Janet Klein, a vegetation specialist who lives and works in Fairfax, says the San Geronimo Ridge—once a diverse forest of oak and Douglas fir as well as home to all kinds of birds and animals—is slowly being overtaken by a nasty and seemingly intractable weed.
“It’s a disheartening situation,” Ms. Klein said. “This patch, it was a grassland, and now it’s a shrubland. It’s a completely different vegetation type.”
The loss is not just one of biodiversity, according to Ms. Klein, the natural resources program manager for the Marin Municipal Water District, which manages the area. In a major wildfire it could also mean a threat to vacationers and residents in West Marin.
“If you’re a boy scout, this is a perfect thing to get the fire started,” said Ms. Klein, reaching in to grab a dry branch in a network of towering weeds that now dominate part of the ridge at a rate that expanded by the size of two football fields between 2004 and 2008. She said that despite efforts to destroy the weed, the overall problem is getting worse. “The problem is knowing it’s expanding behind you.”
Marin’s independent watchdog has endorsed the use of herbicides to arrest the spread of an invasive weed that officials say is putting the county at too high a risk of a massive wildfire that could kill dozens of residents and destroy millions of dollars in property.
The Marin County Civil Grand Jury said the use of the wildly popular weed killer, glyphosate, which is marketed by Monsanto Co. as Roundup and AquaMaster, is the cheapest and most effective way to reduce the fire risk in the Mount Tamalpais watershed.
Officials have proposed two approaches for controlling fire-prone invasive species on the 18,900 watershed acres they own: one involves the use of herbicides and the other does not. The Marin Municipal Water District (MMWD), which released its plans last August, now says the use of chemicals is a dramatically more effective procedure for controlling four types of weeds known as broom.
The yellow-flowered evergreen shrub is known for its anticompetitive behavior, prodigious ability to reproduce and contagious flammability. Both approaches remain under consideration and an environmental-impact report examining several approaches is expected in the fall, according to water district spokeswoman Libby Pischel.
The district plan involves using some organic pesticides and manual methods along with three conventional pesticides: glyphosate, triclopyr and clopyralid. (The latter two pesticides were not directly endorsed by the grand jury.) The district would impose 28 requirements on herbicide use, limiting applications to once a year, requiring that workers wear protective gear and carry spill-cleanup material and notifying the public when and where the pesticides will be used.
The most frequently used herbicide would be the one district officials found to have relatively small impacts, glyphosate, and a solution of it would only be allowed at up to two quarts per acre and no more than 300 acres per year, about 1.6 percent of the total water district land. The pesticides would also not be used within buffer zones of 100 feet of springs, reservoirs and streams that have water throughout the year.
Local fire-impact assessments have shown that highly populated areas from Mill Valley to Fairfax are within miles of watershed property where water district officials say the weed problem is not completely suppressible and the California Department of Forestry rates the land as having a high or very high fire risk. Lagunitas and Stinson Beach are home to some of the 13,200 structures within a mile’s reach of watershed property.
The risk is only enhanced by flammable trees felled by sudden oak death, a pathogen-caused disease that has infested the vast majority of the watershed’s oak, including 1,340 acres in the watershed between 2004 and 2009, the most recent data available.
The grand jury report, issued last week, drew a comparison between the fire risk faced now and the potential for an incident like the 1991 Oakland Hills fire that killed 25 and burned 3,469 structures, as well as the Mount Vision fire, which destroyed 48 structures on the Point Reyes Peninsula in 1995. Nearly all of the Mount Tamalpais watershed burned between 1881 and 1945, including in the last major fire, which burned 20,000 acres from Kent Lake to Bolinas in 1945.
Officials say the key to preventing a similar occurrence today is to fight the spread of non-native species like French broom, which can produce thousands of seeds a year and fling them several meters away, while poisoning livestock and degrading the habitat for other plant species. Perhaps the broom’s most threatening attribute is its height—up to 10 feet—which allows the highly flammable plant to exacerbate fires by extending flames up to trees’ canopy layer, according to Carla D’Antonio, ecology professor at the University of California, Santa Barbara. The other targeted broom species include Scotch, Spanish and Portuguese broom.
The water district’s plan would use a combination of manual methods and herbicide application to contain areas where the weed species are dominant, aggressively target the elimination of weeds in “fuel breaks,” areas designed to be barriers against fire, and eliminate the weed entirely in the vast majority of watershed land where the weeds do not have a strong foothold.
Marin County has allowed some conventional pesticide use in parks and open space under its Integrated Pesticide Management program, approved in 2009. But pesticides have not been used in the Mount Tamalpais watershed since 2005, when safe-water advocates decried the practice.
“Management keeps falling back to that solution,” said Frank Egger, who was a primary pesticide opponent as mayor of Fairfax in 2005. “It’s poison in the watershed. We can’t control what happens on private property, but we should be able to control what happens on public land.”
