Science in the National Parks

We were so encouraged by our reader’s report about the conference of the California Native Plant Society (CNPS) that we decided to attend the conference of the National Park Service (NPS), “Science for Parks, Parks for Science” at UC Berkeley, March 26-27, 2015.  As we have reported many times, the National Park Service is heavily engaged in native plant “restorations.”  Their projects are some of the most aggressive in the Bay Area and some of the most successful, because they seem to have greater resources than other local managers of public land.  Therefore, we were curious about their assessment of those efforts.  Are they starting to have doubts, as expressed by some of the presentations at the CNPS conference?  This is a brief summary of what we learned.

The angry old guard

The keynote speaker was E.O. Wilson, the granddaddy of “biodiversity.”  He spoke of his desire to safeguard biodiversity by preserving one-half of the Earth as “protected areas” and the closely related goal to connect all protected areas. This lofty goal should be compared to the current figure of 13% of the earth which is presently protected and the internationally agreed-upon goal of 17%, according to the second speaker, Ernesto Enkerlin, Chair of the IUCN World Commission on Protected Areas.

The moderator, Steven Beissinger, Professor of Conservation Biology at UC Berkeley, asked Professor Wilson a few pointed questions:

  • “Can working landscapes play a role in conservation?” Professor Wilson said. “That is a stupid, dangerous way of looking at conservation.  Parks cannot be evaluated in terms of their value to humanity.  The natural world is valuable in its own right.  Emma Marris and Peter Kareiva of the Nature Conservancy are pushing this; they have the least experience with studying the natural world.  This dangerous thinking must be countered immediately.”  Granted, Emma Marris is a science journalist, but Peter Kareiva was an academic scientist at University of Washington for decades before becoming Chief Scientist at the Nature Conservancy.
  • “Must protected areas be devoid of people?” Professor Wilson said “Of course not.  Indigenous people might be included.”  In fact, indigenous people have been evicted from many protected areas around the globe.  Furthermore, virtually the entire population of the US is not indigenous.  Where does that leave us?
  • “Given the challenges faced by conservation, is triage necessary to prioritize projects to focus on the most important and threatened species?” Professor Wilson said with some feeling, “That’s ridiculous!  We CAN bring them all back, we must SAVE THEM ALL!”

Professor Daniel Simberloff, the well-known invasion biologist, was another speaker who believes it is necessary and possible to eradicate all non-native plants and animals in our public lands.  He also called out by name Marris, Kareiva and others for their criticism of invasion biology.  Frankly, we think these personal attacks are unseemly in the context of what should be considered a scientific debate about the most effective methods of conservation.  The moderator, Professor Holly Doremus (UC Berkeley, Boalt Hall), asked Professor Simberloff a few tough questions as well:

Most other speakers at the conference had a less sanguine view of our ability to “save every species” and “eradicate every non-native species.”  The need for “triage” was repeated in many presentations and descriptions of past and present projects were often pessimistic about the prospects of success.  Climate change and its impact on the environment was the dominant theme of the conference.

All loss, no gain

Mission Blue butterfly.  Wikimedia Commons
Mission Blue butterfly. Wikimedia Commons

The endangered Mission Blue butterfly exists only in a few locations in the San Francisco Bay Area:  Twin Peaks, San Bruno Mountain, Milagro Ridge in San Mateo County, and the headlands of Marin County.  We recently reported that the 32-year effort to restore butterfly habitat on San Bruno Mountain has been plagued by natural succession to native coyote brush that competes with the butterfly’s host plant, 3 species of lupine.  The status of the butterfly population on San Bruno Mountain is unknown because of inadequate monitoring.  Save Mount Sutro Forest has reported that the butterfly population on Twin Peaks remains very small despite repeated attempts to move butterflies from San Bruno Mountain.  We learned at the NPS science conference that the effort to restore butterfly habitat in the Marin Headlands in order to increase the butterfly population there has experienced its own difficulties.

