Category: Ecology

Nativism: The Hawaiian case

The case for native plant and animal restorations is strongest on islands.  They contain the most endemic species, unique to those places.  More extinction has occurred on islands than on the mainland of the United States because species that evolved in isolation are more vulnerable to new competition than species that have evolved with more competition.  Theoretically, if man were able to eradicate non-native species of plants and animals, it would be easier to prevent re-invasions on an island.  Consequently the Hawaiian Islands are a hot-bed of nativism.

The efforts to eradicate many species of plants and animals in the Hawaiian Islands are just as controversial there as they are here in the Bay Area.   Here is a sampling of the legal, environmental, and ethical questions raised by these eradication projects:

  • Coqui frog

    The coqui is a tiny frog that was inadvertently introduced to Hawaii from Puerto Rico in the 1980s.  There are no native frogs in Hawaii, so efforts to eradicate the coqui aren’t predicated on the usual claim that it will out-compete its native counterpart.  In this case, those who launched this campaign claimed that the frog will eat all the insects on the islands, depriving other animals of this food source.  The proposal was to spray highly concentrated caffeine in the forests occupied by the frog.  No tests were conducted to determine what effect this would have on any of the plants or other animals that would be sprayed in the process.

    Strawberry guava, USDS
  • The strawberry guava was introduced to Hawaii as a fruit tree, just as virtually every fruit tree in America was.  The proposal was to eradicate the strawberry guava with biocontrol, which means an insect was introduced that would theoretically feed solely on the strawberry guava.  The theory of biocontrol is more appealing than the reality, which in practice has often introduced new predators that are more difficult to control than the original target.  This eradication effort was also controversial because the strawberry guava is a valuable source of food for all animals in Hawaii, including humans.
  •  Mangroves are coastal forests that are considered valuable nurseries for marine life.  In Hawaii some have been eradicated with herbicides.  The skeletal remains of the mangrove are left to rot in the water, creating an eyesore and a graveyard for the animals that lived there.

                                                Animals are caught in the middle

The endangered monk seal has been caught in the middle of the nativist debate in Hawaii.  Because it is endangered, government biologists are obligated by law to try to prevent its extinction.  The monk seal has therefore been introduced to places in the Hawaiian Islands in which it hasn’t previously lived, based on the belief that it will have less competition in these areas.  This introduction of the monk seal into new territory has made it vulnerable to two diametrically opposite sides of this debate.  The monk seals are being bludgeoned to death by someone who doesn’t want them there.  Is it a fisherman who believes the legal protections provided for the endangered seal will threaten his fishing rights?  Or is it one of the nativists who are saying that the seals “don’t belong here?”

Monk Seal, Hawaii Wikimedia Commons

Dr. Sydney Singer is a medical anthropologist who lives in Hawaii.  He is in the forefront of the opposition to the eradication of non-native plants and animals, particularly the toxic methods used by the projects.  He has written a tongue-in-cheek quiz for Hawaiians to get at the bottom of that vexing question about what “belongs” in Hawaii.  With Dr. Singer’s permission, we share this quiz with our readers:

What belongs in Hawaii?

“A NOAA[National Oceanic and Atmospheric Administration]report released last year showed 35 percent of those surveyed at beaches and popular fishing areas on Kauai and Molokai believed the [monk] seals aren’t native to the islands.”

This raises a critical question for our legislators to consider as invasive species eradicators come to the public trough for more money to kill plants and animals that “don’t belong in Hawaii”.

How can we tell what does and doesn’t “belong” in Hawaii? Here is a quiz.

 From the following list, pick the item that best matches your personal prejudice:

  • Any plants or animals that were brought to Hawaii by human beings, including by the Hawaiians, don’t belong here.
  • Any plant or animal brought by the Hawaiians is okay, but those brought by any other culture are bad and don’t belong here. However, alien biocontrol agents, such as insects and fungi which attack plants and animals that don’t belong here, do belong here.
  • Any plants or animals that are useful, beautiful, or in some other way make our lives better belong here, but those that are noxious or poisonous don’t belong here.
  • How do I know?  I’m from New Jersey. I’m just glad to be alive and be living here.

This question is especially important for the invasive species committees and their army of eradicators poisoning, trapping, shooting and infesting our islands to kill species that they have decided “don’t belong.” And now, following their lead, members of the public are killing endangered Monk seals.”

