Author: Conservation Sense and Nonsense

Franciscan manzanita: The confiscation of public land

Update:  US Fish & Wildlife published the final rule designating critical habitat for Franciscan manzanita on December 20, 2013.  230.2 acres of land in San Francisco have been designated as critical habitat:  46.6 acres of federal land, 172.8 acres of parks owned by San Francisco’s Recreation and Parks Department, and 10.8 acres of private land.  The complete document is available here.  The document responds to public comments and explains any differences between the proposed designation and the final rule.  It makes interesting reading. 

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On September 5, 2012, US Fish & Wildlife (USFWS) announced that Franciscan manzanita is now an endangered species.  In 2009 the single plant known to exist in the wild was discovered during the reconstruction of Doyle Drive.  It was transplanted to an undisclosed location in the Presidio in San Francisco.

In addition to the conferral of endangered status, US Fish & Wildlife has designated 318 acres of  land in San Francisco as critical habitat for the Franciscan manzanita.   Critical habitats are places where the endangered plant is either known to have existed in the past or they are places that provide what the plant needs to survive.

Five of the eleven places in San Francisco designated as critical habitat are on federal land in the Presidio.  (Details about all the critical habitats are available here.)  Forty of the 318 acres are on private land.  Six of the critical habitats are in 196 acres of San Francisco’s city parks:

  • Corona Heights
  • Twin Peaks
  • Mount Davidson
  • Glen Canyon Park (erroneously called Diamond Heights by US Fish & Wildlife)
  • Bernal Hill Park (erroneously called Bernal Heights by US Fish & Wildlife)
  • Bayview Hill Park

The taxonomy of manzanita is ambiguous

There are 96 species of manzanita in California (1).  The ranges of most of these species are extremely small because the manzanita hybridizes freely and therefore adaptive radiation has resulted in a multitude of species, sub-species, and varieties that are adapted to micro-climates.  Many of these species are locally rare, which is consistent with the fact that 6 species of manzanita have already been designated as endangered, two of which are limited to the San Francisco peninsula:  Raven’s manzanita and Franciscan manzanita.

The genetic relationship between these two species of manzanita is ambiguous, which is reflected in the constantly shifting opinions of biologists about the taxonomy (species classification) of manzanita.  The 2003 Recovery Plan for Raven’s manzanita recounted the long history of these shifting views.  For some time, Raven’s and Franciscan manzanitas were considered the same species.  Then, for an equally long time, they were considered sub-species of the same species, Arctostaphylos hookeri.  It was not until 2007, that Raven’s was reclassified as a sub-species of Arctostaphylos montana.  Presently, Franciscan manzanita is classified as its own species, Arctostaphylos franciscana. 

Clearly, this history of the biological opinion regarding these two species of manzanitas suggests they are closely related and morphologically (AKA anatomically) similar.  The Recovery Plan concludes, “The idea of ‘pure’ species in Arctostaphylos, with its many poorly defined taxa and prevalent hybridization has often been difficult to apply over the history of taxonomic work in the genus.”

To add to the confusion regarding the provenance of Franciscan manzanita, some biologists are of the opinion that the individual plant that was discovered on Doyle Drive is actually a hybrid, not a pure-bred Franciscan manzanita.  The East Bay Regional Park District botanical garden in Tilden Park has planted a clone of the individual plant from Doyle Drive.  It is labeled as a hybrid of Arctostaphylos uva-ursi, which is one of the few species of manzanita with a wide range.

This is the label on the “Doyle Drive” manzanita in Tilden Park Botanical Garden, indicating that it is a hybrid.

The park ranger who led us to this plant in the Tilden garden, pointed out that the plant is morphologically distinct from the Franciscan manzanita that has been resident in that garden for about 50 years.  He expressed his opinion that the Doyle Drive manzanita was properly labeled as a hybrid.

In what sense is the Franciscan manzanita “endangered?”

Franciscan manzanita has been available for purchase in nurseries for about 50 years.  It has been propagated by taking cuttings and therefore they are presumed to be genetically identical clones.  However, given that this plant has been sold to the public for a long time, we have no way of knowing exactly where they have been planted or if some have successfully reproduced by germinating seeds.  For all we know, this plant is thriving somewhere, perhaps even in a place we might call “wild.”  Perhaps the plant found on Doyle Drive was purchased in a nursery!

The individual plant found on Doyle Drive has been defined by USFWS as Franciscan manzanita despite the fact that some biologists consider it a hybrid of another species.  We understand that the motivation for designating this individual as an endangered species and providing it with critical habitat is based on an assumption that it is genetically different from the Franciscan manzanita that can be purchased in nurseries and that the chances of survival of the species may be improved by cross-fertilization of these two plants such that greater genetic diversity results from their union.

Yet we are offered no evidence of the genetic composition of the Doyle Drive individual or Franciscan manzanita sold in nurseries.  Nor are we provided any evidence that the Doyle Drive individual is even a genetically “pure” Franciscan manzanita rather than a hybrid of another species altogether.

If we weren’t being asked to devote 318 acres of land to the propagation of a plant with such ambiguous taxonomy, we might not question how little information we have been provided.  The technology of mapping the genome of this plant is available to us.  Why aren’t we making use of this technology to resolve these ambiguities?  The cost of planting 318 acres with this endangered plant far exceeds the cost of such genetic analysis.

We aren’t told what it will cost to plant 318 acres with this endangered plant, but we know that the cost of the recovery plan for Raven’s manzanita and lessingia was estimated as $23,432,500 in 2003.  Presumably that is an indication that the proposal for Franciscan manzanita will be a multi-million dollar effort.  The cost of transplanting the single plant from Doyle Drive to the Presidio was reported as over $200,000. (1)

Thirty years of endangered status for Raven’s manzanita has not saved this plant

We have already made the point that Raven’s and Franciscan manzanitas are closely related.  In its proposal for the designation of critical habitat for Franciscan, USFWS confirms this close relationship by referring us to the Recovery Plan for Raven’s.  In other words, the characteristics and horticultural requirements of these two species are so similar that a separate Recovery Plan for Franciscan is not necessary.  The Recovery Plan for Raven’s is applicable to Franciscan.

Therefore, we should assume that the fate of the recovery effort for Franciscan will be similar to that for the Raven’s.  Raven’s was designated as endangered in 1979.  Its first recovery plan was published in 1984 and the second in 2003.  Many 5-year reviews of its endangered status have been done during this 33 year period.  The most recent 5-year review was published in June 2012; that is, very recently.