The restoration of butterfly habitat to the Marin Headlands was controversial because about 500 Monterey pines were destroyed to make way for the lupine scrub required by the butterflies.  The pines had been planted by the military over 100 years ago.  They were heavily used by raptors during their annual fall migration through the Bay Area.  The Marin chapter of the Audubon Society was therefore opposed to their destruction.  As usual, this opposition was ignored by the National Park Service, which manages that property, and the trees were destroyed in about 2009.

NPS has been engaged in the effort to restore the habitat needed by the Mission Blue since the trees were removed.  Those engaged in that effort presented a poster at the NPS science conference which reported:

  • In 2010, NPS and its collaborators attempted to promote the growth of the 3 species of lupine required by the Mission Blue by removing all vegetation mechanically and with prescribed burns, then seeding with lupine.
  • Neither burn nor mechanical treatments resulted in increased lupine species cover after one or three years. In fact, both mechanical and burn treatment resulted in increased cover of non-native forbs and grasses after three years.

In other words, 500 trees were destroyed, which were heavily used by migrating raptors, but Mission Blue butterflies did not benefit from the destruction of these trees because efforts to restore the habitat they require have been completely unsuccessful.  This is a familiar scenario:  all loss and no gain.

Karner blue butterfly - USFWS
Karner blue butterfly – USFWS

We also heard a presentation about a 20-year effort to “restore” the habitat required by an endangered butterfly (Karner blue) at Indiana Dunes National Lakeshore.  The complete failure of that effort is attributed to changes in the climate, considered “abnormal:”

Despite advances in our understanding of habitat needs of the Karner blue, and extensive management to meet those needs, Karner numbers at Indiana Dunes have fallen more than 99% over the past fifteen years, with precipitous declines associated with historically abnormal weather in 2012. We have documented a role phenological [seasonal] mismatching between the butterfly and its host plant plays in this population decline and the sensitivity of this species to habitat fragmentation.”

One wonders what “abnormal” weather means during a time of extreme changes in the climate, which are not expected to return to “normal.”  The speaker predicted that the likely outcome for the Karner blue at Indiana Dunes is its complete disappearance and probable replacement with a different butterfly species which is better adapted to the new climate.

Reality Check

Doug Johnson, Executive Director of the California Invasive Plant Council, made a presentation about new digital tools to identify populations of plants considered “invasive:”  CalWeedMapper and WHIPPET.  These tools will enable land managers to set priorities for attempts to eradicate these plants.  Using  a thistle species as an example, he showed a map that indicated this “invasive” plant is present everywhere in northern California, but there are isolated pockets of it south of there.  These small, isolated populations represent potential opportunities to prevent its spread before it is so widespread that eradication is impossible.  This is an example of triage, which was the dominant theme of the conference. 

Oxalis in Glen Canyon Park, San Francisco
Oxalis in Glen Canyon Park, San Francisco

Mr. Johnson was recently interviewed by Bay Nature about a non-native species of oxalis, which San Francisco’s so-called Natural Areas Program has been attempting to eradicate for many years by spraying it with Garlon.  Garlon is the most hazardous pesticide used by the Natural Areas Program.  Mr. Johnson expressed his opinion to Bay Nature that it is futile to attempt to eradicate oxalis: “‘It’s not a target for landscape-level eradication because it’s way too widespread.’”

On March 13, 2015, the California Invasive Plant Council published its final reassessment of Blue Gum Eucalyptus (available HERE).  Cal-IPC has downgraded its rating of invasiveness and ecological impact from “moderate” to “limited.”  Although the detailed assessment is less than perfect, the overall rating itself is an improvement.  We are grateful to our readers who sent comments to Cal-IPC on its deeply flawed first draft of the reassessment.

In other words, the California Invasive Plant Council seems to have entered a new era of realistic expectations.  This looks like a BIG step forward to us, because if that viewpoint is adopted by land managers it should mean less destruction and less use of pesticides.