                                                                  The elusive “baseline”

What is Dr. Singer trying to tell us with these rhetorical questions?  He is reminding us that every living creature in the Hawaiian Islands came from somewhere.  When the islands emerged from the sea as volcanoes they were completely barren.  They were slowly populated over millennia by plants and animals brought by the wind, by the sea, by birds and animals.  Humans arrived on the islands over 1,000 years ago when Polynesians came by boat from neighboring islands.  And Captain Cook and his crew were the first Europeans to arrive in the islands in 1778.  Each of these “invasions” brought new creatures.  Many of those creatures are now extinct. The historical food web cannot be recreated because some pieces are missing and some pieces are unknown. So, how can we arrive at a “baseline” which we now attempt to replicate?  It’s a conundrum that illustrates the fundamental absurdity of the entire concept of restoring historical ecology.

Prejudice destroys more eucalypts

We don’t usually talk about tree destruction projects on private land.  We focus on public lands because, as taxpayers we’re paying for those projects and we consider ourselves the owners of public land.  We also respect private property rights.  We’ll make an exception to that general rule today to tell you about the eradication of eucalypts at the Mountain View Cemetery in Oakland, California.

We learned about this project from one of the cemetery’s periodic mailings to its neighbors.  They informed their neighbors that they planned to plant more trees because they observed that fewer shrubs grew under the canopy of trees.  They also said they “prefer to plant using what grows well in the Bay Area climate with minimal water and intervention.”  Finally, they concluded in what seemed a non sequitur, “We intend to remove unwanted eucalyptus trees that border the cemetery.  Although they provide a useful neighborhood screen and help to architecturally define our outdoor landscape, eucalyptus is a damaging pest to the cemetery.”

Eucalyptus, Mountain View Cemetery

Having received this warning, we weren’t surprised when the eucalypts began to disappear from the cemetery.  The lone specimens in prominent areas in the cemetery seem to us a terrible loss.

Few trees grow more successfully than eucalypts in the San Francisco Bay Area.  They require no supplemental water.  They live for several hundred years in Australia and have grown here for over one-hundred years.  They are not invasive.  We don’t think they deserve to be called a “pest.” 

Gone, but not forgotten

The Mountain View Cemetery was planned by Frederick Law Olmstead in 1863 and building began shortly thereafter.  Although there are native Coast Live Oaks and Redwoods, according to an arborist docent they were all planted after the cemetery was built.  This is as we would expect because, “Vegetation before urbanization in Oakland was dominated by grass, shrub, and marshlands that occupied approximately 98% of the area.  Trees in riparian woodlands covered approximately 1.1% of Oakland’s preurbanized lands…”* 

The vast majority of trees in the cemetery are not native.  The original tree-lined avenue through the center of the cemetery was planted with Magnolias by Olmstead.  There are many stunning specimens of non-native trees:  Dawn Redwood, Copper Beech, Ginkos, etc. 

Ginko in the fall, Mountain View Cemetery

Eucalyptus is not our favorite tree.  We would probably choose to plant many other species before we would consider planting eucalyptus.  However, the decision to plant a tree is very different from the decision to destroy a tree.  We see no justification for destroying mature, healthy trees sequestering thousands of tons of carbon.  The prejudice against eucalyptus remains a mystery to us.

Edited to add:  The Oakland Tribune reported on March 4, 2012 that many neighbors of the Mountain View Cemetery object to the destruction of the eucalyptus trees.  The Tribune reported that the neighbors are concerned about the loss of habitat for birds.   The cemetery claims  they are destroying the eucalyptus because they are flammable.  As we have said many times on Million Trees, this is one of many fabricated fictions used by native plant advocates to justify the eradication of non-native plants and trees.    

*Nowak, David, “Historical vegetation change in Oakland and its implication for urban forest management,” Journal of Arboriculture, 19(5): September 1993

Bowling Alone with the Sierra Club

In 2000 Robert Putnam’s (Harvard University) masterpiece of American social science, Bowling Alone* was published.  He reported the significant decline of all forms of civic participation in American society and politics from the P.T.A. to voting.  Religious participation is the notable exception to this trend. 

We are deeply concerned about the increasing isolation of Americans from one another and we believe that the polarization of viewpoints, particularly in politics, is one of the consequences of this trend.  Only the highly motivated extremes of opinion are still engaged in the civic dialogue.  The middle ground is no longer represented in the debate.  However, we will focus on the topic that is relevant to Million Trees, that is, the implications for the environmental movement. 

