Retreat from invasion biology becomes a stampede

The New Wild by Fred Pearce (1) is the third book to be published in three years which challenges the conventional wisdom that native species are inherently superior to non-native species and the closely related corollary assumption that all non-native species are competitors of native species.  These are the assumptions that underlie invasion biology.  Each book has been progressively more pointed in its criticism of this ideology, masquerading as a scientific discipline.

Rambunctious Garden

Rambunctious GardenThe first book to be published in 2011—Rambunctious Garden by Emma Marris (2)—was timid in its approach in comparison to The New Wild.  Ms. Marris visited “restoration” projects all over the world.  She described unsuccessful efforts to eradicate non-native plants and animals as well as extreme attempts to “rewild” that are often a mishmash of plant and animal species from different native ranges and time periods.  She implied that these projects were futile as well as artificial, but she was not explicitly critical.  Despite her cautious approach, she has been subjected to intense criticism from both academics and practitioners of invasion biology.   The following excerpt of a reader’s review of Marris’s book found on is typical of the criticism:

“Earth as cookie jar”

“Emma Marris, the author of Rambunctious Garden (RG), loves the nature hiding in back street alleys and along the highway median strip. Marris believes it’s time to abandon (or de-emphasize) what she sees as outdated and naïve conservation strategies such as creation of national parks and wilderness reserves. She feels the biggest obstacles to a bold new world of “designer” and “novel” ecosystems is the “wilderness cult” that naively wants to preserve “natural” landscapes–which she says do not exist anymore.

Marris espouses the anthropocentric perspective that the Earth is more or less a resource cookie jar for humans–to be used carefully to be sure–but she doesn’t really question whether ethically or ecologically this is ultimately a good idea…

However, by moving the goalposts to vacant city lots as an acceptable desired future condition of the landscape, she implicitly, if not explicitly, provides cover for all manner of environmental degradation.”

Most of the 35 readers’ reviews about Rambunctious Garden on are equally critical.  This particular review was rated as “helpful” by 141 other readers and 21 comments were also posted in support of the critical review.  Marris and her book have been thrashed in many other venues, including conferences where she is called out by name as an enemy of nature by invasion biologists.

Where do camels belong?

Where do camels belongThe second book, which challenges the assumptions of invasion biology, was published in September 2014.  Where do camels belong? by Ken Thompson, a British academic, (3) is much more explicit in its criticism of invasion biology.  One of its strong suits is the examples of the ambiguity and absurdity of the often muddy distinction between native and non-native.  As we might expect, this distinction is less clear in Britain because it has a much longer history of “invasion” than North America (only because invasion biologists have chosen to define “native” in North America as any species that precedes the arrival of Europeans).  Professor Thompson offers some comic examples of how status as a native has been conferred in Britain and the contortions that are required to provide preferential treatment to these “natives.”

Despite kicking up the level of criticism of invasion biology a notch, reviews of Professor Thompson’s book are far more positive than those of Ms. Marris’s book.

The New Wild

The New Wild was published in the US in April 2015.  Fred Pearce does not pull his punches in The New Wild.  He methodically lays out all the reasons why invasion biology no longer deserves the status of a scientific discipline.  The readers of Million Trees are familiar with all of these arguments, so we will summarize them here and provide links to articles on Million Trees that illustrate each issue:

Although The New Wild is a full frontal assault on invasion biology, it has been very favorably received by reviewers on  Here is a review by a reader for whom the book was an epiphany:

“An important—even essential—look at our global challenges”

“Let me cut to the chase: read this book. I want to follow that statement with several exclamation points, but I’m trying to control my enthusiasm. Perhaps the book seems so important to me because I was so ignorant when I first started reading it. Perhaps my level of ignorance is extraordinary, but I just checked the websites of several environmental organizations I respect and it looks to me like they too need to read the book. Certainly it is provocative, controversial, and challenging. It will anger some, but it is not an ad hominem attack against anyone. Whatever you think of Fred Pearce, Daniel Simberloff, and others on either side of this debate, it is clear that the debate is important, even urgent. It made clear to me that I have put too much faith in environmental organizations to ferret out the facts and explicate the issues for me. Clearly, I have allowed myself to be misled. Even more important, scientific standards are not being rigorously followed. Have you noticed the headlines about all the “invasive” species that “need” to be eradicated? About the billions of dollars that are required to do this purportedly important work? I have been asking why so much killing is necessary. Pearce states that it isn’t. In fact, he goes further and suggests that the species targeted for eradication may be our salvation precisely because they have the adaptability and resilience to survive in environments disturbed and dramatically changed by mankind. His arguments are articulate and persuasive.

Environmental writers and organizations sometimes make conclusory and inflammatory claims about the damage done by those species they choose to characterize as invasive. And supporters such as myself accept those claims unquestioningly. As Pearce points out in his eye-opening treatment of the subject, too often one environmentalist repeats or even amplifies the unsubstantiated claims of another, and when this happens again and again with no one questioning the science along the way, dangerous, counterfactual conclusions are spread and soon become gospel. Pearce’s probing, incisive exploration into several of those claims in his seventh chapter, “Myths of the Aliens” is alone worth the price of the book.

