Pesticides are the primary tool of the “restoration” industry

Over 20 years ago, my initial reaction to native plant “restorations” was horror at the destruction of healthy trees.  It took some years to understand that pesticides are used by most projects to prevent the trees from resprouting and to control the weeds that thrive in the sun when the trees are destroyed.  Herbicides are a specific type of pesticide, just as insecticides and rodenticides are also pesticides.

Because pesticide application notices are not required by California State law for most of the herbicides used by “restoration” projects, the public is unaware of how much herbicide is needed to eradicate non-native vegetation, the first step in every attempt to establish a native plant garden.  California State law does not require pesticide application notices if the manufacturer of the herbicide claims that their product will dry within 24 hours.

Herbicides used to eradicate non-native plants

In 2014, the California Invasive Plant Council conducted a survey of 100 land managers to determine what methods they use to kill the plants they consider “invasive.”  The result of that survey was a wakeup call to those who visit our parks and open spaces.  62% of land managers reported that they frequently use herbicides to control “invasive” plants.  10% said they always used herbicides.  Only 6% said they never use herbicide.  Round Up (glyphosate) is used by virtually all (99%) of the land managers who use herbicides.  Garlon (triclopyr) is used by 74% of those who use herbicide.

Pesticide use by land managers in California. Source California Invasive Plant Council

Land managers in the Bay Area use several other herbicides in addition to Garlon and Round Up.  Products with the active ingredient imazapyr (such as Polaris) are often used, most notably to kill non-native spartina marsh grass.  Locally, the San Francisco Estuary Invasive Spartina Project (ISP) “defines a need for a zero tolerance threshold on invasive Spartina in the San Francisco Bay.” 2,000 acres have been repeatedly sprayed with herbicides on East and West sides of the San Francisco Bay since the project began.  The result of this project has been bare mud where the imazapyr was aerial sprayed from helicopters the first few years of the project with annual spot spraying continuing 15 years later.  Imazapyr is very mobile and persistent in the soil.  That is the probable reason why attempts to replace the non-native species with the native species were unsuccessful. The loss of both native and non-native marsh grass has eliminated the nesting habitat of the endangered Ridgway rail, decimating the small population of this endangered bird in the Bay Area.

Pesticide Application Notice, Heron’s Head, 2012

Aminopyralid (brand name Milestone) is also used.  Although it is considered less toxic than other herbicides, it is the most mobile and persistent in the soil.  New York State banned the sale of Milestone because of concern about contaminating ground water.

With this knowledge of widespread use of herbicides by land managers, we followed up with specific land managers in the Bay Area to determine the scale of local herbicide use.  East Bay Regional Park District significantly reduced their use of Round Up for facilities maintenance in 2018, in response to the public’s concerns after multi-million dollar product liability settlements of lawsuits from users who were deathly ill after using glyphosate products.  In 2019, the Park District announced that it would phase out the use of Round Up in picnic areas, camp grounds, parking lots, and paved trails.

Source: East Bay Regional Park District

At the same time, the Park District restated its commitment to using herbicide to control plants they consider “invasive.”  Unfortunately, the Park District’s use of herbicide for “resource management projects” has skyrocketed and is by far its greatest use of herbicides.  “Resource management project” is the euphemism the Park District uses for its native plant “restorations” that begin by eradicating non-native vegetation such as spartina marsh grass and 65 other plant species.

These trends in pesticides used by East Bay Regional Park District continued in 2019.  Glyphosate use continued to decline by 82% since reduction strategies began in 2016.  Use of Garlon (active ingredient triclopyr) to control resprouts of non-native trees and shrubs increased 23% since 2017.  Use of Polaris (active ingredient imazapyr) to eradicate non-native spartina marsh grass increased 71% since 2017.  “Resource management projects” have been renamed “ecological function.”

San Francisco Recreation and Parks Department (SFRPD) reduced use of herbicide briefly in 2016, after glyphosate was classified as a probable carcinogen.  However, herbicide use has since increased, particularly in the 32 designated “natural areas” where SFRPD is attempting to “restore” native plants by eradicating non-native plants. In 2019, SFRPD applied herbicides 243 times, the most since 2013.  Of these, 144 applications were in the so-called “natural areas” (this includes properties of the Public Utility Commission, San Francisco’s water supplier, managed in the same way; i.e., eradicating plants they don’t like).  Though the “natural areas” are only a quarter of total city park acres in San Francisco, nearly half the herbicides measured by volume of active ingredient were used in those areas.

Data source: San Francisco Recreation and Parks Department. Graphic by San Francisco Forest Alliance

San Francisco’s Parks Department has been using herbicides in these areas for over 20 years.  Plants that are repeatedly sprayed with herbicides eventually develop resistance to the herbicide, just as over use of antibiotics has resulted in many bacteria that are resistant to antibiotics.

Spraying Garlon on Twin Peaks in San Francisco, February 2011

UC Berkeley recently announced a temporary ban on the use of glyphosate on playing fields and similar landscaped areas.  The use of glyphosate to kill non-native plants considered “invasive” was specifically exempted from UC’s temporary ban.

The more pressure the public puts on land managers to restrict the use of herbicides, the more vociferous native plant advocates have become in defense of herbicides.  In October 2017, California Invasive Plant Council published a position statement regarding glyphosate that justified the continued use of glyphosate, despite its classification as a probable human carcinogen by the World Health Organization.

