Use this list to identify Marin's most common fire-prone ("pyrophytic") plants. These plants ignite readily and burn intensely, and should be avoided or removed if present in a home's Defensible Space zones, or close to roads and driveways. If removal is not an option, regular and intensive maintenance is required to reduce combustibility. Your fire department may require removal of the plants on this list within 30' of structures (sometimes up to 100' or more depending on the site conditions and fire-code).
All plants can burn if dead, poorly maintained, or drought stressed. These plants are representative of common species that share one or more of these characteristics: they are biologically prone to burn due to chemical composition (often containing volatile oils); are difficult to maintain in a fire-resistant state (they accumulate dead woody material, dead leaves, or other hazardous dead growth); they have a physical structure that presents challenges to routine maintenance (some thorny or dense shrubs that accumulate dead material in locations where it is difficult to remove); they have a high surface area to volume ratio (such as fine needles or lacey leaves); they are prone to rapid changes in moisture content in response to environmental conditions (they may be adequately hydrated one day, but lose moisture within hours when exposed to hot, dry weather).
Many, but not all, of these plants can be maintained in a manner that makes them relatively fire-resistant - however, FIRESafe MARIN can not recommend them due to the likelihood that even short periods of neglect or dry conditions will result in increased hazard.
This list is not comprehensive and is intended to identify only the species most common in Marin. Learn more about fire-prone plants.
Acacia melanoxylon (Black Acacia) is very quick-growing tree to 40 feet tall or much more with a 20 feet wide and in maturity an oval shaped crown. It has rough dark gray bark with vertical fissures and mid-green leaf-like flattened stems, called "phyllodes", that are 3 to 5 inches long by about an inch wide with one margin straight and the other curved. Small creamy flowers are in a small ball-like cluster from late winter into spring and are followed by thin curling seed pods that hang in brownish sheaves. A durable tree for quick growth, screening and erosion control, however its fire prone nature makes it unsuitable for WUI locations in Marin. The aggressive roots can lift sidewalks, damage foundations and plumbing and together with leaf, seed pod and branch litter and its propensity to sucker and reseed, makes this tree not ideal for street plantings or near living areas.
Thuja is a genus of coniferous trees in the Cupressaceae (cypress family). There are five species in the genus, two native to North America and three native to eastern Asia. The genus is monophyletic and sister to Thujopsis.
They are commonly known as arborvitaes, (from Latin for tree of life) thujas or cedars.
Thuja are an extremely fire prone species, and shoud not be planted in the defensible space zone or near driveways or roadways.
Bamboo includes more than 1500 species in 6 "tribes" - all are considered fire-prone when planted in Marin's climate. Bamboo is commonly grown as a screen or hedge. Bamboo should be removed within 30 ' of structures or 10' of roads and driveways according to the fire code adopted by Marin fire agencies.
No bamboo genus or species is “nonflammable” because they all share the same woody stem structure (culms) and other fire prone characteristics. All bamboos form tight clusters of culms (stems). These tight masses of stems tend to accumulate lots of decay resistant, dead material and inhibit the removal of internal dead culms. They all shed dead, shaded out leaves while retaining dead leafless twigs. Leaf and culm sheaths also get caught up in the dense clumps of culms and dead culms are often buried in the dense clumps of culms making it difficult to impossible to remove them. These characteristics are shared by all bamboos and cause all bamboos to be fire prone.
Some bamboo species are shorter and have more slender culms then others, and therefore have less fuel volume. However they also lose their live fuel moisture more quickly when exposed to hot dry winds compared to species with larger culms. Many species of bamboo are “runners” which means they can expand their clump size rapidly by means of underground rhizomes (modified underground horizontal stems). Dense bamboo screens are typically used between homes and along roads to screen unwanted views and provide privacy. These uses can rapidly spread fire from structure to structure and inhibit suppression water application by firefighters. Along roads bamboo is a fire threat to emergency responders and evacuees
Most species of Bamboo are large (6'-35'), with numerous branches emerging from the nodes, and one or two much larger than the rest. The branches can be as long as 11 m (35 ft). They are native to Southeast Asia, China, Taiwan, the Himalayas, New Guinea, Melanesia, and the Northern Territory of Australia.