Bowling Alone. Attribution: Xiaphias

Membership in environmental organizations reached its peak in 1995, according to Bowling Alone after decades of enormous growth since the 1960s.  This peak was consistent with public opinion regarding environmentalism.  In 1990 three-quarters of Americans considered themselves “environmentalists.”  By the end of the decade, that percentage had dropped to only 50%. 

The growth in membership was achieved by the use of a new marketing tool known as direct mail.  Think about it.  How many invitations do you receive in the mail from non-profit organizations, asking you to contribute to a wide-range of worthy causes?   Typically these organizations spend between 20-30% of their budgets on such fund raising and the rate of return on these solicitations is only 1-3% of the cost depending upon the quality of the mailing list.  Using this technique, Greenpeace tripled its membership between 1985 and 1990 to 2.35 million.

What does “membership” mean?

After tripling its membership, Greenpeace lost 85% of its members in the next 8 years.  The drop-out rate after the first year is typically 30% in these organizations.  

In fact, most contributors to these organizations don’t even consider themselves “members” in the usual sense of that word.  The commitment to the organization doesn’t extend far beyond writing a check.  Only 8% of contributors to the Environmental Defense Fund, for example, described themselves as “active” in the organization. 

These organizations are therefore distinctly different from their historical antecedents.  Participants in the civil rights movement frequently put their lives on the line.  The social lives of Rotary Club members revolved around the Rotary lodge. 

Since few people are active participants in environmental organizations, they have become “bureaucratized,” meaning they are run by and for paid professionals.  Most members have little idea what policies the professional staff has adopted on their behalf. 

The Sierra Club

In 1989, a survey of Sierra Club members determined that only 13% of its members had attended even one meeting of the Sierra Club.  The Bay Area Chapter of the Sierra Club claims to have 10,000 members, but chapter leadership of a group (the chapter is broken into many geographical groups, such as the San Francisco Group)was elected by as few as 59 votes.  The top vote-getter in the Club’s most recent election received 327 votes in a Chapter-wide race, but only one chapter group (Northern Alameda County) had more candidates than there were available seats.  In other words, there was no competition for most of the leadership seats. 

Yet, the incumbents in these leadership positions are free to determine the local policies of the Sierra Club.  Here are a few recent examples of positions taken by the Bay Area Chapter of the Sierra Club:

The opinion of the membership is not asked when these policy positions are taken by the leadership.  However, if members read the chapter’s quarterly newsletter (The Yodeler) they have the opportunity to learn about them after the fact.

The influence of the Sierra Club

We believe that the influence of the Sierra Club exceeds the size of its membership.  The Sierra Club endorses candidates for political office.  These endorsements are highly sought after because politicians believe that the endorsement confers the votes of its membership.  This belief was recently tested in the race for mayor of San Francisco. 

State Senator Leland Yee sought and received the endorsement of the Sierra Club in his bid for mayor of San Francisco.  In the past, he had been critical of the Natural Areas Program.  His stated reason for that criticism was that the veneration of native plants was offensive to his roots as an immigrant.  In particular, the Chinese community suffered horrendous discrimination in California in the 19th Century.  The rhetoric of the native plant movement is reminiscent of the xenophobia from which the Chinese community has suffered historically. 

It seems unlikely that Senator Yee’s emotional reaction to nativism changed when he sought the endorsement of the Sierra Club, but he had to disavow that opinion in order to receive the Club’s endorsement.  He did so because he believed that the votes of Sierra Club members would help him to be elected mayor of San Francisco.  His bet did not pay off.  He did not win.  In fact, he came in fourth. 

We hope that political candidates in the future will heed this warning.  The Sierra Club may have many “members” but that membership does not necessarily confer votes.  The vast majority of “members” have no commitment to the policy positions taken by the Club.

An appeal to Sierra Club members

There were over 4,000 public comments on the Environmental Impact Study for the Dog Management Plan of the Golden Gate National Recreation Area (GGNRA).  The Dog Management Plan proposes to eliminate about 80% of existing off-leash areas, which are now only 1% of the 74,000 acres of GGNRA property.  The Sierra Club supports that plan.  There were thousands of comments from people with dogs who are presently enjoying the small areas now available to them for off-leash recreation.  Sixty-four of those people said they are Sierra Club members.  That’s enough members to elect someone to a leadership position in the Club.