Mounting public pressure to ban the use of glyphosate has also pushed land managers to try newer herbicides as substitutes (e.g., Axxe, Lifeline, Clearcast).  Less is known about these products because less testing has been done on them and we have less experience with them.  It took nearly 40 years to learn how dangerous glyphosate is!

Why are we concerned about herbicides?

The World Health Organization classified glyphosate (the active ingredient in Round Up) as a probable human carcinogen in 2015.  That decision suddenly and radically altered the playing field for the use of glyphosate, which is the most heavily used of all herbicides.

Since that decision was made, many countries have issued outright bans on glyphosate, imposed restrictions on its use or have issued statements of intention to ban or restrict glyphosate-based herbicides. Countless US states and cities have also adopted such restrictions. Locally, the Marin Municipal Water District (MMWD) made a commitment to not using pesticides—including glyphosate—in 2015.  MMWD had stopped using pesticides in 2005 in response to the public’s objections, but engaged in a long process of evaluating the risk of continuing use that resulted in a permanent ban in 2015.

Several jury trials have awarded plaintiffs millions of dollars as compensation for their terminal medical conditions that were successfully attributed to their use of glyphosate products by product liability lawsuits. There are an estimated 125,000 product liability lawsuits in the US against glyphosate awaiting trial. 

In 2020, plaintiffs in a class-action suit against Monsanto alleging that it falsely advertised that the active ingredient in Roundup only affects plants were awarded $39.5 million.  The settlement also requires that the inaccurate claim be removed from the labels of all glyphosate products: “…[plaintiff] says Monsanto falsely claimed through its labeling that glyphosate, the active ingredient in Roundup, targets an enzyme that is only found in plants and would therefore not affect people or pets. According to the suit, that enzyme is in fact found in people and pets and is critical to maintaining the immune system, digestion and brain function.”

It took lawsuits to establish the toxicity of glyphosate because the “studies” that are used to approve the use of pesticides in the US are done by the manufacturers of pesticides.  The studies are manipulated, often with the active participation of government employees who are responsible for regulating dangerous chemicals.  The lawsuits succeeded by revealing the fraudulent studies used to exonerate glyphosate.

What little research is done on the effect of pesticides on wildlife indicates that pesticides are equally toxic to animals.  New research finds that western monarch milkweed habitat contains a “ubiquity of pesticides” that are likely contributing to the decline of the iconic species:  “’We expected to find some pesticides in these plants, but we were rather surprised by the depth and extent of the contamination,’ said Matt Forister, PhD, a butterfly expert, biology professor at the University of Nevada, Reno and co-author of the paper…’From roadsides, from yards, from wildlife refuges, even from plants bought at stores—doesn’t matter from where—it’s all loaded with chemicals. We have previously suggested that pesticides are involved in the decline of low elevation butterflies in California, but the ubiquity and diversity of pesticides we found in these milkweeds was a surprise,’ Dr. Forister said.”

Damage to the environment

In addition to harming humans and other animals, herbicides used by native plant “restorations” are damaging the soil, undoubtedly contributing to the failure to successfully establish native plants. (1)

  • Both glyphosate (Round Up) and triclopyr (Garlon) are known to kill mycorrhizal fungi that live on the roots of plants and trees, facilitating the transfer of moisture and nutrients from the soil to the plants.  The absence of mycorrhizal fungi makes plants more vulnerable to drought because they are less able to obtain the water they need to survive.
  • Glyphosate is known to bind minerals in the soil, making the soil impenetrable to water and plants more vulnerable to drought.
  • Both glyphosate and triclopyr also kill microbes in the soil that contribute to the health of soil by breaking down leaf litter into nutrients that feed plants.
  • Because herbicides are mobile in the soil and the roots of plants and trees are often intertwined, non-target plants are often harmed or killed. 
Pesticides kill the soil food web.

Despite knowing that glyphosate probably causes cancer in humans and that many herbicides cause significant environmental damage, native plant advocates continue to push land managers to use toxic chemicals to kill non-native plants and trees.  They do so because herbicides are the cheapest method of eradicating vegetation.  They do not have the person-power to eradicate all the vegetation that is being killed by herbicides.  Using herbicides enables native plant advocates to claim larger areas of parkland and open space than they would be able to without using herbicides.

(1) Montellano,, “Mind the microbes: below-ground effects of herbicides used for managing invasive plants,” Dispatch, newsletter of California Invasive Plant Council, Winter-Spring 2019-2020.

A late fall walk in the woods

Kaweah Oaks Preserve is a 322-acre remnant of riparian woodland in the Central Valley of California, near the town of Visalia.  The land was purchased by the Nature Conservancy in 1983 and turned over to a land trust 14 years later.  That’s the usual Conservancy strategy.  They buy the land to preserve it, engage in an initial restoration to its pre-settlement condition if necessary, but they look for partners to maintain the land for the long-term.

Kaweah Oaks Preserve

When we parked our car, we were instantly greeted by the chatter of birds.  In a brief visit of less than 2 hours, we saw or heard 15 species of birds.  (1)  In late fall, many of the plants were dormant, but there was still much of interest to see.

