A Cornerstone of Invasion Biology Crumbles

Over 20 years ago a study was published about the economic costs of introduced species. The study by David Pimentel et.al. (1) claimed that the economic costs of introduced species in the United States are $137 billion per year.   Despite many critiques of that study by academic scientists, the study remains a cornerstone of invasion biology and the “restoration” industry it spawned. 

The study has been cited by other academic scientists over 4,500 times and an update of the study published in 2005 has been cited over 5,800 times.  In addition to being influential with academic scientists, most media articles about “invasive species” begin with reference to that study and comments from native plant advocates on Conservation Sense and Nonsense often begin by quoting that study.  In other words, the bloated estimate of the economic costs of introduced species in the US is a powerful tool that continues to fuel attempts to eradicate non-native plants and animals in the US.  Therefore, a new study by Demetrio Boltovskoy et. al. (2) that critiques this estimate is of interest to us and we report that study to you today. 

The abstract of the new study (2) outlines the critique of Pimentel’s study by an international (Argentina, Canada, Switzerland, and US) team of scientists:

“The economic costs of non-indigenous species (NIS) are a key factor for the allocation of efforts and resources to eradicate or control baneful invasions. Their assessments are challenging, but most suffer from major flaws. Among the most important are the following:

  • the inclusion of actual damage costs together with various ancillary expenditures which may or may not be indicative of the real economic damage due to NIS;
  • the inclusion of the costs of unnecessary or counterproductive control initiatives;
  • the inclusion of controversial NIS-related costs whose economic impacts are questionable;
  • the assessment of the negative impacts only, ignoring the positive ones that most NIS have on the economy, either directly or through their ecosystem services. Such estimates necessarily arrive at negative and often highly inflated values, do not reflect the net damage and economic losses due to NIS, and can significantly misguide management and resource allocation decisions.”

The Pimental study misrepresents the economic impact of introduced plant and animal species in the US.  The most significant flaw in the evaluation of costs is that it does not take into consideration the benefits of introduced species.  Pimentel’s formula for evaluating economic impacts of introduced species is simplistic:

Losses & Damages + Control Costs = Total Costs

Source:  David Pimentel, et.al., “Environmental and Economic Costs of Nonindigenous Species in the United States” (1)

We need look no further than Pimentel’s study to see how the absence of economic benefits of introduced species in that equation distorts the evaluation of the economic impact of introduced species.  Pimentel has included the pests of agricultural crops and livestock in his calculation of total economic costs of $137 billion per year.  He calculates the cost of agricultural weeds, insect pests and pathogens as well as livestock diseases as $77.3 billion per year, which is 57% of his estimate of total costs of introduced species. 

In the same study, Pimentel says that 98% of the “US food system” are introduced species (corn, wheat, rice, cattle, and poultry) and he reported that the value of those products was $800 billion per year at the time of his study in 2000.  In other words, if the benefits of agricultural products had been included in Pimentel’s formula, the net benefit to the American economy of introduced species would be $663.4 billion per year ($800 billion of benefits – $136.6 billion of costs = $663.4 net benefit). (3) Similar calculations for most items on Pimentel’s hit list of introduced species would be required to accurately assess the economic costs of introduced species:

Purple loosestrife. GNU Free
  • The Boltovskoy study considers purple loosestrife an “innocuous species.” Studies have shown that purple loosestrife thrives where nutrient pollution feeds it and its presence reduces nutrient pollution, which is a benefit to the ecosystem in which it thrives.  Poisoning loosestrife to control it increases pollutants in the ecosystem.  Controlling the sources of nutrient pollution, such as leaky septic tanks and agricultural runoff, is the only long-term method to control purple loosestrife.
  • Millions of starlings are killed in the US every year because they eat crops, but they also eat insect predators of crops.  When the economic benefits of insect control by starlings are subtracted from the costs of crop predation, European countries choose not to kill starlings.
  • Zebra and Quagga mussels are on Pimentel’s list of troublemakers because they clog the water intake pipes of industrial, water, and power plants.  But there are substantial economic benefits of these mussels“these invasive bivalves significantly clarify the water of lentic waterbodies, which can mitigate phytoplankton blooms, including toxic Cyanobacteria…lessening the costs of [purifying drinking] water, and enhancing recreational activities…” (2) They are also a major source of food for waterfowl and have contributed to significant increases in waterfowl populations.  There are mechanical methods of preventing mussels from clogging water intake pipes.
  • Cats are often the target of eradication efforts, and they also appear on Pimentel’s list.  A fair assessment of the economic costs of cats should include their benefit as predators of rats and rabbits.  Cats are a non-toxic method of rodent control.  In their absence, rodenticides are used to kill rodents and rodenticides are known killers of birds.  Do rodenticides kill as many birds as cats?  Maybe. 
  • Many introduced plants are providing valuable food and habitat for animals, including native animals.  Eucalyptus that provide nectar during winter months, when little else is blooming, is essential to hummingbirds, bees, and other animals.  Eucalyptus are the also the winter homes of migrating monarch butterflies in California.  Yet, they are being destroyed by many public land managers because they are introduced.  Likewise, many berry-producing plants that are important food sources for birds and other animals are being eradicated by native plant advocates.
Monarchs roosting in eucalyptus, Pismo Beach, November 2021

Although the costs of control methods are included in Pimentel’s calculation of the economic costs of introduced species, the collateral damage of control methods are not.  Here are a few examples of the collateral costs associated with methods used to control introduced species.

Lanphere Dunes and Mad River Slough

In summary, a more accurate cost/benefit analysis of introduced species would look something like this:

(Losses & Damages + Control Costs) – Benefits – Damage of Control Methods = Total Cost or Benefit

In the absence of such an accurate assessment, scarce public resources will continue to be wasted on eradication projects that do more harm than good.  “Admittedly, [such an accurate assessment] requires much more knowledge of the effectives of nonindigenous species, yet it does not justify using [Pimentel’s] numbers for weighting the risks and harms involved, let alone using them for engaging in potentially feckless and wasteful eradication and control initiatives.” (2)


  1. David Pimentel, et.al., “Environmental and Economic Costs of Nonindigenous Species in the United States,” BioScience, January 2000
  2. Demetrio Boltovskoy, et.al., “Misleading estimates of economic impacts of biological invasions:  Including the costs but not the benefits,” Ambio, 2022
  3. It seems likely that Pimentel’s estimate of the value of agricultural products is the net value after costs of controlling agricultural pests are subtracted from gross value.  In other words, a more accurate calculation of the economic benefit of agricultural products in Pimentel’s formula is probably $800 billion + $77.3 billion (pest control costs). 

Pesticide use in public parks in the San Francisco Bay Area

San Francisco Forest Alliance (SFFA) is a 501(c)4 not-for-profit organization with a mission of inclusive environmentalism. SFFA fights to protect our environment through outreach and providing information. SFFA opposes the unnecessary destruction of trees, opposes the use of toxic herbicides in parks and public lands, and supports public access to our parks and conservation of our tree canopy.

With permission, Conservation Sense and Nonsense is republishing SFFAs annual report on pesticide use by San Francisco’s Recreation and Park Department.  The report separates pesticide use in so-called “natural areas” from other park areas and finds that most pesticides are used in “natural areas.”  Conservation Sense and Nonsense is grateful to SFFA for compiling and reporting this important information. 

Conservation Sense and Nonsense follows pesticide use by the East Bay Regional Park District (EBRPD), where the pattern of pesticide use is similar to San Francisco’s Recreation and Park Department.  EBRPD has restricted spraying of glyphosate pesticides in developed areas of the park while continuing to use pesticides in naturalized areas to eradicate non-native plants.  In other words, most pesticide use in the public parks of the San Francisco Bay Area is devoted to eradicating non-native plants.

Conservation Sense and Nonsense


As we usually do, we compiled the pesticide usage data for San Francisco Recreation and Parks Department for 2021.  (We exclude Harding Park – but not the other golf courses – from this analysis because it’s externally-managed under a PGA contract to be kept tournament-ready at all times.) We’re pleased to note that SFRPD has reduced its pesticide usage in comparison to 2020 and 2019. 

NATIVE PLANT AREAS USE MORE OF THESE TOXIC HERBICIDES

But this is not true of the Natural Resources Division (this includes PUC areas managed in the same way – i.e. use of toxic herbicides against plants they dislike). Their usage has risen and is the highest it’s ever been from 2016.

The Natural Resources Department (NRD, formerly the Natural Areas Program or NAP) is the entity that is trying to bring “native” plants to more than a thousand acres of our parks, cuts down trees and restricts access to people and their pets.  NRD, which accounts for perhaps a fourth of the land area, used over 70% of the pesticides measured as active ingredients in fluid ounces.

