Refuting Jake Sigg: No, 90% of Insects Do Not Eat Only Native Plants

Jake Sigg, considered the doyen of San Francisco’s native plant activists, has an influential newsletter. Recently, it said: “Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?” It included a link to a video from the California Native Plant Society (CNPS) … which provided no evidence for the statement at all. Nor was there any data to substantiate the claim – which is false. In fact, as Professor Art Shapiro points out, insects easily adapt to using other plants than the ones  they “co-evolved” with. He notes, “… the urban-suburban California butterfly fauna is now overwhelmingly dependent on non-native plants.


Here’s the link to the video:  Plants are the Foundation.

Not only did the video from not contain any reference to 90% of insects, it was in itself an interesting piece of sleight-of-hand. It made the fair point that plants were the foundation of the web of life.

Then, I suppose because it was from CNPS, it said: “None of us can live without them, especially native plants” and “Native plants support local wildlife”… the video shows a Western Tiger Swallowtail butterfly fluttering in. They’re native butterflies, but they don’t need native plants. In San Francisco, they breed on (non-native) London Plane Trees that are found on Market Street and other urban streets, which means their caterpillars readily eat those non-native leaves.

The video continues...”and ecosystems. The web of life depends on them For habitat

And it illustrates this with a photograph of a great horned owl, which nests on large tall trees, usually non-native eucalyptus, as in this photograph below.

Bumblebee on oxalis flower

Bumble bee on wild radish flower


“for food”

Then it shows a bumblebee on a Western thistle (native)… except that bumblebees happily nectar on a vast number of non-native plants, including wild radish and the yellow oxalis that Jake Sigg loves to hate.

Then it adds a picture of a Monarch butterfly… which does indeed depend on milkweed as its nursery plant (though it nectars on non-native ivy flowers as well as eucalyptus blossoms). But it readily breeds on non-native milkweed as well as native milkweed (and contrary to some native species activists, non-native milkweed does not spread disease or reduce breeding success). More to the point, the western migration of the Monarch butterfly relies heavily on (non-native) eucalyptus trees to over-winter in. Without the eucalyptus, the western migration will probably die out.

It argues that habitat is shrinking (with a picture of a highway in LA), which is perhaps reasonable (though farming is more likely the culprit than urban sprawl). And goes on to suggest planting native plant gardens. That’s not objectionable in itself, of course, but it’s planting a mix of various kinds of plants that will benefit the most species.

So though the video certainly shows the need for plants as the basis of an ecosystem, it emphatically does not make the case for native plants.


We reprint, with permission and minor changes, a thorough refutation of the statement from Professor Art Shapiro, published on the Million Trees blog. In sum, Professor Shapiro challenges the statement, and points out that “ecological fitting” – which allows species that didn’t “co-evolve” to interact – is very common. He cites examples from all over the world.


We briefly reactivate the Million Trees blog to publish an interesting and important debate between Jake Sigg and Professor Art Shapiro about the relationship between insects and native plants.  Their debate was initiated by this statement published in Jake Sigg’s Nature News on April 26, 2019:

“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”

Jake Sigg has been the acknowledged leader of the native plant movement in the San Francisco Bay Area for 30 years.  He is a retired gardener for the Recreation and Parks Department in San Francisco. Art Shapiro is Distinguished Professor of Ecology and Evolution at UC Davis.  He has studied the butterflies of Central California for 50 years.

Jake and Art are both passionately committed to the preservation of nature, but their divergent viewpoints reflect their different experiences.  Jake’s viewpoint is based on his personal interpretation of his observations.  As a gardener, his top priority is the preservation of plants rather than the animals that need plants.  As a scientist, Art’s viewpoint is based on empirical data, in particular, his records of plant and butterfly interactions over a period of 47 years as he walked his research transects about 250 days per year. The survival of butterflies is Art’s top priority.

Although their discussion is informative, it does not resolve the questions it raises because Jake and Art “agree to disagree.”  Therefore, Million Trees will step into the vacuum their discussion creates to state definitively that it is patently false to say that “90% of insects can only eat native plants.” That statement grossly exaggerates the degree of specialization of insects and underestimates the speed of adaptation and evolution.

There are several reasons why insects do not benefit from the eradication of non-native plants:

  • Insects use both native and non-native plants.
  • Pesticides used to eradicate non-native plants are harmful to both plants and insects as well as the entire environment.
  • There is no evidence that insects are being harmed by the existence of non-native plants.


