Category: Ecology

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

Nativism in the Natural World

Invasion biology is the scientific discipline that spawned the native plant movement.   Charles Elton published a book in 1958 that is considered the origin of the modern version of invasion biology, although there are precursors centuries earlier.  These are the basic tenets of modern invasion biology:

  • Plants and animals that are “native” to a specific location are considered members of an ideal ecosystem that have co-evolved over thousands of years so that members of the community are dependent upon one another.
  • Plants and animals introduced to an ecosystem by humans are assumed to disrupt the equilibrium balance of the community and threaten its existence because introduced plants and animals do not have predators that would control their spread.  All introduced plants and animals are therefore considered potentially invasive.
  • Animals are believed to be dependent upon the plants with which they evolved—and only these plants–and these mutually exclusive relationships are disturbed by the introduction of new plants and animals. 
  • Adaptation and evolution of introduced plants and animals is believed to be too slow for introduced plants and animals to successfully enter the food web.
  • Native members of the ecosystem are presumed to be inherently superior to introduced plants and animals.  Invasion biology does not acknowledge that introduced plants and animals are often functional members of the ecological community.
  • Native ecosystems are said to be in “balance” and introduced species are presumed to cause “imbalance.”  Introduced species must be eradicated to restore balance to the ecosystem, presumed to be the ideal for a particular location.

Hundreds of empirical studies have been conducted since the 1960s to test these assumptions.  Little scientific evidence has been found to support them. Current knowledge of ecology explains why the assumptions of invasion biology are mistaken. 

What is native?

The native plant movement defines native as the plant species that lived in a specific location prior to the arrival of Europeans.    In the San Francisco Bay Area, “native” is defined by native plant advocates as the plants and animals that lived here prior to 1769 when Europeans first laid eyes on San Francisco Bay.  When Europeans arrived, the San Francisco Bay Area was already occupied by indigenous people who had arrived approximately 10,000 years earlier. 

The arbitrary selection of the pre-European settlement period to define the ideal landscape was based on the mistaken assumption that the indigenous human population had not radically altered the land. Anthropological and paleontological research informs us that the landscape was essentially gardened by the indigenous population to provide food and cultural implements. 

Pomo gathering seeds, 1924. Smithsonian photo archive

The landscape found by Europeans at the end of the 18th century was not “natural.”  It was altered by humans to serve humans who lived as hunters and gatherers.  Since modern society no longer hunts and gathers for its food and shelter, the landscape that served that lifestyle cannot be maintained without mimicking the land management practices of native people such as frequent burning of the landscape and grazing by animals.  Indigenous people in California did not have domesticated animals (except dogs), but the grassland was grazed by wild deer, elk, and antelope. 

Plants and animals have migrated around the world without the assistance of humans since life began.  The seeds of plants are carried in the stomachs of migrating birds and on the winds of storms.  Animals, including humans, move to wherever they can find what they need to survive.  Migration is natural and often necessary for survival.  Making a distinction between species moved by humans and those moved by natural forces is pointless and usually impossible to distinguish. 

Climate change renders the concept of “native plants” meaningless because when the climate changes, the vegetation changes.  The plants that live in tropical climates will not survive in arctic cold and vice versa.  Introduced plants are often better adapted to current climate conditions than their native predecessors because the climate has changed and it will continue to change. 

Mistaken assumptions about evolution

Animals rarely depend upon a single plant species for survival.  Such mutually exclusive relationships rarely exist in nature because they are evolutionary dead-ends. Animals can, and often do, adapt quickly to changes in the environment.  Transitions from native to introduced plants are routinely made by animals, including humans.  Indigenous hunter/gatherers quickly incorporated plants introduced by European settlers into their diets.  Plants in the same family and genus are often chemically similar, making the transition more likely. 

Native plant advocates assume that evolution only occurs slowly, over thousands of years, but evolution can be faster than they assume.  Rapid environmental change accelerates the speed of evolution because extreme weather events caused by climate change increase the speed of natural selection, the primary tool of evolution.  When cataclysmic events such as hurricanes, droughts, floods, extreme temperatures kill many members of a species population, these are selection events in which the fittest members survive to breed and the next generation inherits the genetic traits that helped their parents survive.  The classic example of this principle is the finches in the Galapagos Islands who died if they didn’t have big enough beaks to eat the seeds of the only plant that survived extreme drought.  The next generation of finches had bigger beaks. 

Darwin’s finches are an example of rapid evolution

Evolution occurs when genetic changes enable future generations to inherit the genetic change.  Adaptation occurs when animals respond to environmental challenges by changing behaviors that aren’t necessarily inherited by the next generation.  Adaptation to changed environmental conditions is even more rapid than evolution and equally effective to ensure survival. Genetic changes are not required for an insect to make the transition from a native host plant to a chemically similar introduced plant.   Extreme temperatures require that plants and animals move to more temperate climates.  “Native” ranges must change to survive changes in the environment.  A plant or animal that cannot survive extreme heat will migrate (if it can) into regions where temperatures are not as warm.  They should not be prevented from doing so. 

Adaptation to Climate Change. IPCC

Plant and animal species with large populations and short lives, such as insects, evolve more quickly.  This more rapid pace of evolution enables a more rapid transition from native host plants to closely related introduced plants.

soapberry bug made transition from native to non-native balloon vine in 20-50 years. Scott Carroll, UC Davis

Nativism and the native plant movement

The native plant movement is based on the belief that native plants are superior to introduced plants, that native plants are somehow “better” than immigrant plants.  That assumption of superiority is the definition of nativism.  It is as specious an assumption in the natural world as it is in human society and it is equally dangerous. 

There are pros and cons to everything living in the natural world and there is no right answer to the question of which species is “best.” When evaluating introduced plants, nativists consider only the negative aspects. They refuse to acknowledge that there are also advantages and a death verdict should take both into consideration.  For example, native plant advocates want all eucalyptus trees in California cut down because they were planted here after European settlement.  This negative judgment of eucalyptus does not take into consideration that 75% of monarch butterflies who spend the winter in California use eucalyptus trees for their safe haven. Also, eucalyptus blooms in California from November to May, providing nectar to butterflies, hummingbirds, and bees at a time of year when native plants are not blooming.  Eucalyptus trees are also nesting homes of owls and other raptors.  Cutting down eucalyptus trees simply because they are not native in California ignores the many benefits they provide to wildlife. 

Monarch butterflies over-winter in California’s eucalyptus groves

Confusing cause and effect

The native plant movement mistakenly assumes that the mere existence of introduced plants threatens the existence of native plants.  They believe that native plants will magically emerge if introduced plants are eradicated.  They have spent 25 years eradicating non-native plants and do not seem to have noticed that native plants have not returned.  They make this mistake because they do not acknowledge the changes in the environment that make non-native species better adapted to current environmental conditions. 

Many of the changes in the environment that are inhospitable to native species are caused by structural changes made to accommodate human activities, not by introduced species.  For example, all the major rivers in California have been dammed to prevent floods and store water for use during the dry season.  These dams have fundamentally altered the ecology of our rivers.  There are no longer cleansing spring floods that clear rivers of accumulated mud and vegetation.  Channeled rivers are deeper and warmer.  Salmon can no longer get to their spawning grounds past the dams.  The altered structural conditions are more hospitable to bass than to trout.  Aquatic plants from tropical regions become invasive in warmer water.  None of these conditions are reversed by spraying aquatic plants with herbicide or killing introduced bass.