NRD – and PUC lands that they are managing the same way – continued to increase their use of triclopyr since the new pesticide Vastlan has been designated Tier II (More Hazardous) instead of Garlon, which was Tier I (Most Hazardous). In both herbicides, the active ingredient is triclopyr. They also increased their usage of imazapyr, and continued to use Roundup, though in smaller quantities than before.

Here are the two earlier graphs lined up to show the comparison. The Native Plant areas used more herbicides in 2021 than they had ever used in the last six years – or that the other SFRPD departments together used in the same time. Their failure to reduce usage in 2021 is in stark contrast to the more than 50% drop in the other SFRPD.


SFRPD Other (i.e. other than the Native plant areas) uses mainly Polaris (imazapyr) and Clearcast ( ammonium salt of imazamox). The native plant areas, NRD / SFPUC, use large amounts of triclopyr, (Garlon and Vastlan), as well as some glyphosate (Roundup).

A FAILING STRATEGY

The NRD’s continually growing usage of the herbicides is a sign that this strategy is failing. They have been using hazardous chemicals on some 50 target species of plants year after year. Theoretically, the point of using toxic herbicides on unwanted species is to allow the desired species to replace them.  Instead, the growing usage of these chemicals shows that if anything, the situation is only made worse.

This stands to reason; “invasive” plants are successful because they are better adapted to current conditions. If they are destroyed with herbicides, the replacement is likely to be the next best adapted (thus, invasive) species. Given 50 target species, the bench is deep. This leads to a vicious cycle of hazardous herbicide use, clearly visible in the graph above.

PESTICIDES COME TO SHARP PARK 

For many years since we started compiling these data, Sharp Park has been off-limits for pesticides. We’ve seen very minimal usage – maybe 3 or 4 times over all the years. It’s home to the red-legged frog, and the San Francisco garter snake.

In 2021, that changed. In the space of one year, pesticides were applied 9 times. We did anticipate this would happen as NRD extended its grip on this park.

TIER HAZARD RATINGS

San Francisco’s Department of the Environment (SFEnvironment) assigns Tier hazard ratings to the various pesticides it uses. Tier III is Least Hazardous, Tier II is More Hazardous, and Tier I is Most Hazardous.  Over the years we have been following this usage, we have seen various chemicals being moved from one Tier to another. Milestone was moved from Tier I to Tier II; Glyphosate (Roundup, Aquamaster)  from Tier II to Tier I; and triclopyr (Garlon, Garlon 4 Ultra, Turflon, Vastlan) from Tier I to Tier II (for Vastlan and Turflon). Avenger was moved from Tier II to Tier III, which we think makes sense and makes analysis easier. We analyze the usage of Tier I and Tier II herbicides.

REDUCE OR ELIMINATE HERBICIDE USE

SF Forest Alliance has been trying to encourage SFRPD to reduce or eliminate Tier I and Tier II herbicide use. Some years ago, it appeared that pesticide usage was declining, especially after the Roundup revelations. When we wrote our Pesticides report for 2016, the other areas of SFRPD had slashed their herbicide use; the NRD accounted for 74% of pesticide usage. The 2021 data have renewed our hope that SFRPD’s other departments will adopt a cautious approach to the use of toxic herbicides. Unfortunately, this does not appear true of the nativist departments, NRD / PUC.


Every year, the San Francisco Forest Alliance also makes public comment at the annual review of San Francisco’s Integrated Pest Management program.  Conservation Sense and Nonsense is grateful for SFFA’s vigilance of pesticide use in San Francisco’s public parks.  Below is an excerpt from SFFA’s public comment to the Commission on the Environment regarding San Francisco’s IPM program.

Conservation Sense and Nonsense


Once again we are sending our comments emphasizing the self-evident truth that high toxicity herbicides are dangerous, unnecessary, and should never be used…

Below are the points we have repeated year after year for many years:

  • Herbicidal chemicals are more toxic, more persistent, more mobile and more dangerous than their manufacturers disclose;
  • The aesthetic or ideological “danger” from “weeds” is not a risk to health and welfare;
  • Scientific studies associate exposure to herbicides with cancer, developmental and learning disabilities, nerve and immune system damage, liver or kidney damage, reproductive impairment, birth defects, and disruption of the endocrine system;
  • There is no safe dose of exposure to those chemicals because they persist in soil, water, and animal tissue, so even low levels of exposure could still accumulate and harm humans, animals, and the environment;
  • Especially vulnerable individuals include infants, children, pregnant women, the elderly, people with compromised immune systems and chemical sensitivities;
  • Toxic runoff from herbicides pollute streams and groundwater, and therefore the drinking water sources;
  • Herbicides are harmful to pets and wildlife – including threatened and endangered species, plants, and natural ecosystems;
  • Herbicides are harmful to soil microbiology and contaminate soil into the future, reducing biodiversity in sensitive areas…

San Francisco Forest Alliance, July 11, 2022

Starlings, vagrants, and dead birds

I was introduced to the nativist mindset about birds over 30 years ago by an ominous encounter with a birder in Florida. The sound of gunfire drew our attention to a man with a shot gun on the lawn of our motel.  Starlings were falling around him, where he quickly finished them off with a vigorous stomp of his booted foot.  We were unfamiliar with the hatred of non-native species at that time and asked him why he was killing the birds.  He seemed stunned to be questioned.  He explained, as though speaking to retarded children, that the starlings were “trash birds” that must be killed.  Following a basic rule of survival, we walked away from a person wielding a gun.

Starling in breeding plumage. Creative Commons – Share Alike

I was reminded of that incident by a recent article in the magazine of the Cornell Ornithology Laboratory.  The author of the article studied starlings for her Ph.D. dissertation.  She was well aware of their reputation as competitors of native birds and consumers of agricultural crops, but belatedly she was having second thoughts about their reputation as invaders:  “Our national conversations about racial equity and political dissent in the last year reminded me that I must change my behavior in response to crises. It has also encouraged me to consider my impact on others, human and starling alike.”  She wondered if calling starlings “aliens” might contribute to the negative opinion of human immigrants:  “But I can’t help thinking of the parallels with countless stories about human “aliens.” Whether we intend this comparison or not, labeling immigrants “invaders” and “aliens” iso­lates those who cross a border in search of a safer, stabler life.”

Comments on the article dispel doubts that such a connection between humans and birds perceived as “alien” exists in the minds of at least some nativists. This is the concluding response to my attempt to discuss the issue with a nativist:  “I am glad I will not live to see your crap filled America of endless third world suburbs, starlings, and house sparrows.  I wish I could live long enough to see it gasp its last breath.”  Strangely, this person seems to be angry about something that he fears will happen in the future, but isn’t visible to him now.

The recent fatal shooting of 10 African-American citizens by an 18-year-old self-avowed white supremacist was also an opportunity to witness the fear, hatred, and violence generated by the use of the word “invasion” to describe immigration, as reported by National Public Radio’s News Hour shortly after the shooting:  “The alleged Buffalo gunman isn’t the first mass shooter to talk about an “invasion” of non-whites. Last week’s mass shooting in Buffalo has turned attention once again to something known as the replacement theory. It’s a baseless and racist conspiracy theory that powerful elites are trying to replace white Americans with nonwhites and that these elites are allowing a so-called invasion of nonwhite immigrants. That word, invasion, has been used a lot lately by some Republicans and immigration hard-liners”   

This racist conspiracy theory bears a remarkable resemblance to the theory of invasion biology, which claims that the mere existence of non-native plants and animals is a threat to native species.  Although there is little empirical evidence of that threat, the myth persists and is used to justify the destructive attempts to eradicate harmless plants and animals.   

The consequences of fear, anger, and dread

The misnamed USDA Wildlife Services killed over 1.7 million animals in 2021, including 1,028,648 starlings and “dispersed” 10,631,600 starlings.  Only 400,000 of the animals they killed were native; 1.3 million were considered “invasive.”  The mission of USDA Wildlife Services is “to provide Federal leadership and expertise to resolve wildlife conflicts to allow people and wildlife to coexist.”  Since 1886, Wildlife Services has killed millions of animals every year that are considered pests by humans. 

Is all that killing effective?  Does it actually reduce populations of the species perceived as a threat?  What does it accomplish?