Umbellularia californica is a large hardwood tree native to coastal forests of California and slightly extended into the state of Oregon. It is endemic to the California Floristic Province. It is the sole species in the genus Umbellularia.
The bay tree, like so many others, will develop differently depending upon the conditions in which it is growing. When found on drier hillsides, it is generally smaller, with yellower leaves and smaller nuts. In a canyon with its roots in plentiful water and rich soil, the leaves will be thinner and darker green and whole tree, nuts and leaves will generally be larger.
Because of its thin bark, the tree is easily top-killed by fire, but it sprouts rapidly. Dense clumps are often formed on cutover land, which may prevent the establishment of desired conifers.
Baccharis pilularis, called coyote brush (or bush), chaparral broom, and bush baccharis, is a shrub in the daisy family native to California, Oregon, Washington, and Baja California. The plants are found in a variety of habitats, from coastal bluffs, oak woodlands, and grasslands, including on hillsides and in canyons, below 2,000 feet (610 m).
Coyote brush is known as a secondary pioneer plant in communities such as coastal sage scrub and chaparral. It does not regenerate under a closed shrub canopy because seedling growth is poor in the shade. Coast live oak, California bay, Rhus integrifolia, and other shade producing species replace coastal sage scrub and other coyote bush-dominated areas, particularly when there hasn't been a wildfire or heavy grazing.
In California grasslands, it comes in late and invades and increases in the absence of fire or grazing. Coyote bush invasion of grasslands is important because it helps the establishment of other coastal sage species.
Coyote brush (Baccharis pilularis) is only moderately fire resistant when it is young and green. After 2-5 years, most coyote brush builds up an increasing amount of dead, woody material that is highly combustible. This buildup is nature's way of encouraging fires, which Coyote brush depends on to regenerate.
As with many plants, it can be maintained in a state of relatively low combustibility, however due to the high maintenance and irrigation requirements, FIRESafe MARIN and our panel of experts consider it a fire-prone does not recommend it within 30' of any structures. Beyond 30', it should be maintained well spaced, as single specimens, and cut back regularly to remove deadwood and encourage new, green growth.
They are evergreen trees or large shrubs. The leaves are scale-like, arranged in opposite decussate pairs, and persist for three to five years. On young plants up to two years old, the leaves are needle-like. The cones are long, globose or ovoid with four to 14 scales arranged in opposite decussate pairs; they are mature in 18-24 months from pollination. The seeds are small, 4-7 mm long, with two narrow wings, one along each side of the seed.
Many of the species are adapted to fire, holding their seeds for many years in closed cones until the parent trees are killed by a fire; the seeds are then released to colonise the bare, burnt ground. In other species, the cones open at maturity to release the seeds.
The fast-growing hybrid Leyland cypress, often found in gardens, draws one of its parents from this genus (Monterey cypress C. macrocarpa).
Eucalyptus globulus, blue gum eucalyptus, is a tree that is not native to California. It is an invasive plant that was introduced from Australia and naturalized in the wild. The California Invasive Plant Council (CAL-IPC) classifies the most common blue gum eucalyptus as a moderate invasive because the trees need certain conditions to thrive.
All eucalyptus species are prone to fire, and should be removed or require significant maintenance within 100' of structures to reduce wildfire hazards.
Firs (Abies) are a genus of 48-56 species of evergreen coniferous trees. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range. Firs are most closely related to the genus Cedrus (cedar). Douglas firs are not true firs, being of the genus Pseudotsuga.
They are large trees, reaching heights of 10-80 m (33-262 ft) tall and trunk diameters of 0.5-4 m (1 ft 8 in-13 ft 1 in) when mature. Firs can be distinguished from other members of the pine family by the unique attachment of their needle-like leaves and by their different cones.
Identification of the different species is based on the size and arrangement of the leaves, the size and shape of the cones, and whether the bract scales of the cones are long and exserted, or short and hidden inside the cone.
A popular, drought tolerant grass that forms clumps of purplish maroon blades topped with rose-red flower spikes. While attractive as a landscape specimen or planted in groups, this grass is fire prone and should be removed in the defensible space zone.