Opponents of herbicide use say that what is known about herbicides’ risks to human and animal health are troubling, and that what isn’t yet known about the herbicides and the inactive ingredients they are packaged with could be worse. They also claim many of the studies showing minimal harm from pesticides are funded by companies with a financial interest in the results.
Water district officials say they plan to mitigate potential negative effects by primarily using a product, called AquaMaster, that is simply glyphosate mixed with water. The product restricts a pathway that allows plants to synthesize organic compounds needed for photosynthesis and cell growth. The other two herbicides mimic plant growth hormones, causing plants to grow abnormally and ultimately self-destructively.
Despite the fact that chemicals including glyphosate are widely used, many of its associated long-term chronic health risks are unclear, according to Paul Capel, a research chemist with the United States Geological Survey, who has studied pesticide dispersion in ecosystems in detail.
“There are these nagging concerns about glyphosate, but we’ve used it for, I don’t know, two or three decades in small quantities and a decade in huge quantities, and it doesn’t seem to have any long-term effects in the human populations,” Dr. Capel said by telephone from his home outside of Minneapolis, noting that the synthetic compound has a three-week-long half-life, decaying rapidly in the environment and losing its toxicity. “It wouldn’t bother me if they used these chemicals in a watershed near my house. And I’m sure they probably do.”
The water district says an herbicide-free approach has failed. District officials developed the first weed-control plan in 1995 and began trying to contain the spread of broom with controlled burning, mowing and hand removal. Those strategies led to the killing of non-invasive vegetation and increased weed germination, officials say. Since 2001 the water district has tried a number of methods, including “organic” pesticides like salt slurry, clove oil and acetic acid—the acid in vinegar. The water district has even used goats, and while goats will eat the perennial weed, they tend to prefer eating other, more desirable species.
The most prevalent of the weeds, French broom, is taking up 1,200 acres of land and is expanding its reach by 30 acres per year, according to district officials. Even an ambitious volunteer program would not even be able to halve the annual spread of the French broom. The district also uses labor from a county probation program.
In a 2010 survey of existing research on herbicides and its potential effects in the watershed, the district reviewed a significant amount of data about links between herbicides—all of which have some level toxicity to people—and adverse health impacts. The report concluded triclopyr “poses the highest risk to workers, the general public and most aquatic and terrestrial wildlife,” but that the risk could be minimized by only applying triclopyr to the stumps of plants, like Spanish broom, that do not respond as well to AquaMaster.
Clopyralid was found to have a low risk factor because of the low quantities that would be used. And glyphosate was found to have the “least risk to workers and the general public, moderate risks to terrestrial wildlife from direct sprays, and low risks to aquatic species.”
Dr. Capel endorsed maintaining a distance from water while spraying, and said that days when rain is forecast should also be avoided to prevent runoff. “I would probably say for these chemicals there’s probably not a huge amount of concern. They’re going to be used in the watersheds and only a very small part of what’s going to be used—one tenth of a percent to a hundredth of a percent—finds its way to a stream or a lake,” Dr. Capel said.
The watershed includes some 77 rare, threatened and endangered species, including the Northern spotted owl, coho salmon and the Raven’s manzanita shrub. Officials say they would take special care to avoid harming those creatures.
The pesticide plan is estimated by the water district to cost $1.6 million annually for 15 years, far less than a plan using only manual labor that officials say would cost $5.6 million per year. The district said it cannot afford to budget for full implementation of either plan and will likely have to focus its efforts on high-priority areas.
The grand jury said the cheaper and “more effective” approach, using herbicides, should be selected. If not, “new funding sources should be pursued by the most affected communities,” they wrote. “Decisions concerning the use of herbicides to control fuel load on MMWD lands should be based entirely on science, economics and the broad public welfare.”
Mr. Egger, now president of the Ross Valley Sanitary District board, disputed the district’s estimates of the expense of a manual weed-management program, his preferred solution, and the extent of the weed problem. “That $5.6 million has to be a hugely inflated figure.”
The figure is based on an opaque computation, laid out at length in a 232-page public report, of how much it would cost to extract weeds by hand and burn them compared with far less time spent simply cutting brush and applying herbicide.
Ms. Pischel said the estimates of the cost of broom dispersion are based on “years of experience.”
“Our number one priority is to protect water quality so we would never do anything that would jeopardize water,” she said.
On San Geronimo Ridge, the oak is mostly dead and does not appear to be coming back, leaving an opening to the sky that is gradually being filled by the towering broom. “This is a place that we would consider using herbicides,” Ms. Klein said. “In the absence of herbicides we’re not touching it because we don’t have the money.”
Even if the district did have money for a program without pesticides, “It’s not ecologically sound. It’s not logistically feasible,” she said, describing the amount of soil disturbance and carbon release from pulling and burning the weeds as toxic to the environment. Nonetheless, Ms. Klein said she shared the concerns of people worried about pesticide use.
“I drink the water, my kids drink the water. My kids hike on this ridge. It’s a personal issue.”