Farmers have been at war with birds for as long as humans have engaged in agriculture, some 10,000 years.  Crows, grackles, blackbirds, and starlings are often targets of efforts to eliminate them in agricultural areas.  Between 1939 and 1945 about 3.8 million crows in Oklahoma were killed by dynamiting their roosts.  A study of that effort found no evidence that either the population of crows or crop production was affected by that campaign because nature adjusts:  “Destroy a chunk of a population, now there’s more food for the ones who remain.  Through a variety of physiological responses—shorter gestation periods, larger broods, delayed implantation—a well-fed individual produces more offspring than one that’s struggling or just getting by.” (1)  This balancing act is known to be true of many other animal species, such as coyotes and rodents.

The Four Pests campaign was one of the first actions taken in the Great Leap Forward in China from 1958 to 1962. The four pests to be eliminated were rats, flies, mosquitoes, and sparrows. The campaign depleted the sparrow population nearly to extinction. The sparrows had eaten insects that killed the crops. In the absence of sparrows a plague of locusts contributed to the Great Chinese Famine, killing tens of millions of Chinese between 1958 and 1962.  Ironically, the Chinese ended up importing 250,000 sparrows from the Soviet Union to replenish the population. 

As is often the case with attempts to kill animals, the decision is usually made without understanding the role the animal is playing in the ecosystem. There are usually positive as well as negative impacts of every member of the food web.  When we focus only on the negative impact, there are often unintended negative consequences of eliminating a member of an ecological community.

Starlings are considered an agricultural pest in the US, but they are not routinely killed in England or Europe where they are native, although they probably eat just as much agricultural crops there.  The New York Times recently published an article about starling murmurations in Europe.  The videos and photographs of these huge flocks of starlings moving in coordinated patterns are beautiful and remarkable.  They draw crowds of people who are transfixed by the spectacle. 

A study of the impact of starlings in Europe explains why starlings are usually not killed in Europe:  “Starlings that cause damage on migration or in winter may have bred in countries, some of them outside the EEC, where the birds cause no damage and are held in esteem on account of their valued role as insect predators, their educational and their aesthetic values. Claims from countries where Starlings winter that breeding populations should, by some means, be limited are unlikely to be received sympathetically by those to the northeast who eagerly await the Starlings’ return in spring… On grounds of effectiveness, feasibility, cost, humaneness and environmental safety a population limitation strategy is unlikely to be an appropriate solution…The potential for Starlings to reestablish large flocks at good feeding sites after heavy mortality has been inflicted locally indicates that even local population reduction is only temporarily effective in reducing damage.

The popular urban legend about starlings is that they were brought to the US in the 19th century by a dedicated fan of Shakespeare who wanted to introduce all the birds mentioned by Shakespeare to America.  Over one hundred years later, scientists have used molecular analysis to disprove that myth.  In fact, starlings were brought to America earlier by more than one person to more than one location, including to New York by a Shakespeare fan.  This is a reminder that there is always more to know and that we must remain open minded to learn new information as science moves inexorably forward. 

Words matter:  Vagrants or Scouts?

Birders get excited about seeing birds where they don’t usually see them.  When they do, they usually call them “vagrants,” a word that is a synonym for tramps, drifters, beggars, hobos, even homeless people.  It’s not a surprising word choice in a crowd that is heavily biased in favor of natives. 

An article in New York Times suggests that the word “vagrant” is no longer an accurate description of the birds being seen where they haven’t been seen in the past.  The explanation for their surprise visit is often an indication that they are adapting to changes in the environment, including climate change and associated changes in vegetation and insect populations.  They are in unfamiliar territory in search of what they need to survive.  Perhaps their usual nesting site is now a parking lot.  Or perhaps the vegetation they need did not survive a severe drought. Or pesticides have killed the insects they need to feed their chicks during nesting season.  They are scouts, not vagrants.  They aren’t lost. They are seeking a safe haven.

As the climate changes and human activities continue to encroach on the natural world, plants and animals must move, adapt, or die.  The least we can do is stay out of their way.  The fact that birds are the most mobile animal class is something to celebrate, not lament.  Their mobility makes them more likely to survive changes in the environment.   A recent study reported that 13% of bird species are threatened with extinction, compared to 25% of mammal species, 21% of reptiles and 40% of amphibians. 


  1. Mary Roach, Fuzz, W.W. Norton & Company, 2021

Weeds are making a comeback!

While the native plant movement remains strong in California and locally in the San Francisco Bay Area, some communities are waking up to the fact that weeds make valuable contributions to our gardens and the wildlife that lives in them.  The British have always been ahead of us in welcoming plants from all over the world in their gardens.  The British have been enthusiastic importers of plants from all over the world for hundreds of years.  They had one of the biggest empires in the world, spanning the globe from India to Africa, Australia, New Zealand, and America, which put them in a unique position to sample the botanical riches of the world.

The English garden, where plants from all over the world are welcome

In a recent article in The Guardian, an English gardener describes her journey from fighting the weeds in her garden to her new relationship with them:  “I remember writing, many years ago, about my fight to get rid of these dandelions. Clearly, I didn’t win. Now, when I am greeted by them, I am glad I lost the battle. These days, I truly consider them friends…they are welcome in my garden, because I know they do more good than harm.”

The English gardener reminds us that the war on weeds began only recently.  Going deep into agricultural history, weeds were natural forage that were a part of our diet. Weeds fed our domesticated animals, stuffed our mattresses and made twine and rope. Many have medicinal properties, but most have marketable substitutes now. They were tolerated on the edges of agricultural fields and in our gardens.

The typical American lawn, maintained with pesticides and fertilizer is not habitat for pollinators or other insects. Source: Pristine Lawn Care Plus

The war on weeds began after World War II, when chemicals were introduced to agriculture.  Pesticides were considered benign for decades.  We have learned only recently of the dangers of some pesticides. The promotion of pesticides changed the aesthetics of gardening, initiating an era in which weeds were banished from our agricultural fields and our gardens.  

Note the drone hovering over the children in a strawberry field. Drones are the latest development in chemical warfare. They are used to spot non-native plants in open space as well as to aerial spray pesticides. They are cheaper than other methods of application and for that reason are likely to increase the use of pesticides.

Do not underestimate the power of propaganda to promote the use of pesticides:  “A publishing company linked to the most powerful agricultural lobby group in the U.S. is releasing children’s books extolling the benefits of pesticides and nitrogen fertilizers.”  Industrial agriculture begins the indoctrination of the public at childhood. 

Bumblebee in clover. Source: buzzaboutbees.net

Weeds made their way back into our gardens partly by evolving resistance to the pesticides we used for decades to kill them.  There is growing awareness of the impact of pesticides on insects and wildlife.  As populations of pollinators decline, we are more willing to indulge their preference for weeds such as dandelions and clover.  Weeds are often the first to arrive in the spring garden, as native bees are emerging from their winter hibernation in ground nests.  Weeds prolong the blooming season in our gardens, providing nectar and pollen before cultivated plants are blooming. 

“No Mow May” comes to America!

“No Mow May” originated in Britain out of concern for declining populations of bees.  Communities make a commitment to stop mowing their lawns in May to let the weeds dominate their lawns.  Weeds such as dandelions and clover give the bees an early boost in the spring that studies show increases bee populations.  Lawns maintained with pesticides and fertilizers provide poor habitat for bees. 

Two professors in the Midwest of the US introduced “No Mow May” to their community in Wisconsin in 2020.  They signed up 435 residences to participate in “No Mow May” and studied the impact:  “They found that No Mow May lawns had five times the number of bees and three times the bee species than did mown parks. Armed with this information, they asked other communities to participate.”  According to the New York Times, “By 2021, a dozen communities across Wisconsin had adopted No Mow May. It also spread to communities in Iowa, Minnesota, Illinois and Montana.”

Farmers climb on board

Hedgerows are the backbone of the English countryside.  They are a complex bramble of woody and herbaceous plants that traditionally served as fences, separating roads from agricultural fields and confining domesticated animals.  They nearly disappeared when industrial agriculture dictated that fields be cultivated from edge to edge. They are making a comeback in the English countryside as farmers realize that their loss contributed to the loss of wildlife.  The concept of hedgerows as vital habitat is slowly making its way to America.

US Department of Agriculture reports improvements in agricultural practices in the past 10 years:  more no-till farming that reduces fossil fuel use and carbon loss from the soil; more efficient irrigation methods; broader field borders for pollinators and wildlife; more crop rotations that reduce disease and insect pests; reduction of nitrogen and phosphorous run-off; reduction in diesel fuel use, etc.  These are all well-known methods of reducing environmental damage from industrial agriculture, but there is now evidence that farmers are actually adopting them. 

Nativists are late to the game

We see progress being made to reduce pesticide use and provide more diverse habitat for wildlife, but nativists drag their feet.  They continue to use pesticide to eradicate non-native plants and they deny the value of non-native plants to insects and wildlife, despite overwhelming evidence to the contrary. 