This statement was recently made in an article published by Bay Nature magazine about Jake Sigg:  “More than 90 percent of all insects sampled associate with just one or two plant families.”  (7,500 insect species were sampled by the cited study.  There are millions of insect species and their food preferences are largely unknown.)  This exaggerated description of specialization of insects seems the likely origin of the subsequent, inappropriate extrapolation to the statement that specialized insects require native plants.

Anise Swallowtail butterfly in non-native fennel. Courtesy

There are over 600 plant families and thousands of plant species within those families.  Most plant families include both native and non-native plant species.  An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.

We will use the Oxalidaceae plant family to illustrate that insects can and do use both native and non-native plants.  Oxalidaceae is a small family of about 5 genera and 600 plant species.  We choose that family as an example because Jake Sigg’s highest priority for eradication is a member of that plant family, Oxalis pes-caprae (Bermuda buttercup is the usual common name)In a recent Nature News (April 9, 2019), Jake explained why:  Oxalis is not just another weed; this bugger has a great impact on the present and it will determine the future of the landscapes it invades.”

Five members of the Oxalis genus in the Oxalidaceae family are California natives. An insect that uses native oxalis can probably also use the hated Bermuda buttercup oxalis because they are chemically similar. 

Honeybee on oxalis flower, another non-native plant being eradicated with herbicide



Partly because of Jake’s commitment to eradicating non-native oxalis, San Francisco’s Recreation and Parks Department has been spraying it with herbicide for 20 years Garlon (triclopyr) is the herbicide that is used for that purpose because it is a selective herbicide that does not kill grasses in which oxalis usually grows.  Garlon is one of the most toxic herbicides available on the market.  More is known about Round Up (glyphosate) because it is the most widely used of all herbicides.  However, according to a survey of land managers conducted by California Invasive Plant Council in 2014, Garlon is the second-most commonly used herbicide to eradicate non-native plants.

Garlon is toxic to bees, birds, and fish.  It is an endocrine-disrupter that poses reproductive and developmental risks to female applicators.  It damages the soil by killing mycorrhizal fungi that are essential to plant health by facilitating the transfer of nutrients and moisture from the soil to plant roots. 

A recent article in the quarterly newsletter of Beyond Pesticides explains that insecticides are not the only killers of insects: “Insecticides kill insects, often indiscriminately and with devastating consequences for biodiversity, ecosystem stability, and critical ecosystem services. Herbicides and chemical fertilizers extinguish invaluable habitat and forage critical to insect survival. Taken together, insecticides, fungicides, herbicides and chemical fertilizers make large and growing swaths of land unlivable for vast numbers of insect species and the plants and animals they sustain.” The loss of insects where herbicides are used to kill non-native plants are undoubtedly contributing to the failure of attempts to “restore” native plants which require pollinators and insect predator control as much as non-native plants.

In other words, eradicating non-native oxalis is damaging the environment and the animals that live in the environment.  Furthermore, after twenty years of trying to eradicate it, Jake Sigg admits that there is more of it now than there was when this crusade began:  “Maybe you’ve noticed that there’s more and more of it every year, and fewer and fewer other plants.  That is unlikely to reverse.”  (Nature News, April 9, 2019).

Coyote in oxalis field. Copyright Janet Kessler

In fact, local failure of eradication efforts mirrors global failures of similar attempts:  “…despite international policies aimed at mitigating biological invasions, the implementation of national- and regional-scale measures to prevent or control alien species has done little to slow the increase in extent of invasions and the magnitude of impacts.” 

[Ref: “A four-component classification of uncertainties in biological invasions: implications for management,” G. LATOMBE , S. CANAVAN, H. HIRSCH,1 C. HUI, S. KUMSCHICK,1,3 M. M. NSIKANI, L. J. POTGIETER, T. B. ROBINSON, W.-C. SAUL, S. C. TURNER, J. R. U. WILSON, F. A. YANNELLI, AND D. M. RICHARDSON, Ecosphere, April 2019.]


There is no question that insects are essential members of every ecosystem.  They are the primary food of birds and other members of wildland communities.  They perform many vital functions in the environment, such as consuming much of our waste that would otherwise accumulate.