Pearce woke me up. I respect the scientific method and believe it must be adhered to without fail in environmental writings. I have naively accepted that other environmentalists feel the same. We cannot make intelligent decisions if we are uninformed about true facts. False allegations have no value for any of us. “Invasive” species need new, clear-eyed, unbiased consideration by environmentalists. We need to look again at our underlying assumptions. What does “native” really mean? Which species are natural to an area? Which can survive in the “wild”? Pearce asserts that there is a “New Wild” and that we will do better to respect it sooner rather than later, to work with it rather than against it. I learned so much from Pearce not only about the facts of our situation, but also about new ways of looking at our extremely challenged world. I highly recommend this book and hope you get the opportunity to read Pearce’s insightful and creative ideas.”

This reader understands for the first time that the environmental organizations he/she had previously trusted had misled him/her into believing that non-native species are the cause of environmental damage rather than symptoms of that damage.  He/She was always uncomfortable about all the killing that was motivated by that viewpoint, which is perhaps what opened his/her mind to Pearce’s message.  This sequence of realizations describes my own journey to the other side of invasion biology.  I was initially appalled by the killing, but I did not realize that the justification for the killing was entirely bogus until I began to do my own research.  I initially assumed that they knew what they were doing.  After reading innumerable books and studies, I began to understand that there is little evidence supporting their claims that non-native species are damaging the environment.  Quite the opposite is true.  We hope that Pearce’s book will start many other readers on the same journey of discovery.

(To be fair, the first critique of invasion biology was Invasion Biology:  Critique of a Pseudoscience by David Theodoropoulos, published in 2003.  Although it was ahead of its time, virtually every criticism of invasion biology in that book remains true to this day.  However, at that point in time there were few empirical studies testing the hypotheses of invasion biology and few “restorations” based on those hypotheses.  It was therefore more difficult to make the case against invasion biology.  Theodoropoulos foretold the fate of invasion biology as a discredited ideology based primarily on his personal observations in nature.)


In just three years, three hard-hitting books have been published which confront the unfounded assumptions of invasion biology.  Although each book is progressively more aggressive and explicit in its criticism, the reaction of the public has been progressively more positive.

We admired all three of these books, so we are reluctant to conclude that the more favorable reaction to the more recent books is because of improved quality.  Perhaps the more explicit criticism of the more recent books makes it easier for readers to appreciate the strength of the argument.  Although we are deeply grateful to Emma Marris for leading the way, Rambunctious Garden requires the reader to reach the conclusion she only implies. The New Wild makes no such demands on the reader’s judgment.

However, we have our own optimistic theory about why readers are welcoming The New Wild.  The more experience the public has with the destructive projects which attempt to eradicate non-native species, the more likely they are to understand the futility and the damage being done to the environment.  We choose to interpret the positive reception for The New Wild as an indication that the public is ready to abandon the fantasy of returning our public lands to some mythical ideal landscape.

  1. Fred Pearce, The New Wild, Beacon Press, April 2015
  2. Emma Marris, Rambunctious Garden, Bloomsbury, 2011
  3. Ken Thompson, Where do camels belong?, Greystone Books, 2014

Another lame attempt to defend invasion biology

The Editor of an academic journal, Diversity and Distribution, wrote and published a defense of invasion biology (which he prefers to call “invasion science”) entitled, “Misleading criticisms of invasion science:  a field guide.” (1)  We recently critiqued a similar defense by other invasion biologists, so we’ll “cherry-pick” a few issues from this publication which weren’t covered in our earlier critique.

“Costs and Benefits?”

The authors begin by describing their academic discipline:  “Invasion science is the study of the causes and consequences of the introduction of organisms to the areas outside their native ranges.  It concerns all aspects relating to the transport, establishment, and spread of organisms in a new target region…and the costs and benefits of invasion with reference to human value systems.”  However, the publication makes no mention of any benefits of non-native species nor does it mention the costs to the environment associated with the attempts to eradicate non-native species, such as herbicide use.  Non-native species are said to be “far more likely to cause substantial ecological and socio-ecological damage” than to benefit ecosystems and, in any case, if there are any benefits they are said to be “transient.”

Zebra mussels, open underwater with siphons out.  Creative Commons
Zebra mussels, open underwater with siphons out. Creative Commons

Actually, there is empirical evidence that the negative impacts of non-native species are transient.  For example, the population of zebra mussels in the Great Lakes began to decrease significantly within three years when the population of migrating ducks discovered them and altered their migratory route to take advantage of that new food source.  And the negative effects of garlic mustard on forest regeneration were significantly decreased within 50 years of its arrival in North American forests.

Monarch butterflies roosting in eucalyptus tree.
Monarch butterflies roosting in eucalyptus tree.