So what does USFWS have to show for 33 years of effort to save Raven’s manzanita from extinction?  Almost nothing:

  • Clones of the single plant in the wild exist in several botanical gardens.  These clones are genetically identical and their growth in maintained gardens does not meet ESA standards for recovery.
  • “The wild plant has been observed to set seed although no natural seedling establishment is known to have occurred.” (6)
  • The plant has been the victim of twig blight several times, but the fungus cannot be treated because it would damage the mycorrhizal fungi in the soil upon which the plant is dependent.
  • The seeds depend upon animal predators for dispersal which are largely absent in an urban area.
  • The pollinators of manzanita have not been identified and therefore there is no assurance that they still exist in this location.
  • The 5-year review concludes that:  “…recovery sufficient to warrant full delisting is not projected in the foreseeable future for [Raven’s manzanita] and may not be possible.”

We can’t appreciate the significance of the utter failure of this effort without some mention of the extreme methods used to overcome these obstacles.

The seed of manzanita is germinated by fire.  However, the exact relationship between fire and germination is not known.  Therefore, many complex experiments have been conducted on the few viable seeds produced by the Raven’s manzanita in a futile effort to determine the winning combination.  These experiments are described in detail in an article in Fremontia (1).  In short, various combinations of fire, heat, cold, smoke, liquid smoke, etc., were tried and failed to determine exactly what triggers germination of manzanita seeds.

We should remind our readers of the legal definition of “recovery” according to the Endangered Species Act.  According to the 5-year review for Raven’s manzanita, here are two of the criteria for recovery toward which there has been no progress in 33 years:

  • “At least five spontaneously reproducing variable populations are established in reserves…in San Francisco…”
  • “At least two sexually reproduced generations are established within the Presidio.”

Frankly, it is no longer credible to expect the recovery of Raven’s manzanita and this failure implies the same fate for Franciscan manzanita.

Can the public parks of San Francisco meet the horticultural requirements of Franciscan manzanita?

The public parks of the City of San Francisco cannot meet the horticultural requirements of the Franciscan manzanita because it requires fire to germinate its seeds. 

All of the critical habitats proposed by USFWS in San Francisco’s public parks are designated “natural areas.”  According to the DRAFT Environmental Impact Report of the “Significant Natural Resource Areas Management Plan,” prescribed burns are prohibited in the natural areas.  Therefore, unless there are unplanned wildfires in the six public parks proposed as critical habitat, it will not be physically possible to “spontaneously reproduce” this plant, as required by the Endangered Species Act. 

Granted, the City of San Francisco could revise its management plan for the natural areas to allow—or even require—prescribed burns in the six parks proposed as critical habitat.  In that case, the citizens of San Francisco would be subjected to air pollution and risk of causing an uncontrolled wildfire in surrounding residential communities.  The Natural Areas Program would be subject to even more criticism than it already endures.

The Natural Areas Program is extremely controversial in the City of San Francisco because it destroys healthy non-native trees, it sprays pesticides on non-native vegetation in public areas, it destroys the habitat of wildlife, and it limits the public’s recreational access to trails which are often fenced.  Subjecting the natural areas to prescribed burns is surely the bridge too far for the public which would jeopardize the future of the entire program.  Why would the City of San Francisco be willing to push the public over the edge by requiring prescribed burns in six urban parks in densely populated residential communities?

Furthermore, some of the proposed critical habitat is in heavily forested areas, which are not compatible with the requirement of manzanita for full sun.  As they were on behalf of Raven’s manzanita, these trees would be destroyed.  The City of San Francisco is already planning to destroy 18,500 trees over 15 feet tall to accommodate its desire to reintroduce native plants to forested areas. (3)  How many more trees would need to be destroyed to accommodate Franciscan manzanita?  How much more carbon dioxide would be released into the atmosphere by the destroyed trees?

Bayview Hill is one of the proposed critical habitats which are heavily forested.  According to SNRAMP (3), 17.16 acres of Bayview Hill is forested.  Given that Bayview Hill is the only proposed critical habitat which is outside the known historic range of Franciscan manzanita, the loss of 17 acres of trees does not seem a fair trade for a plant with few prospects for survival.

The proposed critical habitat in Glen Canyon Park (inaccurately called Diamond Heights by the proposal) is also forested in a portion of the 34 proposed acres of critical habitat.  This is a park in which the destruction of trees is being hotly contested.  The community in this park does not need the additional controversy of tree destruction for the sole purpose of planting an endangered species.

Proposed critical habitat in other city parks is likely to be controversial for other reasons, primarily because additional restrictions on recreational access will undoubtedly be required to protect this endangered plant.  Bernal Hill is an example of a city park with a huge community of visitors who will undoubtedly be enraged by further loss of recreational access.  They have already been squeezed by the restrictions imposed by the Natural Areas Program.

This proposal for critical habitat is not good public relations for the Endangered Species Act

The City of San Francisco is the second most densely populated city in the country.  It is comprised of only 29,888 acres.   There are only 3,317 acres of City-managed parks in the city. (2) The proposed critical habitat in City-managed parks is 196 acres, 6% of total City-managed park land in San Francisco.

Please ask yourself these questions:

  • Does it make sense for 6% of all City-managed park land to be permanently committed to planting an endangered plant which can be purchased in nurseries?
  • Does it make sense to confiscate 6% of all public parks for a plant the identity of which we are not certain?
  • Does it make sense to throw the public out of 6% of all public parks on behalf of a plant that will never be able to spontaneously reproduce unless there is an accidental wildfire?

We think the answers to these questions are no, no, and no.  This is an ill-advised proposal which makes a mockery of the Endangered Species Act.  This is an important law that is trivialized by a proposal that will be physically impossible to implement without endangering the public and damaging the environment. 

Comments on the proposed critical habitats will be accepted until November 5, 2012. Comments may be submitted online at the Federal eRulemaking Portal at http://www.regulations.gov (Docket Number FWS–R8–ES–2012–0067) or by U.S. mail to:

Public Comments Processing
Attn:  FWS–R8–ES–2012–0067
Division of Policy and Directives Management
U.S. Fish and Wildlife Service
4401 N. Fairfax Drive, MS 2042-PDM
Arlington, VA 22203.