The Economist magazine has reported the considerable evidence of declining populations of insects in many places all over the world.  (However, the Economist points out that the evidence does not include large regions where insect populations have not been studied. The Economist is therefore unwilling to conclude that the “insect apocalypse” is a global phenomenon.) The report includes the meta-analysis of 73 individual studies that describe declines of 50% and more over decades. The meta-analysis concluded that there are four primary reasons for those declines, in order of their importance:  habitat loss, intensive farming, pesticide use, and spread of diseases and parasites.  The existence of non-native plants is conspicuously absent from this list of threats to insect populations.

In other words, although the preservation of insects is extremely important, there is no evidence that the eradication of non-native plants would benefit insects.  In fact, eradication efforts are detrimental to insects because of the toxic chemicals that are used and the loss of the food the plants are providing to insects.


The discussion begins on April 26, 2019, with this statement published in Jake’s Nature News:

“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”

On April 26, 2019, Arthur Shapiro wrote:

“No, I didn’t know 90% of insects can only eat the native plants with which they’ve co-evolved. I’ve only been studying insect-plant relationships and teaching about them for 50 years and that’s news to me, especially since on a global basis we don’t know what the vast majority of insects species eat, period! That’s even true for butterflies and moths, which are probably the best-studied group. And it’s even true here in California, one of the best-studied places on the planet (though way behind the U.K. and Japan). Where on earth did that bit of non-information come from?”

Jake Sigg responds:

“Art, I did my best to run down source for that statement.  As I suspected, it may lack academic precision.  That kind of precision is hard come by, and what exists is not entirely relevant.  Most of the information comes from Doug Tallamy.  But the statement is not accurate; it should have read “…90 percent of plant-eating insects eat only the native plants they evolved with”.  Whether that is true or not I don’t know, but it accords with my understanding and I am willing to go along with it, even if proof is lacking.  If you wait for scientific proof on everything you may wait a long time and lose a lot of biodiversity.  I have had too much field experience to think that exotic plants can provide the sustenance that natives do.

I expect you will be unhappy with this response.”

On May 2, 2019, Art Shapiro replies:

“If Tallamy said “90% of the plant-eating insects that I have studied…”  or “90% of the plant-eating insects that have been studied in Delaware…” or some such formulation I might take him more seriously. The phenomenon of “ecological fitting,” as described by Dan Janzen, is widespread if not ubiquitous. “Ecological fitting” occurs when two species with no history of coevolution or even sympatry (co-occurrence) are thrown together and “click.”  A.J.Thorsteinson summed up some 60 years ago what is needed for an insect to switch onto a new host plant: the new plant must be nutritionally adequate, possess the requisite chemical signals to trigger egg-laying and feeding, not possess any repellents or antifeedants and not be toxic.

That set of circumstances is met very frequently. To those of us who study it, it seems to happen every other Tuesday.  As we showed, the urban-suburban California butterfly fauna is now overwhelmingly dependent on non-native plants. The weedy mallows (Malva) and annual vetches (Vicia) are fed upon by multiple native butterfly species and are overall the most important butterfly hosts in urban lowland California. . Within the past decade, our Variable Checkerspot has begun breeding spontaneously and successfully on Butterfly Bush (Buddleia davidii). The chemical bridge allowing this is iridoid glycosides. When I was still back East I published that the Wild Indigo Dusky Wing skipper, Erynnis baptisiae, had switched onto the naturalized European crown vetch (Coronilla varia) which had converted it from a scarce and local pine-barrens endemic to a widespread and common species breeding on freeway embankments. And the hitherto obscure skipper Poanes viator, the Broad-Winged Skipper, went from being a rare and local wetland species best collected from a boat to becoming the most abundant early-summer butterfly in the New York metropolitan area by switching from emergent aquatic grasses and sedges to the naturalized Mesopotamian strain of Common Reed, Phragmites australis. I can go on, and on, and on. If you find a sponsor for me to give a lecture about this in the Bay Area, I’ll gladly do it. If you promise to come!

I won’t snow you under with pdfs. Here’s just one, a serendipitous one that resulted from my walking near Ohlone Park in Berkeley. And one from the high Andes in Argentina. That paper cites one of mine in Spanish demonstrating that the southernmost butterfly fauna in the world, in Tierra del Fuego and on the mainland shore of the Straits of Magellan, is breeding successfully on exotic weeds.-! Copy on request.”