In a recent comment posted on Conservation Sense and Nonsense, a nativist explains the justification for using herbicides to eradicate non-native plants:  “No one likes herbicides, but in the absence of a labor force willing to abandon its modern conveniences to do very hard work, they are important tools in restoration ecology, and methods are improving as a result of careful science to determine how the least amount of them could be used to gain the greatest amount of benefits to the maximum amount of species. Throwing those tools away is about like tossing chemotherapy or vaccinations because of that “all-or-nothing” black or white point of view that native plant supporters are being (unjustly) accused of.”

For nativists, the harm done by non-native plants is greater than the harm done by pesticides.  This equation does not take into consideration the benefits of many non-native plants to wildlife and it underestimates the damage caused by pesticides to the environment and its inhabitants.   

Argentine Ants: An “invasion” that wasn’t

Bay Nature article about Argentine ants

Bay Nature published an article about Argentine ants with an alarming title and disturbing accusations, such as:

  • “…from its home range around the Paraná River region in Northern Argentina, this ant has spread to six continents and numerous islands, including Hawaii. In numbers, it is probably the most successful invasive nonhuman creature in California.”  
  • “Argentine ants have been documented aggressively going after other, bigger species of ants.”
  • “…most native ants cannot resist well and are wiped out by the Argentine ants.”
  • When native ants are displaced, it can disrupt whole ecosystems and reduce the diversity of other arthropods in the region.”

After establishing the Argentine ant’s credentials as a dangerous “invasive species,” the article abruptly changes directions by contradicting itself.  According to a 30-year monitoring survey of Argentine ant populations at the 1,200 acre Jasper Ridge Biological Reserve, “…the ants had, counter to expectations, actually retreated from some areas they had occupied in previous years at Jasper Ridge…”  Early survey data showed the Argentine ants spreading rapidly in the preserve.  They reached a stable distribution around 2001, and have since declined. 

The monitoring survey at Jasper Ridge speculates that the decline in Argentine ant populations was caused by drought.  However, that theory is not consistent with similar declines in Argentine ant populations elsewhere, where and when there was no drought. 

Jasper Ridge is just one of many places that have reported declining populations of Argentine ants over many years.  In 2011, Scientists in New Zealand reported the disappearance of the Argentine ant from 40% of sites they populated in the past and their populations have shrunk significantly where they are still found.  Native ants have “reinvaded” the areas vacated by the Argentine ant.  The scientists reporting this finding “concluded the species naturally collapses after 10 to 20 years.”

In an unpublished communication in 2011 with an entomologist at UC Davis, I learned that Argentine ant populations in Davis were declining. 

In 2008, a study of ants in San Francisco’s “natural areas” in city parks reported that the existence of non-native Argentine ants does not have a negative impact on populations of native ants. (1) They report that Argentine ants occupy the perimeter of the “natural areas” where native ants generally are not found.  This observation contradicts the usual nativist claims that non-native plant and animal species have negative impacts on native species.

The “invasion” curve

Introduced species are often accused of being invasive and there is a range of explanations, including the bias against non-native species that assumes every non-native species will eventually becoming invasive.  In some cases, a new species spreads aggressively because it is better adapted to disturbed conditions to which it has been introduced.  The initial success of an introduced species is sometimes enabled by the absence of its predators in its new home.  This is called “predator release,” which does not confer permanent protection to a new species that will eventually encounter new predators.  These and likely other factors are probably operating simultaneously. 

Like most so-called “invasions,” introduced plants and animals may briefly expand, but eventually most find their niche in the ecosystem without causing permanent harm to their neighbors.  The assumption that introduced plants and animals threaten native species is usually unsupported by empirical evidence 

Journalistic due diligence

If the author of the Bay Nature article about Argentine ants had searched research literature about Argentine ants, she could have learned that the negative tone of the article and its hyperbolic title were not justified.  In the author’s defense, the demonization of non-native plants and animals is routine in mainstream media.  The bad news about introduced species always precedes their eventual participation in ecosystems and the record is seldom corrected when they do, as in the case of Argentine ants. The reader can compensate for this journalistic bias by reserving judgment about non-native species until more is known about their fate. 


  • Kevin M. Clarke, et. al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst, 11:317-334, 2008

Beyond the War on Invasive Species: Interview with Tao Orion

I am republishing with permission a portion of Kollibri terre Sonnenblume’s interview of Tao Orion.  Kollibri is a writer, photographer, tree hugger, animal lover, and cultural dissident. Kollibri was born and raised in Nebraska, earned a Bachelor of Arts in Writing at the St. Olaf Paracollege, and lived in the Twin Cities and Boston before moving to Portland in 2001. Since 2011, Kollibri has lived predominantly in rural areas in the Western US, working in agriculture and exploring wildtending. Kollibri has published several books, including The Troubles of ‘Invasive’ Plants (with Nicole Patrice Hill), originally a zine and soon to be published as a book.  Kollibri has also recorded interviews available as podcasts, “Voices for Nature & Peace,” which can be found at radiofreesunroot.com.

Conservation Sense and Nonsense


Tao Orion, author of “Beyond the War on Invasive Species”

Tao Orion is the author of “Beyond the War on Invasive Species: A Permaculture Approach to Ecosystem Restoration.” She is a permaculture designer, teacher, homesteader, and mother living in the southern Willamette Valley of Oregon. I interviewed her on May 18, 2020, for my podcast, “Voices for Nature & Peace.” What follows is a partial transcript of that conversation, edited for clarity. [Listen to the entire interview here]

Kollibri terre Sonnenblume, macska moksha press

K: A lot of people have heard the term, “invasive species” and most of them of course are assuming it’s something bad, but when it comes right down to it, it’s actually very difficult to define the term and we could even say that there isn’t one definition of that term.

T: Yes, that’s something that I found really interesting as I was researching my book, because I was really trying to find out if there was a clear, objective description of what an invasive species is, and I found that even the National Invasive Species Council—which in the US is the federal government level board that looks at invasive species issues—spent years on deliberating on the definition and even so, they weren’t able to come up with something that I felt was purely an objective description that could be [applied] in all contexts. It seemed to vary from place to place and time to time.

K: Monsanto was one of the companies involved in setting [that council] up.

T: That’s another disturbing element about how the big frenzy around invasive species and the purported damage that they do came to be so popular; a lot of that was informed and funded by pesticide interests to spur the sale of products, herbicides in particular, to deal with species invasions.

K: I think that most people are probably not aware of the fact that the use of pesticides and herbicides has been rising over the last 20 years, not falling. I think people hear about organic agriculture and they think we must be on the right path. But due in part to the war on invasives and also due to genetically modifying crops to be Round-up Ready so they can survive the use of pesticides—these two things seem to have driven an increase in the use of pesticides over the last 20 years.

T: Yes, it’s definitely alarming. My background is in organic agriculture. I was immersed in that world. Even before writing this book, I was under the impression that herbicides were somewhat less toxic in the realm of pesticide toxicity [as opposed to insecticides or fungicides, for example]. In researching herbicides more for invasive species management and agriculture in general, I learned a lot more about their toxicity and insidious toxicity to insects and mammals and other lifeforms that I don’t think gets talked about enough. People assume they’re more ecologically benign, but really they’re not, and that’s important to bring to the table.

K: One thing you mentioned in your book that I hadn’t thought about much before is that it’s not only the active ingredient in a pesticide, but also the adjuvants—the things that they add to the active ingredient to help it stick to plants or to help make it soluble in water, etc.

T: Yeah, that was a big realization for me too. We talk about these two different terms: “Round Up” is the trade name of the herbicide, of which “glyphosate” is considered the active ingredient. Glyphosate is the ingredient that’s tested for pesticide registration purposes, but that might be only ten percent of a mixture that’s sold in the bottle. The rest of that solution is made up of other ingredients that help the herbicide stay on the plant if it rains or if its windy, or help the herbicide active ingredient penetrate the cells of the plant. A lot of these are trade secrets so they’re not tested and the manufacturers don’t have to say what’s in there. But one compound that has been pulled out and studied by independent researchers is POEA [polyoxyethyleneamine], which has been shown to make glyphosate penetrate human placental cells. So even if you come into contact with glyphosate itself, that wouldn’t necessarily happen, but if you come into contact with Round Up, which contains this adjuvant, POEA, it can actually then allow the glyphosate to enter into the cell. Because that’s what it’s in there to do.

K: The reason we’ve been talking about pesticides because herbicides are such a big part of getting rid of “invasive” species… But your book tries to turn things on its head and to question the concept of whether we should be trying to eradicate them.

