Evolution didn’t stop in 1492

One of the most appealing of the many arguments used by native plant advocates in support of their ideology is the evolutionary concept of “co-evolution.”  Co-evolution is defined by Forgotten Pollinators(1) as “The idea in evolutionary ecology that certain mutualistic organisms have directed or redirected each other’s evolutionary trajectory.”  The implication of this theory is that plants and animals that have evolved together are interdependent and that loss of a particular plant will result in the loss of the animals with which it evolved.  Native plant advocates sometimes describe these relationships as “a lock and key,” implying that native plants and animals fit together in a mutually beneficial relationship which is exclusive. 

Those who believe this theory are obviously deeply committed to saving all native plants because they believe the loss of any single plant would inevitably lead to the loss of the animals that are dependent upon it.  Likewise, non-native animals are often exterminated based on the assumption that they compete with native animals and that loss of native animals will lead to the loss of native plants.

There are three problems with this theory. First, while there are some examples of truly exclusive co-evolved relationships in which both species cannot survive without the presence of the other, the number of such relationships is quite small.  Second, even these relationships are not immutable because evolution has not stopped, and therefore other species may develop mutualistic relationships with the prior exclusively mutualistic species.  And third, organisms are opportunistic and are quick to take advantage of any new opportunities, meaning that many interactions observed between species in the wild are not co-evolved at all.  For example, the honeybee pollinates hundreds of species of North American plants and it didn’t evolve with any of them (since honeybees were introduced into North America from Europe, which had introduced them from Africa).

Why is “co-evolution” rare in nature?

When defining “co-evolution” Forgotten Pollinators adds this caveat, “Good examples of truly reciprocal coevolution are difficult to find.”  Although the concept of “co-evolution” has a certain logical appeal, the explanation for why it is rare in nature is even more logical:  it is a risky survival strategy in a world that is constantly changing.  If, for example, the specific plant upon which a specific animal depends doesn’t bloom or doesn’t return from its dormant phase because of a sudden, even temporary, change in the climate, the animal that is dependent upon that plant is out of luck.  Since such fluctuations of environmental conditions are common, natural selection does not favor the animal that is restricted to a single plant for which there is no substitute.  Such exclusive relationships therefore do not persist in nature.

Nature provides “back-ups” that will enable plants and animals to respond to fluctuating environmental conditions.  For example, few plants have a single pollinator.  Most have several, usually of several different types.  One bee may be a particularly effective pollinator of a particular plant, but that plant is probably also visited by a fly, a butterfly, a bird, a beetle, etc.  As humans do, plants and animals don’t just give up when conditions change.  We all look for and usually find other alternatives. 

Native bumblebee gathering nectar and/or pollen from non-native cotoneaster. Albany Bulb, Albany, California

“Evolution right under our nose”

The Science Section of yesterday’s New York Times features an article about evolution of animals in New York City In the most densely populated city in the country, founded nearly 400 years ago, 74% of the native plant species that existed when the city was founded in 1624, still exist there.(2)  San Francisco has an even lower rate of extirpation of its native plants since it was founded in 1850.  Ninety-seven percent of the 714 plant species known to exist in San Francisco in 1850 are still found in San Francisco

Midtown Manhattan as seen from the Empire State Building. Creative Commons Attribution Share Alike

The fascinating article in the New York Times reports that the ability of animals to evolve in response to changing environmental conditions has enabled their survival in the urban environment. 

The white-footed mouse is an example of a native animal that is thriving in New York City.  The urban environment creates isolated urban islands, such as parks.  Scientists find that virtually every park in New York City has a population of genetically unique white-footed mice.  In fact, “The amount of [genetic] differences you see among populations of mice in the same borough is similar to what you’d see across the whole southeastern United States,” according to the scientist studying this mouse in New York City.

It’s difficult to imagine a more altered, artificial environment than the road medians on Broadway on the Upper West Side of Manhattan, which are composed of landfill used to cover the subway tunnel.  However, scientists have found 13 species of ants living in some of these medians.  Nine of the thirteen species are native. 

Nature is opportunistic and resilient.  It isn’t necessary to eradicate non-native plants and animals to ensure the survival of native plants and animals.  What greater laboratory to illustrate the resilience of nature than New York City? 