On May 2, 2019, Jake Sigg published his last reply:

“I believe many of your statements, Art, and many of these cases I am familiar with.  A conspicuous local example is the native Anise Swallowtail butterfly that still lays eggs on native members of the Umbelliferae, the parsley family, but which also breeds on the exotic fennel, which is an extremely aggressive weed that in only a few years can transform a healthy and diverse grassland supporting much wildlife into a plant monoculture—that, btw, won’t even support the butterfly, which shuns laying eggs where its larval food plant is too numerous and easy target for a predator, like yellow jackets.

What puzzles me is why you can keep your equanimity at the prospect of losing acres of very diverse habitat to a monoculture of fennel.  You live in the heart of the world’s breadbasket where for hundreds of miles both north and south there are almost no native plants except those planted by humans.  That would tend to distort one’s view.  I don’t mean to be flip, but it is not normal for even an academic to be indifferent about a loss of this magnitude.  I have worked hands-on on the land (I was raised on a ranch) all my life and still work every Wednesday maintaining our natural habitat in San Francisco—a task that hundreds of citizens pitch in on because they value the quality and diversity of the areas.  And why do you remain indifferent, are you just a contrarian?  You cite examples to bolster your view, but the examples are too small a percentage to be meaningful and wouldn’t stand up against a representative presentation.

I got my view from life.  I type this in my second-floor sunroom, which looks into a coast live oak growing from an acorn I planted in the late 1960s, about 50 years ago and which is immediately on the other side of the window.  It is alive with birds of many different species—flocks of bushtits, chickadees, juncos every day (plus individuals of other species), which species-number balloons in the migratory season.  What I can’t figure out is how the tree can be so productive as to stand up to this constant raiding.  I will take instances of this sort as my guide rather than the product of academic lucubrations.  And I will throw in Doug Tallamy; the world he portrays is one I recognize and love.

I think our battle lines are drawn.  This discussion could go on, as we have not even scratched the surface of a deep and complex subject.  But will either of us change our minds?  No.”

“Jake Sigg:  N.B.  Art responded with another long epistle, not for posting.  It clarified some of the points that were contentious and seemed to divide us.  We differ, but not as much as would appear from the above discussion.”

On a personal note, we’d like to point out that one of the writers of this article has a (non-native) red wattle tree outside their window – which also attracts bushtits, juncos, and chickadees, not to mention hummingbirds (both Anna’s and Allens), house finches, white-crowned sparrows, and a bunch of other species. Oak trees are certainly good habitat – but so are a lot of other plant and tree species, where ever they originate.


Dead trees: the life of the forest

Throughout the city and the whole San Francisco Bay area, urban and suburban forests are being destroyed. The Natural Resource Area Management Plan targets 18,000 trees in San Francisco and Pacifica. In the East Bay, more than 50,000 trees may be felled – some estimates go to half a million.

In many cases, the relevant authority argues they are really removing trees that “dead or dying.” We question whether the so-called “dying” trees are actually dying, or merely in a defensive mode against four dry years, from which they would have recovered after this wet winter had they been given the chance.

And importantly, the dead trees have enormous value in the forest. We republish this article by Jack Gescheidt, first published at with permission and minor changes. (The article and all the images are copyright to Jack Gescheidt.)


Even tree lovers may not know the myriad ways trees some label “dying” or “sick” or “infected” or “infested” (with beetles or other insects) are in fact beneficial to a forest. Perhaps you’ve figured this out already, or know it intuitively, but forests do just fine without us humans interfering. Especially when our “helping” is driven by financial gain.

But fans of forest beware: timber companies hellbent on extracting more wood from U.S. and world forests have concocted yet another way of saying down is up, wrong is right, and denuding forests does a forest good. Their newest sell-off-the-forest pitch is to “remove” only “dead” or “dying” trees, to “clean up” or “manage” forests more “responsibly” implying this does no harm. Don’t believe it. All the quotations are used to indicate these terms are euphemisms which don’t convey the reality of how damage is done in “responsibly” “managing” a forest. This would actually entail leaving it alone, and certainly not bringing in heavy machinery.