The Take Away

The old guard is unprepared to compromise their firm belief that it is possible to save every species of native plant and animal and that every non-native plant and animal must be killed to achieve that lofty goal. They defend their indefensible opinion by attacking those who are looking for a more realistic approach to conservation. However, climate change is bringing more and more converts to this viewpoint, which was best expressed by one of the plenary speakers, Hugh Possingham, Professor of Mathematics and Ecology, University of Queensland in Australia.  He was asked how his model of “ecological parks” fits with the mission of the National Park Service to preserve the parks “unimpaired.”  We paraphrase Professor Possingham’s answer:

“The Australian conservation ethic is similar to the United States’.  We yearn for pre-invasion days.  When I grew up in Adelaide we had 7.5 hectares of pristine vegetation for the entire city, which had 750 species at one time and now there are 500 species left.  It’s a museum.  It isn’t a functioning ecosystem.  So, we have got to embrace the creation of ecosystems that are not particularly natural.  However, I’ve learned that the birds don’t care where the plants come from.  Where weeds have been ripped out, bird diversity has plummeted.  I have been converted to the European viewpoint of disturbed landscapes: that is, these new plants have value.  Australia is completely over-run with non-native plants and animals.  Australians would be willing to shoot all the feral cats, but the fact is it’s not possible because we don’t have the resources to attempt it, let alone succeed at it.”

Thank you, Professor Possingham, for your frank acknowledgement of the value of new species to wildlife and your acceptance of more realistic goals for conservation in the 21st Century.

Videos of the plenary speakers are available on the conference website, as well as abstracts of posters and presentations.

What is the goal of ecological “restorations?”

In the not-so-distant past, the goal of ecological “restoration” was usually described as the re-creation of an historical landscape that was believed to have been undamaged by humans, presumed to be “in balance” and therefore sustainable after “restoration” without further human management.  In North America, the pre-European landscape is usually selected as the ideal landscape to be replicated, based on the assumption it had not been radically altered by Native Americans.  New knowledge has overturned this model:

Native Americans setting grass fire, painting by Frederic Remington, 1908
Native Americans setting grass fire, painting by Frederic Remington, 1908

Oddly, many invasion biologists accept these new understandings of ecological science without changing their deep commitment to eradicating all non-native plants and animals.  Daniel Simberloff published an article about the current status of the concept of “balance of nature” simultaneously with the publication of his defense of invasion biology.  He described the current thinking about this concept: “…a widespread rejection of the idea of balance of nature by academic ecologists, who focus rather on a dynamic, often chaotic nature buffeted by constant disturbances.”

Invasion biologists have therefore revised their goal for ecological “restorations” to accommodate their new understanding of the dynamic nature of ecosystems.

The revised goal of ecological “restorations”

If the return to an equilibrium state is no longer the goal of ecological “restorations,” what is the new goal?  This is how invasion biologists writing in defense of their discipline described their goal: “…we should seek to reestablish – or emulate, insofar as possible – the historical trajectory of ecosystems, before they were deflected by human activity, and to allow the restored system to continue responding to various environmental changes…” (1)

In this post we will deconstruct this new definition of the goal of ecological “restorations.”  Our first problem with this new definition is that we don’t know the “historical trajectory” of a landscape because it is fundamentally unknowable.  We would have to reconstruct all the events and changes in the environment in the Bay Area in the past 250 years in the imagined absence of any Europeans.  Even if we knew what would have happened without our presence, we cannot then ensure the continuation of that imagined environment because, the fact is, WE ARE HERE AND WE AREN’T GOING AWAY!

Because we cannot reconstruct an imagined environment that has not been “deflected by human activity,” restorationists—who are the practitioners of invasion biology–focus on the one element in the environment of which there is sufficient historical knowledge, i.e., plants.  Most local restoration projects eradicate all non-native plants and trees, usually using herbicides to accomplish that task.  They rarely plant anything after this eradication attempt because they don’t have the resources to do so.  Those few projects that re-plant after non-natives are eradicated usually irrigate the new landscape for several years.  Here is an incomplete list of everything these projects do not do to replicate an historical landscape:

  • Soils are not restored for many reasons:
    • We have no way of knowing the composition of soil 250 years ago.
    • Soils have been altered by the plants that have been growing in them and by the herbicides used to kill those plants.
    • Urban soils have high nitrogen levels resulting from exposure to fossil fuel exhaust.
  • The atmosphere is not restored:
    • There are much higher levels of ozone and carbon dioxide than there were 250 years ago.
  • The climate is not restored:
    • The temperature is higher than it was 250 years ago.
    • The timing of seasons has therefore changed.
    • Precipitation and fog have changed in known and unknown ways.
  • The disturbance events that sustained historical landscapes or set them on another evolutionary course are not restored:
    • We cannot set fire to urban landscapes annually without polluting our air and endangering our lives.
    • We cannot allow our creeks and rivers to overflow in urban areas without damaging our properties.
  • Most occupants of the historical landscape are not reintroduced:
    • The grazing animals that helped to sustain grassland are gone and cannot be returned to urban landscapes.
    • The top predators such as bears and wolves that kept grazing and other animals in balance with available resources cannot be returned without threatening our safety in an urban setting.
    • Many insects that lived in these historical landscapes are unknown to us and some are extinct.
The El Cerrito Plaza with the Albany Hill in the background, centuries ago.  Oil painting by Laura Cunningham, with permission
Bears roamed the grasslands in the Bay Area, preventing over-population of grazing animals. The El Cerrito Plaza with the Albany Hill in the background, centuries ago. Oil painting by Laura Cunningham, with permission

In other words, destroying plants will not “restore” an historical landscape.  Nor will it return that landscape to its “historical trajectory” even if that trajectory were known or knowable.  Plants live in complex communities in which they are interacting with everything in the environment.  Local “restoration” projects do not “restore” an historical landscape because they do not and cannot change anything other than the plants that occupy the space.  Because most environmental variables have not been altered by these projects, the landscape will quickly return to its unrestored state unless it is intensively gardened.  In that case, the landscape will be continuously “deflected by human activity,” which violates the original goal of invasion biologists.

Misanthropic premise of invasion biology

The revised goal of invasion biology is unattainable because the absence of humans is a prerequisite for its attainment.  We cannot know and we cannot replicate a theoretical historical trajectory for ecosystems in which humans were not present.  And when we modify ecosystems in an attempt to do so, human activities will determine their future trajectory. The premise of invasion biology is that success of ecological “restorations” depends upon the absence of humans. Therefore, invasion biology has no practical application in the real world.   


  1. Carolina Murcia, James Aronson, Gustavo Kattan, David Moreno-Mateos, Kingsley Dixon, Daniel Simberloff, “A critique of the ‘novel ecosystem’ concept,”Trends in Ecology and Evolution, October 2014, Vol. 29, No. 10

A defensive tirade from invasion biologists

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

An international team of invasion biologists has just published a defense of their academic turf, invasion biology.  (1) Daniel Simberloff, an American member of the team, is the most relentless defender of the crusade to eradicate all non-native species, wherever they are found, all over the world.  Their publication acknowledges the mounting criticism of this crusade and attempts to respond to that criticism, but what is most notable is what is missing from their attempt to defend their opinions.  They make no mention of the harmful methods used to eradicate non-native species:

Keep these damaging methods in mind as we visit the hypocritical and contradictory arguments used to justify the projects for which these invasion biologists advocate.  They set up “novel ecosystems” as the straw man to which they compare the goals of invasion biology.  They define novel ecosystems as “a new species combination that arises spontaneously and irreversibly in response to anthropogenic land-use changes, species introductions, and climate change, without correspondence to any historical ecosystem.”

“Lack of rigorous scrutiny”

Their primary criticism of the concept of “novel ecosystems” is that it has not been “subjected to the scrutiny and empirical validation inherent in science” and its definition is “impaired by logical contradictions and ecological imprecisions.”   These criticisms apply equally to invasion biology.

Hypothesis n % of supporting studies % of decline in support
Invasional meltdown




Novel weapons




Enemy release




Biotic resistance




Tens rule




Island Susceptibility




Although support is strongest for the invasional meltdown hypothesis, recent studies are less supportive than early studies, indicating substantial decline in supporting evidence.  Declining evidence of invasional meltdown is consistent with the fact that exotic species are eventually integrated into the food web which reduces their populations, stabilizing their spread. There is apparently little evidence that islands are more susceptible to invasion than continents and few studies have been done to test the hypothesis.

If empirical validation and semantic precision are required to establish the credibility of scientific hypotheses, invasion biology has failed that test.