Butterfly bush (buddleia) is now being eradicated by nativists.. butterflybush.com

Wherever “invasions” are observed, no thought is given to why.  Instead, a convenient plant or animal scapegoat is found and poisoned.  That death sentence doesn’t reverse the underlying reason for the invasion.  Therefore, the invasion persists.  Society is unwilling to make the sacrifices, even inconveniences, needed to address the underlying cause of the “invasion.”  We have done little to address the causes of climate change.  We are unwilling to destroy the dams and the system of supplying water to serve agriculture needs.  Invasions are the symptom, not the cause of the changes in nature.

Conservation Sense and Nonsense

You are receiving this announcement of our changed focus and new name because you are a subscriber to our original Million Trees blog.  This is our revised mission for the Conservation Sense and Nonsense blog:

Conservation Sense and Nonsense began in 2010 as the Million Trees blog to defend urban forests in the San Francisco Bay Area that were being destroyed because they are predominantly non-native.  In renaming the Million Trees blog to Conservation Sense and Nonsense, we shift the focus away from specific projects toward the science that informed our opposition to those projects. 

Many ecological studies have been published in the past 20 years, but most are not readily available to the public and scientists are often talking to one another, not to the general public.  We hope to help you navigate the scientific jargon so that scientific information is more accessible to you.  If this information enables you to evaluate proposed “restoration” projects to decide if you can or cannot support them, so much the better.

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

Since 2010, we have learned more about the ideology of invasion biology that spawned the native plant movement and the “restoration” industry that attempts to eradicate non-native plants and trees, usually using herbicides.  We have read scores of books and studies that find little scientific evidence in support of the hypotheses of invasion biology.  We have studied the dangers of pesticides and the growing body of evidence of the damage they do to the environment and all life. 

Meanwhile, climate change has taken center stage as the environmental issue of our time.  Climate change renders the concept of “native plants” meaningless because when the climate changes, vegetation changes.  The ranges of plants and animals have changed and will continue to change to adapt to the changing climate.  Attempting to freeze the landscape to an arbitrary historical standard is unrealistic because nature is dynamic.  Evolution cannot be stopped, nor should it be.

Destroying healthy trees contributes to climate change by releasing stored carbon into the atmosphere.  Both native and non-native trees store carbon and are therefore equally valuable to combat climate change.  Native vegetation is not inherently less flammable than non-native vegetation.  There are advantages and disadvantages to both native and non-native vegetation. 

The forests of the Earth are storing much of the carbon that is the primary source of greenhouse gases causing climate change.  Deforestation is therefore contributing to climate change.  By destroying healthy trees, the native plant movement is damaging the environment and its inhabitants.

Housekeeping

All of the articles on the Million Trees blog are still available in the archive on the home page.  The search box on the home page will take you to specific subjects of interest.  Visit the pages listed in the sidebar of the new home page for discussion of each of the main topics by clicking on the links above.  Readers who subscribed to the Million Trees blog will receive new articles posted to Conservation Sense and Nonsense unless they unsubscribe.  Thank you for your readership.  Your comments are welcome and will be posted unless they are abusive or repetitive. 

Doug Tallamy speaks…Art Shapiro responds…Million Trees fills in the gaps

Smithsonian Magazine published an interview with Professor Doug Tallamy, the entomologist who is committed to the eradication of non-native plants and most influential with native plant advocates in the United States.  The Smithsonian article gives Professor Art Shapiro an inadequate opportunity to respond to Tallamy’s assertions about the superiority of native plants.  Million Trees steps up to fill in the gaps in response to Tallamy.

  • The Smithsonian article says, “As a scientist, Tallamy realized his initial obligation was to prove his insight empirically. He began with the essential first step of any scientific undertaking, by applying for research grants, the first of which took until 2005 to materialize. Then followed five years of work by relays of students.”

The first study that Tallamy conducted is not mentioned in this article because it disproved his hypothesis:  “Erin [Reed] compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally.  After two years of measurements Erin found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season….Erin’s most important result, however, was that there was no statistical difference in the amount of damage on either landscape type.” (1)

  • The Smithsonian article says, “… insects tend to be specialists, feeding on and pollinating a narrow spectrum of plant life, sometimes just a single species. ‘Ninety percent of the insects that eat plants can develop and reproduce only on the plants with which they share an evolutionary history’…:”

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

A “specialist” insect is rarely confined to using a single plant species.  Mutually exclusive relationships in nature are very rare because they are usually evolutionary dead-ends.  The study in which this claim about “specialization” originated, actually concluded:  “More than 90 percent of all insects sampled associate with just one or two plant families.”* 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.  For example, there are 20,000 plant members of the Asteraceae family, including native sagebrush (Artemisia) and non-native African daisy.  In other words, the insect that confines its diet to one family of plants is not very specialized.

  • The Smithsonian article says, “But he [Tallamy] thinks this [transition of insects to non-native plants] is likely to take thousands of generations to have an impact on the food web. Shapiro maintains he has seen it occur within his own lifetime.”

There are many empirical studies that document the transition that insects make from native to non-native plants within generations.  Professor Tallamy provides a few examples of such rapid transitions in his first book, Bringing Nature Home:  wooly adelgids from Asia have had a devastating effect on native hemlock forests in the eastern United States; Japanese beetles introduced to the United States are eating the foliage of over 400 plant species (according to Professor Tallamy), some of which are native (according to the USDA invasive species website).

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug made a transition from a native plant in the soapberry family in less than 100 generations over a period of 20 to 50 years. The soapberry bug-balloon vine story is especially instructive because it entailed very rapid morphological as well as behavioral change; the beak length was quickly (a few years) selected for the dimensions of the fruit of the new host. (2)

  • Doug Tallamy claims that Art Shapiro’s findings are “anecdotal.” They are not.  Art Shapiro’s published study is based on nearly 40 years of data. (3)

Monachs in eucalyptus, Pacific Grove Museum

In a recent NY Times article about declining populations of monarch butterflies on the West Coast, an academic scientist explains how he used Professor Shapiro’s data set to study the decline:  “The monarch’s decline is part of a larger trend among dozens of butterfly species in the West, including creatures with names like field crescents, large marbles and Nevada skippers,” said Matt Forister, an insect ecologist at the University of Nevada, Reno, whose conclusions are based on a nearly 50-year set of data compiled by Art Shapiro, a researcher at the University of California, Davis. “The monarch is very clearly part of a larger decline of butterflies in the West.”  Clearly, other academic entomologists do not consider Professor Shapiro’s data “anecdotal.”

The Burghardt/Tallamy study (4) does not contradict the findings of Professor Art Shapiro because Professor Shapiro is studying butterflies (not moths) in “natural areas” that have not been artificially created by choosing a limited number of plant species, as Tallamy’s study did.  In other words, the adult and larvae stages of butterflies that Professor Shapiro studies have more options, and when they do they are as likely to choose a non-native plant as a native plant for both host plant and food plant.  You might say, Professor Shapiro’s study occurs in the “real world” and the Burghardt/Tallamy study occurs in an artificially created world.

Dismissing observations as anecdotal is a well-worn rhetorical device.  Creationists often claim that evolution cannot be proven because the theory is based on millions of observations, rather than empirically tested by experiments. Yet, virtually all scientists are firm believers in the validity of evolutionary principles.

  • Tallamy dismisses climate change as a factor in plant and animal extinctions, preferring to place the blame solely on the mere existence of non-native plants.

This claim is contradicted by a multitude of studies, such as a collection of studies recently reported by Yale E360 that concludes:  “A growing number of studies show that warming temperatures are increasing mortality in creatures ranging from birds in the Mojave Desert, to mammals in Australia, to bumblebees in North America. Researchers warn that heat stress could become a major factor in future extinctions.”