Evidence of the benefits of non-native species is too voluminous to enumerate, so we will just offer our local example of the services to wildlife provided by eucalyptus in California.  It is one of the few sources of nectar in the winter and is therefore essential to the survival of honeybees and hummingbirds.  Eucalyptus is the over-wintering roost of 75% of monarch butterflies in the California migration.  It is the preferred nesting habitat for raptors.

We see no evidence in this publication that “costs and benefits” of non-native species have been considered.

Are most “invasions” benign?

The authors respond to the defenders of non-native species who say that most non-native species are benign:

  1. “The impacts of most invasions have not been studied, and so important effects may remain undetected,
  2. Invaders that are apparently innocuous in one region can be disruptive in other regions,
  3. Subtle impacts that may be unrecognizable without careful technical study can produce enormous ecosystem changes over time, and
  4. Many non-native species that currently appear innocuous may become damaging many years later—when it is no longer feasible to eradicate them.” (1)

Here’s how we paraphrase this defense:  “We may not have much evidence that non-native species are doing any harm, but we are sure they are doing harm and even if they aren’t doing any harm, we’re sure they will eventually do a great deal of harm.”  Does this seem an adequate defense of projects that are eradicating all non-native plants on thousands of acres of public land, using harmful methods such as herbicides and prescribed burns?  We think a higher standard of proof is needed to justify such damage to our public lands.

Invasion biologists chastise critics

Invasion biologists are angry that their academic turf is being challenged by other academic scientists:

“In our view, the escalation of cavalier bashing of the discipline is undermining systematic science-based efforts to improve the efficiency of management of problematic non-native species and invaded ecosystems.” (1)

We have seen no “cavalier bashing” of invasion biology.  What we have seen, and provided to readers of Million Trees, are many scientific studies which show that the hypotheses of invasion biology are often not supported by evidence from the field.  Most of the papers don’t even mention “invasion biology,” they just present their evidence in scientific journals.

We wish it were true that these studies were “undermining management” of non-native species.  Unfortunately, we see no evidence that criticisms of invasion biology by academic scientists have any impact on public policy.  Every project in the San Francisco Bay Area which is eradicating or proposing to eradicate all non-native species on our public lands is moving inexorably forward.  There is no apparent connection between the revision of the hypotheses of invasion biology by academic scientists and the practical application of those out-dated hypotheses by managers of public lands.  If the primary goal of invasion biologists is to eradicate non-native species rather than to defend their academic discipline, they seem to have nothing to fear.  They would be wise to shut up and let the destruction continue quietly under the public’s radar.

A new round of criticism of invasion biology

Where do camels belongMeanwhile, the angry reaction of invasion biologists to criticism of their discipline has not stopped that criticism.  Hardly a day goes by without the publication of new critiques of invasion biology by other scientists.  Where do camels belong? by Ken Thompson was published in September 2014.  It is a full frontal assault on the unfounded assumptions of invasion biology.  It is a hard-hitting, often amusing summary of the flaws in the reasoning on which invasion biology was constructed.  Although Mr. Thompson is a British academic scientist, his book is written for the general public, drawing on the scientific studies of his colleagues who share his opinion of the fallacies of invasion biology.  The book is also unique in mentioning the damage that is done by the fruitless attempts to eradicate firmly entrenched non-native species.

Mr. Thompson was recently interviewed by Canadian public radio.  Here is a choice excerpt from that interview:

“He also cautions that our efforts to control or eliminate invasive species can be tremendously expensive, are rarely successful, and often have damaging unintended consequences. For example, the herbicides used to try to eliminate invasive plants often have devastating impact on vulnerable native species. The cure, in some of these cases, is worse than the disease, he says.  Professor Thompson says the invasive species we might worry about most is actually us. Humans have spread to every corner of the globe, and altered a huge amount of the planet.  ‘We’ve chopped down forests, built dams and turned the whole world into a giant cattle pasture, and then we’re surprised that some species quite like what we’ve done. We shouldn’t be surprised.’”

The publication of Where do camels belong? is one of the few bright spots in 2014, a year full of disappointments for those who value our urban forest in the San Francisco Bay Area.  We recommend it to our readers.  It may cheer you up as it did us.

Update:  Professor Richardson recently published (February 11, 2015) an article in Ensia, an on-line science blog, which was written in response to an earlier article(January 21, 2015)  in Ensia by Daniel Simberloff.  Professor Simberloff’s article defended “invasion biology” and criticized any acceptance of “novel ecosystems.”  Professor Richardson’s response seems to defend “novel ecosystems.”   It seems that Professor Richardson has altered his views regarding novel ecosystems since writing his article two years ago about “Misleading criticism of invasion science.”  Welcome to reality, Professor Richardson.  Updated 4/8/15


  1. David Richardson and Anthony Ricciardi, “Misleading criticisms of invasion science: a field guide,” Diversity and Distribution, 19: 1461-1467, 2013