Kaweah  Oaks2

There was no water in the creek.  We wondered if we would find water in the creek in the late fall during a more typical rain year.  We have had almost no rain in California yet this year.

Valley Oak
Valley Oak

Valley Oak (Quercus lobata) is the tallest oak in California, reaching 70 feet or more according to Sunset Western Garden.

California wild grape
California wild grape

California wild grape covered much of the ground and climbed high into the trees.

native blackberry

Native blackberry was also thriving in the understory. We were reminded of its non-native cousin, Himalayan blackberry, which is eradicated for the same “invasive” behavior exhibited here by its native counterpart.


Native willow grows densely near the creek, sprawling on the ground, creating tunnels on the trails.

oak gallThere were oak galls on the trees and lying on the ground under the trees.  “The valley oak trees on the Preserve are hosts to at least nine different kinds of gall wasps.  These tiny cynipid wasps sting the stems of oak leaves in the early spring and lay their eggs there.  The tree responds to the chemicals the wasp leaves behind and quickly produces a growth that the wasp larva live in and consume until they become adult wasps and chew their way out.  The oaks can look like an apple, a tiny pink-and-white chocolate kiss, a wooly ball, a bright pink sea urchin, a brain or even a tiny ball the size of a pinhead that jumps around!” (2)

Valley Oak

This Valley Oak fell over a long time ago, but doesn’t appear to be dead yet.  It is left on the ground to continue to contribute to the ecosystem.  Dead trees are valuable members of the forest community.  As they slowly decay, the nutrients they have accumulated during their long lives will be returned to the soil.

The lessons of the Kaweah Oaks Preserve

These were our thoughts, as we ended our late fall walk in the woods:

  • Native plants sometimes spread just as non-native plants do.  However, they are never called “invasive” as non-native plants are.  We would like to retire the word “invasive” from our horticultural vocabulary.  We don’t wish to call native or non-native plants “invasive.”
  • Nature is wild and free in the Kaweah Oaks Preserve.  It isn’t being manicured to suit the preconceived notions of humans.  Why can’t we leave our public lands in the Bay Area alone to grow as nature dictates?  Human “management” of nature does not achieve better results than nature left to its own devices.
  • An occasional downed tree or trail obstructed by a sprawling limb adds to the adventure of a walk in the forest.  The resulting tangle provides superior habitat for every creature in the forest.


(1)     Our bird list:  Acorn Woodpecker, Nuttal’s Woodpecker, Northern Flicker, White-crowned Sparrow, Golden-crowned Sparrow, Red-tailed Hawk, House Finch, Says Phoebe, Turkey Vulture, Brewer’s Blackbird, Redwinged Blackbird, Brownheaded Cowbird, Northern Mockingbird, Yellow-rumped Warbler, Western Scrub Jay.

(2)    “Kaweah Oaks Preserve Community Access Guide,” Sequoia Riverlands Turst

Low doses of pesticides are also hazardous to our health

We are reprinting, with permission, an article on the Save Sutro website about recent research reporting that even low doses of chemicals can be harmful to our health.  This research has serious implications for the pesticides being used by the many “restoration” projects in the San Francisco Bay Area.  This article is focused on pesticide use by San Francisco’s misnamed Natural Areas Program.  In fact, every manager of public land in the Bay Area that engages in native plant “restorations” uses pesticides to eradicate non-native species. 


When we speak up against the Natural Area Program’s frequent pesticide use, its supporters frequently tell us that – compared with say commercial agriculture – the Natural Areas Program (NAP) uses small amounts of toxic chemicals. “The dose makes the poison,” they argue.

But it’s not true.

For now, we’ll leave aside the question of whether it’s reasonable to compare NAP to  commercial agriculture (where fears of chemicals are driving a growing Organic movement). What we’d like to talk about today is recent research about pesticides, specifically, endocrine disruptors. Here’s a quote from the abstract of a study by a group of scientists:

“For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of “the dose makes the poison,” because EDCs can have effects at low doses that are not predicted by effects at higher doses….

“…Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses.”

[Ref: Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses, Vandeberg et al, in Endocrine Reviews, March 2012]


The NAP uses several pesticides rated as “Hazardous” or “Most Hazardous” by San Francisco’s Department of the Environment. But the one they’ve favored is glyphosate — better known as Roundup or Aquamaster.

It’s strongly suspected of being an endocrine disruptor.

Here’s a 2009 study: Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines.

Another study, also published in 2009, looked at puberty and testosterone: Prepubertal exposure to commercial formulation of the herbicide glyphosate alters testosterone levels and testicular morphology. The abstract of the study ends with this sentence, “These results suggest that commercial formulation of glyphosate is a potent endocrine disruptor in vivo, causing disturbances in the reproductive development of rats when the exposure was performed during the puberty period.”

And here’s a study published in 2007, reflecting the research of a group of scientists from Texas A&M: Alteration of estrogen-regulated gene expression in human cells induced by the agricultural and horticultural herbicide glyphosate


Most people weren’t aware that pesticides were being used in so-called “Natural Areas.” The notices were small and well below eye-level. You had to be looking for them, which isn’t likely for most people out hiking or jogging by, or keeping an eye on small kids. In recent months, the labeling has improved, with taller posts and clearer information.

Now that people are beginning to notice, they’re also objecting. The response we hear most often is “Why would they use herbicides in a natural area?”