Climate change is the environmental issue of our time.  When the climate changes, the vegetation changes.  When the vegetation changes, wildlife adapts or dies.  Non-native plants are one of the consequences, not the cause of climate change or plant and animal extinctions.

*Professor Shapiro has provided a caveat to this definition of specialization of insects in a private communication, published with his permission:  “A couple of observations: Hardly any insects feed on entire plant families. Rather, they feed on specific lineages within those families, typically defined by secondary chemistry (which is the necessary releaser for oviposition and/or feeding behavior). The relationship was summed up symbolically by A.J.Thorsteinson half a century ago: feeding=presence of nutrients+presence of required secondary chemicals-deterrents-antifeedants-toxins. Thus the Anise Swallowtail species-group feeds on the carrot family, Apiaceae, but NOT on Apiaceae lacking the proper chemistry.But they DO feed on some Rutaceae (including Citrus) that, though unrelated, are chemically similar. That was worked out by Vincent Dethier in the 1940s and further developed by John Thompson at UC Santa Cruz. A whole slew of things require iridoid glycosides as oviposition and feeding stimulants. Most plants containing these were in the family Scrophulariaceae before DNA systematics led to its dismemberment, but one whole branch of Scrophs is chemically unsuitable. Milkweed bugs eat milkweed, but they also eat the Brassicaceous genera Erysimum and Cheiranthus, which are chemically similar to milkweeds but not to other Brassicaceae…and so on. Native vs. non-native has nothing to do with it.”  (emphasis added)

  1. Tallamy, Doug, “Flipping the Paradigm:  Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011
  2. Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433
  4. Karin Burghardt, Doug Tallamy, et. al., “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities,” Ecosphere,November 2010

Study design determines study findings

Million Trees can never resist a response to misinformation we find in Jake Sigg’s Nature News. (In this case, the statement originates with one of Jake’s readers, not Jake himself.)

“This study takes some of the life out of Art Shapiro’s ecological fitting theory:  Non‐native plants supported significantly fewer caterpillars of significantly fewer specialist and generalist species even when the non‐natives were close relatives of native host plants.”  “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities” by Karin Burghardt, Doug Tallamy, et, al. (Ecosphere, November 2010).

We’ll get to the study later, but first let’s address the statement about ecological fitting.  Ecological fitting is more accurately described as an observation, rather than a theory or hypothesis and it does not originate with Art Shapiro.  The first observation of ecological fitting was recorded by Dan Janzen in 1980 and described by other ecologists as “the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition.” (1) Ecological fitting is an alternative to the view that relationships between plants and insects and parasites and hosts are the result of co-evolution.  It is consistent with the observation that adaptation to new arrivals in an ecosystem often occurs without evolutionary change and can occur more rapidly than co-evolution would require.

The Colorado potato beetle readily devours an introduced relative of its Solanum hosts as a result of ecological fitting.  (Hsiao, T. H. (1978). “Host plant adaptations among geographic populations of the Colorado potato beetle”. Entomologia Experimentalis et Applicata. 24 (3)) USDA photo

Ecological Laboratory Science

The Burghardt/Tallamy study is a laboratory experiment in the sense that it creates an artificial environment by planting a garden in which it chooses the plant species and then inventories the insect visitors to the garden.  In one garden, native plant species were paired with a closely related species of non-native plant in the same genus (called congeners).  In another, distant garden, native plant species were paired with unrelated species of non-native plants.  The insect visitors that were counted are specifically the larvae stages (caterpillars) of lepidoptera (moths and butterflies).  The adult stage of the caterpillars (moths and butterflies) were not inventoried, nor were members of the other 28 insect orders.

Source: handsontheland.org

The study considers caterpillars “specialists” if they feed on three or fewer plant families.  The authors make this determination based on scientific literature and on observations of their artificially created garden.  Using scientific literature, 30% of visiting caterpillar species to the experimental garden were specialists.  Using actual visits to their experimental garden, 64% of visiting caterpillars were specialists.  The difference is as we should expect because the scientific literature is based on the behavior of caterpillars in the field, but the study confines the choices of the caterpillars to a few specific plant species chosen by the authors of the study.  In other words, caterpillars in the experimental garden had fewer choices of plant species.

The inventory of caterpillars was conducted over two summer months in 2008 and three summer months in 2009.  Findings were very different in the two years of the study:  “We found no difference between the total Lepidoptera larvae supported by native plants and their non-native congeners in 2008, but found over three fold more larvae on natives in 2009.  In 2008 there was no difference in the abundance of generalists on native and non-native congeners, but natives supported more than twice as many generalists as non-natives in 2009.” (2) Similar results were reported for species richness (number of different larvae species).  When paired with unrelated non-native plants, caterpillars showed a significant preference for native plant species, as we should expect because the plants were not chemically similar.

Caterpillar of Anise swallowtail butterfly on its host plant, non-native fennel. Berkeley, California

Although on average, native species attracted more caterpillars than the non-native congener with which they were paired, the strength of that difference varied significantly.  One matched pair attracted eight times as many caterpillars to the native plant compared to the non-native plant.  Another matched pair attracted slightly more caterpillars to the non-native plant compared to the native plant.  

The study authors interpret the significant differences between findings in the first and second years as an indication that caterpillars accumulated more rapidly on native plants than on non-native plants.  They speculate that a longer study would have found even greater preferences for native plants compared to non-native congeners.  Given that adaptation to introduced species occurs over time that is a counter-intuitive prediction.  In fact, many studies find that insects have made a successful transition from native to non-native hosts within a few generations.

Limitations of laboratory studies

The Burghardt/Tallamy study is often cited by native plant advocates in support of their belief that insects require native plants for survival.  This generalization is not supported by the results of the Burghardt/Tallamy study because:

  • The study results are not relevant to all insects.  The findings apply only to the larvae stages of moths and butterflies.  The adult stages of moths and butterflies also require nectar and pollen from a much broader range of plants than their host plant, where the adult lays its eggs and caterpillars feed before becoming flying adults.  At the adult stage of their lives, they become pollinators.  Studies of the preferences of pollinators consistently find that a diverse garden that prolongs the blooming period is most useful to them. 
  • The study does not support the claim that caterpillars consistently choose native plants in preference to closely related non-native plants over time.  In fact, other studies find such preferences fade over longer periods of time.
  • Statements made by native plant advocates about the degree to which caterpillars are “specialized” are often exaggerated.  When a diverse landscape is available to caterpillars, scientific literature reports that specialization to a few plant families is found in only 30% of the 72 caterpillar species identified by this study. 
  • The Burghardt/Tallamy study was conducted on the East Coast where the climate is different than California.  It snows in the winter and it rains during the summer, unlike most of California.  Our native plants are therefore different from natives on the East Coast.  The Burghardt/Tallamy study was conducted in the summer months from June to August.  Native plants in California are no longer blooming and many are dormant during summer months unless they are irrigated.  The findings of the Burghardt/Tallamy study are therefore not applicable to California unless they can be replicated here.
This is the Serpentine Prairie in Oakland. It is one of the native plant “restorations” done by East Bay Regional Park District. About 500 trees (including native oaks) were destroyed to return the prairie to native grassland. This is what it looks like in June.

Comparison of laboratory with field studies

The Burghardt/Tallamy study does not contradict the findings of Professor Art Shapiro because Professor Shapiro is studying butterflies (not moths) in “natural areas” that have not been artificially created by choosing a limited number of plant species.  In other words, the adult and larvae stages of butterflies that Professor Shapiro studies have more options, and when they do they are as likely to choose a non-native plant as a native plant for both host plant and food plant.  You might say, Professor Shapiro’s study occurs in the “real world” and the Burghardt/Tallamy study occurs in an artificially created world. 

