Coyote brush and French broom: invasive ROW fuels in the North Bay
French broom is a California listed noxious weed rated C, which bars sale in the state and requires nobody to remove it from a right-of-way. Coyote brush is native and, at 12 feet, is a compatible low-growing species. Neither reaches a primary conductor. Both sprout after cutting. The rule that reaches both is the PRC 4292 pole firebreak.
In April 1994, a crew at Mt. Tamalpais State Park in Marin County took chainsaws to 27 acres of French broom on a unit called Panoramic. They cut the adult stems to within 3 to 24 inches of the ground and left the material where it fell, which built a fuel bed 2 to 3 feet deep. They burned it in May. Two more units followed on the same pattern.
Unit | Acres | Cut | Burned |
Panoramic | 27 | April 1994 | May 1994 |
Upper Muir Woods | 12 | December 1994 to March 1995 | June 1995 |
Lower Muir Woods | 20 | November 1995 | April 1996 |
The Forest Service record of what those three burns produced runs to one sentence:
All burns resulted in complete mortality of mature broom, broom seedling establishment, and vigorous coyote bush sprouting.
Three outcomes, two species, one treatment. The mature broom died. Its seed bank germinated. And the native shrub standing in the same ground came back hard, from a root crown the fire never got hot enough at the base to kill.
That is the North Bay problem in a corridor, and it is not really a clearance problem. One of these plants is on California's noxious weed list and the other is native to the ground it stands on. Neither of those facts tells a crew what to do at a pole.
What the noxious weed listing on French broom actually requires
French broom, Genista monspessulana, is a listed California noxious weed. The listing lives at 3 CCR section 4500, which names it directly, and the term it triggers is defined in statute at Food and Agricultural Code section 5004:
"Noxious weed" means any species of plant that is, or is liable to be, troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or important native species, and difficult to control or eradicate, which the director, by regulation, designates to be a noxious weed.
The listing is only half the answer. CDFA also assigns a letter rating, and the letter is what determines whether anybody does anything. CDFA's pest rating proposal for the species, open for comment from April 16 through May 31, 2020, gives both the current and the proposed rating as C. Its rating justification closes with the reason:
Because it is already very widespread in California, regulation of this weedy species will have little or no affect; a rating of "C" is justified.
The same document records French broom from vouchered specimens in at least 32 California counties. Marin, Sonoma, Napa and Solano are all on that list.
What a C rating does, per CDFA's own primary state botanist in a 2021 presentation on the state's weed lists, is prohibit the plant from being sold in California and from entering the state, and subject it to tolerances in crop seed. C-rated species are "Not under statewide official control unless they are also listed noxious weeds." No part of that reaches a line clearance contractor standing in a right-of-way in Novato.
Coyote brush, Baccharis pilularis, appears on no list at all, because it is native. The California Invasive Plant Council rates French broom High on its inventory and does not rate natives.
French broom | Coyote brush | |
Status in California | Introduced, listed at 3 CCR 4500 | Native |
CDFA rating | C | Not rated |
Cal-IPC rating | High | Not rated |
What the status requires of a utility | Nothing | Nothing |
Two plants, opposite legal characters, identical obligations. The rules that reach either one in a corridor reach them as fuel or as vegetation, never as a weed.
Neither reaches a primary, and both live inside the firebreak
The Forest Service Fire Effects Information System puts French broom "commonly less than 10 feet (3 m) tall, occasionally to 16 feet (5 m) tall." CDFA's description says up to 3 meters. Coyote brush runs in two forms: a matted form 4 to 6 inches high and 3 to 12 feet across, and an arborescent form "up to 12 feet (4 m) high."
On level ground under an ordinary distribution span, those numbers put both plants below any clearance measured from the conductor. How the clearance geometry works, and where rising ground under a span puts a short shrub back into it, is the same arithmetic that applies to any chaparral species.
The rule that reaches them is the pole firebreak. PRC 4292 requires a clearing of "not less than 10 feet in each direction from the outer circumference" of a pole or tower carrying a switch, fuse, transformer, lightning arrester, line junction, or standing as a dead end or corner. The statute reaches grass-covered land as well as brush-covered land, which matters for coyote brush specifically, because grass is the ground it colonizes. Which poles qualify and how the clearing becomes a cylinder is its own subject.