If you are a member of the Sierra Club, here’s what you can do to influence the Club’s policies:

  • Inform yourself of the policies of the Sierra Club. 
  • If you don’t agree with those policies, we urge you to vote in the election of officers to the leadership positions in the Sierra Club.
  •  If you don’t know the policies of the candidates, ask them. 
  •  If there are no candidates that represent your viewpoint, find candidates who do.
  • If you can’t find a candidate you can support, it’s time to vote with your feet.
  • If you leave the Club tell them why. 

Quit Bowling Alone!

Attribution: GNU Free Documentation

*Putnam, Robert, Bowling Alone:  The Collapse and Revival of American Community, Simon & Schuster, New York, 2000.  All quotes in this post are from Bowling Alone unless otherwise noted.

Pangaea: The first but not the last globalization of ecology

The continents have been sliding about on the Earth since it was “created”(1) approximately 4.5 billion years ago.  Although geologists tell us that the continents came together and broke apart several times prior to the formation of the supercontinent geologists call Pangaea, this is the geologic period of most interest to us because life forms were sufficiently complex by that period that we can recognize their modern counterparts.

The supercontinent Pangaea

Pangaea is said to have been assembled about 237 million years ago, during the Early Triassic Period, shortly after the great Permian extinction, the period of the most extensive extinctions of plant and animal species in the history of the Earth.   Pangaea began to break apart about 50 million years later, but the African and South American continents remained fused–into a continent dubbed Gondwana–until about 100 million years ago. (1)

During that period of nearly 160 million years, many new life forms emerged and others died out.  Cone-bearing plants replaced some spore-bearing plants before Pangaea formed and dominated the Earth during much of Pangaea’s existence.  The first true mammals, flowering plants, birds, lizards, and salamanders appeared before the break up of Pangaea was complete.

What are the implications of the development of new species of life on Earth at a time when there was a single, unified continent?  That is the question we are considering today.  Obviously, the transport of plant and animal species into new territories is facilitated by their proximity.  Seeds are more easily transported by wind and animals if they need not cross barriers such as oceans, as they must today.   As a result there was greater homogeneity of species during the geologic periods of Pangaea.  And species diversified rapidly when Pangaea broke up into the 7 continents of today. (2)  These diversified species have common ancestors. 

Even after Pangaea began to break up into separate continents, there were land bridges between some of the continents during periods of glaciations when water was locked into ice, draining the oceans.  Animals could travel over these land bridges from one continent to another, often bringing plant species with them, usually unwittingly.  That’s how the first humans in North America and ultimately South America traveled from Asia about 13,000 years ago at the time of the last ice age.

The common ancestry of many plants and animals is one of many reasons why the concept of “native” is ambiguous and is often debated.  We will consider a few examples in which the designation of a particular plant as native or non-native seems debatable.

Is the Dawn Redwood native to California?

Dawn redwood (Metasequoia glyptostroboides) is closely related to our redwood trees, Coast Redwood and Giant Sequoia.  Dawn redwood is unique in being a conifer that is also deciduous (loses its foliage in winter), unlike our redwood trees which are evergreen.  Dawn redwoods were until recently considered native to remote regions of China where they are considered “critically endangered.”

Dawn redwood in spring. Wikimedia Commons

However, scientists at the Museum of Paleontology at UC Berkeley tell us that there is fossil evidence that dawn redwoods grew in California about 40 million years ago.  Dawn redwoods now grow successfully in the Bay Area.  There is a famous specimen in front of McLaren Lodge in Golden Gate Park, headquarters of San Francisco’s Recreation and Park Department.  Every autumn, when the tree turns red, park staff receives calls from the public expressing their concern that the beautiful tree is dying.

Dawn redwoods died out in California during the last ice age because the climate was cooler than dawn redwoods could tolerate.  So, now that the climate has warmed again, and dawn redwoods are back, why not welcome them as a “return of the natives?”  That’s the kind of flexibility that makes sense to us, particularly in a time of rapidly changing climate.

Dawn redwood in autumn. Wikimedia Commons

Unfortunately, we don’t find such flexibility in the native plant ideology.  Dawn redwoods are rare both in California and in China from which it was reintroduced, and it is therefore not one of the trees that native plant advocates demand be eradicated.  Monterey pine and Monterey cypress are not so fortunate.  These are also trees for which fossil evidence suggests that they lived in San Francisco in the distant past and their native range is less than 150 miles down the coast in Monterey.  Both tree species are also considered threatened in their native range.  Yet, native plant advocates demand their eradication in San Francisco.