T: Yes. I was shocked when I started working in the field of ecological restoration, coming from a background in organic agriculture. I had heard of “invasive species” before but when I got into this context, I was around people who did this professionally, it was just assumed that I was going to use herbicides and I would be totally fine with that, because that’s just what everybody did. The whole context was, “we have to get rid of these plants at all costs, and if we do, everything will be okay.” [Laughs.] That’s the the framework in which we’re approaching ecosystem restoration, and to me, I was amazed because from a more holistic perspective, I could see right off the bat that in every case where invasive species were thriving, there were other things going on in the ecosystem that pesticides weren’t going to address.

It’s the same in conventional agriculture. If you’re having, quote, pest pressure issues, the issue isn’t the pest, the issue is the soil or the plant stress or drought stress. There’s all these different things playing into the manifestation of pest pressure in the ecosystem. So, taking that knowledge a few steps further to ecosystem restoration I think is really necessary. A lot of people involved in these contexts are really highly trained ecologists and it’s still hard for me to square that with the belief that herbicides, pesticides are the only solution. These are often people who are shopping at organic food markets, and only buy organic food, and believe really strongly in that framework for food production, and yet are making decisions about ecosystem restoration outside of agricultural contexts that rely on pesticides and I just think that really needs to be questioned.

I had some very interesting discussions over the years and maybe the needle is starting to shift a little bit, although as you mention, sometimes these discussions flare up online where people are really quite defensive about their position and belief around this.

K: The issue tends to infect any discussion around plants. I’ve been using a couple of plant ID groups on Facebook because I’m in a new area and I’m seeing things coming up and I’m like, “What is this?” Of course if you’re in a native plant group, that’s definitely going to be someplace where [the invasive framework] is strong. You know, a native-plants-equals-good, non-native-plants-equals-bad, black and white paradigm. Which brings us around to looking at the invasive plant not being a problem in and of itself but of being a symptom of something going on.

T: That’s a huge part of the conversation that a lot of folks really aren’t willing to easily engage in, but the design of our livelihood system has really degraded ecosystems to a place where native flora and fauna aren’t thriving. You know, to really sit with that, and acknowledge it, think about how we might approach things differently as a basis for our understanding is challenging. It’s a lot easier to blame the messenger. Also I think one of the things that’s really missing from the discussion of native plants is the fact that native ecosystems were or are managed by indigenous people. They don’t just exist in a vacuum, free from people’s influence and the whole idea of this “pristine” wilderness is very much a western, colonial thought pattern that definitely needs to be disrupted.

K: What you’re referring to in part is that when people are designating a plant as invasive or non-native, there’s a point in time they’re referring to, and that might be different from place to place, but it’s generally accepted in the United States that anything anything that showed up after 1492 is not native. There are people who are willing to describe most non-native plants as “invasive” or throw them in that bin as soon as possible, and then the poisons come out, so this is an important issue.

T: Yes, but we don’t really know the social, ecological, economic context that was going on at that point in time that led to a particular assemblage of plants. There’s no doubt that the floral and faunal assemblies were different, but we should think really hard about why they’ve changed. Draining the wetlands of the Sacramento and San Joaquin valleys in California has major ecological implications. Damming the Colorado River for hydro-power and irrigation capacity has major ecological implications. These bigger scale things that we do—that we support—are going to change the surrounding ecosystem. If we can acknowledge that and observe what’s happening because of those major shifts, I think we’ll be in a better position to understand so called “invasions” from a more holistic perspective.

K: Because the entry of an invasive plant or animal into a landscape is in virtually all cases preceded by a human-caused disturbance of some kind.

T: It’s interesting. When I was writing, [I wondered if I] should I put forward the idea of reclaiming a different name because “invasive species” has kind of this negative connotation, but the more I looked into evolutionary biology and some of the ways—in the deep time perspective—how systems have changed, “invasion” is one of these processes and it’s not unnatural. Taking that longer term perspective is important as well. That’s how plants came to be on land. There were marine beds of algae hanging out in the shallow seas a couple billion years ago and eventually, speciation happened because of changing conditions and the land was “invaded” by those plants. You just see that change over time leading to the type of biodiversity that we have now, punctuated by other kinds of events of course, but it’s not something that’s “outside the realm of nature,” which is how invasive species are situated in a lot of discussions.

The Global War on Non-Native Trees

“In some cases, removal of urban trees because they are non-native may represent an ‘over-shoot’ where the removal of non-natives becomes an end unto itself… the non-native trees being removed are not necessarily highly invasive, and removal is more driven by a desire for native species rather than any real or perceived problems caused by the non-native species.”

An international team of academic scientists studied the many conflicts around the world between those who find value in introduced trees and those who demand their destruction. (1) Team members were from Australia, France, New Zealand, and South Africa.  Professor Marcel Rejmanek at UC Davis was the only American on the team.

Professor Rejmanek is well known to us as the author of the chapter about eucalyptus in Daniel Simberloff’s encyclopedic tome about biological “invasions.”  Rejmanek said, “…eucalypts are markedly less invasive than many other widely cultivated trees and shrubs…they have been orders of magnitude less successful as invaders than pines and several other widely planted trees…Where eucalypts have invaded, they have very seldom spread considerable distances from planting sites, and their regeneration is frequently sporadic.  He noted that eucalyptus is useful to bees and hummingbirds and I add here that it blooms throughout winter months when little else is blooming in California.  He said,  “Conclusions about positive or negative environmental and economic impacts of eucalypts are often anecdotal, highly controversial and context dependent.”    Professor Rejmanek’s assessment was instrumental in my effort to convince the California Invasive Plant Council to remove blue gum eucalyptus from its list of invasive species.  Cal-IPC downgraded its assessment of invasiveness of blue gum eucalyptus from “medium” to “limited” in response to my request. 

Professor Rejmanek is also the author of the most recent report on plant extinctions in California, published in 2017.  At that time there were 13 plant species and 17 sub-species native to California known to be globally extinct and another 30 species and sub-species extirpated in California but still found in other states.  Over half the globally extinct taxa were reported as extinct over 100 years ago.  Although grassland in California had been converted to Mediterranean annual grasses by grazing domesticated animals nearly 100 years before then, most of the plants now designated as “invasive” in California were not widespread over 100 years ago.  Only one extinction mentions “invasive species” as one of the factors in its disappearance.  Rejmanek speculates that livestock grazing is the probable cause.  He said, “Indeed, one needs quite a bit of imagination to predict that any native plant species may be driven to extinction by invasive plants per se.”

This recap of Rejmanek’s expertise about so-called “invasive” trees and plants establishes his credentials as a reliable witness as the co-author of “Conflicting values:  ecosystem services and invasive tree management,” which I will summarize for readers today.

Setting the stage for conflict

As Europeans colonized the new world in the 18th and 19th centuries, they often brought trees from home with them, motivated primarily by an aesthetic preference. When the colonial era came to an end, nationalism during the 19th century encouraged a new appreciation of indigenous flora.  When planting their own gardens and farms, America’s founding fathers had a strong preference for planting native trees.  While fighting the Revolutionary War, George Washington wrote to the caretakers of his farm at Mount Vernon instructing them to plant NO English trees, but rather to transplant trees from the surrounding forests.

Sources of conflict

By mid-20th century, this preference for indigenous trees escalated to the current belief that non-native trees are threatening indigenous ecosystems.  Conflict arises when there is a “failure to account for, assess, and balance trade-offs between the eco-system services or, at times, a failure to agree on the relative value of particular services.” (1) The study identifies the tree species that are the focus of such conflicts around the world and the ecosystem services those species provide:

Conservation Sense and Nonsense has reported on many of these conflicts around the world:

  • The stated purpose of the destruction of forests in Chicago was the “restoration” of grassland that existed prior to the arrival of Europeans.  Conservation Sense and Nonsense described the conflict regarding that destruction in one of my first articles in 2011 because the issues were similar to those in the San Francisco Bay Area. The debate raged in Chicago for over 15 years, but the destruction of the forest was finally accomplished, despite opposition.  Likewise, in San Francisco after 20 years of conflict, the eradication of eucalyptus forests is being achieved.
  • In 2012, we republished an article by Christian Kull about the practical value of acacia trees to Vietnamese farmers and their opposition to the attempt to destroy them.
  •  We republished an article in 2014 about opposition to the destruction of willow trees in Australia that were planted to control erosion.  Willows are one of many examples of a tree that is considered valuable in North America where it is native and hated in Australia where it is not. The authors of the article described the arguments used to justify the project, ‘Sure, it makes a big mess and causes erosion, and nutrient release, and carbon emissions, and local temperature increases, and loss of habitat, but it’s necessary because we’re going to make Australia a place for natives-only again.’
  • Conservation Sense and Nonsense published a guest post by Matt Chew in 2017 about the eradication of tamarisk trees that were introduced for erosion control in southwestern US.  In that case, the survival of an endangered bird is threatened by this misguided attempt to eradicate tamarisk by introducing a non-native insect.
  • Conservation Sense and Nonsense published a guest post in 2015 by a South African who objected to the destruction of jacaranda trees.  In that case, the beauty of these iconic trees was the primary objection to their destruction.
Jacaranda trees in Pretoria, South Africa

Many similar conflicts around the world are described by the study, which categorizes the conflicts as focused in three areas:  urban and near-urban trees; trees that provide direct economic benefits; and invasive trees that are used by native species for habitat or food.  I will focus on conflicts in urban and suburban areas because they are close to home.