One number changes the geometry, and it belongs to French broom. FEIS records that the pods "burst open explosively, ejecting seeds up to 13 feet (4 m)." Thirteen feet is longer than the firebreak radius. A broom standing three feet outside a cleared circle is inside the circle every June. Nothing in PRC 4292 obliges anyone to cut it, and the clearing cannot stay a clearing while it is there.
The cut is a treatment that both species survive
Both plants sprout from a root crown, and a cut lands above it.
FEIS on French broom: the species "sprouts from the root crown and aboveground stem after top-kill from fire or cutting." The sprouting rate is specific and high. "Once seedlings are taller than approximately 8 inches (20 cm), their rate of sprouting after cutting can be over 90%, particularly if cut in the rainy season."
Cutting lower does not solve it. FEIS records that "Cutting French broom in June in Mendocino County at 2 to 3 inches (5-8 cm) above the soil surface resulted in extensive sprouting." Brush hogs twist material off rather than sever it. FEIS calls them more destructive to perennating tissue than cutting, and records that sprouting still occurs.
Coyote brush "sprouts from the root crown and roots. It may also grow roots where branch nodes contact soil." FEIS is precise about what kills it:
Fire is most detrimental to coyotebrush when high temperatures are present at stem bases. These conditions girdle and kill root crowns, particularly those less than 1 inch (2.5 cm) in diameter. Conversely, fires with peak temperatures at canopy height only top-kill coyotebrush.
McBride and Heady tested exactly that. Eleven plants had their aerial portions burned, simulating a crown fire. All eleven sprouted from the root crown within five weeks. Eleven plants had their bases burned, simulating a grass fire moving through herbaceous fuel. Eight died.
That is the whole mechanism, and it explains the Mt. Tamalpais line. A brush saw, a mower deck and a masticator head all work at canopy height as far as a root crown is concerned. So does a fire burning a slash pile that sits above the ground. The plant that dies is the small one whose base gets heated, and on a maintained corridor floor the small ones are the ones a crew is least likely to treat.
PG&E states the operational consequence in the Bay Area operations and maintenance Final EIR: "because cutting or mowing can stimulate resprouting of incompatible vegetation, PG&E vegetation management staff monitors the ROW for resprouting and reinvasion by incompatible vegetation."
The standing shrub is hard to burn, and the slash is not
The common claim about French broom is that it is a fire hazard. FEIS hedges it, and the hedge is worth reading before anybody writes a prescription around it:
While it has been suggested that French broom invasion increases fire hazard (e.g. [11,54]), this relationship may be site-specific, as other authors (e.g. [49]) indicate that French broom is difficult to burn
The measurement behind that came from the North Bay. FEIS reports that "Despite high temperatures and low humidities, researchers in Marin County, California were unable to burn a mature, uncut French broom stand, and a young uncut stand had only spotty combustion."
Now put that beside Panoramic. Cut and cured, the same species built a fuel bed 2 to 3 feet deep. FEIS records that the material burned in May 1994 "was very dry and extremely flammable," at 73 degrees Fahrenheit and 52 percent relative humidity. Very intense upslope headfires were possible on a moderate weather day.
The fuel a crew creates is the one that carries fire, and it sits at the pole butt under the hardware. What the ground has to look like when a firebreak unit is closed is written into the regulation, and the BMPs for leaving the site clean close the same unit.
Coyote brush contributes a different profile. FEIS describes the coastal scrub community it dominates as "a flammable vegetation type that may burn 1 to 2 years after fire if dry conditions exist." The plant does not need years of stand age to become receptive.
The crew is a dispersal vector, and the measure that says so does not cover brushing
Cal-IPC's plant assessment form for French broom lists the long-distance vectors as "Soil contaminated with seed, road grading equipment, maintenance machinery, and mud." FEIS adds vehicles and machinery to the same list. A mature stand lays down a bank to carry: FEIS reports an average of 10,000 dormant seeds per square meter in the litter and soil under mature stands in Marin County. Between 60 and 82 percent of French broom seed is dormant when it drops, and the seed survives at least five years in the ground.
There is a utility measure written for this, and a North Bay crew should know its exact scope. The California Department of Fish and Wildlife certified the Final EIR for PG&E's Bay Area Operations and Maintenance Incidental Take Permit on June 16, 2022.
It covers a nine-county region including Marin, Napa, Sonoma and Solano, for 30 years. Applicant proposed measure APM BIO-1 is titled "Prevent or minimize spread of invasive weeds." The Final EIR prints it with its revisions from the Draft still showing, so "would" appears immediately before "will" in the source text:
During covered activities involving ground disturbance, mud and/or accumulated soils [would] will be removed from equipment and vehicles, to the extent feasible. Vehicles and equipment [would] will be cleaned or washed before entering a new work site. A log will be kept for each job site and would be completed to document each cleaning or washing of vehicles or equipment before entering each new work site.