This is an example of the rigidity of the native plant ideology that has earned them the reputation of fanatics.

Does Rhododendron ponticum “belong” in Britain?

We told our readers in a recent post that Rhododendron ponticum is one of only about a dozen plants in Britain that are considered “invasive.”  It is a stunningly beautiful plant which is being aggressively eradicated in Britain.  Richard Mabey in Weeds:  In Defense of Nature’s Most Unloved Plants offers this explanation for why this particular plant is “invasive” in Britain:

“The next most serious weed is probably rhododendron which, unusually, has the ability to invade existing ancient woodland, especially in the west of Britain.  This may be because, if one employs a very long time scale, it is not strictly an alien.  The species that forms impenetrable thickets in western Britain is Rhododendron ponticum, whose pollen remains have been found in deposits in Ireland dating back to the last interglacial.  The species was plainly accustomed to growing in Atlantic woodland and may have retained a genetic “memory” of how to cope with this habitat and its competing species.  But it didn’t grow spontaneously in Britain for the next 30,000 years, and all the current feral colonies are regarded as originating from garden escapes.”(3)

Rhododendron ponticum. Wikimedia Commons

Once again, we wonder if “welcome home” isn’t a more appropriate response to this beautiful plant.  We find the definition of “native” as arbitrary as the definition of “invasive.”  Both seem to be terms used by people who abhor change.  And in a rapidly changing world, does such resistance to change make any sense?  We don’t think so. 

(1) The use of the word “created” implies no particular origin of the earth, merely its beginning.  https://www.usgs.gov/faqs/what-was-pangea-0?qt-news_science_products=0#qt-news_science_products

(2) Crosby,Alfred, Ecological Imperialism, 2nd Edition, Cambridge, University Press, 2004

(3) Mabey, Richard, Weeds:  In Defense of Nature’s Most Unloved Plants, Harper-Collins, 2010

Eradicating non-native plants is taking the food out of the mouths of birds

Plants have many different strategies to ensure their reproductive success.  Sometimes they are passive participants in their propagation.  Charles Darwin studied the dispersal of the seeds of plants and reported a particularly stunning example:  “He raised more than eighty plants from the mud-ball gathered round a wounded French partridge’s leg.”*  He also raised plants from seeds found in the stomachs of birds, which brings us to today’s topic:  the non-native plants which are eaten by birds are categorized as “invasive” plants and are therefore doomed to be eradicated.

We often puzzle over the list of nearly 200 non-native plants on the list compiled by the California Invasive Plant Council (Update:  Now nearly 300 in 2020).  We know from horticultural experience and scientific studies that at least two of the trees on this list are not invasive.  Aerial photographs of open space in the Bay Area taken over a period of 60 to 80 years, proves that neither the eucalyptus nor the Monterey pine forests are spreading. 

Cotoneaster lacteus. Jackson Nursery, UK

There are also several species of non-native shrubs which produce berries on the list of “invasive” plants that we know don’t spread in our gardens:  English holly trees, Cotoneaster, and Pyracantha.  So, why are they on the hit list?  The garden columnist in the San Francisco Chronicle recently told us why in answer to a question about planting a non-native holly tree for Christmas foliage in the garden:

“Berries are a little harder to come by if we follow the advice of native plant specialists who are concerned about escape of holly, cotoneaster and pyracantha into nearby wildlands, particularly in coastal counties. Birds that eat the fruit and deposit seeds are the culprits.” 

Pyracantha. Wikimedia Commons

In other words, native plant advocates don’t want gardeners to plant non-native plants that produce berries that birds eat because they don’t want the plants to spread.  Obviously, their dedication to native plants trumps whatever concern or interest they might have in the welfare of birds.  Native plant advocates frequently claim that their “restorations” will benefit wildlife.  Clearly the eradication of berry-producing shrubs does not qualify for such a claim.

The loss of food and habitat for the wildlife that lives in our public lands is only one of many issues in the debate about native plant “restorations.”  But for bird lovers, this is a high priority.  In this regard, we were struck by one of the public comments that was recently submitted on the Draft Environmental Impact Report for the Natural Areas Program.  This self-identified “birder” said this about the radical “restorations” in San Francisco:

“Restoration areas such as Land’s End, El Polin Spring, Crissy Field are seldom spoken about anymore by birders or others looking for populations of wildlife.  Since the vast majority of the city’s resident bird species feed, roost and breed in trees, they leave, starve or are predated when their habitat is destroyed.”