Extracting “dead” or “down” or “dying” trees is only the latest insidious way of doing additional harm while ignoring the reality of our current situation: global warming is threatening humanity, which is caused in large part by decades of massive, and ongoing deforestation, nationally and globally. What we humans should instead be doing is leaving existing forests be, especially old-growth forests, not inflicting more damage or extractions of any kind. And planting more trees than we cut down — I mean, “harvest.” Important note: planting a sapling is NOT an equivalent replacement for cutting down a mature tree. Leave mature trees stand AND plant more trees. This would benefit us humans — as well as animals and plants and planet, because we’re actually all in this together. Deforestation for short term profit equals environmental and societal catastrophe in the long term.

The timber industry’s latest assaults begin ideologically. If they win over your mind, and public opinion, they will destroy our forests, and harm all of us in the end. In the public relations assault you’ll hear and read this lie: that forests benefit from industrial removal of “dead” or “dying” trees; that doing so has little or no impact on a forest’s health. Nothing could be further from the truth. Standing dead trees, and trees that have fallen over, and trees in any and every state of decay, are essential to the life cycles of decay and regeneration of a forest. And thus our health depends upon these, since we depend upon forests for carbon sequestration, oxygen production, soil creation, water filtration, wildlife habitat, and so much more.

Chad Hanson, Director of the John Muir Project, UC Davis researcher, and Sierra Club board member, says this about dead trees and forests:

We are trapped by an outdated cultural idea that a healthy forest is one with nothing but green trees. An ecologically healthy forest has dead trees, broken tops, and down logs. Such forests may not look tidy from the perception of a forester, but it (a forest with lots of dead trees) is the most biologically diverse and healthy, from a forest ecosystem perspective….Pound for pound, ton for ton, there is probably no more important habitat element in western conifer forests than large snags and large down logs.

The old practice of killing trees — what modern industry euphemistically calls “harvesting” — to make too many products that are either unnecessary or readily replaced with non-tree sources, has now become a suicidal practice. By killing trees and destroying forests everywhere, we are also killing ourselves, slowly, surely, and increasingly not so slowly.
Beware, too, other misleading, non-scientific labels like “invasive” and “non-native” which are also now commonly used to justify killing trees, plants, and animals, sometimes even by well-intentioned but tragically misled environmentalists. All have drunk the industrial agricultural public relations Kool-Aid. Meaning they kill wild plants and animals, imagining they are doing good, even justifying toxic herbicide use to do so.

READ MORE: Biology

Beware, too, other misleading, non-scientific labels like “invasive” and “non-native” which are also now commonly used to justify killing trees, plants, and animals, sometimes even by well-intentioned but tragically misled environmentalists. All have drunk the industrial agricultural public relations Kool-Aid. Meaning they kill wild plants and animals, imagining they are doing good, even justifying toxic herbicide use to do so. READ MORE: Biology

Dead and decaying trees are precious to a forest. Here’s a short list of services they perform:

DEAD TREES are wildlife habitat — homes! — for many species of insects, birds and mammals including beetles, bees, wasps, ants, mice, squirrels, salamanders, shrews, bats, rats, and wildcats (lynx, bobcat), raccoons, martens, and even cover for larger mammals including mountain lions and bears.

Forest cafeteria…

DEAD TREES feed numerous fungi like mushrooms which in turn feed myriad animals, including rodents like voles.
DEAD TREES provide crucial habitat (nesting, roosting and food storage) for many species of woodpeckers that rely solely upon them. Woodpeckers require dead wood that’s easier to penetrate than living wood. So woodpecker habitat is destroyed when timber companies extract dead trees, and forest health suffers as woodpecker services are diminished.
DEAD TREES are food for insects which in turn feed larger animals including birds and mammals, all essential to forest health.
DEAD TREES create new soil, a critical component from which all life springs
DEAD TREES retain critical moisture in a forest as decomposing woody material

We must protect all remaining un-logged, or old-growth (over 200 years old) forests and leave intact any and all forests for their critical ecological service in our era of anthropogenic global warming. These include carbon sequestration (CO2 storage) as double duty; keeping the carbon in a living tree in its wood and out of the atmosphere, as well as allowing living trees to continue extracting additional CO2 from the atmosphere every day it is alive.

In addition to these obvious, rational-minded functions, now is also an ideal time for us planetary citizens to become more aware of the equally valuable emotional and spiritual tonic trees provide us. Notice and appreciate each individual tree growing near you, regardless of its species or its country of origin.