The log is the part that turns a practice into a record, and it arrived through comment. Volume 1 of the same Final EIR carries the request: "This mitigation measure should include a requirement for daily monitoring or a log of inspection reports to ensure the required actions are implemented effectively and daily."
Then read the measure's first line. APM BIO-1 applies to "E9a (Reconductoring), G9 (Pipeline Lowering), G11 (Pipeline Replacement), and minor new construction." Vegetation management is a different covered activity in the same document, listed as E10, and it is not in that sentence. A crew reconductoring a span in Sonoma County washes its equipment and signs a log. A crew brushing the same corridor the following spring is outside the measure.
What fills the gap is voluntary. Cal-IPC Publication 2012-01 is a manual of prevention practices written for transportation and utility corridors. It says as much on its own terms. "These voluntary BMPs were developed with the understanding that each situation and entity has different needs, constraints and resources." Its mowing measure gives the timing rule:
Mow invasive plants when they have reached the early flowering stage (or well before seed development) to avoid spreading viable invasive plant seeds.
Set that against the plant's calendar. FEIS records French broom flowering "from March to July on the northern coast," with seeds maturing in June and July and pods bursting in the heat of spring and summer. A North Bay firebreak cycle that works poles in July is moving seed on the mower deck. A cycle that works them in April is not. Neither crew is out of compliance. The difference sits in the work plan, and it belongs to whoever builds the schedule rather than to anyone grading the clearing.
Coyote brush is the community the program is trying to grow
Here is where the native shrub stops being a nuisance and becomes the objective. The same PG&E Final EIR states the integrated vegetation management goal:
The long-term goal of an integrated vegetation management program in the transmission ROW is to convert tall-growing plant communities to low-growing communities. Low-growing shrubs, grasslands, or plants are preferred at the belly of the span, which is the middle 50% of the line between towers or poles. Vegetation may be taller near towers.
A 12-foot native shrub standing in the middle 50 percent of a transmission span is a low-growing shrub by that definition. It is what the program spends money to establish.
That does not make it untouchable. Volume 1 of the Final EIR answers the removal question without hedging:
It should be noted that native trees or other vegetation in a right-of-way (ROW) that conflict or potentially conflict with utility infrastructure have been removed as standard practice; they cannot be restored or allowed to regrow in ROW, which should be considered 'baseline' conditions.
Conflict is the test, and the utility's compatible-species list decides what conflicts. Inside a PRC 4292 firebreak, a coyote brush whose stems break the ten-foot line conflicts and comes out. In the belly of a span, the same plant may be the reason the span needs no work. Whether a stem is pruned or removed, and who makes that call is a program decision. The code does not resolve it.
Two consequences follow from the plant's biology, and a planner should hold both.
The first is that clearing produces coyote brush. FEIS records that "Exposed mineral soil gives coyotebrush an advantage over perennial grasses and chaparral shrubs." The seed germinates on mineral soil with no stratification requirement. In California grasslands the species is "a late seral species that invades and increases in the absence of fire or grazing."
PG&E's own restoration protocol, FP-14, reseeds disturbed ground with California annual grassland species. Annual grassland with neither fire nor grazing is the exact successional starting condition for coyote brush, and a firebreak scraped annually is the exact seedbed.
The second is the one that shows up a cycle or two later. FEIS records that coyote brush "is a nurse shrub for shade-tolerant tree seedlings, particularly coast live oak and California bay," and that transition from coyote brush scrub to mixed evergreen forest "takes place in about 50 years."
The shrub that is compatible at the belly of the span is growing the coast live oak that will not be. That is a 50-year clock, which is longer than most inventories, and the record that carries it is the only place it survives a staff change.
What a coyote brush or French broom record has to carry
Neither species belongs in a tree inventory, and neither is a hazard tree. They are fuel and community records, written against a pole or a span rather than against a stem.