(1) Buchmann and Nabhan, The Forgotten Pollinators, Island Press, 1996

(2) Duncan et al, “Plant traits and extinction in urban areas:  a meta-analysis of 11 cities,” Global Ecology and Biogeography, July 2011

Cultural Lag: Public policy lags behind science regarding “invasion biology”

This is a good-news-bad-news story.  The good news is that the most successful environmental organization devoted to the preservation and conservation of wildlands, The Nature Conservancy, has announced its intention to reorder its priorities in what we hope will be a less destructive direction.  The Conservancy is a science-based environmental organization that is unique in that regard.  It employs over 600 scientists to guide and inform its projects, in contrast to many other organizations that employ more lawyers than scientists.  The scientific orientation of the Conservancy undoubtedly puts it in a position to reflect and respond to the increasingly loud voices of other scientists who are expressing concern about the costs and environmental damage that are the unintended consequences of the “restorations” which have evolved out of invasion biology.

The bad news is that public policy regarding native plant “restorations” lags far behind the developing scientific consensus regarding invasion biology, namely that original theories require revision.  This is the consequence of the cultural lag that is inevitable when science moves forward, but communication of its findings to the general public lags behind. 

The Nature Conservancy redefines its goals

In the past few months, the Chief Scientist of the Nature Conservancy, Peter Kareiva, has written several articles in the Conservancy’s publications expressing his views about the future of conservation.  In “Beyond Man vs Nature,”(1) Kareiva is quoted as saying that species preservation should not be the top priority of the Conservancy.  He admits he is “not a biodiversity guy.”  Rather, he says, “The ultimate goal [should] be better management of nature for human beings.”  He does not agree with those who claim that the earth is fragile and man must be excluded from nature in order to protect it.  He considers nature resilient.  He calls the concept of “biodiversity hot spots” sham science and he rejects the notion that conservation and development are mutually exclusive.  We wants conservation efforts to focus on the things that people need from nature such as clean water and clean air.  If and when people experience the benefits of conservation, they will support and participate in those efforts.  The Conservancy can’t save the world alone.  The active participation of the human population is required to achieve the Conservancy’s conservation goals. 

Golden Gate Park San Francisco. Most plants and trees in GG Park are not native. Creative Commons Attribution - Share Alike

In “Conservation should be a walk in the park, not just in the woods,”(2) Kareiva says that the Conservancy should participate in more urban conservation projects because that’s where most people live and even more will live in the future.  He wants conservation to be more visible to people and he wants people to benefit directly from the projects.

In his most recent publication, “Invasive Species:  Guilty until proven innocent?” Kareiva acknowledges the debate about invasive species.  On the one hand, a few invasive species have done a great deal of harm, particularly on islands.  On the other hand, many invasive species aren’t doing any harm and some are benefitting native species, even endangered species in some cases (e.g., Southwestern Willow Flycatcher in Tamarisk).  He concludes, “Science-based conservation cannot be about knee-jerk platitudes and simple views of good and evil…the fact is we cannot control all invasive species, and in many cases, yesterday’s invaders have become plants and animals that are beloved by local people.” 

There is nothing scientifically new to us in what Kareiva has said recently.  What’s new is that he speaks as a representative of one of the most important environmental organizations in the world.  Therefore, he makes a connection between scientific theory and action.  That is new….very, very, new and very encouraging.

Public policy always lags behind science

Public policy is inherently conservative.  It usually reflects consensus and consensus occurs late in every scientific debate.  Once that consensus is finally reached, changing it is a slow process.  And so, we are not surprised by the most recent example of a local community continuing the crusade to eradicate non-native trees.  Two ordinances were recently passed in the Los Altos Hills on the San Francisco peninsula, to do just that. 

  • Citizens building or expanding buildings on their properties will be required by ordinance 10-2.802 to cut down all eucalypts within 150 feet of any roadway or structure.
  • “Town guidelines concerning restoration action” (5-8.08) “deems certain trees undesirable,” including Monterey pine and cypress, as well as eucalyptus.

We are heartened by the publication which announces these new policies.  The author objects to being dictated to regarding her tree preferences.   She also responds to the usual myths regarding the negative qualities of eucalyptus.  In response to the usual justification for its eradication, that it is not native, the author says, “Who cares?”  Indeed, who cares?  We certainly don’t care and we speculate that the vast majority of people in Los Altos Hills don’t care either.  When we speak up on behalf of our trees, we speed the process of changing public policy to reflect the considerable scientific evidence that non-native trees are not harming anything or anyone.   Indeed, their eradication is causing far more harm to the environment by releasing tons of sequestered carbon and requiring greater herbicide use.    