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Bibliography

(1)      Gluesenkamp, Michael, et al., “Back from the Brink:  A Second Chance at Discovery and Conservation of the Franciscan Manzanita,” Fremontia, V37:4/38:1, 2009-2010

(2)      Harnik, Peter, Inside City Parks, Trust for Public Land, 2000

(3)      San Francisco Recreation and Park Department, “Significant Natural Research Area Management Plan (SNRAMP),” 2006

(4)      San Francisco Recreation and Park Department, “DRAFT Environmental Impact Report for SNRAMP,” 2011

(5)      USFWS, “Designation of Critical Habitat for Franciscan Manzanita,” September 5, 2012

(6)      USFWS, “5-Year Review of Endangered Status of Raven’s Manzanita,” June 2012

(7)      USFWS, “Recovery Plan for Coastal Plants of the Northern San Francisco Peninsula,” 2003

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Trees at Lake Chabot which East Bay Regional Park District plans to destroy.

Authenticity: A modern definition of wilderness

Conservation biology is being revised so rapidly that we are struggling to keep up with it.  In our previous post, we introduced our readers to Professor Scott Carroll’s proposal that a more realistic approach to conservation would accommodate non-native species because they are often better adapted to present conditions than their native predecessors.  He calls his approach Conciliation Biology.

Today, we are introducing our readers to another proposal to redefine wilderness to a new standard which acknowledges that the environment has been radically altered by man.  The author of this proposal is Nigel Dudley, a practicing British conservationist.  He calls his new standard “authenticity,” which he defines as follows:

“An authentic ecosystem is a resilient ecosystem with the level of biodiversity and range of ecological interactions that can be predicted as a result of the combination of historic, geographic and climatic conditions in a particular location.”*

Let’s focus for a moment on this portion of that definition:  “…historic, geographic and climatic conditions in a particular location.”  Mr. Dudley explains this particular parameter of his definition of authenticity:  “…some ecosystems have unusually high levels of diversity…through being isolated or undisturbed for exceptionally long periods.  Other ecosystems have already been hugely changed and in some cases impoverished…it will not always be possible either to recover lost elements or to remove additions.  What an ecosystem is likely to contain in the future needs to be based on current realities…”   

Clearly places like the Berkeley Meadow are not candidates for “authenticity.”  This particular native plant museum was the former garbage dump for the city of Berkeley, built on landfill.  This seems an extreme example of denial of current realities.

The Berkeley Meadow, a 72-acre fenced pen for native plants on the former city garbage dump

Choosing candidates for authenticity

Dudley’s point in proposing this new standard is to focus conservation efforts where they are most likely to be fruitful.  Our interest in this new standard is in the stark contrast it provides to the local projects which fail by every measure introduced by Mr. Dudley in his book about authenticity.

  • Natural species composition:  Virtually all predators and grazing animals are gone from the urbanized San Francisco Bay Area.  San Francisco’s Natural Areas Program claims to have designated only “remnants of native vegetation” as natural areas.  In fact, vegetation cover in the 1,105 acres of natural areas is on average only 46% native.  Some of the 31 natural areas are populated by as little as 11% native vegetation.
  • Migrant composition:  Some bird migrations are intact, but others have been changed by existing vegetation such as the tall, non-native trees of which there were few in the native landscape.  Migrations of ungulates are long gone.
  • Invasive species:  Non-native plants and trees outnumber native species throughout the Bay Area.
  • Chemical composition:  Air, water, and soil composition are vastly different than they were 200 years ago.
  • Functioning food web:  The food web has been radically altered by the loss of top predators and ungulates and cannot be recreated in a densely populated urban environment.  Bears may be welcome in the zoo, but are not wandering our streets looking for their next meal.
  • Functioning ecological processes:    Funneling most creeks into underground culverts is an example of a lost ecological process in the urban environment.
  • Regeneration process:  Fire is a regeneration process that is lost in the urban environment.  Prescribed burns are allowed by some managers of public land in the Bay Area, but San Francisco’s Natural Areas Program has reluctantly agreed not to conduct prescribed burns.
  • Resilience:  Although the original goal of San Francisco’s Natural Areas Program was that once “restored” the natural areas would be self-sustaining, fifteen years later, NAP concedes that on-going maintenance will be required to sustain the natural areas.  Dudley says, “Ideally, authentic ecosystems should also be self-sustaining:  they should not need constant and often expensive manipulation to maintain their values.”  Clearly, the “natural areas” in San Francisco’s parks do not meet this criterion for authenticity.
  • Area:  Most of the restoration projects in the Bay Area are too small to be sustainable.  The average size of San Francisco’s 31 natural areas is only 35 acres.  The smallest is only one-third of an acre.  Size is a proxy for the ability to isolate a restored site from repeated re-invasion.  The natural areas are small and are surrounded by non-native vegetation which will quickly return.
  • Connectivity:  Virtually every restoration project in urbanized Bay Area is physically isolated.

It may be possible to compensate for these bad odds of a sustainable, authentic restoration project in the urbanized San Francisco Bay Area.  If so, it will be extremely costly, which is undoubtedly why most projects have not been successful.  The National Park Service has had some success with its projects because they seem to have greater resources than other managers of public land.  But is this the top priority of taxpayers?  As the presidential election season heats up and the debate rages about raising taxes and cutting federal spending, one wonders why these projects are not in the budget-cutting cross-hairs.

Looking on the bright side

Grey squirrel. Creative Commons

We make every effort to end each story with a positive outlook.  In this case, we turn to Mr. Dudley to remind our readers that the environment is not necessarily destroyed by the mere existence of non-native species.  Being British, he uses British examples to make his point.  The North American grey squirrel is considered an invasive species in Britain and the native red squirrel is now rare.  While the British are not happy about the loss of their native squirrel, Mr. Dudley reminds them that the non-native grey squirrel is performing the same ecological functions as its native predecessor.  There is apparently no evidence that the environment has been harmed by this substitution.

We don’t like change.  But is change actually doing any harm?  If not, let’s accept it, because fighting against it is costly and probably futile.  That is the definition of wisdom:  that we accept what we cannot change.

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*Nigel Dudley, Authenticity in Nature. Earthscan, 2011

Conciliation Biology: Revising Conservation Biology

Our interest in invasion biology is primarily in its application, specifically to “restoration” projects.  Therefore, as science revises the assumptions of invasion biology we are equally interested in the implications for ecological restorations.

Professor Scott Carroll (UC Davis) is a particularly good candidate to lead the way in revising ecological restoration practices, as informed by current scientific theories of invasion biology.  His study of rapid evolution of the native soapberry bug to accommodate use of non-native vegetation puts him in the forefront of the effort to integrate evolutionary theory into invasion biology.