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

The credibility and relevance of Professor Shapiro’s studies are also based on 47 years of visiting his research plots at least 250 days per year, that is, year around.  During that period of time, he recorded his observations and they were statistically analyzed for the study he published in 2003. (3)  His study is of particular interest as the climate changes rapidly because the length of the study also enables us to observe the impact of climate change on our butterfly population in the Bay Area.  In contrast the Burghardt/Tallamy study was conducted in a total of 5 months over a total of two years.  Population trends cannot be determined from such a short study.

Burghardt/Tallamy study is consistent with mission of Million Trees

The Burghardt/Tallamy study does not contradict anything Million Trees advocates for.  Decisions to plant a particular species and the decision to eradicate a particular species are entirely different.  Gardeners should plant whatever they prefer, in my opinion.  When planting decisions are made for public land, I prefer that plants be capable of surviving current local and climate conditions.  When my tax dollars are being spent, I prefer that they not be wasted. Besides, I hate watching plants and trees die in the parks I visit.

This study is consistent with my view that non-native plants don’t threaten the survival of insects unless they replace native plants that insects prefer.  The Burghardt/Tallamy study quite rightly does not say that they do.  Local experience in the Bay Area informs me that they rarely do.  To the extent that they have replaced native plants, they are better adapted to current conditions in a specific location.  Eradicating them rarely results in native plants successfully replacing them.  As the climate continues to rapidly change, the failure of native plant “restorations” is inevitable because vegetation changes when the climate changes.

Site 29 on Claremont Blvd in Oakland is one of the places where UC Berkeley destroyed about 19,000 trees about 14 years ago. Non-native weeds thrive in the sun where trees were destroyed. Poison hemlock and thistle (both non-native) are 8 feet tall where not sprayed with herbicide. Site 29, May 2016.

The Burghardt/Tallamy study does not justify eradication of non-native plants because it does not take into account the damage done by the methods used to eradicate non-native plants.  Since most eradication projects use herbicides, we speculate that more harm is done to insects by herbicides than by the existence of non-native plants.

The decision to eradicate non-native plants must also take into consideration whatever benefit the plants may provide, such as food for wildlife.  For example, even if a plant species isn’t a host plant, it might be a food plant. Butterfly bush (Buddleia) is an example of a plant that is very useful to pollinators, including butterflies, but native plant activists advocate for its eradication. 

Monarch nectaring on butterfly bush. butterflybush.com

Many thanks to Jake Sigg for creating this opportunity for dialogue with native plant advocates.  I am grateful for the window into the community of native plant advocates that Jake’s Nature News provides.

  1. Agosta, Salvatore J.; Jeffrey A. Klemens (2008). “Ecological fitting by phenotypically flexible genotypes: implications for species associations, community assembly and evolution”. Ecology Letters. 11 (11): 1123–1134. 
  2. “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities” by Karin Burghardt, Doug Tallamy, et, al. (Ecosphere, November 2010).
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433

“San Francisco’s Natural History”: A mixed bag of fact and fiction

Million Trees breaks its self-imposed silence to bring you this book review of San Francisco’s Natural History:  Sand Dunes to Streetcars, by Harry G Fuller.  It was frustrating to read this book because I had high expectations that I would like it and learn from it.  And to some extent, I did.  However, the book also repeats old myths about eucalyptus that have long ago been debunked and fabricates a new myth.  It also supports deadly and dangerous “restoration” projects in the Bay Area without acknowledging the loss of wildlife they cause. On the other hand, historical records of San Francisco’s natural history seem to be accurately reported by Fuller and he paints the picture of pre-settlement San Francisco as drifting sand dunes and treeless grass and chaparral. 

Persistent myths about eucalyptus

Fuller says, “There is evidence…that eucalyptus trees may be deadly to both wintering birds and monarch butterflies…At the same time the trees provide necessary shelter, their chemical make-up and their sticky leaves may prove deadly.”

Hummingbird in eucalyptus flower. Courtesy Melanie Hoffman

Fuller does not provide the “evidence” for this statement, so we must speculate about what he means.  It seems likely that he is repeating the 23-year old claim that eucalyptus kills birds by suffocating them with their sticky nectar when eucalyptus blooms in winter months. (Neither the nectar, nor the leaves of eucalyptus is sticky.)  A local birder reported seeing two dead birds in eucalyptus forest over the course of his long career as a serious birder and parlayed those isolated observations into the generalization that birds are killed by eucalyptus trees.  Decades of research was required to put that accusation to rest. (1, 2) Officially, the myth died when the California Invasive Plant Council updated the classification of eucalyptus in 2015.  The claim that eucalyptus kills birds was deleted from Cal-IPC’s revised classification. It was aggravating to see this claim repeated by Mr. Fuller in his book, which was published in 2017.

Fuller’s claim that eucalyptus is also deadly to monarch butterflies is unprecedented.  I have heard innumerable stories about the bad habits of eucalyptus, but I have never heard that eucalyptus kills monarch butterflies.  You won’t find that accusation anywhere on the internet and you won’t find it anywhere in the scientific literature.  I confirmed with Art Shapiro, Distinguished Professor of Ecology and Evolution at UC Davis and author of Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, that he had never heard that claim either. 

In fact, available empirical evidence contradicts that claim. Eucalypts are the preferred trees for over-wintering monarchs in California:  “Three types of trees were used most frequently by roosting monarchs:  eucalyptus (75% of the habitats primarily Eucalyptus globulus), pine (20% of the habitats primarily Pinus radiata), and cypress (16% of the habitats Cupressus macrocarpa).  Twelve other tree species were identified…with a combined prevalence of only 10%.” (3)  Monarchs migrate down the coast of California during the winter months, when eucalyptus is flowering at a time when there is little else blooming in California.  They are an essential source of nectar during the monarch migration. 

Fuller says, “The eucalyptus’s natural herbicides prevent many other plants from growing beneath their canopy.”   

This is another accusation that has been repeatedly disproven by empirical research.  The eucalyptus forest is as biodiverse as native oak woodland (4).  The 2015 revision of the California Invasive Plant Council assessment of eucalyptus deleted previous mention of the allelopathic (the scientific term for “natural herbicide”) properties of eucalyptus.  A rigorous study at Cal Poly concluded, “In these experiments, we found that germination and seedling growth of the species tested were not inhibited by chemical extracts of blue gum foliage, either at naturally-occurring or artificially concentrated levels.” (5)  This study was presented by its author at the most recent conference of the California Native Plant Society, which should establish its credibility with native plant advocates.

Presentation at conference of California Native Plant Society

Fuller says in support of his “natural herbicide” theory, “You never see moss or lichen on a healthy eucalyptus trees.”

We don’t see moss or lichen on eucalyptus tree trunks because the thin, papery bark on the trunk sloughs off annually, leaving the trunk bare.  Moss and lichen grow slowly on tree trunks in the bark that remains on the tree throughout the tree’s life.