There are no “invasive” trees! You may have your favorites kinds of trees, but all provide critical ecological service. Maintain trees, care for them, plant more of them, and feel how they can reconnect us to the natural world we have for too long abandoned. If more of us do this more often, we just might be able to save our own species from dying too.

– Jack Gescheidt


2018 Herbicides in San Francisco: NRD Use Rises (Again)

For many years now, we have been obtaining and compiling monthly pesticide use reports from San Francisco Recreation and Parks Department (SFRPD).  This is our report for 2018.

Our analysis omits Harding Park, which is under contract to the PGA and must be tournament-ready at all times. We do include other golf courses, including the nearly pesticide-free Sharp Park in Pacifica (of which more later).

We analyze the data separately for the Natural Resources Department (NRD, formerly the Natural Areas Program or NAP). This is the entity that is trying to bring “native” plants to more than a thousand acres of our parks,  cuts down trees and restrict access to people and their pets. (For details, see this LINK.) It  uses toxic herbicides against non-native plants it considers invasive, currently nearly 50 species.

The NRD was the largest single user of herbicides within SFRPD. In fact, it used significantly more herbicides than the rest of SFRPD put together, including all the golf courses except Harding. SFRPD applied herbicides 223 times, of which 175 176 were in “Natural Areas” (this includes PUC areas managed in the same way – i.e. use of toxic herbicides against plants they dislike).

[Edited to Add: We have changed the chart above to correct the data.]



SFRPD (excluding Harding, and excluding NRD) continued to reduce its use of herbicides. Which is good news. They’ve also almost stopped using Tier I products. (SF Department of the Environment – SFEnvironment – groups those pesticides that the city permits to be used on city properties into three Tiers. Tier III is least hazardous; Tier II is More Hazardous; and Tier I is Most Hazardous.) The only usage in 2018 was Roundup Custom on a tree stump in Duboce.

There are some disturbing developments; the drop was a mere 6%, compared to a 34% fall in 2017, a 56% decline in 2016, and 30% in 2015.


NRD dropped its pesticide usage sharply in 2014, and continued the decline through 2016. But in the last two years it started climbing again, and it now is at the highest it’s been in five years (see the graph below).

They’ve added another Tier II pesticide to their arsenal: Axxe, which they tried on oxalis. On the whole, this herbicide is probably not as bad as some others; it has an OMRI listing for organic use. They also used Clearcast on Lake Merced against waterplants.


Honeybee in oxalis flower

The really bad news, though, is the increase in the use of Garlon (triclopyr), the most toxic herbicide that SFEnvironment permits. It’s what they use in their perennial, pointless, and apparently escalating war on oxalis.

The increase is clearer in the graph below. (The orange columns are Garlon.) NRD increased its use of Garlon by about 90% from 2017, and it’s the highest it has been in the last five years.

Oxalis is a beneficial plant: It produces copious amounts of nectar, which is food for bees, butterflies, and other pollinators. Its bulbs provide food for (native!) pocket gophers and some birds. Its brilliant yellow flowers bloom early in spring, before most other flowers. Kids like to chew on its sour stems (it’s also called sourgrass) and even adults have fond memories of this plant. Other than nativist purists, most people love it for its beauty – it’s a sign of spring in San Francisco.


Last year, SFRPD declared war on Cape Marigold, arctotheca. This is a ground-cover plant that’s attractive to butterflies, bees, and other pollinators, but is considered “invasive” – i.e., successful in the urban environment we currently have in San Francisco. In 2018, this attempt resulted in 21 applications of herbicides (of a total of 223), including the first time since August 2010 that pesticides have been used in Sharp Park, habitat for the endangered red-legged frog and the California garter snake.

Nearly all applications were of Milestone VM (aminopyralid) but one was of Sapphire (penoxsulam) – hitherto restricted to golf-courses ONLY in preparation for tournaments. On this occasion, it was being used on the St Mary’s playing field.

Cape Marigold (also called the Plain Treasure Flower) has bright yellow flowers that look like daisies. It’s in the aster family, has a fairly long flowering period, and also provides food for butterflies and bees.


As we said in our half-year report, three new herbicides have been added to the list permissible for use in San Francisco: Axxe (which we mentioned above), Lifeline, and Clearcast.