And so we introduce to our readers, Professor Carroll’s proposal that we turn from efforts to eradicate non-native species in favor of a new approach which manages the co-existence of native and non-native species.  He calls this approach Conciliation Biology.*

Conciliation Biology is based on these premises:

  • The environment has been radically altered by the activities of humans
  • The environment will continue to change in the future.
  • It is not feasible to eradicate non-native species.
  • The cost of attempting to do so is prohibitive.

These are familiar themes on Million Trees and we will not belabor them in this post.  Rather we will focus on those aspects of Professor Carroll’s proposal that are new to us.

Rapid evolution can resolve apparent ecological problems

Garlic mustard. GNU Free

Garlic mustard is an invasive non-native plant which tolerates shade and emits a powerful root toxin known to inhibit the germination of other plants, notably forest trees.  This chemical tool to reduce competition is known as allelopathy,  a weapon used by many plant species, both native and non-native.

Since garlic mustard arrived first in the eastern US and spread slowly west, scientists compared the allelopathic toxicity of a population of garlic mustard known to have arrived 50 or more years ago with a population which arrived only 10 years ago.  The toxicity of the recently arrived garlic mustard was significantly greater than that of the older population.  In fact, the understory and seedling germination were rebounding in the forest with the older population of garlic mustard.

In other words, science informs us that ecological problems caused by the arrival of new exotic species can resolve themselves over time.

New exotic species are sometimes better adapted to the changed environment

Professor Carroll cites a study of two aquatic species (Phragmite and Hydrilla) which provide superior ecological services than their native counterparts because of changes in the environment.  The extreme weather events associated with climate change are subjecting our coasts to unprecedented storm surges.  Native species of marsh grass are not as successful in protecting the coast against the ravages of these storm surges.

We have our own local example of the same phenomenon.  Non-native Spartina marsh grass is being eradicated along the entire west coast of the country.  It grows taller and thicker than native Spartina and it does not die back during the winter months as the native species does.  Since storm surges occur during the winter months, surely the non-native Spartina provides superior protection to our coast.  We have yet to see a scientific experiment which proves this point, but common sense tells us that it is a study that needs to be done, particularly since ornithologists have reported that the eradication of non-native Spartina has been harmful to our dwindling population of endangered California Clapper Rail.

The harmful effects of eradication efforts

Iberian lynx. Creative Commons

We have seen many such harmful consequences of eradication efforts, but Professor Carroll provides his own example.  Iberian rabbits are native to Spain.  They were intentionally imported to Australia where they quickly became a problem.  The Australians imported a virus from South America that killed the rabbits.  The virus was also introduced to Britain for the same purpose.  The virus has spread back to Spain where it is killing the rabbits in their native range.  The rabbits are prey of several rare species of animals in Spain, including the Iberian lynx.  The absence of their prey is now decimating those native predator populations as well.

Biological controls are one of many dangerous games being played by those who share in the fantasy that it is possible to eradicate non-native species without paying a price.  Sometimes that price is greater than whatever cost may be associated with the non-native species.

Simply eradicating non-native species will not necessarily result in the return of natives

Professor Carroll tells us the story of the failed attempt to save the Large Blue butterfly in Britain from extinction to illustrate this point.  This was apparently a spectacularly beautiful butterfly, and so the British spent 50 years trying to bring it back from extinction.  They failed because they figured out too late that the butterfly is dependent upon an ant which lives only in heavily grazed vegetation.  The ant population no longer existed within the range of the butterfly because grazing had long ago been abandoned.

How many other pointless efforts to reintroduce endangered species are there?  We recently told our readers about the effort to reintroduce the endangered Mission Blue butterfly to Twin Peaks in San Francisco.  This is a radically altered environment with high levels of nitrogen and carbon dioxide associated with the urban environment.  The annual brush fires of pre-settlement San Francisco are no longer capable of sustaining the scrub required by the butterfly and the prescribed burns, which are the artificial equivalent, are not allowed in San Francisco.  The scrub is therefore maintained with repeated applications of pesticides which are unlikely to benefit the endangered butterfly.

What is Conciliation Biology

Conservation biology has been “constrained by often futile efforts to restore historical communities, and [does] not appreciate the unavoidable and dynamic contributions of ongoing adaptive evolution.” * Conciliation biology proposes to address these shortcomings by:

  • Taking a longer-term view of the chronic effects of changes in the environment.
  • Making greater use of evolutionary theory
  • Fostering ongoing adaptation by accepting the hybridization that increases genetic variability
  • Identifying and supporting community mechanisms that increase resiliency
  • Improving the effectiveness of the science of invasion biology by using a multidisciplinary approach

How long will It take for this new approach to filter into the minds of those who are busily destroying non-native vegetation and damaging the environment in the process?  How much damage will be done before these destructive methods are abandoned in favor of an approach that accommodates the reality, inevitability, and often the advantages of change?

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*Carroll, Scott, “Conciliation biology:  the eco-evolutionary management of permanently invaded biotic systems,”  Evolutionary Applications, 2011, 184-199.

Invasion Biology: The way forward

We’re following up on our previous post in which we reported that empirical studies do not support the hypotheses of invasion biology.  In that case, six hypotheses of invasion biology were tested by empirical studies and largely failed.  Furthermore, more recent studies are less supportive than older studies, indicating declining support for the assumptions of invasion biology.

Now we are going to tell you about a new publication by another team of scientists who challenged other assumptions about invasive plants and also conducted their own original research of one of the most basic assumptions of invasion biology:  that invasions are facilitated by disturbance.

Wildfire, Bitterroot National Park, 2000. Wildfires are a type of disturbance that has increased with global warming and drought.

We introduced our readers to the leader of this research team, Professor Angela Moles, in a recent post about the mounting evidence that attempts to eradicate non-native species are futile.  Professor Moles (University of New South Wales, Australia ) gave a TED (Technology, Entertainment, Design) presentation in which she reported that introduced species have changed significantly since their introduction and that if they weren’t yet new species, they soon would be.  She proposed that non-native plants in Australia be granted citizenship.