Spartina (aka cordgrass) eradication

Ironically, Mr. Fuller prefaces his strong support for cordgrass eradication with this admonition:  “Do not forgive ignorance, please.”  Then, he displays profound ignorance of the consequences of cordgrass eradication in the San Francisco Bay Area.  Fuller is a professional birder, yet he is seemingly unaware of the fact that the eradication of cordgrass has nearly wiped out the population of endangered Ridgway Rail (formerly Clapper Rail) in the Bay Area.  He is also unaware of the huge quantities of herbicide that have been used to eradicate cordgrass.  Elsewhere in his book, he expresses concern about pesticides and other forms of pollution, yet in the case of cordgrass eradication he turns a blind eye.  (6)

Pesticide Application Notice, Heron’s Head, 2012

Eradication of mice on Farallon Islands

Mr. Fuller also supports plans to eradicate mice on the Farallon Islands:  “The latest effort to return the Farallones to a more natural preserve is an attempt to remove all the house mice.”  He is either unaware of plans to aerial bomb rodenticides on the Farallons to kill the mice or he chooses to use the euphemism “remove” to avoid the issue.  Elsewhere in the book, he mentions that rodenticides used in Golden Gate Park to kill rats also killed Great Horned Owls that ate the dead or dying rats.  He seems to understand that non-target birds are killed by rodenticides, yet he apparently supports the use of rodenticides on the Farallons, a national marine sanctuary.  (7)

Farallon Islands, NOAA

A Cautionary Tale

Mr. Fuller displays a sincere concern for the wildlife of San Francisco throughout his book.  He also acknowledges the very real threats of climate change and pollution for the future of the environment in the Bay Area.  I do not doubt his sincerity and I believe he has written a valuable book that is unfortunately damaged by his uncritical acceptance of inaccurate versions of several important environmental issues in the Bay Area.  I believe Mr. Fuller has been a victim of “incestuous amplification” in his acceptance of these myths.  Let that be a lesson to all of us to look deeply at every issue and to verify any tale you are told by an amateur or someone with a vested interest in those issues, such as employment. 

I cannot recommend this book to anyone who is not prepared to read it critically.  If you don’t already have a basic knowledge of the natural history of San Francisco you could easily be led astray by baseless rumors. 

  1. https://milliontrees.me/2013/11/05/eucalyptus-trees-do-not-kill-birds/
  2. https://milliontrees.me/2014/07/26/birds-and-butterflies-in-the-eucalyptus-forest/
  3. Dennis Frey and Andrew Schaffner, “Spatial and Temporal Pattern of Monarch Overwintering Abundance in Western North America,” in The Monarch Butterfly Biology and Conservation, Cornell University Press, 2004.
  4. https://milliontrees.me/2011/02/04/biodiversity-another-myth-busted-2/
  5. https://milliontrees.me/2018/02/06/highs-and-lows-of-the-2018-conference-of-the-california-native-plant-society/
  6. https://milliontrees.me/2014/06/02/spartina-eradication-herbicides-are-their-dirty-little-secret/
  7. https://milliontrees.me/2014/01/10/the-mouse-eradication-project-on-the-farallon-islands-the-con-in-conservation/

Eradicating non-native plants does NOT benefit insects

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.

Insects use both native and 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 urbanwildness.org

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.

The consequences of eradicating non-native plants

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.” (1)

Update:  The California Invasive Plant Council has published “Land Manager’s Guide to Developing an Invasive Plant Management Plan.”  It says very little about the disadvantages of using herbicides to eradicate plants they consider “invasive” other than a vague reference to “unintended consequences,” without discussion of what they are or how to avoid them. 

However, it does give us another clue about why eradication efforts are often unsuccessful. When herbicides are used repeatedly, as they have been in the past 20 years, weeds develop resistance to them:   “The International Survey of Herbicide Resistant Weeds (2018) reports there are currently 496 unique cases (species x site of action) of herbicide-resistant weeds globally, with 255 species…Further, weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides.”  The Guide therefore recommends that land managers rotate herbicides so that the “invasive” plants do not develop resistance to any particular herbicide.  The Guide gives only generic advice to use “herbicide X” initially and “herbicide Y or Z” for subsequent applications.

In other words, the California Invasive Plant Council continues to promote the use of herbicides to kill plants they consider “invasive.”  They give advice about ensuring the effectiveness of herbicides, but they do not give advice about how to avoid damaging the soil, killing insects, and harming the health of the public and the workers who apply the herbicides. 

Do insects benefit from eradicating non-native plants?

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.

Jake Sigg and Art Shapiro discuss insects and native plants

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.”

(1) “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.

Happy New Year and Farewell

The Million Trees blog is folding its tent and moving on because most of the projects in the San Francisco Bay Area that I have followed for 20 years have been approved, funded, and are being implemented.  Every public land manager in the Bay Area has made a commitment to destroying most non-native trees and using pesticides for that purpose.

If you wish to continue following the development of these projects, I recommend these websites:  San Francisco Forest Alliance,  Defend East Bay Forests, Save the East Bay Hills, and Hills Conservation Network.

For the record, this is a brief summary of my beliefs about the environment:

If I return to the blogosphere in the future, the title and mission of a new blog would change.  The focus would be the science that informs my commitment to the cosmopolitan landscape that exists, rather than the fantasized landscape of the past.  I will also continue to inform readers of new studies that find evidence of the damage that pesticides do to the environment and its inhabitants.  If you are a subscriber to the Million Trees blog, you will be informed if I publish a new blog.

Thank you for your readership.

Million Trees

Conference of the California Invasive Plant Council: Fallacies and Failures

The California Invasive Plant Council held their 27th annual conference in Monterey in November.  It was their biggest conference, with about 400 attendees and more sponsors than ever before.  Clearly the industry that promotes the eradication of non-native plants is alive and well.  However, a closer look at the conference presentations suggests otherwise.  Eradication efforts are growing, but eradication success is not and establishing a native landscape after eradication is proving elusive.

A few common themes emerged from the presentations:

  • Eradication cannot be accomplished without using pesticides.
  • When eradication is achieved with pesticides, non-natives are rarely replaced by native plants.
  • Planting natives after non-natives are eradicated reduces re-invasion, but secondary invasions of different non-native plants are common.
  • “Managing” forests with prescribed burns did not result in more biodiversity than leaving the forest alone.

Goals of these eradication projects have shifted in response to these failures to achieve original goals:

  • Replacement plantings after eradication are sometimes a mix of natives and non-natives.
  • Inability to establish native grassland has given way to different goals.
  • Language used to describe the projects are evolving to be more appealing to potential volunteers.

Here are a few examples of presentations that illustrate these themes:

Eradicating beach grass in Point Reyes National Seashore

About 60% of sand dunes in the Point Reyes National Seashore were covered in European beach grass when the eradication effort began in 2000.  The goal of the project was to restore native dune plants and increase the population of endangered snowy plovers that nest on bare sand.

The project began by manually pulling beach grass from 30 acres of dunes at Abbott’s Lagoon.  The grass grew back within one year, presumably because the roots of the beach grass are about 10 feet long.  Manually pulling the grass from the surface does not destroy the roots.

A new method was devised that was more successful with respect to eradicating the beach grass.  The grass and its roots were plowed up by bulldozers and buried deep in the sand.  The cost of that method was prohibitively expensive at $25,000 to $30,000 per acre and the barren sand caused other problems.

The barren dunes were mobile in the wind.  Sand blew into adjacent ranches and residential areas, causing neighbors of the park to object to the project.  The sand also encroached into areas where there were native plants, burying them.  The bare sand was eventually colonized by “secondary invaders.”  Different non-native plants replaced the beach grass because they were more competitive than the desired native plants.

In 2011, the National Park Services adopted a third strategy for converting beach grass to native dune plants.  They sprayed the beach grass with a mixture of glyphosate and imazapyr.  At $2,500 to $3,000 per acre, this eradication method was significantly cheaper than the mechanical method.