The list of target species is also growing, and we’ve now counted 47 types of plants that are being sprayed with herbicides. The 2018 newcomers to the list are a couple of succulents: Aeonium, and crassula. Also added to the list is “Cat’s Ear,” an edible plant resembling dandelions and widespread enough that if it’s a target it would provide an excuse for considerable pesticide use. There’s another plant listed as Cape vertigo (sometimes the form is unclear!), which may be an ornamental grass.

We slightly modify our conclusions from our Half-Year report in July: While we are glad that SFRPD has moved to reduce herbicide use (at least in non-Natural areas), we’re disappointed that it continues to consider pesticides a viable strategy. We’re also disappointed at the opening of more battle-fronts against plants, which will inevitably push for more pesticide usage. We’re disappointed at the rising usage by the NRD.

We would like to see SF Environment take the leadership in moving San Francisco to a policy of No Pesticides in our Parks and Watersheds.




Sutro Forest Tree Destruction Started

In 2017, UCSF introduced a Plan that reduces the UCSF forest area by one-third, removes around 6,000 trees (new estimate!) and all the understory/ midstory shrubs. This  has started. The article below is republished with permission and minor changes from, the website to publicize and resist the destruction of the forest.

A short time ago, UCSF sent out a circular saying it was going to start the tree-felling in Sutro Forest. [ETA: The circular from UCSF used a header surprisingly like SFForest’s current logo above. We would like to clarify: We absolutely oppose the destruction of Sutro Forest and the felling of thousands of its trees.]

We were surprised, because they’re supposed to avoid doing this in the winter when the ground is unstable with rain, and in the spring and summer when it’s the bird-nesting season. Tree-felling season was supposed to be in the Fall. But no, it’s happening now and they intend to finish by March. Thousands of trees will be gone, and the forest as we know it will be severely depleted.

Well, it’s started. Recently, a forest-supporter sent us these pictures:

The email that accompanied the pictures was unhappy. “Not much of a canopy anymore. This sucks.”

“In that location there were also trees marked with red paint, presumably for future removal?” they said in a follow-up email regarding tree-cutting near Clarendon Avenue. “Feel free to use my photos on your site. It wasn’t very long ago when running or walking these trails transported you into a different almost magical world. Increasingly as more and more trees are cut down, the surrounding city intrudes. Thank you very much for your advocacy.


Tree cutting has started in the East Ridge area (above the UCSF student housing at Aldea), Clarendon area (parallel to Christopher Drive), the Woodland Canyon Area (below Medical Center Way), the Farnsworth area (between Edgewood Avenue and the UCSF campus).

These are, coincidentally, the areas of the forest that as long ago as 2009, UCSF had targeted for tree destruction. (This was back when they were seeking a FEMA grant to pay for it – which they withdrew when FEMA wanted evidence.) The language of the memo presents this as removal of dead and dying trees, though we have concerns both about the definition of ‘dead and dying’ and about the habitat impact of so much tree removal. (And dead trees, are, in fact, a habitat treasure for wildlife.)

The memo says they plan to bring in goats to eat the understory in February 2019, but a subsequent memo says it’s happening earlier.

Anyway, what we can expect in Sutro Forest this year is a lot less forest – thousands of trees removed, missing canopy, and bare open patches where the understory is also gone.

We hope you have made memories of the beautiful forest as it used to be. This site has been fighting the battle since 2009; others started in 1999. Sadly, the Sutro Stewards, who partner with UCSF in working in this forest, support this felling of trees and destruction of the understory.

This 130-year-old forest is no longer going to be a forest.




Native Plants are Flammable Too

Three of the most flammable plants in California landscapes are bay laurels, coyote brush, and chamise – all native. An evenhanded presentation of fire hazard ratings for all plants that does not downplay the danger of native plants or exaggerate the danger of non-native plants would better serve people working to address fire hazards. So we wrote this letter to the California Native Plant Society, which is updating its Fire Recovery Guide. (You can see it here as a 64-page PDF document: cnps-fire-recovery-guide-lr-040618 )


To: Daniel Gluesenkamp, Executive Director of the California Native Plant Society

Dear Mr. Gluesenkamp,

We have read the CNPS Fire Recovery Guide. Property owners will undoubtedly find it useful advice to prevent post-fire erosion and unnecessary destruction of trees and plants that are likely to survive in the long term. The specific advice about creating defensible space also seems helpful.