Cedar Waxwings in crab apple tree. Wikimedia Commons

As the Cedar Waxwings pass through the Bay Area on their annual migration, we see them eating the berries in our holly tree.  They remind us that the eradication of non-native trees benefits neither animals nor birds, nor insects.  Who benefits from these destructive projects besides the people making their living at it?  It’s a mystery.

* Mabey, Richard, Weeds:  In Defense of Nature’s Most Unloved Plants, HarperCollins, 2010, page 29

Some “alien invasions” are a bust!

The Argentine ant is one of a gazillion non-native species that have been labeled “invasive species.”  Like most non-native species, they are considered aggressive competitors of native ants.  The usual tools are employed to eradicate them, e.g., pesticides. 

Argentine ant. UC Davis

But wait!  Now scientists are suddenly noticing that the Argentine ant is disappearing from some of their colonial haunts.  Scientists in New Zealand have recently reported the disappearance of the Argentine ant from 40% of sites they populated in the past and their populations have shrunk significantly where they are still found.  Native ants have “reinvaded” the areas vacated by the Argentine ant.  The scientists reporting this finding “concluded the species naturally collapses after 10 to 20 years.”

The scientists in New Zealand don’t claim to know why the populations of Argentine ant have disappeared.  They speculate that a virus is to blame.  They don’t claim “pest control” deserves credit for the disappearance which is estimated to have cost $53 million (NZ$68) per year since the Argentine ant was originally found there in 1990. That’s right, New Zealand spent approximately $53 million per year trying to eradicate the Argentine ant, which apparently is disappearing on its own.

This is apparently not an isolated phenomenon.  An entomologist at UC Davis reports that the Argentine ant has been declining in California as well.  How much pesticide was poured on Argentine ants before they showed the good grace to just disappear?

The Africanized Bee:  Another scary story that didn’t materialize

Another example of an “invasion” that seems to have resolved itself is the Africanized bee.  Do you remember about 15 years ago when the media created a panic about the Africanized bee?  We were told that it was spreading rapidly from Latin America, headed our way and that it was so dangerous that it was capable of swarming people and animals and stinging them to death! 

Africanized honeybee USDA

What happened to that particular “alien invasion” story?  Professor Gordon Frankie (UC Berkeley), our local expert about bees, was asked that question in a lecture he was giving to Cal Alumni in October 2011.  He said that the Africanized bee didn’t turn out to be as aggressive as it was originally thought to be and that it didn’t spread as far or as fast as predicted.

Does “Invasion Biology” make more problems than it solves?

Some months ago we created a Google alert for “invasive species.”  Now we are treated to a daily barrage of scary “alien invasion” stories from all over the world.  We wonder how many of these “invasions” will eventually prove to be benign.  We wonder how much money will be spent, how many animals will be killed, how much pesticide will be poured on our public lands, before we figure out that we need not be afraid of everything that is new in the environment.  We wonder how many people are making their living on these eradication efforts and what role they play in frightening the public into funding their projects and tolerating the destruction they inflict on the environment.

Weeds: In Defense of Nature’s Most Unloved Plants

We would like to tell our readers about a charming little book about weeds, by the same name.  Weeds:  In Defense of Nature’s Most Unloved Plants, by Richard Mabey, contains an eclectic collection of information about the weeds of Britain, their origins, the history of their use–including as medicine, the role they have played in literature, and much more.

First, we venture a definition of weeds, though any definition is likely to be controversial.  The concept of “weed” originated with agriculture, some 5,000 years ago in the Old World*, when man began to distinguish between those plants that are edible or otherwise useful and those that are not.  And so, plants that are not perceived as useful or turn up in the wrong place, were defined by man as “weeds.” 

It’s a shifting concept, because a plant that was useful historically, either because it was believed to be a cure for some malady, or was otherwise useful, might be replaced by some superior remedy.   Such a changing concept of the value of particular plants is a central theme to the book as well as to the Million Trees blog.  We often invite our readers to consider that much of the current interest in native plants is a horticultural fad that is likely to change in the future as it has in the past.

We also often question the designation of hundreds of non-native plant species as “invasive” in California, a designation that makes them a target for eradication.   Mabey’s book about weeds helps us to put this designation into perspective.  Britain obviously has a much longer history of trade with its neighbors on continental Europe, which increased the potential for the introduction of non-native species.  Yet, despite Britain’s longer history of ecological globalization, Mabey tells us that only about one dozen species of plants are presently considered invasive in Britain compared to hundreds in California. 