However, it resulted in different problems that prevented the establishment of native dune plants.  The poisoned thatch of dead beach grass was a physical barrier to successful seed germination and establishment of a new landscape.  Where secondary invaders were capable of penetrating the dead thatch, the resulting vegetation does not resemble native dunes.

Presentation at California Invasive Plant Council conference regarding attempt to eradicate European beach grass at Point Reyes National Seashore

The concluding slides of this presentation were stunning.  They said it is a “Restoration fallacy that killing an invader will result in native vegetation.”  My 20 years of watching these futile efforts confirm this reality.  However, I never expected to hear that said by someone actually engaged in this effort.  The presenter mused that such projects are like Sisyphus trying to roll a boulder up hill. 

Presentation at California Invasive Plant Council conference regarding attempt to eradicate European beach grass at Point Reyes National Seashore

Attempting to plant Douglas fir after eradication of broom

Over a period of 5.5 years, broom was eradicated in plots in Oregon by spraying glyphosate.  The plots were then planted with Douglas fir seedlings that soon died.  They were replanted the following year and died in the second year.

There were two theories about why the plantings failed, both broadly described as “legacy” effects in the soil left by the broom.  One theory is that nitrogen levels were too high for successful growth of Douglas fir.  That theory is consistent with the fact that broom is a nitrogen fixer.  That is, broom—like all legumes—have the ability to transfer nitrogen in the atmosphere to nitrogen in the soil with the help of bacteria that facilitate that transfer.  Nitrogen generally benefits plant growth, but there can also be too much nitrogen.

The second theory is that Douglas fir requires a specific suite of mycorrhizal fungi for successful growth.  Mycorrhizal fungi live in roots of plants and trees.  They transfer moisture and nutrients from the soil to the plants.  Plants with a healthy suite of mycorrhizal fungi are more drought tolerant because they extract more moisture from the soil.

Neither of these theories has been successfully proven by this project.  They remain unanswered questions.  We were struck that the researchers had not considered the possibility that the repeated use of glyphosate could have been a factor in the failure of the Douglas fir.  Glyphosate is known to kill bacteria in the soil.  Could it also kill mycorrhizal fungi?  (We know that triclopyr kills mycorrhizal fungi.) That possibility was not considered by this project. Did the project consider that glyphosate also changes the consistency of the soil by binding certain minerals together?  It is more difficult for roots and water to penetrate the hard soil.  Were soil samples taken before and after repeated applications of glyphosate to determine how the soil had been changed by pesticide applications?

The published abstract for this project made this observation:  “It is typically assumed that once an invasive species is successfully removed, the impact of that species on the community is also eliminated.  However, invasive species may change the environment in ways that persist, as legacy effects, long after the species itself is gone.”  In fact, it seems likely that the pesticides used to eradicate the “invasive” species could also be the source of the “legacy effects.”

Does “managing” a forest result in greater biodiversity in the understory?

California State Parks tested that hypothesis by conducting prescribed burns in some of their forests in the Sierra Nevada 20 years ago, while leaving other portions of the forest “unmanaged.”

The abstract for this presentation describes the goals and expectations for the prescribed burns:  “Prescribed fire is a tool used to reduce fuels in the forests in the Sierra Nevada and mimic the low and moderate severity wildfires that burned before the onset of fire suppression.  A manager’s hope is that prescribed fire will create the disturbance necessary to stimulate the development of species rich understory communities and increase species richness, compared to unburned forests, which are often viewed as species depauperate.”

Twenty years after the burns, abundance and species composition of the understory in the burned areas were compared to the unburned areas.  They found little difference in the biodiversity of the understory of burned areas compared to unmanaged forests:

  • “Species richness was highly variable within burned and passively managed areas but was not statistically different.”
  • “Passively managed areas did not appear to be depauperate in understory species diversity compared to areas managed with prescribed fire.”
  • “Fire did not appear to reduce or enhance species richness numbers in burned areas, as compared to passively managed areas.”

No fires occurred in either the burned areas or the unmanaged areas during the 20-year period.  Therefore, this study did not test the theory that prescribed burning reduces fire hazards in forests.  This study found no significant differences in diversity of forest understory resulting from prescribed burns.

There are significant risks associated with prescribed burns.  They cause air pollution and they frequently escape the controlled perimeter of the fire, becoming wildfires that destroy far more than intended.  This study does not provide evidence that would justify taking those risks.  In fact, available evidence supports the “leave-it-alone” approach to land management.

Moving the goal posts

If at first you don’t succeed, you have the option of redefining success.  Here are a few of the projects presented at the conference that seemed to take that approach.

Make projects so small that success can be achieved

Eric Wrubel introduced himself as the National Park Service staff who is responsible for prioritizing invasive plants for removal in the National Parks in the Bay Area (GGNRA, PRNS, Muir Woods, and Pinnacles).  His work is based on the premise that the most successful eradications are those that are small.  The bigger the infestation, the greater the investment of time and resources it takes to eradicate it and the smaller the likelihood of success.  This is illustrated by a graph showing this inverse relationship between the size of the invasive population and the success of eradication.

Source: Rejmanek and Pitcairn, “When is eradication of an exotic pest plant a realistic goal?,” 2002

The process of prioritizing eradication projects began over 10 years ago with a survey of over 100 species of plants considered invasive.  Cal-IPC’s “watch list” was used to identify the plants that are not yet widely spread in California, but considered a potential problem in the future.  Cal-IPC’s risk assessment was the third element in the analysis.  Plants with “High” risk ratings by Cal-IPC were put higher on the priority list than those with “Moderate” or “Limited” ratings.  Plants that did not exist elsewhere in the region or watershed were also given higher priority, based on the assumption that re-invasion was less likely.

This is the list of eradication projects in the National Parks in the Bay Area that was presented at the conference of the California Invasive Plant Council. The projects marked with the red symbol for crossing out are completed projects. Nearly half of the plants on this hit list are not considered invasive in California.

The priority list showed that the highest priority eradication projects were quite small.  Some were just a few acres.  Buddleia jumped out as the 7th highest priority on only 13 acres.  Buddleia was recently added to a new category of plants on Cal-IPC’s “invasive” inventory.  It is not considered invasive in California, although it is considered invasive elsewhere.

In placing buddleia on its “hit list,” Cal-IPC illustrates one of the fundamental weaknesses of its evaluation method.  Cal-IPC does not evaluate pros and cons of non-native plants.  Only traits considered negative are taken into consideration.

Monarch sanctuary in Monterey, California. November 2018

Buddleia is one of the most useful nectar plants for pollinators in California.  We took the time to visit the monarch butterfly sanctuary in Monterey while attending the conference.  The monarchs are arriving now to begin their winter roost in the eucalyptus, Monterey pine and cypress in this small grove.  At the entrance to the sanctuary a sign instructs visitors to plant only native milkweed as the monarch’s host plant and only native flowers for nectar.  Fortunately whoever planted the flowering shrubs in the sanctuary didn’t follow the advice of the sign-makers.  They planted buddleia and other flowering non-natives such as bottle-brush.  Several species of butterflies and hummingbirds were enjoying those plants in the Sanctuary. Strict adherence to the native plant agenda is not beneficial to wildlife because animals do not share our prejudices.

Monarch nectaring on butterfly bush. butterflybush.com

Acknowledging the difficulties of converting non-native annual grass to native perennial grass

Pinnacles National Park acquired 2000 acres of former ranchland in 2006.  The park wanted to convert the non-native annual grasses and yellow-star thistle on the former ranch to perennial bunch grasses and oak woodland.  They were able to reduce the amount of yellow-star thistle by burning and spraying with herbicide, but cover of native species remained low.  Conversion of grasses from non-native annuals to native perennial grass has been tried many times, in many places, and for long periods of time.  These projects were notoriously unsuccessful.