We understand that your organization is working on an update of this Guide. We are therefore writing to make a few suggestions for improving its accuracy and therefore its credibility.

If the Guide is going to suggest that home owners avoid planting specific plants within their defensible space, we would suggest a more neutral approach that would focus more on fire hazard and less on nativity. The Guide cites eucalyptus and non-native pines as presenting severe fire hazard. See pages 5, 30 and 52. However, the evidence from the recent fires does not implicate non-native trees. The documents cited in your guide (pages 44-45) show that the acreage of non-native tree species that burned in the recent fires was insignificant compared to the overwhelmingly native vegetation that burned. Two papers are cited to support the claim that non-native trees are more hazardous than native trees, Lambert and Landis. Neither paper presents and analyzes data to support the claim. Each paper contains a table of non-native plants considered to be fire hazards, but no information is presented to support them. There is a large quote about the fire hazard of eucalyptus on page 30, but with no indication who made the statement.

There are many available lists of flammable plants that should be avoided within defensible space. Marin Fire Safe lists both native and non-native plants on its list of flammable plants:

The Oakland Firesafe Council also provides a link to that list on their website. Three of the most flammable plants in California landscapes are are bay laurels, coyote brush, and chamise. An evenhanded presentation of fire hazard ratings for all plants that does not downplay the danger of native plants or exaggerate the danger of non-native plants would better serve people working to address fire hazards.

Page 56 of the Guide dismisses the role SOD may have played in the fires. The Big Basin fires are discussed in support of this, but there is no analysis of the Napa, Sonoma and Mendocino fires. Matteo Garbelotto, the scientist at UC Berkeley who conducts the annual survey of SOD infections reports that “A dramatic increase this year in the number of oaks, manzanita and native plants infected by the tree-killing disease known as sudden oak death likely helped spread the massive fires that raged through the North Bay…
It seems likely the vegetation killed by SOD did play a role in fires. Why downplay the possibility?
SOD is a terrible thing. We should not ignore its consequences.

When recommending that property owners plant oaks on their land (page 21), it might be wise to steer them toward other tree choices if the SOD pathogen is known to exist at their location. A detailed map of where SOD infections have been found is available here:

There is some confusion in the guide between plants that are flammable versus fire intolerant. BayLaurels are flammable, but fire tolerant. See page 56.

We hope you will take our comments into account,

San Francisco Forest Alliance



Season’s Greetings and a Hopeful New Year in 2019

We hope that the year ahead will bring a more positive attitude in the world to the environment, to preserving trees and growing more of them, and getting rid of toxic pesticides in our parks and watersheds. It’s a long battle, but we are hopeful.

Season’s greetings to all our readers and supporters! And thank you for your continuing support and voice!



Vote NO on San Francisco’s Prop B

The San Francisco Forest Alliance recommends that you vote no on Proposition B in November 2018.

The proposition, City Privacy Guidelines, would set guidelines for future privacy laws, regulations, policies, and practices for the City. All parts of City government would be authorized to implement any, all or none of these principles. The measure would require that the City Administrator, by May 31, 2019, propose an ordinance establishing the actual criteria and rules for the City. Proposition B is not actually necessary, as it only contains guidelines that may or may not be incorporated into the actual ordinance to be proposed by the City Administrator.

However, the proposition would codify one very important and dangerous thing. Subsection (i) says:
“Notwithstanding any other provision of the Charter, the Board of Supervisors is authorized by ordinance to amend voter-approved ordinances regarding privacy, open meetings, or public records, provided that any such amendment is not inconsistent with the purpose or intent of the voter-approved ordinance.”

In other words, the Board of Supervisors is granting themselves the authority to re-interpret and change Chapter 67 of the San Francisco Administrative Code. This Sunshine Ordinance, is intended to “to ensure that deliberations of commissions, boards, councils and other agencies of the City and County are conducted before the people and that City operations are open to the people’s review.” (You can see the Sunshine Ordinance HERE.)

The Sunshine Ordinance is vital to the rights of individuals to know clearly what their government is doing, and to our free press to fulfill its duty to help the public uphold a fully informed democracy.

City Hall already has too much power to resist transparency and scrutiny. Prop B would unacceptably give our decision makers even more power to further marginalize public accountability and community participation.