Professor Moles collaborated with 21 scientists all over the world (Uganda, Indonesia, Mexico, USA, Australia, New Zealand, Japan, Argentina, Estonia, New Zealand) in the study that resulted in a recently published article entitled, “Invasions:  The trail behind, the path ahead, and a test of a disturbing idea.”  *

The trail of invasion biology

As the title suggests, the article begins by reporting that after 30 years and 10,000 publications, invasion biology has tested many assumptions and found inconsistent evidence to support them:

  • The search for traits of introduced plants that predict invasiveness has been a dead end:  “…it is not currently possible and will probably never be possible to predict which species are likely to become problem invaders on the basis of traits alone.  We therefore suggest that this is one area of invasion biology that merits less attention in the future.”
  • Invasion biology predicted that lack of genetic variability would hinder evolutionary adaptation in introduced species.  This assumption has not been supported by empirical studies:  “…rapid evolution has been repeatedly demonstrated in introduced populations, and the predicted reduction in genetic variance has not been observed.” 
  • Rapid evolution of introduced species has been well established by empirical studies:  “We have reached the point where additional case studies demonstrating rapid evolutionary change in introduced species are unlikely to have a major impact on our understanding of invasions.”  New research questions are needed.
  • There is little evidence to support the assumption that introduced plant species will cause extinction In native communities:  “…there are astonishingly few documented cases of native plants being driven to extinction by competition from introduced plants.  There is no evidence for any native species in the United States being driven to extinction even within a state, by competition from an introduced plant species.”

The way forward in invasion biology

Professor Moles and her team then tell us why invasion biology has not been able to prove the assumptions on which the theory is based.  The theory of invasion biology was based on untested assumptions that have been accepted as true although there is no empirical evidence to support them.  The goal for the future of invasion biology should be to identify these assumptions that have been accepted as dogma, test them, and abandon those that are not consistent with empirical facts. 

The authors of this study also, “…join a growing chorus, suggesting that our approach to invasion biology has been too simplistic.”  Studies have tended to focus on the features of introduced plants in isolation.  A more fruitful line of inquiry will consider the complex interactions between newly introduced species and their new environment:

“Rather than focusing on one factor at a time, we need to find ways (including multivariate analysis) to synthesize information about the recipient habitats/ communities, the characteristics of both resident species and the invaders, demographic processes, propagule pressure [measure of the number of species released into a region in which they are not native], the differences between current conditions and those with which the resident species evolved, evolutionary change to both native and introduced species, plasticity and feedbacks and interactions between different species and processes.”

You might say, “Phew! That sounds like a daunting task.”  And so it is, but this team of scientists takes it on with an elaborate and complex study of one of the most basic assumptions of invasion biology:  that disturbance facilitates plant invasions.

Does disturbance facilitate plant invasions?

“Disturbance is thought to facilitate invasion by simultaneously opening new ground for colonization, decreasing the competition from resident native species and releasing pulses of resources.”  The definition of “disturbance” has varied in different studies, but generally includes fire, grazing, agriculture, erosion, wind, and flood.  Empirical tests of this theory have produced mixed results.  Even when the results have been positive, they have not persisted over the long-term.

Because disturbance is a natural feature of all ecosystems, native species have adaptive features that enable them to respond to natural disturbances.  Therefore, the research team theorized that it is not disturbance per se which creates opportunity for invasions by introduced species, but rather changes in the disturbance regime.  Their research study was therefore designed to distinguish between the level of disturbance and changes in the level of disturbance.

Given the international composition of their research team, they were able to select 200 sites in eight countries.  They selected only those sites for which the natural patterns of disturbance were known.  Their research methods were statistically complex and a detailed description of them is beyond our comprehension and probably many of our readers, but we encourage those with the necessary scientific knowledge to read the article which is available on the internet.

Their analysis of these 200 sites led them to the conclusion that the change in disturbance regimes was far more predictive of the success of invasions than the level of disturbance but that both variables explained only 7% of the variation in the percent of cover or species richness contributed by introduced species.

In other words, one of the most basic assumptions of invasion biology did not pass an empirical test of its validity.  Invasions by introduced plants are largely unexplained by disturbance.

Post Katrina New Orleans. Floods are another type of disturbance that is likely to increase with climate change.

The future of invasion biology

Science is rapidly revising the assumptions of invasion biology.  We strongly believe that it is just a matter of time before science informs us that introduced species are here to stay and that this is not the terrible news we have been led to believe.  It is inevitable that this information will filter slowly from the scientific community to the community of native plant advocates.  We hope that they hear and accept this good news before our non-native trees are destroyed.

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*Moles, Angela, et. al., “Invasions:  The trail behind, the path ahead, and a test of a disturbing idea,” Journal of Ecology, British Ecological Society, 2012, 100, 116-`127.  All quotes are from this article

Support for hypotheses in invasion biology is uneven and declining

“Support for major hypotheses in invasion biology is uneven and declining” is the title of a paper recently published in NeoBiota* co-authored by seven scientists from all over the world (Germany, USA, Spain, Canada, Czech Republic).  The title captured our attention because it is consistent with our viewpoint.

The international team of scientists analyzed 371 empirical studies which tested six major hypotheses in invasion biology.  They found that empirical evidence for these hypotheses is uneven and declining.  The hypotheses that were tested by the studies were:

  • Invasional meltdown:  the presence of invasive species facilitates invasion and survival of additional new species.
  • Novel weapons:   invasive species with traits new to an exotic habitat have a competitive advantage over native species.
  • Enemy release:  introduced species have a competitive advantage in the exotic range because they are released from their enemies in the new environment.
  • Biotic resistance:  More biologically diverse ecosystems are more resistant to invasion.
  • Tens rule:  10% of newly introduced species escape to the wild; 10% of those naturalize in the wild; 10% of those become invasive.
  • Island susceptibility:  Invasive species are more likely to become established and have major ecological impacts on islands than on continents.

The scientists counted the number of studies that support, question/oppose, or are undecided/inconclusive about each hypothesis.  They also compared the number of supporting studies when the hypothesis was new with the number of supporting studies published recently to determine the decline in support for the hypothesis.  Here’s what they found:

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

30

77%

41%
Novel weapons

23

74%

25%
Enemy release

106

54%

10%
Biotic resistance

129

29%

5%
Tens rule

74

28%

10%
Island Susceptibility

9

11%

25%

Although support is strongest for the invasional meltdown hypothesis, recent studies are less supportive than early studies, indicating substantial decline in support.  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.

Declining support for scientific hypotheses has been observed in many disciplines, particularly medicine, ecology, and psychology.  The scientists who study this phenomenon theorize that the decline is attributable to some combination of these factors:

  • Over time the amount of available long-term data increases.
  • The best examples which are the strongest cases for the hypothesis are most likely to be studied first.
  • Publication bias favors new hypotheses and those for which the results are conclusive.