French broom (Genista monspessulana) is a fire prone, upright, evergreen shrub, commonly to ten feet tall. The round stems are covered with silvery, silky hair, and the small leaves are ususally arranged in groups of three. About eighty-five percent of the photosynthetic tissue of French broom is in leaf tissue. The small (less than half-inch) yellow flowers are pea-like and clustered in groups of four to ten. The mostly inch-long pods are covered with hairs.
This species sometimes is confused with Scotch broom (Cytisus scoparius), which has pods with hairs only at the seam, green stems that are five-angled and ridged, flowers that are golden yellow and larger than half an inch, and only about fifty-five percent of total green tissue as leaves.
French broom is found primarily in central coastal counties from Monterey County north to Mendocino County and inland in Lake, Solano, and Contra Costa counties. It is also known from Del Norte County, northern Sierra Nevada foothill counties to 800 meters, and in Kern, San Bernardino, and San Diego counties.
This broom is common on coastal plains, mountain slopes, and in disturbed places such as river banks, road cuts, and forest clearcuts, but it can colonize grassland and open canopy forest. It is found growing in varied soil moisture conditions, but prefers siliceous soils. Unlike other broom species in California, it grows reasonably well on alkaline soils with pH 8. It is competitive in low-fertility soils because of mutualistic relationships with nitrogen-fixing bacteria found in small nodules on roots.
French broom currently occupies approximately 100,000 acres in California. It displaces native plant and forage species, and makes reforestation difficult. It is a strong competitor and can dominate a plant community, forming dense monospecific stands.
Common gorse (Ulex europaea) is a prickly evergreen shrub less than ten feet tall, with a profusion of yellow pea-like flowers from March to May. By May plants are covered with half-inch- to one-inch-long brown pods. The short, stout branches are densely packed and may appear leafless. Spines, approximately half an inch long, are located at base of leaves. The somewhat similar species, Scotch broom (Cytisus scoparius), is not prickly.
orse may be slow in spreading and becoming established, but where it gains a hold, there are few other plants that will so completely dominate an area. Besides becoming a significant fire hazard, it can successfully outcompete native plants in part because of its association with nitrogen-fixing bacteria, which facilitate its colonization of nitrogen-poor soils. Gorse leaf litter acidifies and lowers the cation exchange capacity of moderately fertile soils by immobilizing the bases, making it more difficult for native species to establish. On San Bruno Mountain, San Mateo County, gorse is considered the most difficult exotic species to control, and it has caused considerable loss of valuable grassland habitat.
Tsuga is a genus of conifers in the pine family Pinaceae. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock. Unlike the latter, Tsuga species are not poisonous.
Eight to ten species are within the genus (depending on the authority), with four species occurring in North America and four to six in eastern Asia.
They are medium-sized to large evergreen trees, ranging from 10-60 m (33-197 ft) tall, with a conical to irregular crown, the latter occurring especially in some of the Asian species. The leading shoots generally droop. The bark is scaly and commonly deeply furrowed, with the colour ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips.
Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. Junipers (Juniperus spp.) are one of the hardiest, most versatile and drought-tolerant shrubs. They are also one of the most fire prone species, and are sometimes referred to as a "gasoline bush" by firefighters. They are conifers with prickly young foliage that becomes flatter and softer with age. All junipers should be removed within 100' of structures or 10' of roads and driveways (as required by fire code adopted by Marin fire agencies). Additional clearance may be required depending on the site and local conditions. Juniper does not belond in the landscaped environment or defensible space zones of structures in California.
FIRESafe MARIN recommends that junipers be removed within 100' or structures and 10' (minimum) of roadways and driveways. Period.
Should also be kept widely spaced from one another and regularly maintained by thinning and pruning out ALL dead branches and twigs. When well maintained, most manzanita species are relatively fire resistant. Without proper maintenance, manzanita can contribute significantly to wildfires - based on this, it should be avoided in the defensible space zone of houses in Marin's WUI.
Cortaderia selloana and Cortaderia jubata, Pampas grass or Jubata Grass, are species of grass known by several common names, including purple pampas grass and Andean pampas grass. Jubata is similar to its more widespread relative, the pampas grass Cortaderia selloana, but it can get quite a bit taller, approaching seven meters in height at maximum.
All Corataderia are fire prone and should be avoided or removed in the defensible space zone.