Rhododendron ponticum, one of only a dozen plants considered invasive in Britain. Wikimedia Commons

Mabey defends several of the non-native plants considered invasive in Britain.  He believes that some are merely responding to the disturbance of native vegetation by the activities of man.  Nature hates a vacuum.  When native vegetation is no longer adapted to the changed soil, water, and air quality conditions created by man, any plant that will grow in these new conditions is preferable to bare ground.  Plants—including weeds—help the soil absorb rainwater into the ground which would otherwise run off the land, silting streams and causing erosion.

There is much food for thought in this little book.  It invites us to compare our list of nearly 200 plants in California that have been officially designated as “invasive” to a short list of only a dozen plants in Britain.  What accounts for this big difference?  Different conditions or different attitudes?  We don’t know the answer to this question, but we think it is a question worthy of consideration.

* Crosby, Alfred, Ecological Imperialism, Cambridge University Press, 2009

A rare sighting of a Summer Tanager in San Francisco

We are reprinting a post from the Save Sutro Forest blog about a rare sighting of a Summer Tanager in San Francisco.  With permission and with minimal edits necessary to change the source of the pictures of  tanagers, we share this story with our readers.  Please visit the story on the Save Sutro Forest website to see photos of the actual female bird that was seen in San Francisco.

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One of the more interesting groups to watch, if you like birds, is the Yahoo group SF Birds. (Anyone can read it, but you must join to post in it. [ETA: It’s apparently been changed to a members-only group; only members can read it.]) It has over 1,000 members at this writing, but a smaller dedicated group of local birders use it to communicate the whereabouts of rare-in-San Francisco species. Often, someone follows up with links to beautiful photographs. That’s where we found the story of the Summer Tanager.

Male Summer Tanager. Wikipedia Commons

THE SUMMER TANAGER VISITS SAN FRANCISCO

This is a small songbird that’s a rare winter visitor to San Francisco. The males are a bright red color, the females and immature males are yellow. They feed on insects (bees, wasps and so on) and berries. Recently, birder Alan Hopkins reported seeing a female Summer Tanager in Golden Gate Park: “… you will find English Ivy growing up some trees. The tanager was catching bees that are feeding on the ivy.”

Of course, other birders followed up. Steven Tucker wrote: “…the Summer Tanager was where Alan described it. There are 2 huge columns of ivy adjacent to one another; the tanager was often in the right-hand clump or in the Eucalyptus trees around it.”

Then birder Mark Rauzon posted some wonderful pictures of this little bird in his Zenfolio portfolio. “I found it by it’s ‘churrip’ call at 1:30pm, Monday in the ivy covered Eucalyptus … It was bee-eating and occasionally dropping down to eat blackberries, where I had this face to face encounter.” (The pictures here are reproduced with his permission. They’re copyright. Anyone who wants to use them should check with him at mjrauz@aol.com )

NON-NATIVE PLANTS AS HABITAT

It’ll come as no surprise to birders that non-native plants provide habitat. After all, many of the posts in the SF Bird group describe birds in flowering eucalyptus trees, either for the nectar or the insects attracted to the nectar. (We hope that any birders who still believe eucalyptus trees suffocate birds will check this article, Another Eucalyptus Myth: Bird Death) They mention birds in the blackberry bushes, which provide not only food by way of berries and insects, but excellent cover. Like the notes above, they mention birds hiding in ivy.

In our article Interwoven and Integrated: Non-native and Native Species in Life’s Web, we described how native species and non-native species are part of the same functional habitat. This is another example.

  • The eucalyptus (non-native) provides support for the ivy (non-native)
  • which attracts insects (both native and non-native),
  • which become food for the Summer Tanager and other birds (mostly native).

The blackberry bushes work in much the same way; they attract insects, they provide berries, and they provide hiding places. So does eucalyptus – it flowers through the year, and particularly in winter, provides sustenance to birds and insects. It also provides nesting spots and cover.

Pointing this up was the most recent post [ETA:  No longer available to non-members] on the Summer Tanager, from Richard Bradus: “…an immature Red-tailed Hawk alighted, drawing an even dozen Ravens in pursuit. As they rose and flew off the bushes came alive, and out popped the female Summer Tanager. It made a few sorties from the ivy then, after devouring a particularly fat insect (bee?), it retreated to cover.”