(1) Nature Conservancy, Spring 2011

(2) Nature Conservancy, Issue 2, 2011

Mark Davis, “A Friend to Aliens”

Mark Davis, Professor of Biology at Macalester College is interviewed in the February issue of Scientific American.  He tells us that invasion biology must distinguish between change and harm when labeling non-native species as “invasive,” a term which he believes should be used only in those rare cases when the non-native species pose “health threats” or economic harm.  With the exception of isolated places, such as islands, Mr. Davis tells us that non-natives have not been the cause of extinctions of native species.

 He believes it is irresponsible to label non-native species as “invaders” if they do not cause such harm because attempts to eradicate them are wasteful of scarce resources and often harm the environment more than the mere existence of non-natives.   He advises us to learn to live with those species that are not harmful. 

 He also points out that the eradication of non-natives is often futile and is likely to become even more futile in the future as global travel and commerce increase and the climate continues to change.  All species are going to move, both natives and non-natives and in fact, natives are as likely to cause problems in their expanded range as the non-natives in those regions.  He offers the example of the mountain pine beetle in Western coniferous forests, which is killing half the timber forest in British Columbia as it expands its range, probably in response to increasing temperatures.

Mr. Davis was also interviewed by Environment 360, a publication of Yale University, in November 2009.  In that interview, he is joined by Dov Sax, assistant professor of biology at Brown University, one of the growing number of biologists who are questioning the assumptions of invasion biology.  He provides a local example  of exaggerated claims of invasiveness:  “Dr. Sax says he began to question exotic species orthodoxy as an undergraduate at the University of California, Berkeley.  A professor leading a field trip described the Bay Area’s abandoned plantations of Australian eucalyptus trees as a “biological desert.”  Says, Sax, ‘There was all kinds of stuff growing in there.  I found there were really a similar number of species in both [native oak and eucalyptus] woodland types.  Exotics weren’t always doing the awful things people seemed to think they were doing.’” 

 
Owlets in eucalyptus, Claremont Canyon, Oakland

We attended a few lectures of an undergraduate course at UC Berkeley that fit with Dr. Sax’s experience.  Students in this undergraduate course were required to “volunteer” in a variety of different “restoration” projects in the Bay Area.  One of the projects on the property of UC Berkeley focused on the eradication of eucalypts.  The leader of this project and supervisor of the students who chose his project had an undergraduate degree in “natural resources” and an MBA in “operations management.”  He made a number of unsubstantiated claims to justify the eradication of eucalypts, but the most flagrantly stupid statement was this:  “The carbon sequestered in non-natives doesn’t count.  Only the carbon sequestered in natives counts.”  This statement has no scientific meaning.  We assume it is intended as a philosophical statement.  In any case, students aren’t learning any science from such a statement. 

Critics of native plant ideology are accustomed to criticism from true believers and Mark Davis is no exception.  In an interview available on the Macalester College website, Mr. Davis says he,  “…received rebuttals that, he felt, veered toward ad hominem attacks on his inexperience in the field.”  But he has not backed down and has come to view this debate as an example of the “values and age-old religious attitudes toward nature [that] frame scientific study and debates more than most scientists would acknowledge.”  He concludes that interview with this observation:  “People can get addicted to paradigms.  Then paradigms become an ideology.  Belief and conviction are very difficult adversaries since they are little affected by data and evidence.”   

Invasion Biology: Confusion about cause and effect

We have said before on Million Trees that eradicating non-native plants will not result in the return of native plants because the underlying conditions that supported those native plants have changed and they are no longer competitive within their historic ranges.  In those earlier posts we have focused on higher levels of CO₂ and the resulting climate change as the environmental variables to which non-natives are better adapted.  Changes in water quality and flows have also resulted in changes in animal and plant populations and we will provide a few specific examples in this post. 