So the NAP has started posting explanations, justifying its use of toxic herbicides justifiable against “invasive plants.”

These plants, they say, are “a handful of non-native species” that are “displacing the rich biodiversity of native flora and degrading our natural heritage.”


We have several problems with this statement.

  • If it’s a “handful,” the NAP must have very big hands. From the pesticide application records, we’ve counted nearly twenty-five different plant species under attack by chemicals — including a couple that aren’t actually non-native.
  • There’s no evidence that all these plants are invasive and that they’re “displacing the rich biodiversity.” Native plants and non-native plants thrive together in natural mixed ecosystems. NAP can never eliminate all the non-native plants; the best it can achieve is a different mix, precariously maintained through intensive gardening.
  • There’s also no evidence it’s working. Using chemicals to kills things is cheap and easy, but it leaves a gap where something else will grow. Given that San Francisco’s environment has changed greatly since the 1776 cut-off used to define “native” plants, it’s not going to be those plants. Rather, what will naturally grow back will be the most invasive plant at the site. An excuse for more herbicides.
  • The NAP is destroying habitat in its quest to kill native plants. Many of the plants destroyed are bushes that provide cover and nesting places, or flowering plants that offer nectar to butterflies, bees and other pollinators and the birds and animals that feed on them. The “native flora” don’t necessarily provide much of either, even if they can be successfully gardened.

Plants from all over the world are welcome in the English garden

In a recent post about weeds in Britain, we pondered the interesting question of why there are so few plants in Britain that are considered invasive, a mere dozen compared to the nearly 200 labeled “invasive” by the California Invasive Plant Council.  The Brother Gardeners* enabled us to dismiss one possible explanation. 

The English Garden, Creative Commons

The fact that fewer plants are considered invasive in Britain is not the result of fewer non-native plants in their gardensThe Brother Gardeners informs us that the British have been enthusiastic importers of plants from all over the world for hundreds of years.  They had one of the biggest empires in the world, spanning the globe from India to Africa, Australia, New Zealand, and America, which put them in a unique position to sample the botanical riches of the world.

The Brother Gardeners was written by a German who immigrated to Britain about 10 years before writing this book.  She was immediately struck with the importance of gardening in Britain compared to her home country, and she quickly became immersed in the British obsession with gardening. 

She tells us the history of botany and gardening in Britain, going back to the 17th century.  This is no stale retelling of dry history.  This is an engaging tale of the personal relationships that reshaped the English garden, focusing on a 40-year business relationship between an English businessman and a Quaker farmer in Pennsylvania.  The American farmer supplied the Englishman with thousands of plants and seeds from the American landscape. 

The evolution of their relationship from a business relationship to a friendship is analogous to the relationship between America and Britain.  The Englishman was wealthier and more educated than the American and predictably he was condescending to the American at the beginning of their relationship.  Over the years, the American acquired both wealth and botanical knowledge, so that eventually they were on an equal footing.  But we digress.

Magnolia grandiflora. Creative Commons

 Magnolias, tulip trees, wisteria, and dogwoods were early favorites in this trade from America to England, but over time thousands of different species made the trip into English gardens.  The American trees “were thoroughly naturalized, growing side by side with native trees” by 1760 and “Many of the American plants had become so common in the English landscape that gardeners needed new species to parade as rarities in their shrubberies…” 

Joseph Banks, the intrepid botanical explorer, brought many new species of plants to Britain.  He joined the maiden voyage of Captain Cook into the Pacific in 1769.  His team collected plants in Brazil, Tahiti, New Zealand, and Australia on their three year voyage, bringing home specimens of 3,600 species of which 1,400 were new to Britain’s botanical knowledge.  Joseph Banks returned to become the head of the Kew Royal Botanical Garden and the Royal Academy of Science.  He continued to acquire botanical specimens from all over the world in that capacity.

Banksia, named for Joseph Banks. Creative Commons

 The crowning glory of Banks’ acquisitions was the specimen collection of Carl Linneaus, after Linneaus died in 1783. This collection was the “base reference” used by Linneaus to develop the system of categorizing all species, which is still used to this day.  The Brother Gardeners tells us the fascinating story of how the Swedish botanist, Linneaus, “sold” his system to botanists throughout the world.  It wasn’t an easy sell, particularly to the British.  They were initially scandalized by the sexual metaphors used by the system of categories which is based on counting the female (stamens) and male (pistils) parts of the plant, using explicit terms such as the “bridal bed which God adorned with such precious bedcurtains, and perfumed with so many sweet scents.”  You may have heard the saying, “No sex please. We’re British.”

The English garden is to this day an eclectic mix of species from all over the world.  It is a rich mix of color and texture that seems a mad jumble until the eye can make sense of its logic.  It is admired the world over and has influenced gardening everywhere.  It rejects the meaningless and artificial distinction between native and non-native.  Beauty is its only standard for judgment.  Whatever grows and adds color and texture is welcome in the English garden. 


*Andrea Wulf, The Brother Gardeners, Alfred Knopf, 2008.  All quotes are from Brother Gardeners

Ivy Eradication: A Comedy of Errors

When the concert meadow in San Francisco’s Stern Grove was renovated in 2005, at a cost of $15 million, we were surprised that ivy was planted as the ground cover because ivy grows rampant in Stern Grove, shrouding many of the trees.  But, hey!  Who are we to question the choices of horticultural professionals? 