The NeoBiota paper also observes that the empirical evidence supporting each hypothesis varies by taxonomic group (plants, invertebrates, vertebrates) and habitat type (terrestrial, freshwater, marine).  For example:

  • The novel weapons hypothesis has been tested only for plants in terrestrial habitats.
  • Support for the invasional meltdown hypothesis is even across taxa and habitats.
  • Support for biotic resistance is strongest in marine habitats.

Where is invasion biology headed?

The authors of the NeoBiota paper are not suggesting that invasion biology be abandoned.  Rather their goal is to redirect scientists in the field to more productive efforts, such as:

  • Where a hypothesis cannot be generalized to all taxa and habitats specify exactly where it is applicable.
  • Rather than focusing on newly introduced species, focus on the interaction of a those species with their new environment. 
  • Discard those hypotheses that don’t work.

Based on our fifteen years of experience studying the native plant movement and its theoretical underpinnings in invasion biology we wholeheartedly support the advice of the authors to focus scientific efforts on the interaction of new species with their new environment.  We strongly believe that the success of newly introduced species is based largely on changes in the environment into which they are introduced.  In other words, invasions are more a result of changes in the environment than on the characteristics of the introduced species.

We also endorse the advice that scientists be more specific about the applicability of the assumptions of invasion biology.  We have seen the damage done by sweeping generalizations about how ecosystems operate in the hands of hobbyists.  Nature is complex and we do not necessarily understand all the factors operating in a given environment.  We hope that scientists will lead the way to the public’s more nuanced understanding of ecosystems. 

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*Jeschke, Jonathan, et. al., “Support for major hypotheses in invasion biology is uneven and declining,” NeoBiota, 14: 1-20 (2012)

More vandalism in our public parks

We recently reported the history of vandalism by native plant advocates in public parks in San Francisco such as cutting down trees as well as killing trees by girdling them.  We were prompted to recount this history by a recent study reporting the probable intentional and unauthorized introduction of Australian insect pests of eucalyptus. 

Now we must report a more recent incident in San Francisco’s parks.  A park visitor observed and photographed a “volunteer” spraying herbicide on non-native plants early in the morning (6:30 am).  The herbicide that he was spraying is not included in the city’s list of approved pesticides.  We are reprinting with permission the story of this incident published recently by the San Francisco Forest Alliance (with 3 edits in brackets).

Native plant advocates are treating San Francisco’s parks like their personal property, destroying plants they don’t like and endangering the public with pesticides that are not approved for use in the city.

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Some time back, we’d posted an article about the puzzling brown spot in Glen Canyon Park, around a rock near a trail. It looked like herbicide use, but regular visitors to the park hadn’t seen the signs SF Rec and Park must post before spraying herbicides. Also, as the picture below shows, it was close to a trail. Both the Natural Areas Program and the Department of the Environment had said there would be no spraying for 15 feet on either side of a trail. We asked them what was going on, and got no answer.

Now we know.

A “volunteer” was spotted spraying the area early one morning.We’d heard anecdotal reports, but this time, an actual incident was reported to us with evidence of unsupervised use of unapproved products without warning notices, and without public records, in a place where pesticides are not supposed to be sprayed.

Rock formation in Glen Canyon Park

These pictures show the pesticide being used in precisely the area we were concerned about.

So in addition to the recorded herbicide use by the Natural Areas Program, there’s unrecorded and unquantified toxins being used in Glen Canyon by sympathizers.

The herbicide in use – at least on this occasion, as far as we could gauge [by reading the label on the pesticide being sprayed by the person who was seen spraying] – was Roundup Ready-to-Use Plus. The product is described on sale websites as not “pet and livestock-friendly.”

It is not on the Department of the Environment’s approved list of pesticides for use on city-owned properties.

WHAT IS ROUNDUP READY-TO-USE PLUS?

[ETA: This is an actual photograph of the person seen spraying herbicide in Glen Park.]
This product contains Glyphosate (the main ingredient in all types of Roundup products, which we’ve described in an earlier article). It also contains Pelargonic Acid, which the University of Florida IFAS extension described as “like diquat.”

About pelargonic acid, the Material Safety Data Sheet (linked here as a PDF) says “Potential for mobility in soil is very high.” This means it doesn’t stay where it’s sprayed. It moves around.It also says it is slightly toxic to marine organisms – fish and amphibians.

Besides glyphosate and pelargonic acid, Roundup Ready-to-Use Plus contains “other ingredients” that the manufacturer, Monsanto, does not (and is not required to) reveal.

HOW MUCH TOXIN IN GLEN CANYON?

This makes it clear that no one actually knows how much (or what) pesticides are being sprayed in Glen Canyon.

The Natural Areas Program (NAP) sprayed this park at least 6 times in 2011. Clearly, sympathizers are also spraying it with unapproved products not safe for pets and wildlife, without posting warning notices, and without keeping any public records. It’s likely that they are spraying even more frequently than the NAP [judging by the many dead spots scattered around the park for which no signs were posted] – which is apparently turning a blind eye to the problem.

The NAP is based on community “stewardship.” Evidently, this has encouraged its “volunteers” to take matters into their own hands and work unsupervised in ways that threaten our environment.

Hybridization is an adaptive strategy for species survival

Large ground finch. Linda Hall Library

We introduced Darwin’s finches to our readers in our previous post.  We told you about the research of Rosemary and Peter Grant on the Galápagos Islands that documented the rapid adaptation of the finches to radical changes in their food sources resulting from extreme weather events.  In this post we will continue the story by telling you about another of the amazing discoveries of the scientists studying the finches over a period of nearly 30 years.

Natural selection resulted in the survival of finches with body sizes and shapes that were best suited to the availability and type of food.  Sexual selection enhanced those physical characteristics during periods in which females had more choice because they were greatly outnumbered by males.  In addition to these adaptations, the birds increased their cross-breeding with other species and the resulting hybrids actually had a survival and breeding advantage over their species “pure” parents.*

In the first five years of the research study, there was little evidence of different finch species interbreeding, known as hybridizing.  On those rare occasions when species interbred, the resulting generation was not as successful as their parents, with respect to finding a mate and raising another generation.

Such lack of success of hybrids is considered the norm in nature.  In fact, many hybrids are sterile, incapable of reproducing.  Think of the sure-footed but sterile mule—the offspring of a horse and a donkey—as the classic example of a hybrid.