Pine trees (Pinus spp.) are the most common coniferous tree worldwide, numbering around 100 species. These trees form large forests characterized by wide open areas with sunlight spilling to the forest floor. Pines are sun-loving trees that do not grow well under shady conditions.
All pines are prone to fire, and may contribute significantly to wildfires.
Rosmarinus officinalis, commonly known as rosemary, is a woody, perennial herb with fragrant, evergreen, needle-like leaves and white, pink, purple, or blue flowers, native to the Mediterranean region.
Scotch broom (Cytisus scoparius) is an invasive perennial shrub six to ten feet tall. Its sharply angled branches generally have five green ridges with hairs on them when young; as the branches mature the hairs fall off, and the branches become tan and lose the distinct ridges. Pods have hairs along the seams only. One or two golden yellow pea-like flowers cluster between the leaf base and stem. About half the photosynthetic (green) tissue is in the leaves and half is in twig tissue. Sometimes this species is confused with French broom (Genista monspessulana), which has pods with hairs all over them, stems that are not ridged or green, and more than eighty-five percent of its photosynthetic tissue in leaf tissue.
Found along the California coast from Monterey north to Oregon border, Scotch broom is prevalent in interior mountains of northern California on lower slopes and very prevalent in Eldorado, Nevada, and Placer counties in the Sierra Nevada foothills. It is also reported from Los Angeles and San Bernardino counties. It is common in disturbed places, such as river banks, road cuts, and forest clearcuts, but can colonize undisturbed grassland, shrubland, and open canopy forest below 4,000 feet.
Scotch broom currently occupies more than 700,000 acres in California. It displaces native plant and forage species and makes reforestation difficult. It is a strong competitor and can dominate a plant community, forming a dense monospecific stand. Seeds are toxic to ungulates. Mature shoots are unpalatable and are not used for forage except by rabbits in the seedling stage. Foliage causes digestive disorders in horses (Parsons 1992). Since Scotch broom can grow more rapidly than most trees used in forestry, it shades out tree seedlings in areas that are revegetated after tree harvest. Scotch broom burns readily and carries fire to the tree canopy, increasing both the frequency and intensity of fires (Parsons 1992). This species is difficult to control because of its substantial and long-lived seedbank.
Spartium junceum, a dicot, is a shrub that is not native to California; it was introduced from elsewhere and naturalized in the wild. It is an invasive plant and is fire prone.
It is an invasive plant. The California Invasive Plant Council classifies its potential impact on native ecosystems as high.
A spruce is a tree of the genus Picea, a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the earth. Spruces are large trees, from about 20-60 m (about 60-200 ft) tall when mature, and can be distinguished by their whorled branches and conical form. The needles, or leaves, of spruce trees are attached singly to the branches in a spiral fashion, each needle on a small, peg-like structure. The needles are shed when 4-10 years old, leaving the branches rough with the retained pegs (an easy means of distinguishing them from other similar genera, where the branches are fairly smooth).
Notholithocarpus densiflorus, commonly known as the tanoak or tanbark-oak, is an evergreen tree in the beech family (Fagaceae), native to the western United States, in California as far south as the Transverse Ranges, north to southwest Oregon, and east in the Sierra Nevada. It can reach 40 m (130 ft) tall (though 15-25 m (49-82 ft) is more usual) in the California Coast Ranges, and can have a trunk diameter of 60-190 cm (24-75 in).
Tanbark-oak was recently moved into a new genus, Notholithocarpus (from Lithocarpus), based on multiple lines of evidence. It is most closely related to the north temperate oaks, Quercus, and not as closely related to the Asian tropical stone oaks, Lithocarpus (where it was previously placed), but instead is an example of convergent morphological evolution.
Tanoak is very tolerant, and it commonly occurs in any crown position. Seedlings and saplings are quite common in the understory of hardwood or conifer stands. Understory tanoak can grow rapidly in response to death or removal of overstory trees. Tanoak of any age seem to prefer some shading from codominant stems within clumps. Sudden, excessive exposure of stems or crowns is detrimental. Tanoak typically occurs as a codominant tree with other hardwoods, often with an overstory of conifers. Pure stands of tanoak are also common during early stages of succession after fire or logging, however.