Ivy planted in Stern Grove, 2005

Now ivy is being sprayed with herbicide–presumably with the intention of killing it–by San Francisco’s Natural Areas Program in other parks in San Francisco, so one wonders if the staff who plant it are aware of the future of the ivy they plant.  Seems like another case of man creating problems which he then must solve.  Perhaps full employment is the objective, rather than the creation of a beautiful garden.  But we digress.

Ivy climbing trees in Stern Grove

Combining pesticides

Many members of the public are of the opinion that all pesticide (herbicides, insecticides, etc.) applications are inappropriate in a park that has been designated as a “natural area.”  Last year, the public complained about the spraying of Garlon in the natural areas by the Natural Areas Program because it is classified by the city’s Integrated Pest Management (IPM) policy as “Most Hazardous.”  Consequently, the Natural Areas Program significantly reduced its use of Garlon in 2011. 

For the most part they have substituted a mixture of glyphosate and imazapyr for Garlon. Is this an improvement?  Maybe not.  Although glyphosate and imazapyr have a lower hazard rating of “More Hazardous,” the Natural Areas Program increased their pesticide applications in 2011 at least 20% compared to 2010.  But more importantly, little is known about the toxicity of imazapyr and nothing is known about the toxicity of combining glyphosate and imazapyr.(1)  Imazapyr was approved for use in California in 2005, so only the minimal tests required by law have been done on it.

The manufacturer’s labels for these herbicides suggest that combining them is not an approved use.  The label for Aquamaster (glyphosate) does not include imazapyr on the list of pesticides with which it can be safely combined.  And the Polaris (imazapyr) label says it should not be combined with another pesticide unless it is expressly recommended by the manufacturer of that pesticide.

The “Aquatic Pesticide Application Plan for the San Francisco Estuary Invasive Spartina Project” is cited by San Francisco’s IPM program as the evaluation upon which it based its decision to add imazapyr to the list of pesticides approved for use in San Francisco in 2010.   The evaluation explained why imazapyr is being combined with glyphosate by the non-native Spartina eradication project. 

Imazapyr is apparently slow acting.  It can take some months before it kills the plant on which it is sprayed.  Glyphosate, on the other hand, is fast acting.  The plant on which it is sprayed begins to yellow and die within a few weeks.  Glyphosate is therefore used by the Spartina eradication project to provide quicker feedback to those spraying the herbicide.  They know within a few weeks if they have sprayed in the right place.  They don’t have to wait for the next season to spray again if necessary. 

Pesticide Application Notice, Glen Canyon Park, December 2011

 However, glyphosate should be applied to perennial broadleaf plants during their reproductive stage of growth, when they are budding in the late spring and summer, according to the manufacturer.  In Glen Canyon Park, a mixture of glyphosate and imazapyr was sprayed on ivy in December 2011, clearly not the recommended time period for spraying.  A month later, there is no indication that the ivy was damaged by this spraying.  This suggests that there was no point in combining glyphosate and imazapyr in this application.  The public was exposed to the unnecessary risk of combining these herbicides, with no potential benefit of taking that risk.


Pesticides accumulate and persist in the soil

Was it appropriate for the city’s IPM program to use the evaluation of imazapyr for the Spartina project as the basis of their decision to approve its use by the Natural Areas Program?  We don’t think so.  The circumstances of the Spartina project are substantially different from those of its use by the Natural Areas Program.

Imazapyr is used to eradicate non-native Spartina in a tidal estuary.  For that reason the evaluation of its use assured the public that this herbicide would not accumulate in the environment because it would be flushed away from the ground by the tide twice each day. 

The evaluation also said that when imazapyr was used in a pond or stable water source, it persisted in the ground for a longer period of time.  In fact, that’s exactly how imazapyr is being used by the Natural Areas Program.  It has been used at Lake Merced and at Pine Lake, both stable water sources.  It is also being used in Glen Canyon Park, which is a watershed. 

We don’t assume that imazapyr is being used safely to eradicate Spartina.  However, even if it is, it does NOT follow that it is safe for use in watersheds that are not tidal, such as those being sprayed by the Natural Areas Program. 

Collateral damage of pesticides

Glyphosate is a non-selective herbicide.  That is, it kills any plant it is sprayed on at the right stage of its growth.  But imazapyr is far more insidious as a killer of plants because it is known to travel from the roots of the plant that has been sprayed to the roots of other plants.  For that reason, the manufacturer cautions the user NOT to spray near the roots of any plant you don’t want to kill.  For example, the manufacturer says explicitly that imazapyr should not be sprayed under trees, because that tree is likely to be killed, whether or not that was the intention. 

Pesticide Application Notice under willow trees in Glen Canyon Park, December 2011

Much of the ivy that was sprayed by the Natural Areas Program in Glen Park in December 2011 was sprayed under willow trees.  The willow trees are native, so it seems unlikely that they intended to kill them.

Resistance to pesticides

The Federal Drug Administration recently banned some use of antibiotics in domesticated animals because the bacteria antibiotics are intended to kill are developing resistance to the antibiotics.  This resistance is becoming increasingly dangerous to humans who are also the victims of those bacteria.  Antibiotics are being rendered useless by overuse on domesticated animals.  When humans need them, they won’t work because bacteria have developed a resistance to them.