After the severe drought of 1977 and the flood of 1983, the Grants began to notice an increasing number of cross-breeding birds.  It seemed that the resulting hybrids were having more breeding success than the pre-drought hybrids and the data confirmed their observation.

This counter-intuitive conclusion required some careful consideration and the conclusion is a valuable lesson in our rapidly changing environment.  The environment on the islands was radically transformed by the severe drought and subsequent flood.  The cactus was overwhelmed by a vine that smothered it.  The plants with big, hard seeds were attacked by a fungus that decimated the population.  The small seeded plants thrived and became the dominant food source.

The rapidly changing environment was causing more rapid evolution and the genetic variability of hybrids was giving them an advantage.  If the environment is changing rapidly in unpredictable ways, the birds could increase the odds of finding a winning strategy by increasing the variability of their genes, sometimes resulting in novel traits.

We cannot and should not, however, anthropomorphize the birds by imputing motives to the selection of a mate of another species.  The starving cactus finch probably observes that a male of another species—a seed-eating ground finch, for example—appears to be more fit than a male of her own species.  She is not thinking of the odds of increasing genetic variability.  Natural selection operates without the conscious effort of species.

The implications of hybridization

We are experiencing a period of rapid change because of the anthropogenic (caused by humans) impacts on the environment, most notably climate change, but surely many other impacts which we don’t necessarily understand.  These would seem the ideal conditions for the hybridization of species which speeds up evolution by increasing genetic variability. 

Unfortunately, one of many strategies of the native plant movement and nativism in the animal kingdom is to prevent hybridization because it is perceived as a threat to native plants and animals.  We have reported to our readers some examples of such attempts to prevent hybridization and there are many more in the literature:

The variety of California poppy being eradicated from the Presidio in San Francisco.

Are efforts to prevent hybridization depriving plant and animal species of opportunities to adapt to the rapidly changing environment?  We don’t know the answer to that question, but we find it a provocative line of inquiry.

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*This information is drawn from:   Jonathan Weiner, The Beak of the Finch, Vintage Books, 1994

Darwin’s Finches: An opportunity to observe evolution in action

The finches on the Galápagos Islands are called Darwin’s finches because of the important role they played in the development of his theory of natural selection and evolution of species.

Galapagos Islands, satellite photo. Daphne Major is too small to be visible.

Charles Darwin spent five weeks on the Galápagos Islands in 1835, near the end of a five year expedition.  Although he noticed the similarity of the birds on the different islands, he didn’t realize they were all related to one common ancestor until he returned home.  Fortunately, he collected many specimens of the birds to bring home for study.  It wasn’t until those specimens were examined by an ornithologist that he learned they were 13 species of finches, distinguished primarily by variations in the size of the bird and its beak size and shape.

Unfortunately, he hadn’t recorded which islands the specimens were from, so the implications of their differences were somewhat of a mystery.  He lamented in Voyage of the Beagle, “It is the fate of every voyager, when he has just discovered what object in any place is most particularly worthy of his attention, to be hurried from it.”

But Darwin was no dummy, so despite lacking the data necessary to prove his point, he speculated in his memoir, “…in the thirteen species of ground-finches, a nearly perfect gradation may be traced from a beak extraordinarily thick, to one so fine, that it may be compared to that of a warbler.  I very much suspect that certain members of the series are confined to different islands…”

Such development of new species from a common ancestor in response to varying environmental conditions is called adaptive radiation.  Species also diverge from one another to reduce competition by specializing in a particular food forage type or technique.  Nearly 200 years later, science has proven Darwin’s hunch, but just as he had no way of knowing how long this process of speciation took, modern science still cannot answer that question.

Darwin’s finches continue to change in response to changing conditions

Large ground finch (Geospiza magnirostris). Linda Hall Library

Rosemary and Peter Grant have studied the finches on two Galápagos Islands (Daphne Major & Genovesa) for about thirty years.  Nearly every year they visited the finches, weighing and measuring every appendage of the birds, especially their beaks.  They banded the birds so they could follow their breeding success. They also measured their food:  how much food but more importantly how accessible the food is to the birds such as the difficulty of opening seeds.

The availability and type of food is what determines the shape and size of the birds’ beaks.  In a year in which there is plenty of rain, there is usually plenty of food which is relatively easy for the birds to eat.  When it doesn’t rain, the birds are reduced to the difficult task of trying to crack open a large, hard seed pod.  That’s when a big bird with a big beak has an advantage.   

Extreme weather is therefore a “selection event,” a time when not every bird is equipped to survive.  And the birds that survive are best equipped for those extreme conditions.  When the conditions improve, the bird that survived the hard time is not necessarily best equipped for the good times.

These are the principles of natural selection, but they were largely theoretical until the Grants spent many years watching the birds and how they survived such selection events.  They had the good fortune to witness two such events in the first twelve years of their study.

The drought

In the fifth year of the Grants’ study, 1977, there was a severe drought.  After one short storm in early January, there was no more rain for the remainder of the year.  In January, there were 1,300 finches on the island they studied that year.  At the end of the year, there were less than 300 finches left on the island.

The Grants measured and weighed the birds that survived the drought.  Then they returned to their lab at Princeton University to study their data:

  • Not a single finch was born and survived on the island in 1977
  • The surviving birds were 5-6% larger than the dead birds
  • The average beak size of the birds that survived was 11.07 mm long and 9.96 mm deep.  The average beak size of the birds that did not survive was 10.68 mm long and 9.42 mm deep.  These critical differences were too small to see with the naked eye, but became evident when the measurements were analyzed by computer.  This makes a strong case for scientific measurement verses anecdotal observation, which passes for “evidence” amongst native plant advocates.
  • Few female birds survived the drought, presumably because male birds are larger than females.

In the years following that drought, sexual selection played an important role in maintaining the population of larger birds with larger beaks.  Because the female birds were scarce, they could be very selective in their mates.  Who did they choose?  Of course, they chose the males with the traits that allowed the birds to survive the drought year.  When the ratio of males to females is more even, sexual selection plays a less important role in natural selection in monogamous species such as the finches.

The flood

Here on the West Coast, we are familiar with the weather phenomenon of El Niño, the nickname given to a heavy rain year resulting from an unusually warm ocean current.  In 1983, we experienced the strongest El Niño on record, as did the Galápagos Islands. 