Where is conflict greatest?

The study searched for examples of such conflicts around the world and found that most were in developed countries where ecological knowledge has suggested that eradication is necessary and democracy is strong enough to enable dissent.  Such conflicts are well documented in urban areas where many non-native trees have been introduced. Based on my experience with many of these urban conflicts, I can agree with the authors of the study that they are “frequently vitriolic, as seen in letters to editors, public protests, websites, and blogs.” (1)

How NOT to reduce conflict

The authors of this study dismiss suggestions that “educating” those who object to eradication projects can reduce conflict.  Their assessment of why that approach intensifies conflict is consistent with my own reaction to being lectured about the claimed benefits of eradication projects:

“However, the concept of ‘education’ implies that opponents of tree removal are inherently ignorant or unaware and discounts the importance of their views and values.  Sceptics of environmental issues are frequently highly educated and scientifically literate, with conflict driven by fundamental values, not lack of knowledge.  Further, what one party in a conflict views as education can be viewed as propaganda by those with opposing priorities.” (1)

The authors suggest that the planning process for such projects must be a two-way dialogue that recognizes shared values, such as a strong commitment to conservation of the environment.  The authors describe some of my own reservations about eradication projects:

“In some cases, removal of urban trees because they are non-native may represent an ‘over-shoot’ where the removal of non-natives becomes an end unto itself…Objective evaluation of the ecological services affected may not result in the removal of non-native trees being justified.  Indeed, in some cases the non-native trees being removed are not necessarily highly invasive, and removal is more driven by a desire for native species rather than any real or perceived problems caused by the non-native species.” (1)

There is no doubt that the demand to destroy eucalyptus in California is a case in which removal has become an end in itself that is not justified.  These are some of the accusations used to justify the destruction of eucalyptus that have been disproven by academic scientists without getting eucalyptus off nativists’ hit list.

Source: Conference of California Native Plant Society, 2018

Pessimistic conclusion

The study concludes that we should expect plant invasions around the world to increase and that increased wealth and democracy will make conflicts about tree eradications more widespread.  The authors “suggest that conflict should be seen as a normal occurrence in invasive species removal…Avoiding conflict entirely may be impossible…”

I can’t disagree with the authors of this study about the poor prospects of resolving conflict regarding the destruction of non-native trees that are the heart of our urban forest in California.  However, I am grateful to the authors for their understanding of the issues and their respect for introduced trees as well as those who advocate for their preservation. They understand that lectures by those who demand that trees be destroyed despite the functions they perform are condescending and exacerbate conflict rather than resolving it. 

A Postscript

Jake Sigg has been the leader of the crusade to destroy eucalyptus forests in the San Francisco Bay Area for over 30 years.  He and I have debated this issue many times, without resolution.  In his newsletter of January 20th, Jake seems to acknowledge the futility of our debate as well as his motivation to create a native landscape. It seems he has reached the same conclusion as the authors of the international study of the inevitability of conflict about the destruction of non-native trees, although he concedes that he won’t quit trying…and neither will I. 

“For years I’ve been fighting tree huggers, who understandably don’t want to cut healthy trees down.  The blue gums are handsome brutes.  In my eye I see the rich diverse native biological communities that they displaced; those I fight with don’t see that and don’t value that.  So you can see the communication problem at the beginning.  The same consideration plagues many contentious issues in the world.

How do you explain this to them?  Mostly, you can’t; you do what you are able to do.  This is not an age for listening to fellow beings.  I find it hard to do.  David Brooks, a favorite, wrote a fraught opinion piece in today’s 
NYT.  He has just about thrown up his hands, as have I—except that I can’t—and neither can Brooks.”

Eucalyptus canopy on east side of Glen Canyon Park, taken from Turquoise Way December 2012, before tree destruction escalated beyond riparian areas. Glen Cayon Park is one of 33 parks in San Francisco where most eucalyptus trees are being destroyed because they are not native. Courtesy San Francisco Forest Alliance

  1. Ian Dickie, et. al., “Conflicting values:  ecosystem services and invasive tree management,” Biological Invasions, 2014.

When ideas remain unexamined and unchallenged, they intimidate ©

My last article of the year is a guest post by Marlene A. Condon, the author/photographer of The Nature-friendly Garden:  Creating a Backyard Haven for Plants, Wildlife, and People (Stackpole Books; information available HERE.)   You can read her blog In Defense of Nature.

Merry Christmas !

Million Trees

A birds-eye view of the University of Virginia (UHall seen in first photo) in Charlottesville, Virginia, makes clear that there are plenty of native trees to be found in developed areas.

The novelist E. L. Doctorow, in a 1989 conversation with PBS journalist Bill Moyers, said, “When ideas go unexamined and unchallenged for a long enough time, they become mythological and very, very powerful. They create conformity. They intimidate.”

He could have been speaking about the current environmental narrative regarding so-called invasive plants. Anyone who speaks out feels the wrath of the folks pushing their fictional environmental manifesto; I’ve lost jobs because of these people.

Most neo-scientists and -environmentalists, having arrived late to the party, have no clue as to why some alien plants exist in profusion along roadways, in former farm fields, and along trails in forests. The popular notion that native plants would otherwise be filling those areas is easily accepted by people who don’t possess knowledge of soil science, or who lack experience with gardening and/or closely observing the natural progression of plants in unmanaged, disturbed areas.

Knowing the prior history of the land is essential to understanding why particular nonnative plants fill some areas. Road building discomposes soil. Trail development/use and cows/farming-equipment moving over the land compact soil. Only “colonizer plants”—those capable of thriving under the altered and nutrient-poor conditions of these sites—can grow there.

Usually such areas, after many years, support a mix of native and nonnative pioneers, but sometimes alien plants outnumber the natives because they are best suited to the constraints imposed by the physical attributes of the site. Anyone (no Ph.D. required) can verify this statement by taking the time to observe the progression of plants in an area not revegetated by people. Doing so would make clear that alien plants do not “push out” native plants by “invading” and “taking over”, but rather, they fill disrupted areas where few native plants can successfully grow.

Yet, the desire by scientists and environmentalists is so great to get folks to remove supposedly invasive plants from the environment that we now have tall tales being spread. Herewith a sampling of some of the most egregiously untrue declarations regarding alien plants.

Johnny Randall, Director of Conservation Programs at the North Carolina Botanical Garden (University of North Carolina at Chapel Hill) wrote a New Hope [North Carolina] Audubon blog post called “Invasive Plants Are NOT for the Birds.”

  • He writes that, “The scientific literature on invasive plants and bird-dispersal is moderate but growing, and almost all of the research warns that this is a serious and multi-layered phenomenon. First off – birds either do not discriminate between native and invasive plants or often prefer invasives over natives. One reason for this is that a large proportion of invasives are high in carbohydrates, whereas the natives are often higher in protein and lipids/fats. Birds are consequently (pardon the analogy) choosing candy bars over cheeseburgers, which could affect bird nutrition, particularly during fall migration”.

The suggestion that birds are choosing “autumn olive berries [that] are sugary sweet treats, the junk food of the bird diet” is echoed by many people. This quote, from a letter to the editor of The Crozet Gazette by Susan A. Roth, William Hamersky, and Manuel T. Lerdau, Ph.D., is supposedly based upon a study published by the Wilson Journal of Ornithology in March, 2007, entitled “Fruit Quality and Consumption by Songbirds during Autumn Migration”.

Yet this study states that “Most common fruits on Block Island [where the study took place in Rhode Island] contained primarily carbohydrates…and little protein…and fat.” As the research paper’s authors were mainly speaking of native plants, this statement directly contradicts that of Mr. Randall that natives are often higher in proteins and fats than so-called invasives.

Additionally, the research paper’s authors state that “fruit selection by birds on Block Island was not simply related to differences in macronutrient composition between fruits…studies of wild and captive songbirds have shown that some species preferentially select high-fat fruits…or high-sugar fruits…”, which hardly implies that Autumn Olive fruits are a necessarily inferior food choice, as declared by Roth, et al.