Likewise, plants and animals are also capable of developing resistance to pesticides.  Glyphosate is the most heavily used herbicide in agriculture.  Recent research indicates that weeds are developing resistance to glyphosate

The manufacturer of imazapyr says explicitly that repeated use of this herbicide is likely to result in resistance to it over the long term:  “When herbicides with the same mode of action are used repeatedly over several years to control the same weed species in the same application site, naturally occurring resistant weed biotypes may survive…propagate and become dominant in that site.”   So, does it make sense to use imazapyr on a plant as persistent as ivy? 

The GGNRA reported spending $600,000 over 3 years trying to eradicate ivy from 127 sites.  They were successful in only 7 of the sites.(2)  Obviously eradicating ivy is not a one-shot deal.

If ivy must be eradicated, pesticides do not have to be used to do it.  The Audubon Canyon Ranch in Bolinas Lagoon reported “qualified” success using hand-pulling methods on 5 acres over 5 years “utilizing 2375 volunteer hours.”  Biannual monitoring of resprouts will be required for the foreseeable future.  It’s a big commitment, but at least it is safe. 

All risk, no reward

Congratulations to any reader with the patience to slog through this tedious list of apparently incompetent use of pesticides by San Francisco’s misnamed Natural Areas Program.  We reward your persistence with this summary:

  • Combining pesticides is risky business because the toxicity of such combinations has not been tested.  Therefore, when there is no benefit in doing so, these combinations should be avoided.
  • A pesticide that is appropriate for one purpose is not necessarily appropriate for another.  In this case, imazapyr may not accumulate and persist in a tidal estuary, but it is more likely to do so in a stable watershed.
  • The Natural Areas Program may be killing plants it does not intend to kill by using herbicides indiscriminately.
  • Herbicides should not be used repeatedly on the same plants in the same locations because the plants will develop resistance to those herbicides. 
  • If the Recreation and Park Department is planting ivy in one park and destroying it another, could it be such a bad plant that it is worthwhile to expose the public to toxic pesticides?  We don’t think so, but if we are wrong, then ivy should be removed by hand without using pesticides.

(1) “Aquatic Pesticide Application Plan for the San Francisco Estuary Invasive Spartina Project,” August 2010, page 32.

(2) Liston, Heather, “Reuniting old adversaries can beat back exotic invaders,” California Wild, Winter 2006

Eradicating non-native plants is taking the food out of the mouths of birds

Plants have many different strategies to ensure their reproductive success.  Sometimes they are passive participants in their propagation.  Charles Darwin studied the dispersal of the seeds of plants and reported a particularly stunning example:  “He raised more than eighty plants from the mud-ball gathered round a wounded French partridge’s leg.”*  He also raised plants from seeds found in the stomachs of birds, which brings us to today’s topic:  the non-native plants which are eaten by birds are categorized as “invasive” plants and are therefore doomed to be eradicated.

We often puzzle over the list of nearly 200 non-native plants on the list compiled by the California Invasive Plant Council (Update:  Now nearly 300 in 2020).  We know from horticultural experience and scientific studies that at least two of the trees on this list are not invasive.  Aerial photographs of open space in the Bay Area taken over a period of 60 to 80 years, proves that neither the eucalyptus nor the Monterey pine forests are spreading. 

Cotoneaster lacteus. Jackson Nursery, UK

There are also several species of non-native shrubs which produce berries on the list of “invasive” plants that we know don’t spread in our gardens:  English holly trees, Cotoneaster, and Pyracantha.  So, why are they on the hit list?  The garden columnist in the San Francisco Chronicle recently told us why in answer to a question about planting a non-native holly tree for Christmas foliage in the garden:

Berries are a little harder to come by if we follow the advice of native plant specialists who are concerned about escape of holly, cotoneaster and pyracantha into nearby wildlands, particularly in coastal counties. Birds that eat the fruit and deposit seeds are the culprits.” 

Pyracantha. Wikimedia Commons

In other words, native plant advocates don’t want gardeners to plant non-native plants that produce berries that birds eat because they don’t want the plants to spread.  Obviously, their dedication to native plants trumps whatever concern or interest they might have in the welfare of birds.  Native plant advocates frequently claim that their “restorations” will benefit wildlife.  Clearly the eradication of berry-producing shrubs does not qualify for such a claim.

The loss of food and habitat for the wildlife that lives in our public lands is only one of many issues in the debate about native plant “restorations.”  But for bird lovers, this is a high priority.  In this regard, we were struck by one of the public comments that was recently submitted on the Draft Environmental Impact Report for the Natural Areas Program.  This self-identified “birder” said this about the radical “restorations” in San Francisco:

“Restoration areas such as Land’s End, El Polin Spring, Crissy Field are seldom spoken about anymore by birders or others looking for populations of wildlife.  Since the vast majority of the city’s resident bird species feed, roost and breed in trees, they leave, starve or are predated when their habitat is destroyed.”

Cedar Waxwings in crab apple tree. Wikimedia Commons

As the Cedar Waxwings pass through the Bay Area on their annual migration, we see them eating the berries in our holly tree.  They remind us that the eradication of non-native trees benefits neither animals nor birds, nor insects.  Who benefits from these destructive projects besides the people making their living at it?  It’s a mystery.