“Precautionary principle of conservation and restoration”

These invasion biologists define the precautionary principle of conservation and restoration as follows:  “we should seek to reestablish –or emulate, insofar as possible—the historical trajectory of ecosystems, before they were deflected by human activity.”  This is an unusual use of the precautionary principle, which is more typically defined as avoiding damage to the environment by not using potentially harmful methods, even in the absence of solid evidence of such harm.  The precautionary principle was not used when the following “restoration” projects were defined or implemented:

Ivy in the Conservatory in Central Park, New York City
Ivy in the Conservatory in Central Park, New York City

In 1996, Daniel Simberloff made this statement in his publication about the hazards of biological controls:  “…are there any protocols for biological-control introductions that would prevent all disasters?  Probably not…” (2) Yet, in 2013, he expressed his support for the introduction of non-native insects to control cape ivy at a conference at UC Davis sponsored by the California Department of Food and Agriculture.  Although cape ivy is despised by native plant advocates, it is not an agricultural pest and therefore causes no economic damage to ecosystems, unless money is wasted on attempts to eradicate it.

“All ecosystems should be considered candidates for restoration”

In response to those who find value in novel ecosystems, these invasion biologists find none.  They reject the possibility that there is ever a point at which it may not be possible to re-create a historical landscape.  They continue to believe that ANY and ALL radically altered landscapes CAN and SHOULD be considered candidates for restoration.  Their only caveat to this universal goal is that “damaged ecosystems…should be evaluated for feasibility, desirability, and cost-effectiveness, on a case-by-case basis, so that informed and science-based policy decisions can be made, in consultations with scientists, restoration practitioners, stakeholders, and advisors.”

These criteria for potential “restoration” have nothing to do with reality:

  • Most projects in the San Francisco Bay Area have not provided cost estimates when they were planned. The public demanded cost estimates for the projects of the Natural Areas Program in San Francisco, but these demands were ignored.  Therefore, “cost-effectiveness” is not usually considered when these projects have been shoved down the public’s throat.
  • We consider the public to be “stakeholders” in decisions to radically alter our public open spaces. We are the visitors to these areas and our tax dollars pay for their acquisition, maintenance, and “restoration.”  Yet, managers of public land are consistently making those decisions without taking the public’s opinion into consideration.  Most projects are planned and executed without any public participation.  In the few cases in which there are environmental impact reviews, the projects are implemented regardless of overwhelming opposition of the public.

 “Human-damaged ecosystems can be at least partially restored”

The demonstrated futility of “restoration” projects is one of many reasons why there is waning public support for attempting them.  Yet, invasion biologists who authored this diatribe claim that “restored sites recovered on average 80-86% of biodiversity and ecosystem services…and showed improvements of 125-144% over degraded ones.”  This claim is contradicted both by other scientific studies and by experience with local projects:

  • “…this paper analyses 249 plant species reintroductions worldwide by assessing the methods used and the results obtained from these reintroduction experiments…Results indicate that survival, flowering and fruiting rates of reintroduced plants are generally quite low (on average 52%, 19%, and 16% respectively). Furthermore, our results show a success rate decline in individual experiments with time.  Survival rates reported in the literature are also much higher (78% on average) than those mentioned by survey participants (33% on average).” (3)
  • Dunnigan Test Plot, Augusst 2011.  The result of an eight-year effort to restore native grassland.  Does it look "biodiverse?"
    Dunnigan Test Plot, August 2011. The result of an eight-year effort to restore native grassland. Does it look “biodiverse?”

    There is frequently a discrepancy between the success rates claimed in papers and those actually observed. For example, Cal-Trans gave researchers at UC Davis $450,000 to restore 2 acres of non-native annual grassland to native grassland.  UC Davis researchers spent 8 years and used multiple methods to achieve this transition.  When they ran out of money, they declared success in their published report.  They defined success as 50% native plants which they expected to last 10 years before being entirely replaced by non-native annual grasses again.  Do you consider that a success?

  • On a more anecdotal level, we watch established landscapes that have required no maintenance in the past being transformed into weedy messes by failed “restoration” projects. Then, adding insult to injury, we hear those who are responsible for these failures tell us how successful they are.

