Ceanothus (California lilac): fire-prone chaparral near lines
Ceanothus species in California chaparral mature at roughly 2 to 13 feet, so they rarely reach a conductor. The rules that reach them are the PRC 4292 pole firebreak, access-road limits, and project mitigation measures. On the Cleveland National Forest projects, crushing California lilac at a pole entrance was written up under MM BIO-1.
On November 18, 2020, a monitor observed tire tracks at the site entrance to Pole P258530 on San Diego Gas & Electric's TL 626 Conversion South. About three feet of vegetation on each side of the entrance had been crushed. The report names what was under the wheels: California lilac (Ceanothus sp.), scrub oak, and California buckwheat.
That got written up. It went into the California Public Utilities Commission's compliance status report 109 for the Cleveland National Forest Power Line Replacement Projects, dated November 29, 2020, as a violation of mitigation measure MM BIO-1 and a Level 1 Minor Deviation. Four other deviations went in alongside it, out of a two-week reporting period.
The ceanothus in that paragraph was not standing in the way of a conductor. It was the thing a crew got written up for driving over. Those are two different jobs, they run on the same corridor, and on this genus the second one comes up more often than the first.
The measure that reached Pole P258530 is not a clearance rule
The measure is MM BIO-1, adopted in the Final Record of Decision Mitigation Appendix of March 11, 2016. Its heading is "Confine all construction and construction-related activities to the minimum necessary area." The operative text:
All construction areas, access to construction areas, and construction-related activities shall be strictly limited to the areas identified in Section B, Project Description, Table B-7. The limits of approved work spaces (not including existing access roads) shall be delineated with stakes and/or flagging prior to beginning work in any area.
That is a boundary, and every foot outside it is a finding. The same measure builds in who catches it:
An environmental monitor shall complete weekly observations to ensure that all work is completed within the approved work limits, and in the event any work occurs beyond the approved limits, it shall be reported by SDG&E's compliance team in accordance with the Mitigation Monitoring, Compliance, and Reporting program (see Section H).
Two things follow for a crew working chaparral inside a project footprint. The first is that self-reporting is the design. Report 109 attributes all five deviations in that period to SDG&E's own reports, not to a monitor's catch. The second is the cadence: weekly observations, a report every two weeks, and an incident described down to the species list and the dimensions of the impact.
None of this displaces the PRC 4292 firebreak or the PRC 4293 clearance. It runs on top of them, on a different calendar, graded by a different set of people. Report 109 traces the measures to the CPUC's Decision D.16-05-038, adopted May 26, 2016, so they are conditions of a certificate rather than fire code. What the crew at P258530 got wrong was three feet of boundary.
The genus is short, and that decides which rules reach it
California chaparral ceanothus matures below the height of ordinary distribution framing. The Forest Service Fire Effects Information System puts numbers on the three species most likely to be standing in a corridor.
Species | Height at maturity | What happens after top removal |
Buckbrush (C. cuneatus) | 3.3 to 11.5 feet | Obligate seeder; fire kills the plant |
Snowbrush (C. velutinus) | 2 to 9 feet, occasionally 12 to 13 | Sprouts from the root crown |
Whitethorn (C. cordulatus) | 2 to 5 feet, spreading to 12 feet across | Prolific sprouting from a lignotuber |
A 5-foot whitethorn under a 12 kV conductor hung at 25 feet is 20 feet clear, and PRC 4293 asks for four. That span passes on the day it is measured. The height question is settled the same way it is settled for chamise, and manzanita is the genus where the answer changes, because common manzanita reaches 26 feet and ceanothus in these species does not.
So the rules that reach a ceanothus in a corridor are the ones measured from something other than the wire.
The ten-foot cylinder at a subject pole.
The edge of an approved work area.
The width of an access road.
Whatever the utility's own program adds beyond the statutory floor.
Everything below in this piece sits under one of those four.
The subgenus shortcut fails in California
The genus divides into two subgenera, and the field rule of thumb is that subgenus Ceanothus resprouts and subgenus Cerastes does not. In California that rule of thumb points the wrong way often enough to be worth discarding. Keeley, Thomas Parker, Zedler and Brandon Pratt state it plainly in the November 2024 American Journal of Botany:
Ceanothus is widely considered to comprise mostly resprouting species and Cerastes to consist of only obligate seeders. The subgenus Ceanothus includes resprouting species throughout their range from the eastern United States and Midwest to western United States. Within the California Floristic Province (CFP), a few species are unique in producing massive lignotubers that develop from repeated fires; however, within the CFP, the majority of species in this subgenus do not resprout and are obligate seeders.