Field | What it settles |
Species, to genus at minimum | French broom and coyote brush take opposite treatments and opposite restoration outcomes |
Native or listed | Decides whether seed spread is a consideration for this unit at all |
Distance from the firebreak edge | A broom throws seed 13 feet, so the plants outside the circle set the re-clear interval |
Month of treatment | Before or after seed maturation in June and July, and inside or outside the rainy season |
Where the cut landed | At the root crown or above it, which decides whether the plant is gone or top-killed |
Whether slash was removed | The cured material is the fuel, not the standing shrub |
Equipment cleaning, if logged | Only required where an adopted measure reaches the activity, so its absence is a finding about scope |
The last row is the one most programs will not have. APM BIO-1's log exists for reconductoring and for minor new construction. Nothing in the Final EIR extends it to E10, and nothing in PRC 4292, the noxious weed list or the CDFA rating creates it. If a utility wants that record from a brushing crew in Marin, it writes the requirement into its own specification, and the documentation the unit produces is where it lands.
Where a corridor runs through State Parks land, a third instrument applies. Volume 1 of the Final EIR cites a Near Term Process for Utility Right of Way Maintenance Activities Agreement between PG&E and the California Department of Parks and Recreation, dated April 27, 2020, covering notification and resource protection for O&M inside the parks. Mt. Tamalpais is one of them. The park's fire program and the utility's clearing program work the same ground on different calendars, and they grow the same two shrubs.
Further reading
PRC 4292: the ten-foot firebreak around a pole, and what counts: Which poles are subject poles, and how 14 CCR 1254 turns the ten-foot clearing into a cylinder.
Chamise (Adenostoma fasciculatum): chaparral fuel in rights-of-way: The ground-level standard for what a crew leaves behind, and why a cut chaparral shrub comes back.
Coast live oak (Quercus agrifolia) in the utility right-of-way: The species coyote brush nurses into the corridor, and what it does once it is there.
Frequently asked questions
Is a utility required to remove French broom from a right-of-way?
No California statute requires it as a weed. French broom is on the noxious weed list at 3 CCR 4500, and CDFA rates it C. In CDFA's own words, in the pest rating proposal open for comment from April 16 through May 31, 2020, 'Because it is already very widespread in California, regulation of this weedy species will have little or no affect; a rating of "C" is justified.' The listing prohibits sale in California and entry into the state. It imposes no removal duty on a landowner or a line clearance contractor. What reaches French broom in a corridor is the PRC 4292 pole firebreak, treating it as fuel, plus whatever a project's adopted mitigation measures or a utility's own specification say.
Can you remove coyote brush from a corridor if it is a native plant?
Under PG&E's Bay Area operations and maintenance program, yes, and the Final EIR says so directly. Volume 1 of the June 16, 2022 Final EIR states that 'native trees or other vegetation in a right-of-way (ROW) that conflict or potentially conflict with utility infrastructure have been removed as standard practice; they cannot be restored or allowed to regrow in ROW, which should be considered "baseline" conditions.' The separate question is whether a 12-foot shrub conflicts at all. The same document names low-growing shrubs and grasslands as the preferred community at the belly of a transmission span, which makes coyote brush a candidate for the target state rather than the problem.
Does cutting French broom kill it?
Usually not. FEIS records that 'French broom sprouts from the root crown and aboveground stem after top-kill from fire or cutting,' and that once seedlings pass about 8 inches, 'their rate of sprouting after cutting can be over 90%, particularly if cut in the rainy season.' A June cut in Mendocino County at 2 to 3 inches above the soil surface produced extensive sprouting. Cutting also does nothing to the seed bank, which ran to an average of 10,000 dormant seeds per square meter under mature stands in Marin County.
Is standing French broom the fire hazard, or is the slash?
The record points at the slash. FEIS reports that researchers in Marin County 'were unable to burn a mature, uncut French broom stand, and a young uncut stand had only spotty combustion,' and hedges the general claim by noting other authors find the species difficult to burn. The same source records that at Mt. Tamalpais State Park, broom cut and left in place formed a 2 to 3-foot deep fuel bed, and the material burned in May 1994 was 'very dry and extremely flammable' at 73 degrees Fahrenheit and 52 percent relative humidity. Cut material left inside a pole firebreak is the condition that carries fire.
When in the year should a North Bay crew work French broom?
Before the seed matures, if seed spread is a consideration on that circuit. FEIS records French broom flowering 'from March to July on the northern coast,' with seeds maturing in June and July and pods bursting in the heat of spring and summer. Cal-IPC's 2012 manual for transportation and utility corridors advises mowing invasive plants 'when they have reached the early flowering stage (or well before seed development).' Those BMPs are voluntary, so the calendar is a program choice, not a compliance one.