* Mabey, Richard, Weeds:  In Defense of Nature’s Most Unloved Plants, HarperCollins, 2010, page 29

Weeds: In Defense of Nature’s Most Unloved Plants

We would like to tell our readers about a charming little book about weeds, by the same name.  Weeds:  In Defense of Nature’s Most Unloved Plants, by Richard Mabey, contains an eclectic collection of information about the weeds of Britain, their origins, the history of their use–including as medicine, the role they have played in literature, and much more. 

First, we venture a definition of weeds, though any definition is likely to be controversial.  The concept of “weed” originated with agriculture, some 5,000 years ago in the Old World*, when man began to distinguish between those plants that are edible or otherwise useful and those that are not.  And so, plants that are not perceived as useful or turn up in the wrong place, were defined by man as “weeds.” 

It’s a shifting concept, because a plant that was useful historically, either because it was believed to be a cure for some malady, or was otherwise useful, might be replaced by some superior remedy.   Such a changing concept of the value of particular plants is a central theme to the book as well as to the Million Trees blog.  We often invite our readers to consider that much of the current interest in native plants is a horticultural fad that is likely to change in the future as it has in the past. 

We also often question the designation of hundreds of non-native plant species as “invasive” in California, a designation that makes them a target for eradication.   Mabey’s book about weeds helps us to put this designation into perspective.  Britain obviously has a much longer history of trade with its neighbors on continental Europe, which increased the potential for the introduction of non-native species.  Yet, despite Britain’s longer history of ecological globalization, Mabey tells us that only about one dozen species of plants are presently considered invasive in Britain compared to hundreds in California. 

Rhododendron ponticum, one of only a dozen plants considered invasive in Britain. Wikimedia Commons

Mabey defends several of the non-native plants considered as invasive in Britain.  He believes that some are merely responding to the disturbance of native vegetation by the activities of man.  Nature hates a vacuum.  When native vegetation is no longer adapted to the changed soil, water, and air quality conditions created by man, any plant that will grow in these new conditions is preferable to bare ground.  Plants—including weeds—help the soil absorb rainwater into the ground which would otherwise run off the land, silting streams and causing erosion.

There is much food for thought in this little book.  It invites us to compare our list of nearly 200 plants in California that have been officially designated as “invasive” to a short list of only a dozen plants in Britain.  What accounts for this big difference?  Different conditions or different attitudes?  We don’t know the answer to this question, but we think it is a question worthy of consideration.  

* Crosby, Alfred, Ecological Imperialism, Cambridge University Press, 2009

Broom: “I’m ba-ack”

Leona Canyon, Spring 2011

One of our first posts, nearly one year ago, was about attempts to eradicate broom (see “Broom:  I’ll be back!”).  It’s that time of year again, when the broom is blooming around the Bay Area, adding a dash of bright yellow color to our public lands.

Despite continuing efforts to eradicate broom, it makes this annual comeback, regardless of the method used to kill it.  Mechanical destruction is one of the methods used.  In the photograph taken in fall 2010 of a trail in Redwood Park we see the unsightly result of such an attempt to eradicate the broom shown in our first post about broom in spring 2010.

Redwood Park, Spring 2010

Redwood Park, Fall 2010

The UC Davis Statewide Integrated Pest Management Program  predicts the results of this effort to eradicate broom:  “Brush rakes and bulldozers often leave pieces of rootstalks that readily can resprout…using large equipment to clear land creates a perfect environment for new seedling establishment, making follow-up control essential.”  So, we shouldn’t be surprised when we revisit this same site the next spring to find that although it is still unsightly, it is also covered with the resprouts of the broom.

Broom resprouts, Redwood Park, Spring 2011

Herbicides are also used to eradicate broom.  The East Bay Regional Park District uses Garlon for foliar spraying of broom, despite the public’s concern about herbicide use in our parks.  In contrast, Marin Municipal Water District (MMWD) has not used herbicides on its properties since 2005, in response to public protests.  In December 2010, the Marin Independent Journal reported that MMWD is considering using Roundup (which is considered less toxic than Garlon) for broom control, but that a proposal will not be made until 2012 at the earliest, after an environmental impact study that will consider all alternatives for “pest management.”

Even if we are willing to accept the health and environmental risks associated with herbicides, they are not a guarantee of success.  According to UC Davis, “One application of an herbicide does not always completely control brooms…Watch treated areas closely for at least a year, and retreat as necessary.”


Since the seeds of broom are known to live in the ground from 50 to 60 years, we should expect that it is very difficult to eradicate.  Unless we make a commitment to kill the plant above the ground every year for as long as the seeds live in the ground, we cannot expect to be successful in that effort.

We were therefore amused by this exchange that Jake Sigg had with one of the readers of his “nature newsletter” (December 20, 2010):

Reader:  “…We have been up there every year for about 3-1/2 years now…It has been quite instructive about how flat out difficult it is to reverse the process [of “displacement” of native plants].  Like most invaders, the non-native plants like it here and want to stay.  The broom in particular are [sic] astoundingly persistent in holding whatever territory that they have gained.  It sounds strange to say, that sometimes I think the project is an exercise in futility while at the same time is extremely satisfying work and will continue it into the indefinite future.”