In 1983, the Grants witnessed the reversal of the results of the 1977 drought:  “Natural selection had swung around against the birds from the other side.  Big birds with big beaks were dying.  Small birds with small beaks were flourishing.  Selection has flipped.” *

Lessons learned

Darwin’s finches give us reason for optimism about the future.  Nature can and will respond to changes in the environment.  Natural selection is not just an historical process that stopped when The Origin of Species was written nearly 200 years ago.  Natural selection is operating at all times, whether we notice it or not. 

However, the loss of nearly 80% of the birds on a Galápagos Island during a severe drought is not cause for celebration.  Although the species survived, hundreds of individual birds did not.  So, we are quick to add that our confidence in the adaptive abilities of nature is not an argument for abusing the environment.

Climate change has caused extreme weather events which are undoubtedly selection events for many species of plants and animals.  Unless we take action to reduce greenhouse gas emissions we can predict more of such events.  Destroying millions of trees solely because they are not native is irresponsible given the contribution their destruction makes to the greenhouse gases causing climate change.

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*Jonathan Weiner, The Beak of the Finch, Vintage Books, 1994

Integrating new species into the food web

Zebra mussels, open underwater with siphons out. Creative Commons

We have been reading panic-stricken news reports about zebra mussels for over 10 years, but we weren’t paying much attention until a recent news report that they have arrived in California.  We decided it was time to educate ourselves about this “invasive species.”

Zebra mussels and their close relative, the quagga mussel, arrived in the Great Lakes Region of the United States in 1988, probably in the ballast water of big ships.  Although they are native to southern Russia and Ukraine, they are now found throughout Europe and England.

The negative side of the ledger

What the mussels lack in size, they make up for in numbers.  Though they are tiny—about the size of a dime–they are prolific breeders capable of creating big colonies rapidly.  They are a fresh-water mussel which means they exist where there are often water treatment facilities that supply our drinking water.  Their larvae are microscopic so they can enter water treatment facilities through the intake pipes and clog the system. 

They filter huge quantities of water, consuming plankton (microscopic plants and organisms) depriving other animals of nutrition.  This filtering of the water also increases water clarity and light penetration, changing the entire ecosystem in complex and unpredictable ways.

The positive side of the ledger

Where the mussels have gained a foothold, they have quickly entered the food web.  A monitoring program was started soon after mussels were found at Long Point Bay in Lake Erie.  The first sampling done in 1991 found mussels in 27% of the sampling stations, an estimated 1,189 tons of mussels.  By 1992, mussels were found in 80% of the sites, an estimated 4,536 tons of mussels.  (1)

In 1992, the monitoring program also started conducting stomach analysis of ducks killed at Long Point Bay.  Three species of duck (Greater and Lesser Scaup and Bufflehead) were found to be feeding heavily on the mussels.  Between 1993 and 1995 the population of mussels declined significantly from the highpoint of 4,536 tons to only 758 tons in 1995.  The population of the duck predators increased correspondingly during the same period of time. (1)

The authors of this study speculate that the mussels were also depleting their food source at the peak of their population and that they had exhausted available attachment sites, but the scientists believe duck predation was the primary reason for the declining population of mussels.  As always, there are many variables operating simultaneously in the ecosystem, and it isn’t possible to isolate one from the others.  (2)

Ducks aren’t the only predators of the mussels.  Crayfish are apparently capable of consuming large quantities of the mussels.  And some fish eat the mussels.  One study found that yellow perch didn’t eat the mussels in 1994, but a later study in 2004 reported that the perch were eating the mussels.  Plankton waste from the mussels settles on the lake bottom and the bottom feeders benefit from that fall out.

There is a downside to this story, however.  Remember that the mussels filter the water as they eat.  In addition to filtering plankton, they also filter pollutants and contaminants.  Researchers assume that the predators of the mussels are consuming those pollutants which then become a part of the food chain.  The mussel-consuming ducks at Long Point Bay apparently had elevated levels of contaminants in their tissue compared to ducks that consume only aquatic plants. (2)

What should we do?

According to the news story about the mussels in a local paper, the California legislature is considering increasing the registration fee for boats which would raise about $5 to $8 million dollars.  Although the news story isn’t clear about how this money would be used, let’s assume for the sake of argument that it would be used to prevent the spread of these mussels beyond the 25 lakes in California where they are now found.  That would apparently involve more inspection of boats being put into the water where the mussels don’t presently exist.  If that’s the plan, we enthusiastically endorse it.  Prevention is the best medicine, as they say.

But once the mussels have arrived, all scientists agree that eradicating them is not a realistic option.  Therefore, dousing them with chemicals—which is one of the recommended treatments—will undoubtedly do more harm than good. 

New species quickly become a part of the landscape.  Our initial reaction to them tends to be negative because we are suspicious of change.  In fact, there may be benefits that aren’t immediately evident and even if there isn’t an immediate benefit, they are often integrated into the environment over time.  Their populations often stabilize once they have exhausted available resources.  We should be patient because nature is resilient and our time frame is much shorter than nature’s time frame.    

Are we learning this lesson?

Broom, Redwood Park, Oakland, California

The California Invasive Plant Council (Cal-IPC) is dedicated to the eradication of non-native plants.  Scotch broom is one of their favorite targets for eradication.  Little progress has been made in this effort (see “Broom:  ‘I’ll be back’” and “Broom:  ‘I’m ba-ack’”) and recently Cal-IPC acknowledged this in their newsletter.  However, they urged their supporters not to lose heart because they reported that broom is now being browsed by herbivores.  So, what native plant advocates could not accomplish with manual labor and chemical warfare, the animals may accomplish by incorporating broom into their diets.  One hopes the animals aren’t eating broom doused with herbicides.

Cal-IPC also acknowledges in this article that broom does not grow in shade:  “Broom cannot tolerate heavy shade.  It usually established following logging or other activities that remove tree canopy.”  Could it be that they have finally noticed that the result of clear-cutting non-native trees in the East Bay hills is more broom, not more native plants?  We can only hope so.

There are pros and cons to every decision we make.  We don’t always know in advance what they are.  So, it pays to be cautious.  If we are patient, maybe nature will sort it out without our interference.  Particularly when our interference damages nature, we should exercise restraint.  We should give nature more credit for healing itself.  It has a much better track record than we do.

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(1)    Cox, George W., Alien Species and Evolution, Island Press, 2004

(2)    Petrie, Scott A., Knapton, Richard H., “Rapid Increase and Subsequent Decline of Zebra and Quagga Mussels in Long Point Bay, Lake Erie:  Possible Influence of Waterfowl Predation,” J. Great Lakes Research, 25(4) 772-782