The project at Pinnacles has changed its goal to plant forbs (herbaceous flower plants) instead of grasses and they report that they are having some success.   They justify that shift in goal on soil analysis that suggests forbs were more prevalent than perennial grasses in inland valleys in California than previously thought.

This change in goal could be described as “adaptive management,” which adjusts methods and goals in response to observable outcomes of existing methods.  You could also call it “trial and error.”  We would like to see more land managers make such adjustments to their strategies, rather than doing the same thing over and over again and expecting a different outcome.

Recruiting volunteers with appealing messages

There were several presentations about effective methods of recruiting volunteers to participate in restoration projects.  Some of their messages seem to acknowledge that the language used in the past may have alienated some potential volunteers.  Speaking from personal experience, I can confirm that observation.  Here are just a few of the cringe-worthy native plant mottos that I hope have been abandoned in favor of a more positive message:

  • “That plant doesn’t belong here.”
  • “That is a good plant and the other is a bad plant.”
  • “The invasive landscape is sick and requires chemotherapy.” (to justify the use of pesticides)
  • “That’s a trash bird.” (said of common, introduced birds, such as starlings and house sparrows)

The speaker advised those who work with volunteers to focus on why an unwanted plant is a problem rather than where it comes from.  Unfortunately, the list of problems is heavily influenced by the preferences of native plant advocates.  If their criticisms are not accurate, or they don’t acknowledge the advantages of the plant, little has been achieved by using euphemisms.  Here are a few of the inaccurate criticisms made of eucalyptus:

What was missing?

Ecological restoration is a major industry. Thousands of people are employed by the industry, which is funded by many different sources of public money.  Whether individual projects are successful or not, the industry will survive and thrive as long as it is funded.  Greater care should be taken to design and implement projects that will be successful.

Stepping back from the conference presentations of specific restoration projects, here are a few issues that were conspicuously absent from the conference. 

  • Pesticides are being widely used by the restoration industry. When projects don’t achieve desired outcomes, pesticides should be considered as a factor.  Did pesticides alter the soil?  Were beneficial microbes and fungi killed? How persistent was the pesticide in the soil?  How mobile was the pesticide in the soil?  Was pesticide applied in the right manner?  Could aerial drift account for death of non-target plants?  There are many other useful questions that could be asked.

Update:  The California Invasive Plant Council has published “Land Manager’s Guide to Developing an Invasive Plant Management Plan.”  It says very little about the disadvantages of using herbicides to eradicate plants they consider “invasive” other than a vague reference to “unintended consequences,” without discussion of what they are or how to avoid them. 

However, it does give us another clue about why eradication efforts are often unsuccessful. When herbicides are used repeatedly, as they have been in the past 20 years, weeds develop resistance to them:   “The International Survey of Herbicide Resistant Weeds (2018) reports there are currently 496 unique cases (species x site of action) of herbicide-resistant weeds globally, with 255 species…Further, weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides.”  The Guide therefore recommends that land managers rotate herbicides so that the “invasive” plants do not develop resistance to any particular herbicide.  The Guide gives only generic advice to use “herbicide X” initially and “herbicide Y or Z” for subsequent applications.

In other words, the California Invasive Plant Council continues to promote the use of herbicides to kill plants they consider “invasive.”  They give advice about ensuring the effectiveness of herbicides, but they do not give advice about how to avoid damaging the soil, killing insects, and harming the health of the public and the workers who apply the herbicides.  May 20, 2019

  • Are workers who apply pesticides being adequately trained and supervised by certified applicators? The safety of workers should be one of many goals of restoration projects.
  • When non-native plants are eradicated, serious thought should be given in advance to the probable outcome. Will native plants return?  Will wildlife be harmed?  Will the risks of failure outweigh the potential benefits of success?
  • Is climate change taken into consideration when planning the replacement landscape? Are the plants that grew in the project location 200 years ago still adapted to that location?  Is there enough available water?
  • If new plantings require irrigation to be established, what is the water source? Is it recycled water with high salt content that will kill many plants, including redwoods?
  • Are the new plantings vulnerable to new infectious diseases, such as phytopthera or infestations of new insects such as shot-hole borer?
  • Does the project team have sufficient horticultural knowledge to choose plants that can survive in current conditions? Does the project team know the horticultural needs of the plants they are planting?  Is there enough sunlight, water and wind protection for the trees they are planting?

The public is investing heavily in the “restoration” of ecosystems.  We can only hope that our investment is being used wisely and that projects will not do more harm than good.  Cal-IPC can play a role in raising the questions that have the potential to improve projects and enable them to succeed.  The long-term survival of the “restoration” industry depends on it.

Most quotes are from abstracts of presentations published in the conference program.

Trophic cascades are initiated by pesticide use

Although the Environmental Protection Agency requires that pesticides be tested before they can be sold in the US, we know that the required tests are inadequate to determine if the pesticide is dangerous to human health and the environment.  The tests are only as accurate as the test protocols and procedures.  There are many flaws in the testing methods required by federal law.  Here are a few of them:

  • Tests are conducted on laboratory animals in which the dose is limited to a single chemical. In the real world, humans and other animals are subjected to many chemicals simultaneously in doses that are unknown and unknowable, because little testing is done of contamination in the environment. Only the active ingredient in pesticide is tested, not the formulated product that is a cocktail of many chemicals.
  • Tests are done for relatively short periods of time, compared to the long lives of humans during which chemicals accumulate in our bodies.
  • The chemical threshold deemed “safe” is not the dose at which no adverse effect occurred. It is only the dose at which no adverse effect was observed:  “Subclinical affects—reduced fertility, compromised immune systems, and reduced intelligence, for example—are not observed not because they have not occurred but because they are seldom sought.” (1) In other words, the testing regimen does not test for many potential health problems.
  • The testing regimen is also limited to a few animal species at certain stages of development. For example, bees are the only species of insect on which pesticide tests are required and they are only tested at the adult stage.  Bee keepers will tell you that larvae stages of bee development are far more vulnerable to pesticides than adult bees, yet no tests are required on that stage of development.  Bees are probably less vulnerable to pesticides than caterpillars which eat vegetation, but caterpillars are not tested.  If caterpillars are killed, there are no moths and butterflies.

A proposal for a new testing standard of the impact on the entire ecosystem

Beyond Pesticides has published a review of many scientific studies about the impact of pesticides on the entire ecosystem in which they are applied.  The article reports substantial empirical evidence that pesticides are initiating trophic cascades in the entire ecosystem in which pesticides are used.  The article concludes that such studies of the entire food web are needed to identify and prevent such damage. (2)

What is a trophic cascade?

A change in the population of one member of an ecosystem can trigger a trophic cascade by altering the balance of the entire food web. 

The classic example of a “top-down” trophic cascade is the sequence of events in Yellowstone National Park when wolves were exterminated in the park.  In the absence of the top predator in the ecosystem, the population of elk that were their prey exploded.  The grazing animals ate trees and shrubs that were the food of the beavers.  The beaver population declined, which altered the hydrology of the ecosystem.  Wetlands maintained by beaver dams dried up and the community of plants and animals in the wetlands died off.  Although there were other predators of the grazing animals, such as bears and mountain lions, the packs of wolves subjected the herds of grazing animals to harassment that kept them moving, reducing damage to the vegetation.