A variety of foods exists to serve a variety of purposes. Turning sugar into something “bad” for birds comes as a result, perhaps, of this same application to human nutrition. But sugar is not in and of itself, “bad”. A runner in need of glucose who eats some jelly beans gets a quick burst of energy to continue exercising. There’s absolutely nothing wrong with that.

Sugar is only a problem if it’s eaten in excess, as might be done by children. But birds are not children; if they feel the need for protein and fat, they will search for insects and fruits that offer what they need.

  • Furthermore, Director Randall wrote that “Researchers have also shown that many invasive plants have fruits that persist longer than do native plant fruits into the fall and winter. The invasives are therefore available when our natives are not.”

In a world of disappearing habitat for wildlife because of human development, the fact that fruits on invasive plants are available when native-plant fruits are depleted should be seen as a positive rather than a negative.

Charlottesville, Virginia, residential area, has so many trees that you can’t see the roadways interspersed among them. In other words, insects and birds aren’t disappearing because alien plants have replaced native trees.

“Recent research published by Narango et al., in the October 22, 2018, issue of the Proceedings of the National Academy of Science demonstrates that native plants are best for birds. The research showed that yards landscaped with the usual garden center plants, which are mostly nonnative ornamentals, could not support a stable population of chickadees. Yards where native plants composed at least 70 percent of the plantings were able to do so. This is because native plants host more insects than non-natives and therefore provide the necessary high-protein food that birds need to feed their chicks.” [from a letter to the editor of The Crozet Gazette by Susan A. Roth, William Hamersky, and Manuel T. Lerdau, Ph.D.]

Narango’s study cannot be generalized to all birds, although many people have made the mistake of claiming it can. This study applies only to chickadees and certain other birds that inhabit forest because such species are dependent upon the native plants (trees) that comprise our forestland. In other words, if you want forest birds to reproduce in your yard, your yard must be forest. For a fuller explanation, please read “Chickadee Chicanery” at In Defense of Nature.

“These invasive species not only impact our forests, wetlands and streams, but also our economy, health and safety. They kill the trees that shade our homes and that our kids play hide-and-seek around. They increase the presence of other disease-spreading species like ticks. They diminish visibility along trails where safety is important”. [quote from an article from the Central Ohio Partnership for Regional Invasive Species Management at a Nature Conservancy-sponsored website]

The only “forests” where you will see alien-plant species are those that are either managed improperly (overly thinned and thus allowing too much sunlight to reach the ground under the trees) or those that are actually “woods” in the process of succession (transforming from a field to a forest that has not yet reached maturity). “Invasive” plant species are sun-loving and therefore do not inhabit shady mature forests.

As for killing trees, if “they” refers to vines (a common complaint in the eastern U.S.) one must ask, why was the homeowner unable (or unwilling) to keep a vine from killing a tree in his yard that his “kids play hide-and-seek around”? However, if “they” refers to nonnative animals and/or diseases killing trees, that is a different situation altogether, which is not the point of this article. It’s unfortunate the writer did not make clear what “they” referred to. As far as I can tell, there’s no proof that “invasive” plants, in general—as stated above—increase the presence of organisms such as ticks. A study published in Environmental Entomology

purportedly shows that barberry-infested plots support more mice and thus ticks than plots in wooded areas with no barberry.

However, the “no barberry” plots were severely browsed by deer and thus “little understory vegetation was present.” In other words, these scientists compared two completely different habitats, which explains the greater number of ticks in the shrubby (Japanese Barberry) area that provided “questing habitat [for] blacklegged ticks [whereas] little other suitable vegetation exist[ed] in [the] severely browsed forests.”

“Questing habitat” refers to plants upon which ticks can wait at the appropriate height to grab onto an animal that comes by. Obviously, ticks are not going to be found in an area with little understory vegetation as they have nowhere to sit and wait for their quarry.

And we’re to believe “invasive” plants diminish visibility along trails, and native plants don’t? It sounds more like the folks who are supposed to be maintaining the trails have been derelict in their duties!

It’s clear that scientists and journalists are doing everything they can to assure that government and the general public view so-called invasive plants in a negative light. Yet, to my knowledge, no study condemning “invasive plants” exists that has the least bit of merit.

Marlene A. Condon


Addendum by Million Trees

Polarized views of nature mirror our politics

This article about the polarized views of conservation and how similar they are to our polarized politics was published by Conservation Sense and Nonsense 7 years ago.  It is truer now than it was then.  Where are the moderates in American society who are willing to work together to find a way forward?  Conflict produces stalemate.  We can’t address the very real issues in the environment on such an antagonistic battle ground.


We recently posted an article about our on-going debate with the Audubon Society regarding its misguided support for the projects that are destroying the urban forest in the San Francisco Bay Area.  That article provided a few examples of our widely divergent views of nature:

  • We don’t see how birds will benefit from the destruction of tens of thousands of trees and countless plants that provide food and cover for birds and animals.
  • We don’t enjoy walking in nature with a judgmental eye, which points fingers at plants and animals that others claim “don’t belong there.” We are unwilling to divide nature into “good” and “bad” categories.
  • We don’t think humans have the right to pass a death sentence on wild animals because they prefer another animal, which they claim will benefit from the death of a potential competitor.
  • We don’t consider a “managed” forest a “more natural forest.” We don’t think humans are capable of improving what nature can accomplish without our interference.  We don’t think a public park that is routinely sprayed with herbicides can be accurately described as a “natural area.”

However, these widely divergent viewpoints about nature are not inconsistent with the extremes of our polarized politics in America.  Just as we don’t expect to change the minds of those at the opposite end of the political spectrum, we don’t expect to change the minds of those who view nature through the darkly colored lens of nativism.  Just as elections for public office are decided by the independents in the middle of the political spectrum, the debate about the future of our public lands will be decided by those who have not yet formed an opinion about what is best for nature.  Today’s post is addressed to them.  We will tell the “independents” about two recent op-eds published by The New York Times which represent the two extreme viewpoints about nature.  Both op-eds use sparrows as representatives of the natural world, which we hope will make the differences in these viewpoints starker and therefore clearer.

First a word about how important the “independents” are to the debate about the ecological “restorations” which are dictated by invasion biology.  Political independents are usually not more than a third of the electorate.  But, a survey conducted by University of Florida suggests the majority of the public are still open to learning more about “invasive species.”  They report that 62% of Floridians they surveyed said they are not knowledgeable or only slightly knowledgeable about invasive species.  Ironically, the same survey claimed that “a majority voiced support for raising sales tax to combat invasive species.”  One wonders why voters who acknowledge that they know nothing or next to nothing about invasive species would be willing to tax themselves to combat something they don’t understand.  In any case, if Floridians are typical, the majority of the public needs to know more about invasion biology.  We hope they have access to balanced information that is not written by those who make their living killing animals and poisoning our public lands.  Million Trees was created over four years ago for that purpose.

“The Truth About Sparrows”

Some time ago, we told the story of how sparrows were brought to America in the 1850s by people who believed they would eat the insects that were killing trees.  We concluded that article by saying that 150 years later house sparrows are no longer despised as alien intruders.  We were wrong.

House sparrow Cornell Ornithology Lab
House sparrow, Cornell Ornithology Lab

In May 2014, the New York Times published an op-ed entitled “The Truth About Sparrows.”  The op-ed was written by Peyton Marshall, whose mother was an exterminator of house sparrows.  This was no idle pastime for Ms. Marshall’s mother.  It was her mission.

Eastern bluebird, public domain
Eastern bluebird, public domain

Mom’s crusade against house sparrows began when Ms. Marshall was a child.  Mom loved bluebirds at a time when their population was dwindling in the east where they lived.  Mom decided that house sparrows were to blame and so she took it upon herself to kill every house sparrow that had the misfortune of entering her yard or within reach of it.

Mom began by trapping the house sparrows.  “Good” birds caught in the traps were freed, but the house sparrows were put into plastic garbage bags and asphyxiated.  Mom started the family car in the garage and wrapped the open end of the garbage bag around the tailpipe.  When the birds did not die, she consulted her husband who informed her that the car was a diesel and would not produce enough carbon monoxide to kill the birds.

So, mom took her operation on the road.  She helped elderly ladies with their groceries in the parking lot in exchange for a shot at their tailpipe.  When dropping off her children for play dates and birthday parties, she asked their parents if she could make brief use of their cars to kill birds.  Polite parents watched in horror as they became accessories to this execution.

