prolific seeding. It can be seen in each of its sizes in dense stands, and many pole-size stands are heavy with dead and dying trees, since it tends to successfully sprout in much greater density than can be sustained over time. The natural forest sows seedlings of its own death, since these dense forest stands tend to be totally consumed in stand-replacing fires every century or so. Many of the huge fires in Napa County (1890, 1923, 1964) which destroyed thousands of acres and many homes saw embers carried into the fir crowns, spreading rapidly over the landscape through crown fire.
Fir does not resprout and it is easy to get rid of the worst of the fire dangers by cutting the dead and unhealthy trees. Thinning the remaining trees to space them out will reduce the ability of fire to spread, while pruning the branches of the residual trees to an 8 to 10 foot height will markedly decrease the flammability of the forest. Care must be taken to remove the dead branches from within the forest stand.
One of the worst impacts of this species is to overtop and kill the hardwood trees which over time are shaded out by these tall trees. Madrone and oak do not do well in fir shade, and throughout the Mayacamas Mountains fir is overtopping, overtaking, and killing the hardwood forest. Those wishing to retain the less-flammable hardwoods are encouraged to remove fir trees before they become huge flammable problems with a dying forest underneath.
JUNIPER is a coniferous pyrophyte that grows easily and well in most environments. There are many species, some low shrubs and some growing into trees. Juniper is often used as a quick ground cover, since it grows fast, acts as a visual screen, and is easily cared for. Its berries attracts birds and mammals. However, beware this plant, which develops great volumes of dead litter underneath, and whose foliage is highly flammable. No juniper should be planted within 30′ of a structure, and preferably much further.
MADRONE is a hardwood native to the west coast. Its bright orange bark, white flowers and red berries make it attractive to have nearby. It is moderately flammable, and needs management in order to be sustained in the landscape. Susceptible to fire and a host of diseases, many madrones are actively dying and dead parts are contributing significant fuel loads where madrone exists.
Madrone is not tolerant of shade and unless provided with full sunlight can be expected to fade in vigor over time.
MANZANITA comes in a variety of forms. It has a large number of species and is related to madrone, easy to recognize by the bright smooth orange or red bark. It has abundant oils and tends to become twiggy and dry with a lot of dead material in the lower crown. Some species may be only 12 inches high, while some are over 15 feet tall. Some resprout after cutting and some do not. A local nursery should be able to advise about the desirability of each species.
All manzanita can be highly flammable, with rapid burning potential. A dense hillside of this is terrifying when flaming. Many sprouting species can be very difficult to permanently remove, since they have deep roots with great vigor in few shoots. In addition, many manzanita species have seeds triggered by fire, so a profusion of seedlings can follow a fire. This plant should not be allowed near structures; further away, single specimens with 20 feet of non-flammable terrain in all directions may be kept, as long as they are maintained and all dead vegetation is removed.
OAKSare Napa’s hallmark species, and Napa County is home to more oak species than any other county in America. The oaks range from towering heritage trees to small and barely significant scrub oaks. The deciduous oaks are less flammable than the live oaks (which are evergreen). Some of the oak species are low-growing and difficult to protect from fire due to their low profile and inability to separate ground fuels from canopy fuels. All parts of all trees are flammable, particularly when dry.
It is desirable from a number of standpoints to keep oaks in the landscape and only thin or prune oaks to prevent fire spread. Oaks are extremely important for wildlife. Oak stands are often different on neighboring properties, since regeneration has been aided by the lack of wildfire, while grazing of oak woodlands has contributed to the loss of oak regeneration.
Many oaks actively resprout following pruning, removal cutting or fire, and continued diligence is needed to create a landscape which is healthy and growing, but kept fire safe. The wood is among the best for burning, and it is best to remove cut or fallen materials from the landscape near homes to avoid feeding a wildfire. Some oaks are susceptible to Sudden Oak Death (live oaks, tanoak, black oak), and rapid tree failure and breakup may follow this disease.
PALMS deserve a special mention because they are planted throughout the Napa area despite being non-native. The reason they are of concern herein is the tendency for dead fronds to develop over time either high in the crowns or low in the skirts. Because they are difficult and even dangerous to work in, they are often left with highly flammable dry parts which can easily catch flying embers and become torched. Annual removal of the dead parts is the only remedy to counteract fire tendencies, unless the entire plant is removed.
PINE trees are native almost worldwide. The leaves consist of bundles of needles which may number 1 to 5 held together by a fascicle. While not deciduous, many pines lose great quantities of needles in the fall, which contributes to the accumulation of light flashy fuels at the worst time of year. In addition, pines are pyrophytic, and many depend upon periodic fire for the survival of the species. Pine tends to be heavy with pitch and have flammable bark, cones, and branches. They do not resprout, but seeding success can be prolific and they can often be found in thickets.
Pines should either be removed with a low stump, or left and pruned high into the crown. Trees need to be separated from each other and should have perhaps 10 feet between crowns of other trees, with no understory fuels. Needles should be raked for at least 30 feet around houses, further if the pine is downslope from the house. All dead branches and twigs (more than 1/2 inch in diameter) should be removed within 100 feet of structures.
POISON OAK is not flammable, but is ubiquitous in the wildlands of Napa County. It is often the reason many people avoid doing work in defensible space. It is most often obvious by remembering “leaves of three – let it be.” Unfortunately, it is most contagious when it is least noticeable, in January and February, when it may appear as only a slightly purple stem with no leaves. The stem tends to extend and crawl just underneath the soil ground surface to arise in new places. It can be killed by a diligent digging out of the roots, but otherwise will sprout evermore, ready to do its itchy worst.
Having fought it for over three decades (unsuccessfully), the author has some advice: Find some unsusceptible person (there are a few) to remove it for you. Otherwise, go after it hard after liberally applying Tecnu (www.tecnuextreme.com), cutting wherever visible and digging where possible, leaving it on the surface to dry out. Go inside and take a bath with Tecnu, and keep the clothing in a bag to go into the washing machine without more contact. Return to the site with a shovel after several weeks and dig out the roots that have resprouted. Remember that tools and clothes and body will once again be saturated in oils, but that once washed off it will not spread further.
REDWOOD – Non-Pyrophytic Species Redwood is considered a non-pyrophytic species, due to its verdant crown, thick bark, and moist growing environment. It can burn, however, as evidenced by the large fire scars that can be found in native forests. Active in sprouting from the stump, redwood is commonly found in clumps or rings that surround the original tree stump. Redwood does produce large quantities of needles and branches which can dry out, making removal of ground fuels a necessity from time to time and also demanding pruning of the lower branches until a clear, fire-free bole is created.