Wolves have returned to Yellowstone National Park because of the Endangered Species Act that protected them and the ecosystem has been restored by the natural forces of predator and prey relationships.  The endangered status that protected wolves was recently rescinded in response to the demands of ranchers with domesticated animals.  Although wolves may not be killed inside Yellowstone, they may be killed when they leave the park.  We may eventually see a reversal of the improvements in an ecosystem ruled by wolves.

Update:  Emma Marris has critiqued the theory that the absence of wolves in Yellowstone National Park caused a trophic cascade that damaged the entire ecosystem in Yellowstone National Park and the reintroduction of wolves restored the ecosystem.  Her article, entitled “A good story:  Media bias in trophic cascade research in Yellowstone National Park,” was published in Peter Kareiva’s et al. new book, Effective Conservation Science, Data not Dogma.

Marris details the lack of data supporting the existence of a trophic cascade or its reversal when wolves were reintroduced.  She calls those claims speculative, an unproven hypothesis.  More importantly, Marris believes that proof of that hypothesis is unattainable:  “…even ecosystems as well studied as Yellowstone remain beyond our ken…lifetimes will be required to understand them and even then they may always remain, by virtue of changing faster than we are able to follow, essentially unknowable.”

More humility is needed to guide conservation.  If we are to avoid damaging the environment further, we need to keep in mind how little we know.  Nature may be far wiser in managing itself than humans presume to be. 

There are also examples of “bottom-up” trophic cascades when increases or decreases in the abundance of microscopic plants and animals disrupt the entire food web, ultimately impacting the top of the food chain.

Insects are also near the bottom of the food chain.  They are essential food for birds, particularly to young nestlings.  Scientists began noticing that insect populations were disappearing some time ago, but their anecdotal observations were not empirically tested until 2016 when an entomological society in Germany published a study about the decline:  “The German study found that, measured simply by weight, the overall abundance of flying insects in German nature reserves had decreased by 75 percent over just 27 years.” (3)  Although there are undoubtedly many reasons for this rapid disappearance of insects, including pesticides, there is almost no research being done to determine the causes:  “Rob Dunn, an entomologist at North Carolina State University…recently searched for studies showing the effect of pesticide spraying on the quantity of insects living in nearby forests.  He was surprised to find that no such studies existed.  ‘We ignored really basic questions,’ he said.  ‘It feels like we’ve dropped the ball in some giant collective way.’” (3)  Professor Dunn should not feel badly.  Almost no research is being done on the effects of pesticides on anyone, any animal or anything in the environment  Turning a blind eye to the possibility of such harm done by pesticides is one of the ways in which the industry is shielded from regulation.

Trophic cascades caused by pesticides

The review article published by Beyond Pesticides reports that many empirical studies have discovered trophic cascades initiated by pesticide applications.  Here is one example from agriculture:

“Mesleard et al. (2005) found that the insecticide fipronil, used to control midge pests in conventional rice fields, causes a trophic cascade that reduces the nutritional value of the area for waterfowl. Comparing a chemical intensive rice field to one managed organically, the trophic cascade ultimately neutralized the efficacy of synthetic pesticide use in the first place.

“Direct toxicity from fipronil reduced the number of invertebrate predators in chemical-intensive rice fields. This led to a trophic cascade that allowed herbivorous animals to flourish. On the surface, organic and chemically-managed rice fields both contained the same amount of invertebrate biomass. However, in chemical-intensive fields, this biomass was primarily in the form of gastropods (snails and slugs). When researchers surveyed the fields in late summer, only 12% of the invertebrate community were predators, while in organic fields that proportion was 70%. Slugs and snails are not a major food source for the most common waterfowl in the region studied, the heron, making organic plots a more valuable source of sustenance.” (2)

The review article also provides examples of trophic cascades initiated by pesticides in aquatic environments and in “invasive species” control projects.  Both herbicides and insecticides have initiated trophic cascades.  The effect on the food web of one pesticide is sometimes different from another.  The timing of a pesticide application sometimes has different impacts on the food web.  The effects of pesticides vary widely and are very complex.

A local example of a trophic cascade

There are many aquatic weeds in the Delta where the Sacramento and San Joaquin rivers slowly meander into the San Francisco Bay.  The weeds come from warmer climates and they are thriving here because of climate change.  Lower water levels are also a factor because shallower water is warmer.  The water level is lower because of drought and the diversion of water from the rivers and the Delta to irrigate agricultural crops.  Annual spring floods that cleansed the Delta system in the distant past have been stopped by upstream dams that keep water levels constant.

Instead of addressing the underlying reasons why the aquatic weeds have become a problem, the powers that be (State Parks Division of Boating and Waterways and approved by US Fish & Wildlife Service) have been spraying the aquatic weeds with pesticide and dumping pesticide pellets into the water.  These pesticide applications have been steadily increasing:  “Charts provided by the state show a 50 percent hike in the amount of pellets used from 2014 to 2017 and a 66 percent increase in the amount of spray that was administered during the same time period.” 

Fortunately, there are thousands of fishermen in the Delta who have noticed massive die-offs of fish, turtles, goats, ducks, muskrats, and otters since the spring. They have reported these deaths to California State Parks, who deny knowledge of such die-offs.

The fishermen have formed an organization, Norcal Delta Anglers Coalition.  They have organized to document this trophic cascade that was probably initiated by unnecessary pesticide applications.  We wish them luck.  We hope they have more success than we have had convincing public land managers that they are damaging the environment and its inhabitants with pesticides.

Testing and evaluation of pesticides must be improved

This important review article (1) concludes that pesticides can upset and imbalance ecosystem health and stability.  Studies find “increased risk of disease transmission, dangers to declining species, algae blooms, the loss of ecosystem services like nutrient cycling, and importantly, ineffective pest management.”  Therefore, there is a “critical need for EPA to consistently assess ecosystem level trophic effects as part of the pesticide registration process.” In the absence of a truly precautionary system where independent science is adequately considered by regulators, pesticides are likely to cause trophic cascades or other ecosystem disruption.

Such ecosystem evaluations of pesticides are not going to happen in the foreseeable future.  The 180-degree turn in American politics that would be required to improve pesticide regulation is unlikely.  Although most of the meager federal regulation we had in place prior to 2017 has been dismantled, regulation in the prior administration was also inadequate.

Courtesy Beyond Pesticides

Therefore, our fallback position should be DON’T USE ANY MORE PESTICIDE THAN ABSOLUTELY NECESSARY.  Buy organic food to protect your family and to put industrial agriculture using pesticides out of business.  Fight for rigorous pesticide regulation locally, in your city, your county and your state.

The end of another nativist myth

Native plant advocates promote the use of pesticides to eradicate non-native plants.  The myth they use to justify their use of pesticides is that damage is confined to the target plant or animal.  Clearly that is not true. Pesticides can be aimed at a specific plant, but non-target plants are often killed unintentionally because pesticides are mobile in the soil, they drift in the air and they are carried by the roots of the target plant to the intertwined roots of non-target plants.

Furthermore, killing one plant or animal in an ecosystem ultimately effects the entire community of plants and animals.  The collateral damage to the entire ecosystem caused by pesticides can be devastating to the entire food web.  Clearly the word “restoration” is a misnomer when used to describe eradication projects using pesticides.

Given the inevitable damage to entire ecosystems, the claim that native plant “restorations” benefit wildlife is clearly unlikely, if not patently false. 

  1. Joe Thornton, Pandora’s Poison, MIT Press, 2000
  2. Drew Toher, “Pesticide Use Harming Key Species Ripples through the Ecosystem,” Pesticides and You, Summer 2018.
  3. Brooks Jarvis, “The Insect Apocalypse Is Here,” New York Times, November 27, 2018