Ms. Marshall concludes her story by noting that the population of bluebirds has rebounded since she was a child.  But mom continues to trap house sparrows in her yard and now uses a less public means of killing them:  “Now, she uses a carving knife and cutting board, at her leisure, in the privacy of her own kitchen.”

Although Ms. Marshall doesn’t say so, we doubt that the recovery of the bluebird population has much to do with the extermination of house sparrows in her mother’s backyard.  The recovery of the bluebird population is attributed to building nest boxes that substitute for the dead trees which are their preferred nest sites.  There are few dead trees in urban and suburban areas because people consider them hazardous and unsightly.  Once again, animals pay the price for the choices of humans.

“What the Sparrows Told Me”

The New York Times published “What the Sparrows Told Me” in August 2014.  It is a fitting antidote to the grisly tale of the sparrow exterminator.

Trish O’Kane, the author, was a human rights investigative journalist in Central America for 10 years before moving to New Orleans to teach journalism.  Less than a month after arriving in New Orleans, she and her family were displaced by hurricane Katrina in 2005.  Four months after the hurricane, she rented a room in a dry part of town so that she could return to her teaching job.  It was a hard time for everyone in New Orleans, but her gloom was deepened by learning of her father’s terminal cancer which would kill him in a matter of months.

Ms. O’Kane had never had an interest in birds before, but she knew she needed “to focus on something beautiful, something positive, something alive,” and so she did:

“I bought two bird feeders.  Each morning I sat on that back stoop and watched those sparrows.  Instead of wondering what was going to happen to the city, to the Gulf Coast, to the planet, I started wondering why one sparrow was hogging all the seed.  I started thinking about their resilience, their pluck, their focus on immediate needs.  If they couldn’t find food, they went somewhere else.  If they lost a nest, they built another.  They had no time or energy for grief.  They clung to the fence in raggedy lines heckling one another like drunken revelers on Bourbon Street.  Their sparring made me laugh.“

Audubon Park, New Orleans.  Public domain
Audubon Park, New Orleans. Public domain

Ms. O’Kane started holding her classes in Audubon Park, named for John James Audubon.  Her students began to find the same solace in watching the birds going about their business, finding a way to survive, carrying on.  And that gave her and her students the strength and the will to do the same at a time when life was hard in New Orleans.

Ms. O’Kane is now a doctoral student in environmental studies at University of Wisconsin, Madison.  She has found a way to connect her interest in human rights with her new found interest in birds.  She teaches an undergraduate course in environmental justice in which she pairs undergraduate students with middle school students in a mentoring program called Nature Explorers.  Many of the middle school children are immigrants from Central America.  She finds that they enjoy learning about the birds that migrate between Central America and Wisconsin, just as their families did.  The birds, like the people of America, are citizens of the world.

Ms. O’Kane tells us that many of her undergraduate students are frightened of the future of our planet.  She likes to start each new class with the story of the sparrows in New Orleans:  “I tell them that the birds are a gift to help them get through each day, a way to enjoy the world while we change it so that young people, everywhere, have a chance.”

Whose eyes do you choose to look through?

It’s no secret that our viewpoint regarding nature is more closely aligned with Ms. O’Kane’s.  If you haven’t yet taken a stand on the issue of what plants and animals are welcome in your ideal nature, think for a moment.  Which of these starkly different viewpoints do you prefer?

Nativism turns a blind eye to climate change

“Reflexive demonization of alien species ignores the beautiful but complex truth that nature fights to find a way—and for a planet navigating the pressures of climate change and overpopulation, that just might be our saving grace.” – Marianne Willburn, Garden Rant

Margaret Renkl writes an opinion column for the New York Times that I usually enjoy because she frequently writes about nature, often based on observations of wildlife in her own garden.  She lives in her childhood home in Nashville, Tennessee.  Much of her garden was planted with non-native plants and trees decades ago by her deceased mother.  Yet, in a recent column, Ms. Renkl blames non-native plants for a variety of crimes against nature. 

  • She suggests that non-native trees are blooming earlier than native trees, which she says has “skewed our experience of spring.”  She is apparently unaware that spring does indeed arrive earlier than it has in the past because of climate change.  Warmer weather arrives earlier, triggering the blooms of spring, not vice versa.  Both native and non-native plants are blooming earlier than they did in the past. 
  • She suggests that gardens planted with non-native plants are “blooming wastelands where the flowers feed nobody at all,” yet her columns are usually filled with the wildlife that lives in her own garden, with introduced plant species.
  • Although she does not use pesticides in her own garden, she believes that her neighbors’ non-native gardens require them to use pesticides that kill wildlife.  She says, “The typical suburban yard is actually worse than a wasteland. It’s a death trap.” She does not seem to know that most herbicide is used to kill non-native plants, not native plants nor does she seem to realize the contradiction in her indictment of gardening with non-native plants.  If there are more insects living in native gardens than non-native gardens, why would more pesticide be needed in non-native gardens?  If people could learn to love the clover, dandelions, and English daisies in their lawns as much as I do, they would use less “weed killers” on their lawns.

Ms. Renkl’s misperceptions about non-native plants seem to be based on a mistaken belief in their origins.  She says, “Ambulatory and omnivorous, human beings are a migratory species. That’s not true for the vast majority of plants.”  In fact, plants are just as mobile as animals, including humans.  Plants are carried by birds, animals, wind, ocean currents, etc.  They come and go as the climate changes, as it has many times in the past 500 million years that plants have existed on Earth.  Plants now considered non-native existed here in the distant past, in a different climate.  Here are a few examples of such dispersals; most occurred before humans even existed:

The ability to migrate is essential to the survival of plant and animal species.  As the climate changes, this survival strategy is quickly becoming even more important.  When we demand that plants be restricted to their historical “native” ranges, we doom them to extinction because when the climate changes, the vegetation must change.

Where did Ms. Renkl learn these myths?

Ms. Renkl’s cites Doug Tallamy’s Nature’s Best Hope as one of the sources of her mistaken beliefs.  Tallamy considers the existence of non-native plants the root of all evil in nature.  He calls them “ecological tumors.” He blames non-native plants for declining populations of both native plants and insects, and by extension to declining populations of birds that eat insects. 

In Nature’s Best Hope, Tallamy says, “…we must not use climate change as an excuse to do nothing.  Most species of plants and animals are far more resilient to climate variability than we give them credit for.  Besides, increasing the number and biomass of the plantings in our yards and public spaces is one of our most accessible and convenient tools to fight climate change.”  The problem with Tallamy’s dogma is that it inspires the public and land managers to eradicate established landscapes that are not native based on Tallamy’s claims that non-natives are “crowding out” native species and depriving wildlife of food. All native plant “restorations” begin by eradicating non-native plants, usually with herbicides that retard new growth.  In other words, the native plant ideology is causing the loss of vegetation and therefore the loss of stored carbon and the reduced capacity for carbon sequestration in the future.  The native plant ideology is not increasing biodiversity, nor is it “fighting climate change.”  It is more destructive than constructive. 

I’m not looking for “an excuse to do nothing.”  On the contrary, I believe every effort must be made to stop or at least slow down the inexorable advance of climate change.  The most basic effort we can make is to stop destroying functional vegetation, especially trees.  Then, there is a lengthy list of what we should be doing to reduce greenhouse gas emissions, which is another, equally important topic. 

Native plant advocates consider climate change irrelevant because they believe the existence of non-native plants is the sole culprit of all problems in the environment.  They see every environmental issue through the narrow lens of their dogma.  This comment on an article about the value of non-native plants by Marlene Condon published in [Chesapeake] Bay Journal is an example of such a misinterpretation of an environmental issue:

“English ivy is an evergreen, non-native, invasive groundcover that has demolished undisturbed natural areas…In salmon country that’s the difference between clean, cold streams and warmer streams filled with sediment.”

Eradicating ivy on stream banks is likely to produce more sediment because it will take some time for replacement vegetation to cover the ground, especially if herbicides are used to eradicate the ivy. Water is warmer in streams because of climate change and because there is less water due to water diversion and droughts. There are many other reasons for declining populations of salmon, particularly dams that prevent salmon from reaching their spawning grounds upstream.

Treat the cause, not the symptom

The native plant ideology ignores the underlying causes of changing ecosystems. Most changes are caused by the activities of humans, such as agriculture, development, water diversion, and pesticides.  Climate change is the underlying cause of some changes in nature and it will steadily become a more important factor.  Eradicating non-native plants will not reverse any of those changes nor will it prevent changes in the climate.    


  1. Alan de Queiroz, “The resurrection of oceanic dispersal in historical biogeography,” Trends in Ecology and Evolution, 20 No. 2, February 2005

Photo credit for featured photo: Garden Rant, Marianne Willburn