Water levels in the Sacramento River delta have been hotly debated for decades and that debate has recently heated up as a commission gets close to making recommendations that will be legally binding.(1)  On one side of the debate, the cities of Southern California and agriculture throughout the state want more water from the delta.  They have been getting a lot of it for decades, but they want much more of it.  On the other side of the debate, environmentalists object to exporting “our” water because they believe that the decline in the populations of native fish such as smelt and salmon is a direct result of the reduction in water flow from the delta to the ocean via the San Francisco bay.   They object to further diversion of delta water and have legally challenged historic levels of water diversion using the Endangered Species Act. 

USFWS Recovery Plan for Native Fish in the Sacramento River Delta

The non-native bass in the delta are the proverbial red herring in this debate.  Those who want yet more water diverted to agriculture claim that the bass are to blame for the declining salmon population.  They demand that the bass be eradicated and they predict that the salmon population will recover once their non-native competitor is removed.(2)  

The diversion of fresh water flow from the delta reduces the speed of the flow of the water, making it turbid and brackish as the ocean water overwhelms the fresh water from the Sacramento River.  The warmer temperature of the water also promotes the growth of water weeds and algae.  The bass benefit from these conditions, but the salmon do not.  Eradicating the bass will not change these underlying conditions.  Salmon populations are unlikely to rebound unless these underlying conditions are changed.

This is not an isolated example of the fallacy of invasion biology.   There are as many examples of similar arguments as there are non-native animal and plant species now occupying spaces previously occupied by natives.  Native plant advocates and their allies want non-native turtles eradicated because they believe they are responsible for declining populations of native turtles.  They want to eradicate non-native bull frogs which they believe would benefit the native red-legged frogs.  Etc., etc., etc., ad nauseum.

And there are as many examples of how such eradication strategies may not benefit natives as there are demands for eradication efforts.  Here are just a couple. 

The Tamarisk or saltcedar tree is one of hundreds of non-native trees that are considered invasive by native plant advocates.  Here’s a description of an expedition on the Colorado River to eradicate Tamarisk that was published by the Sierra Club magazine.(3)

“’Kamikase!’  The most enthusiastic team members start to yell…and fall upon the larger plants with samarai fervor…’Kill tammys!’  someone yells.  ‘Boy, that was satisfying.’ says a fellow tammy warrior…”  And these are their tools of the trade:  “…a veritable armory of tamarisk-killing tools, 32 gallons of herbicide, more than 40 cases of beer…and a Virgin Mary votive candle that…the camp cook has christened with a label reading, ‘Our Lady of Biodiversity.’”

Herbicide is being used in one of the country’s most important watersheds, yet there is no evidence that the Tamarisk is harming the environment:

  • One study found the “mean values for 22 of 30 soil, geomorphology, and vegetation structure traits did not differ significantly between saltcedar and Fremont cottonwood stands.”(4)
  • The same study found that saltcedar increased floristic biodiversity.
  • Another study stated, “As for the claim that salt cedar has little or no value to insects, birds, and mammals, that has been obliterated by available data.”(5)
Tamarisk in natural habitat in Isreal, taken by Michael Baranovsky, Wikimedia Commons

But more importantly, eradicating the saltcedar is not likely to result in the return of the native cottonwoods because the natural flood cycle upon which the cottonwood depends has been altered by man.  The saltcedar thrives in the reduced water flow.  Unless the water flow is restored, the native trees will not return no matter how many saltcedar are destroyed.  Not only are we wasting our time and effort trying to eradicate saltcedar, we are also poisoning our water in the process.

In our final example, cause and effect were not confused, and a restoration was successful.   The Yuba Pass area in California is one of the most important migratory bird routes in the state.  The breeding population of Willow flycatchers disappeared from one of the wet meadows east of the pass.  The native willows upon which the flycatcher is dependent were disappearing from the meadow because channels caused by man along the edge of the meadow diverted water out of the meadow and dried it up.  Ponderosa pines and sage, which prefer the drier conditions, were taking over the meadow.  If native plant advocates had been in charge of remediating this situation their reaction may have been to eradicate the “invading” pines and sage.  That would have been fruitless effort; conditions in the meadow were suitable for pines and sage, not for willows.   But in this case biologists provided a more sophisticated solution.  They eradicated no plants.  They redirected the water from the channel back into its original slow flow through the meadow.  The meadow is again wet, the willows are now thriving, and the Willow flycatcher has returned.