Jake Sigg:  “…It is such a lop-sided struggle…And yet, we all keep going.  It is a paradox that I don’t understand.  While working I’m fully aware of the seeming futility of what we’re doing, and yet keep going—and enjoying it!!”

Jake Sigg and his readers would benefit from the advice of Mark Davis in his book, Invasion Biology.*  Professor Davis suggests that unless a non-native species causes great health or economic harm, we adopt the “LTL approach” i.e., “Learn to love ‘em” or at least “Learn to live with them.” 

If it is futile to eradicate a plant we don’t like, if that plant isn’t doing us or any other plant any harm, and if we are damaging our environment in our futile attempt, let’s change our attitude toward that plant.  If we can’t change the plant, it is still within our power to change ourselves.  Surely we can find something more fruitful to do that is equally satisfying such as planting more native plants rather than destroying non-native plants.

Broom is an especially good candidate for LTL.  It is green all year around.  It requires no care whatsoever.  And in the spring it treats us to a lovely carpet of bright yellow.   What’s not to love?

* Mark Davis, Invasion Biology, Oxford University Press, 2009, page 150

Photographic evidence that eucalypts are not invasive

One of native plant advocates’ favorite justifications for eradicating eucalypts is the claim that they are invasive.  But are they?  In one of our early posts (“ALIEN INVADERS!!  Another Scary Story”) we reported a scientific study, based on photographic evidence over a 60 year period, that eucalyptus and other non-native trees have not invaded public lands in Marin, Alameda and San Mateo counties.  In fact, the non-native forests in these public lands decreased in size, while native forests increased in size. 

Now we have photographic evidence that eucalyptus has not been invasive when planted in San Francisco.  Adolph Sutro purchased Mt. Davidson in 1881.(1)  He planted it—and other properties he owned in San Francisco—with eucalyptus because he preferred a forest to the grassland that is native to the hills of San Francisco.  Here is a historical photo of what Mt. Davidson looked like in 1885:

Sutro foretold the future of his property:

“…people… will wander through the majestic groves rising from the trees we are now planting, reverencing the memory of those whose foresight clothed the earth with emerald robes and made nature beautiful to look upon.”(2)

Since Sutro didn’t own all of Mt. Davidson, there was a sharp line between the forest he planted and the grassland when this photo was taken in 1927.

Over 80 years later, in a photo taken in 2010, there is still a sharp line between the forest and the grassland.  We see more trees in the foreground where residential areas have been developed and home owners have planted more trees, but the dividing line on the mountain is nearly unchanged.  The eucalyptus forest has not invaded the grassland.

Adolph Sutro would be saddened by a walk in the forest on Mt. Davidson to see over 50 dead and dying trees that have been girdled by native plant advocates.  And the Natural Areas Program’s management plans for Mt. Davidson also announce the intention to destroy 1,600 more trees over 15 feet tall.  Smaller trees to be destroyed are not quantified by the plan. 

Despite the lack of evidence, the California Invasive Plant Council (CIPC) has designated both the eucalyptus and the Monterey pine as “moderately invasive.”  There is even less evidence that Monterey pine grow where not intentionally planted.  These trees and many of the nearly 200 plants on the CIPC “hit list” are on that list because they aren’t native, not because they are invasive.  Few of these plants are truly invasive, but CIPC designates them as such so that their eradication can be justified.  

Broom: “I’ll be back…”

Broom is a non-native shrub frequently targeted for eradication in native plant restorations. Its seedbed lives in the ground for up to 60 years.  If broom is not eradicated before every bloom cycle, that 60 year seed-cycle continues ad infinitum.   Foliar spraying of glyphosate (Roundup) is the preferred method of eradication because it is the cheapest.  Although trees are the main focus of A Million Trees, we will talk about broom because it illustrates two important issues:  (1) The futility of trying to eradicate a completely entrenched non-native species, and (2) the largely unknown risks of using herbicides.


How much Roundup will it take to eradicate this broom?

We know that Roundup is harmful to amphibians.  This fact was established by a suit brought by the Center for Biological Diversity on behalf of the Red-Legged frog (RLF), an endangered species.  As a result of that suit, US Fish and Game has banned the use of Roundup in proximity of known populations of the RLF (and more recently extended to other herbicides in proximity of other endangered amphibians).

However, the Center for Biological Diversity is closely allied with the native plant movement.  Therefore, when negotiating for a ban on the use of toxic herbicides in proximity of endangered amphibians, they also negotiated for an exception to the ban when the herbicides are used  for the purpose of eradicating invasive plants, as defined by the California Invasive Plant Council.  Broom is one of hundreds of plants deemed invasive by that council, which is dominated by native plant advocates.   

Recent research has found evidence that Roundup may also be harmful to humansScientific American reports, “But now researchers have found that one of Roundup’s inert ingredients can kill human cells, particularly embryonic, placental and umbilical cord cells…scientists found that Roundup’s inert ingredients amplified the toxic effect on human cells—even at concentrations much more diluted than those used on farms and lawns.”

This research has implications for other pesticides and herbicides.  Presently, the EPA does not require that the manufacturers of these chemicals list all the inert ingredients.  If the inert ingredients in other herbicides were known to us, we would be in a better position to assess the potential danger.