“Inadequate political will”

The authors of this publication conclude:

“No proof of ecological thresholds that would prevent restoration has ever been demonstrated.  Often the threshold that obstructs a restoration project is not its ecological feasibility, but its cost, and the political will to commit to such cost.” (1)

We are reminded of an old football adage:  “The best defense is a good offense.”  In other words, invasion biology is under fire, but the reaction of invasion biologists is to demand more….more money, more effort, and the commitment of public land managers to “restore” all ecosystems, regardless of what the public wants.  And in support of that aggressive strategy, they refuse to acknowledge the damage that is being done to the environment and the animals that live in it, by the projects they demand.

The authors of this defensive tirade have hammered another nail in the coffin of invasion biology.

  1. Carolina Murcia, James Aronson, Gustavo Kattan, David Moreno-Mateos, Kingsley Dixon, Daniel Simberloff, “A critique of the ‘novel ecosystem’ concept,” Trends in Ecology and Evolution, October 2014, Vol. 29, No. 10
  2. Daniel Simberloff and Peter Stiling, “How Risky is Biological Control?” Ecology, 77(7), 1996, pp 1965-1974
  3. Sandrine Godefroid, et. al., “How successful are plant species reintroductions?” Biological Conservation,   144, Issue 2, February 2011

Are critics of invasion biology pessimists or realists?

The California Department of Food and Agriculture held a symposium about invasive pest management in the 21st Century on October 17, 2013, at UC Davis.  This second in a series was focused on insects and diseases.  The first symposium held in Oakland in June 2013, focused on “invasive” plants.

The keynote speaker at the second symposium was Professor Daniel Simberloff of University of Tennessee.  He is a prominent invasion biologist and a self-appointed defender of that scientific discipline.  When the assumptions of invasion biology are questioned by other scientists, Professor Simberloff often publishes a heated response and recruits others to join him.  (For an example, see our recent post about Ascension Island and visit his “Counterpoint” to the article on which our post was based.)

Given the many recent defections of scientists from the central assumptions of invasion biology, we anticipated that Professor Simberloff would acknowledge that invasion biology is under siege.  We were not disappointed.  He started his talk by showing a quote from a scientist on the Galapagos Islands who, after decades of trying to eradicate non-native blackberry, was admitting defeat.  To paraphrase the scientist, he no longer believes that eradication is possible.  Therefore, he is now willing to call it a native plant.

These blackberries were mowed to the ground sometime in the past year.  Herbicides haven't been used in the Sutro forest for several years, but UCSF plans to use them in the future.  Courtesy Save Sutro
These blackberries in the Sutro forest were mowed to the ground sometime in the past year. Herbicides haven’t been used in the Sutro forest for several years, but UCSF plans to use them in the future. Courtesy Save Sutro

We were reminded of Professor Matt Chew’s criterion for what species “belong” in any particular location.  If the species persists unassisted in that location, Professor Chew believes it belongs there.  Surely a corollary to that criterion should be, “if you can’t eradicate it, it belongs there.”

Professor Simberloff diagnoses this acceptance of non-native species as pessimism.  He is not alone in this characterization of people who are no longer willing to spend unlimited amounts of time and money trying to kill non-native species.  This is the standard criticism of that viewpoint.  We are called defeatists who have “given up” in the internet debates we read.

Why are we critics of invasion biology?

Although we agree that it is usually futile to try to eradicate non-native plants with large, well-established populations that have long ago naturalized in our environment, this is not the primary reason why we reject the notion that there is some benefit to trying anyway.  The main reason why we reject the fruitless crusade against non-native plants is because of the damage it does:  the herbicides that are sprayed on our public lands; the release of tons of carbon dioxide into the atmosphere when trees are destroyed; the loss of habitat for wildlife, etc.

At the same time, we acknowledge that some invasions of insects and diseases have posed such serious economic and health threats that we have no choice but to make every effort to eradicate them.  The species of mosquitoes that carry yellow fever and malaria are examples of justified eradication efforts.  We hope that those who are engaged in that effort are also mindful that the methods used are not more harmful than the targets.