Willow flycatcher, USFWS

“Invasion biology” is an ideology, not a science.  It frequently confuses cause with effect.  A proper diagnosis of what may superficially appear to be an “invasion” requires an understanding of the complexity of nature.  Most often the underlying reasons for an “invasion” are man-made conditions such as pollution and competition for scarce resources that are extremely difficult to fix.  It may be convenient to scapegoat a plant or animal for what man has caused, but it is unlikely to reverse the conditions that create an opportunity for a non-native plant or animal that is better adapted to those new conditions.


(1) “Delta plan may do more harm than good,” Oakland Tribune, 11/5/10

“Effort Falters on San Francisco Bay Delta,” NY Times, 12/15/10

(2) http://www.sfgate.com/cgi-bin/article/article?f=/c/a/2010/12/11/EDG21GN1MJ.DTL

(3) http://www.sierraclub.org/sierra/200407/grand_canyon.asp

(4) Stromberg, JC 1998, “Dynamics of Fremont cottonwood and saltcedar populations along the San Pedro River,” Journal of Arid Environments, 40:133-155

(5) Anderson, BW 1998, “The Case for Salt cedar,” Restoration and Management Notes, 16: -130-134, 138

Restoration or Destruction?

A recent trip to the Channel Islands off the coast of California inspires us to consider the pros and cons of restorations.  Islands are particularly attractive targets for restorations. They often contain endemic species that do not exist anywhere else because they have adapted to unique conditions in isolation.  And the relative isolation of islands implies that once non-native species of plants and animals are eradicated, re-introduction of those species can be prevented.

Santa Cruz Island, Wikimedia Commons

Some of the Channel Islands were inhabited by Native Americans as long as 13,000 years ago.  Ranching by Europeans began on some of the islands in the 1850s. Europeans brought sheep, cattle, pigs, mule deer, and elk to some of the islands.  Five of the eight Channel Islands were designated as a National Park about 30 years ago. 

Restoration began in earnest in the 1990s when ranching operations were ceased and tens of thousands of sheep and cattle were either removed from the islands or destroyed.  Black rats were eradicated from some islands after native mice were herded into protective enclosures so the rats could be poisoned.  Rabbits were eradicated from another island.  We don’t know how that was achieved. 

The next big effort was the eradication of about 6,000 feral pigs. When this was accomplished by sharp shooters, the first unintended consequence of this ambitious restoration was revealed.  It seems that the feral pigs had been the chief diet of a population of Golden Eagles, considered non-native to the Channel Islands.  When the pigs were removed from their menu, they turned to the rare, endemic Channel Island Fox. 

Channel Island Fox, Wikimedia Commons

The population of Channel Island Foxes plummeted.  Those that remained were captured so they could breed in protected conditions while the Golden Eagles were captured and removed to a remote location.  The Channel Island Fox is making a come-back, but the Golden Eagles are apparently gone for good. 

The eagle considered native to the Channel Island, the Bald Eagle, has been reintroduced.  It apparently lives in peace with the Channel Island Fox because it eats fish. 

Mule deer and elk are next up on the eradication agenda for fauna.  Non-native plants are also doomed.  Ice-plant and fennel are the top priorities for eradication by 2011.  Herbicides and prescribed burns are used for this purpose.   

Prescribed burn, Santa Cruz Island, NPS photo

We were surprised to see notice of herbicide application for Garlon 4 Ultra during our visit to this fragile place.  Someone dressed from head to toe in protective clothing was spraying this chemical on a steep hillside.  We have reported the toxic effects of Garlon in our post about herbicides.

This is a complex ecosystem in which simplistic solutions—such as killing all the non-natives—can result in a big mistake.  For example, do we know if there are native Anise Swallowtail Butterflies on the islands that are now dependent upon non-native fennel for their survival?  Do we know how the application of Garlon will impact the survival of the rare, endemic Island Jay?  The US Forest Service found in its risk assessment done for the EPA that the application of Garlon had a significant negative impact on the reproductive success of birds.  Are those who decided to spray Garlon aware of this study?

Herbicide application notice, Santa Cruz Island

We went to the Channel Islands with open minds.  We thought the strongest arguments could be made for restorations on islands.  However, when we learned of the thousands of animals who were sacrificed to this effort and the dangerous and toxic methods used to accomplish the restorations, we were not convinced.  We nearly lost the Channel Island Fox because of the unforeseen consequences of killing feral pigs.  Man would like to believe that he is capable of managing nature.  But can he do so without causing more harm than good?