The authors filled the gaps in the published record with field work on more than 60 recent California wildfires, which is to say the correction comes from the same ground a California crew works on. What a cut accomplishes on a sprouter versus a seeder is already set out on the manzanita page. The point here is narrower: on ceanothus, the shortcut that would let a planner apply it by subgenus does not survive contact with the California Floristic Province, and the province is where the corridors are.
Whitethorn shows how far the species-level answer can drift from a single label. FEIS calls it "an obligate sprouter in moderate fuel-consumption burns and a facultative seeder following high fuel-consumption burns." The same plant is two different management problems depending on how hot the last event was.
The seed under the corridor is older than the corridor
FEIS on snowbrush:
Snowbrush ceanothus seed is stored in the soil for up to 200 years, and can regenerate from seed stored in the soil for up to "several centuries". In British Columbia, germination of soil-stored seed occurred following fire on sites where snowbrush ceanothus had been excluded at least 200 years. Counts made on tree stumps indicated that the intermission between 2 generations of snowbrush ceanothus might be as long as 575 years.
Two numbers make that operational rather than interesting. Buckbrush seed requires "relatively high temperatures during burning," which FEIS gives as 158 to 212 °F. On snowbrush, temperatures of 176 to 203 °F "are optimal to break the seedcoat," by way of "a heat-induced, irreversible cracking of the hylar fissure in the seedcoat."
Those temperatures are reachable inside a right-of-way without a wildfire. A slash pile burned on site reaches them. So does the soil under one. FEIS adds the second route: "[m]echanical disturbance (e.g. timber harvest) may stimulate snowbrush ceanothus germination by abrading the seedcoat." Grading an access road is mechanical disturbance of exactly that kind, and the three feet of crushed ground at the P258530 entrance is the smallest version of it.
The dose is narrow. A Sierra Nevada mixed-conifer study found that at 64 percent duff consumption or less, "few whitethorn ceanothus shrubs were killed and few seeds were stimulated to germinate." Above 64 percent, "the number of seedlings increased exponentially while survival of resprouters decreased from 94 to 50%." A treatment that is too cool does nothing, and a treatment hot enough to kill the existing plants is hot enough to germinate the bank underneath them. Nobody in a bucket controls duff consumption to a percentage point.
A hundred percent top kill is twenty percent dead
The herbicide record on whitethorn is the number to carry into a sign-off. FEIS:
Initial applications of herbicide resulted in 100% top kill and 20% whitethorn ceanothus mortality with plant mortality reaching 90% after the 3rd application.
The first pass looks like a complete kill from the road and leaves four plants in five alive. Getting to nine in ten took three passes.
Cutting behaves the same way, and the variable is the age of the plant. In a Cascade Range study, "the percentage of sprouting plants decreased from 100% for 5-year-old plants to 50% for 11-year-old plants," which reads like an argument for waiting. It does not hold: "vigorous sprouting followed the cutting of 35- to 50-year-old snowbrush ceanothus in the Sierra Nevada."
The consequence for the record is a field most unit tickets do not have. "Treated" and "removed" are different states on this genus, the difference is invisible from a truck at the time of work, and it resolves in the following spring. A ticket that says the ceanothus was sprayed, without saying which application number it was, has not told the next crew anything they can plan against.
Fifteen years of a cleared floor, measured
A utility clearing is functionally a clearcut on a strip, and the research has measured what that strip does. FEIS publishes a table of snowbrush stand development on a Douglas-fir clearcut and slash-burn site in Oregon.
Postfire year | Density (plants/ha) | Cover (%) | Dry weight (kg/ha) | N accretion (kg/ha) |
1 | 142,100 | trace | 99 | 2.0 |
2 | 149,000 | trace | 655 | 9.0 |
3 | 96,100 | 17 | 2,789 | 38.2 |
4 | 70,100 | 17 | 9,548 | 121.3 |
5 | 61,700 | 25 | 23,084 | 243.4 |
7 | 61,700 | 50 | 30,992 | 359.5 |
10 | 36,400 | 58 | 54,287 | 358.3 |
15 | 35,500 | 70 | 62,100 | 298.8 |
Read the first two columns against each other. At year 2 the cover is still a trace, and the density is at its peak of 149,000 plants per hectare. Everything that will close that ground is already standing in it. Cover reaches a quarter at year 5, half at year 7 and seven-tenths at year 15, while density falls by three-quarters over the same span.
Height moves on a different curve, which is why a height trigger misreads this genus. After 5 years snowbrush "may be less than 3 feet (1 m) tall, but doubles its height in the next 5 years," then gains "only 1.5 feet (0.5 m) in the following 5 years." A three-year patrol sees plants under 3 feet and 2,789 kilograms per hectare. A ten-year return on the same ground finds 54,287. What a growth rate implies for an interval has to be read off biomass here rather than off height.