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Million Trees Webmaster:  People who like birds pay attention to where they are and know they make good use of non-native plants and trees in San Francisco.  We had two old English holly trees in our yard in San Francisco which were probably planted around the same time our house was built in 1908.  They were visited every year by a flock of Cedar Waxwings, one of the most beautiful birds I have seen in the United States.  Their arrival each year was announced by the high-pitched, thin whistle of their call.  Then we could watch them with binoculars from our second story as they feasted on the berries of the holly trees.  It was an annual treat both for us and for the Waxwings as they passed through San Francisco.  Would they find enough to eat if there were no non-native trees and plants?  I don’t know, but I DO wonder.

Cedar Waxwing. Wikimedia Commons

Quibbling with the terminology of invasion biology

We believe the key word in Invasion Biology—invasion—is overused and that the adjective—invasive—is used indiscriminately to describe non-native plants, whether they are invasive or not.  We have already told our readers about photographic evidence of open space in the Bay Area taken over decades which proves the eucalypts and Monterey pines are not expanding their range.  Yet, these are two of the nearly 200 species of non-native plants on the California Invasive Plant Council’s list of “invasive species.”

Now we will use another non-native species as an example of how invasiveness is exaggerated by invasion biology.  Apparently many earthworms in the United States are non-native.  That’s because much of the population of native earthworms was wiped out by the glaciers that receded about 10,000 years ago. 

When Europeans began to colonize the country 500 years ago, earthworms were one of many species of plants and animals that they brought with them.  Like many non-native species, earthworms were transported unwittingly, first in the ballast of ships and then in the soil that accompanied plants that were purposefully transported.  In modern times, most earthworms are said to be introduced into new areas primarily by fishermen who use them as bait and then dispose of their surplus bait by throwing them on the ground.

Some 500 years later, invasion biologists are concerned about the impact that non-native earthworms are having on the ecology that evolved without earthworms.  Since glaciers did not extend as far south and west as California and the Bay Area, we don’t know if there are native earthworms here.  So, as you read about the impact that earthworms are said to have on the northern hardwood forests of the Great Lakes Region (Minnesota, Wisconsin, Michigan) and the northeast, you can’t assume that these observations apply locally.

The last period of glaciation in the United States

Since the hardwood forests of the northern and eastern states of the country evolved without earthworms for about 10,000 years, the duff (organic matter) on the forest floor is essential to the sustainability and health of the understory as well as the regeneration of the forest.  Earthworms digest the duff, incorporating it into the soil, and thereby deprive the native plants and trees of the nutrients that they depend upon for germination and survival. 

Although we accept that non-native earthworms may be having a negative impact on the native forests in these areas, we don’t think it is appropriate to call the earthworms invasive because they aren’t moving.  They exist only where man has introduced them.  Genetic studies have determined that isolated populations of non-native earthworms are unrelated to one another.  Their location in urban areas and around lakes and streams where fishermen visit implies that the earthworms are dispersed by man.  And they move very slowly, one-half to 1 kilometer (5/8th of a mile) every 100 years!*

Yet, those who study the earthworms and the managers of public lands who are trying to prevent the further introductions of earthworms consistently describe the worms as “invasive.”  Granted, it is a quibble, but we think this is a misleading description because it implies that the earthworm is to blame for whatever damage is being done to the native ecology when the blame clearly belongs to man.  The earthworms aren’t going anywhere.  Wherever they are found, they were put there by man.  The earthworm is another scapegoat for the harmful activities of man. 

On the bright side, invasion biologists and land managers aren’t trying to eradicate the non-native earthworm.  They are merely trying to educate fishermen to dispose of their surplus worms in the trash, rather than leaving them on the ground.  They concede that it’s impossible to get rid of earthworms where they now exist.  So, at least the soil isn’t being poisoned with pesticides in a futile attempt to return the land to its wormless history.

Once again, we urge invasion biologists to be more discriminating with their designation of “invasive species.”  We believe this term should only be applied to species that are expanding their ranges rapidly and that are actually causing damage in the environment.  Given the impact of climate change, native species are as likely to become invasive as non-native species.  If the term is used more accurately and less often, fewer efforts to eradicate hundreds of plant and animal species would be required.  Therefore those eradication efforts that are truly necessary would be less destructive and more successful.  The field of invasion biology would be more credible and enjoy more public support.

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* Hale, Cindy, “Evidence for human-mediated dispersal of exotic earthworms:  support for exploring strategies to limit further spread,” Molecular Ecology, (2008) 17, 1165-1169