Scientists defend “novel” ecosystems

We harp on these issues because they are not discussed by the scientists who either defend or critique invasion biology.  Their concerns are, so to speak, academic.

Sutro Forest is a novel ecosystem. Courtesy Save Sutro

There is an excellent description of the scientific debate about “invasive species” in the on-line newsletter of the American Society of Landscape Architecture (ASLA).  They report that novel ecosystems were featured at the recent conference of the Society for Ecological Restoration (SER) held in Madison, Wisconsin.  Novel ecosystems were defined by one of the speakers (Eric Higgs, University of Victoria) as ecosystems in which changes from historical conditions are considered irreversible: “Even if plants are removed, ‘the system will revert back immediately’ to a state of invasion.”  This is an accurate description of 15 years of effort by San Francisco’s so-called Natural Areas Program.  Non-native plants are repeatedly yanked out and/or poisoned, native plants are planted, native plants die, non-native plants return.  That cycle is repeated annually in some high-priority locations.

Apparently, we are not alone in observing this futile cycle.  The ASLA description of the conference of the Society of Ecological Restoration summarizes current thinking of practitioners of that profession:

“In the face of this overwhelming struggle against novelty, there has been a shift in values among society. Years ago, restoration ecologists wanted to restore ecosystems to their “historic fidelity” as much as possible. Now, ecologists, scientists, and landscape architects discuss the value of novel ecosystems’ services, which to some extent are plant-agnostic.”

While this viewpoint is a welcome improvement over the previous fantasies of restorationists, this information has not yet reached managers of public lands in the San Francisco Bay Area.  Nor does it acknowledge the very real damage that is being done by those who cling to the fantasy that non-native plants can be eradicated and replaced with native species, particularly in an urban setting such as the Bay Area.

The mission of Million Trees is not an academic exercise.  Our objective is to stop the damage being inflicted on our environment and the animals that live in it.  And we don’t intend to shut up until the damage has stopped.  We hope to be put out of business within our lifetime.

More evidence that eucalypts are not invasive

Eucalyptus, Mountain View Cemetery, Oakland

We have provided our readers with photographic evidence that eucalypts are not invasive in the San Francisco Bay Area (click here and here).  Now we are going to tell you about more confirmation of this fact from a reputable source that will be difficult for native plant advocates to ignore:  Encyclopedia of Biological Invasions.

The Encyclopedia was edited by Daniel Simberloff (U of Tennessee) and Marcel Rejmanek (UC Davis) and published by UC Berkeley Press in 2011.  Many of our readers will recognize Simberloff as a prominent scientist in invasion biology.  He is responsible for the “invasional meltdown” hypothesis which is central to invasion biology.  A recent survey of empirical tests of the hypotheses of invasion biology found that there is considerable support for the “invasional meltdown” hypothesis, but that support is declining. 

Professor Simberloff has aggressively defended the assumptions of invasion biology against scientists who think that a revision of those assumptions is required by recent empirical evidence.  When Professor Mark Davis and 18 of his colleagues in ecology signed a comment in the Nature journal entitled, “Don’t judge species on their origins,” Professor Simberloff promptly recruited 140 of his colleagues to publish a rebuttal. 

We establish Professor Simberloff’s credentials for our readers as a scientist who firmly believes that non-native species are a serious threat to biodiversity so that native plant advocates will consider him a credible source of information regarding eucalyptus.   

“Eucalypts” according to the Encyclopedia of Biological Invasions

According to the Encyclopedia of Biological Invasions, eucalypts are “some of the most important solid timber and paper pulp forestry trees in the world.”  There are about 40 million acres of eucalypts planted in tropical, sub-tropical, and temperate countries.  The predominant species of eucalyptus in the Bay Area, Blue Gum (E. globulus), is grown in 13 countries in addition to the US and Australia.  About 70 species of eucalypts are naturalized outside their native ranges. “However, given the extent of cultivation, 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. “ (1)

Although the Encyclopedia admits to being puzzled by why eucalypts aren’t invasive, it offers “three major reasons for the limited invasiveness of eucalypts:”

Reason One:  Seed dispersal of eucalypts is limited

The seeds of eucalypts have no natural means of dispersal, such as fleshy tissue which can function as wings on the wind.  Tests have shown that the seeds “are dispersed over quite short distances.”  (1) “Seed dispersal is mainly by wind or gravity and is virtually limited to twice the tree height.” (2) 

The seeds of the Blue Gum are encapsulated in a woody pod which makes them inedible to birds and mammals.  So, the seeds of the Blue Gum are not dispersed by animals.