The nitrogen column is the part that pays forward. Net accretion over the 15 years was 1,110 pounds per acre, and root nodulation went from zero percent of roots in the first two years to 100 percent by year 15. Buckbrush runs the same trade at "an estimated rate of 54 pounds per acre" a year. The plant being cleared is fertilizing the ground it is cleared from, which is a real input to how fast everything else in the corridor comes back.
The green foliage gets more flammable as the summer runs
Snowbrush "burns 'quite hot,'" FEIS says, and "[t]he foliage contains volatile oils that may contribute to fire hazard." The oils have been measured as solvent extractives, meaning waxes, oils, terpenes and fats, by dry weight.
Fuel type | Solvent extractives (%) |
Foliage | 18.3 |
Woody, under 0.25 in | 6 |
Woody, 0.26 to 0.50 in | 4.2 |
Woody, 0.51 to 1.00 in | 3.3 |
Woody, over 1.00 in | 2.6 |
The foliage carries roughly three times the extractive fraction of the finest woody material and seven times that of the coarse. Its extractive heating value has been reported at 11,942 Btu per pound. On this genus the live crown is the hazardous part of the plant, which inverts the usual reading of a shrub where the dead fraction is the concern.
The number moves through the season while the plant stays green. FEIS reports that the potential rate of spread through snowbrush "can be expected to increase as the growing season progresses from June 20 to September 10." The basis is "an increase in caloric content (from 1,400-2,400 calories/gram) and a decrease in the water content (from 68% to 53%) of green vegetation."
So a unit cleared to specification on June 20 sits, on September 10, under a fuelbed that has nearly doubled in caloric content and shed a fifth of its water. The measured clearance has not changed. Nothing about the unit is out of compliance. The fire behavior over it is a different problem from the one the inspector signed. That gap is the argument for reading a ceanothus unit against the seasonal calendar rather than against the date it was closed.
Where the corridor runs under conifers, the same fuel becomes vertical. FEIS records that "[e]xtensive stands of whitethorn ceanothus and montane chaparral patches exhibited the greatest mean fire spread/minute and the greatest flame lengths compared to forested types," and that persisting stands "could act as ladder fuels, increasing the possibility of a stand replacing fire." A Douglas-fir edge above a whitethorn floor is the configuration that sentence describes.
Chaparral is compensated two acres for one on Forest Service land
Clearing chaparral permanently has a price on a project with adopted mitigation. MM BIO-5 sets it:
Impacts to vegetation communities on Forest Service land will be mitigated as follows: 2:1 for habitats that are sensitive or support listed species; 2:1 for coastal sage scrub, chaparral, grassland, or oak/conifer forest; and 3:1 for riparian oak woodland.
The floor for permanent impacts to any native vegetation community is 1:1, and where the ratios differ the higher one governs. Chaparral on Cleveland National Forest land is therefore two acres of compensation for one acre removed, through agency-approved land preservation or a mitigation fee.
MM BIO-4 draws the line that matters to a vegetation program. Restoration under a Habitat Restoration Plan reaches "[a]ll previously undisturbed temporary work areas not subject to long-term use or ongoing vegetation maintenance." The maintained corridor floor sits outside that obligation, because it is under ongoing vegetation maintenance by definition. The one-time access spur sits inside it.
That is the cleanest way to see what happened at Pole P258530. Crushing three feet of California lilac at a site entrance turns on which side of the maintained-versus-temporary line the tires were on. The answer decides whether that ground gets a restoration plan with success criteria attached to it.
What the county approves is measured from a house
The planted side of this genus is the reason "California lilac" is the name on the work order in the first place. Los Angeles County Fire Department's Fuel Modification Plant Selection Guidelines list it as an acceptable shrub, in one row of a table:
Botanical Name | Common Name | Zone | Minimum distance from structure |
Ceanothus species | Wild Lilac | B | 30 |
Zone B is "30'-100' from the edge of any qualifying structure," and the last column is the minimum distance from that structure. So a homeowner can plant wild lilac under an approved fuel modification plan, at 30 feet from the house, and be in compliance.
Every distance in that document is measured from a structure. None of it is measured from a conductor. An approved Zone B planting can sit directly under a service drop and nothing in the approval says otherwise, which puts the conversation about it in the notice and refusal track rather than in the fuel modification plan. The guidelines also tell designers, in their own words, what the approval does not mean:
Don't assume any plant is "fire proof." All plants will burn and assuming a plant is ignition resistant can be very misleading.
There is no contradiction between a county approving wild lilac at 30 feet from a house and the Forest Service measuring 18.3 percent solvent extractives in its foliage. The county is regulating a spaced, irrigated, maintained specimen in a landscape. FEIS is describing a continuous stand of the same genus on a hillside. A corridor can contain both, sometimes in the same span.
What a ceanothus record has to carry
The genus name settles less here than on most species. These are the fields that make a ceanothus unit readable a season later.
Field | Why it has to be there |
Species, or at least whether it resprouts | The subgenus shortcut fails in California; the species is the answer |
Treatment and application number | The first herbicide pass is 100 percent top kill and 20 percent mortality |
Plant or stand age | Sprouting ran 100 percent at 5 years and 50 percent at 11 |
Cover at the last look, alongside height | Height stalls for five years while cover and biomass climb |
Inside a monitored project footprint, yes or no | Decides whether MM BIO-1 and its weekly observation apply |
Maintained corridor or temporary work area | Decides whether restoration under a Habitat Restoration Plan is owed |
Soil disturbed or heated on site | 158 to 212 °F and abrasion are both germination triggers |
Planted specimen or wild stand | Decides whether this is a notice conversation or a clearing |
The first, fourth and seventh of those are not fields a standard unit ticket carries, and none of them can be reconstructed later from a photograph of cleared ground. They belong in the inventory, with the rest of the ordinary closeout on top.
Report 109 runs to fifteen pages and gives the Pole P258530 incident five sentences. Three feet each side, three species named, one measure cited, one deviation level, one tailboard reminder. Nothing in it concerns a conductor. A crew reading only the clearance rules on that span would never have found it, and it is on the record all the same.
Further reading
PRC 4292: the ten-foot firebreak around a pole, and what counts: The cylinder, the three treatment layers by elevation, and which poles are subject poles.
Manzanita (Arctostaphylos spp.) as ROW and pole-clearance fuel: The other chaparral genus that splits into sprouters and obligate seeders, and what a cut does to each.
Growth rate and the re-clear cycle: What a species' growth curve implies for the interval, and where a height-based trigger misreads it.
Frequently asked questions
Does ceanothus have to be cleared away from a power line?
Usually not by a clearance measurement. The California chaparral species mature between about 2 and 13 feet, so a mature plant standing on level ground under a distribution span is rarely inside the PRC 4293 band. Where it gets cleared is inside the ten-foot PRC 4292 firebreak around a subject pole, along access roads, and wherever a utility's own program calls for fuel reduction beyond the statutory minimum.
Will cutting or spraying ceanothus kill it?
Often not on the first pass. The Forest Service Fire Effects Information System reports that on whitethorn ceanothus, initial herbicide applications produced 100 percent top kill and 20 percent plant mortality, with mortality reaching 90 percent after the third application. On snowbrush ceanothus, the share of plants that sprouted after damage fell from 100 percent for 5-year-old plants to 50 percent for 11-year-old plants, and vigorous sprouting still followed the cutting of 35- to 50-year-old plants in the Sierra Nevada.
How long does ceanothus seed stay viable under a corridor, and what sets it off?
FEIS records snowbrush ceanothus seed stored in the soil for up to 200 years, regenerating from soil-stored seed for up to several centuries, and germinating in British Columbia on sites where the species had been excluded for at least 200 years. Tree stump counts suggested the interval between two generations might run as long as 575 years. The trigger is heat or abrasion. Buckbrush seed requires 158 to 212 degrees Fahrenheit during burning, 176 to 203 degrees Fahrenheit is optimal for breaking the snowbrush seedcoat, and mechanical disturbance may stimulate germination by abrading the coat.
Is California lilac a fire-safe landscaping plant?
Los Angeles County Fire Department's Fuel Modification Plant Selection Guidelines list Ceanothus species under the common name Wild Lilac as acceptable in Zone B, which runs 30 to 100 feet from a qualifying structure, with a minimum distance from the structure of 30 feet. Every distance in that document is measured from a house. None of it is measured from a conductor, and the same guidelines tell designers not to assume any plant is fire proof.
Does driving over ceanothus in a right-of-way create a compliance problem?
On a project carrying adopted mitigation measures, yes. San Diego Gas & Electric reported that on November 18, 2020, a monitor observed tire tracks and crushed vegetation at the site entrance to Pole P258530 on TL 626 Conversion South, affecting about three feet of vegetation on each side, consisting of California lilac, scrub oak and California buckwheat. The CPUC compliance status report recorded it as a violation of MM BIO-1 and a Level 1 Minor Deviation.