Reason Two:  High mortality of eucalyptus seedlings

Eucalyptus seedlings die quickly if they don’t establish roots in moist soil quickly.  If the soil is too moist they are susceptible to destruction by fungus.  If there is too much leaf litter or there is an understory, they are unlikely to find the quick access to the soil they need to survive.  There is a narrow range of conditions needed to successfully establish eucalyptus seedlings.

Reason Three:  Lack of compatible mycorrhizal fungi

Mycorrhizal fungi exist in the soil and sometimes form a symbiotic relationship with the roots of plants. They are often essential to the health of the plant because they facilitate the absorption of water and nutrients by the plant.  Some biologists speculate that the specific species of mycorrhizal fungi needed for successful seedling development have not been exported with the eucalypts to foreign soils. 

A balanced discussion of the pros and cons of eucalypts

Given the strong commitment of the authors of the Encyclopedia of Biological Invasions to invasion biology, we are impressed with its even-handed discussion of the ecological pros and cons of eucalypts as well as its recognition of the lack of hard data to support a particular conclusion:  “Conclusions about positive or negative environmental and economic impacts of eucalypts are often anecdotal, highly controversial and context dependent.”   

The authors suggest that eucalypts not be planted near streams as the moving water is a means of seed dispersal.  On the other hand, when planted on degraded soil, the eucalypts have provided a fuel source which reduces pressure on remnants of native forests.  Eucalypts have been a valuable source of nectar for honey production all over the world.  More birds are said to be found in native forests than eucalyptus forests in California.  However, three times as many salamanders are found in the eucalyptus forests compared to native forests in California. 

Eucalyptus and honeybee. Painting by Brian Stewart

The Encyclopedia also addresses the controversial question of whether or not eucalypts are allelopathic, which means chemicals in their roots or leaves suppress the germination of the seeds of other plants.  It reports that there is no conclusive evidence on this question.  However, the accumulation of leaf litter is probably a physical barrier to the germination of seeds in its understory, which is not an allelopathic method of suppressing competition.  This is clearly true of other trees as well.  For example, the tannins present in both oak and eucalyptus leaves prevent the rapid break down of the leaf litter which accumulates and creates a physical barrier to competing vegetation.  This is one of many examples of the characteristics that both native and non-native plants have in common.

The Encyclopedia attributes the flammability of the eucalyptus forest to leaf litter which is exacerbated in California by rare deep freezes.  These deep freezes cause die-back of eucalypts, contributing to fuel loads.   It makes no mention of the oiliness of leaves as a factor in flammability. 

There has not been such a deep freeze in the East Bay in over 20 years and 20-year intervals of such weather events have been historically typical.  These deep freezes do not occur on the San Francisco peninsula because its climate is moderated by the ocean and bay surrounding it.  Its climate is therefore warmer in winter and cooler in summer.  Therefore, this caveat about the flammability of eucalypts does not apply in San Francisco.

The myth lives on…..

Despite the fact that there is no evidence—scientific or experiential—that eucalypts are invasive, the myth lives on amongst the community of native plants advocates.  We will continue to provide the evidence that eucalypts are not invasive.  We hope that eventually the public will be sufficiently informed that they will become resistant to this claim of native plant advocates which is one of many myths used to justify the needless destruction of eucalypts.


(1)    Marcel Rejmanek and David Richardson, “Eucalypts,” in Encyclopedia of Biological Invasions, eds, Daniel Simberloff and Marcel Rejmanek, University of California Berkeley Press, 2011.

(2)    Craig Hardner, et. al., “The Relationship between Cross Success and Spatial Proximity of Eucalypts Globulus ssp. Globulus Parents,”  in Evolution, 212, 1998, 614-618.