We spent nearly two months analyzing the California Invasive Plant Council’s draft reassessment of blue gum eucalyptus and informing our readers of the fallacious reasoning used to continue its classification of blue gum as “invasive.” We are badly in need of comic relief and we assume our readers could use some as well. We are republishing with permission an article by Robert Platt Bell from his blog, “Living Stingy.” Mr. Platt is a patent attorney on Jekyll Island, Georgia. His blog gives advice about “how to live a better life with less money.”
His sarcastic criticism of invasion biology reveals that he is a man of considerable good sense. Although we tend to use scientific arguments on Million Trees to critique invasion biology, Mr. Platt’s article demonstrates that a little common sense is really all that’s needed. Mr. Platt ends his article with the disclaimer that he doesn’t have a cat and we will do the same. We don’t have a cat, never have, never will.
Some folks claim that the ordinary house cat is an “invasive species”
Your tax dollars at work. Here on the island, they have attached little cameras to cats to monitor their behavior. The University of Georgia is funding the study, which in turn is funded by your taxes.
They also have sent out a “feral cat awareness survey” to everyone on the island, and again, this is funded by UGA. The “survey” is more of a “push-poll” in that it asks questions that are more answers than questions. “Did you know that cats are responsible for killing billions of songbirds every year?” – that sort of thing, courtesy of the bureau of specious statistics.
Actually, the results of “kitty-cam” so far are that cats (1) lick themselves a lot, (2) sleep, and (3) eat cat food. Only one cat has been caught killing for food, and no word on whether it was a rodent or a bird.
But the oddest thing about this “poll” was that they were trying to characterize house cats as “invasive species” by the way the questions were asked.
“Invasive Species” is the hot, new, trendy term for biologists and wildlife managers to use – and one they use to justify poisoning the air, water, and soil, all in the name of “preserving nature”.
We are told (get this) that some species are “native” and others are “invasive” and that the latter need to be slaughtered, as they will push out the “native” species over time.
This may or may not be true. The point is, the species doesn’t consider itself “invasive” anymore than the species it is displacing (which at one time was no doubt “invasive” as well).
Some try to put a spin on this based on a human vector. If the species is relocated due to some act of mankind, then it is “invasive”, whereas if it just migrated here, I guess it is natural. This also is a load of hooey, as the vectors that move species from one area to another have little to do with whether the species would eventually get there under its own power, or whether it would adapt to the new environment.
And speaking of “invasive species,” this sort of discussion usually neglects to address the most invasive species on the planet – a species that has occupied every ecological nook and cranny on the planet and adapted itself to harsh environments and even space.
Yea, I’m talking about you and me – human beings. We have over-run the planet, but no one talks about euthanizing or neutering people on a massive scale.
On the other hand, we can poison some trees or a carp or whatever, and that’s going to fix everything up just Jim-Dandy!
I think biologists who believe that have their head up their ass, or are just looking for grant money.
In the Northeast, we are told the Zebra Mussel is “invasive” – but it has turned murky brown lakes crystal clear. The powerplant that has to clean its inlet screens, we are told, is justification for dumping poison in the water, or for fining some unwitting fisherman hundreds of dollars for dragging a piece of seaweed on his boat trailer. The upshot is, the zebra mussels are winning, much as the lamprey eels are (and the snakehead fish).
In the Everglades, we watched as “wildlife managers” drilled holes in trees and filled them with poison. Their crime? Being non-native. Whether this will permanently kill off these trees is debatable, and the long-term effect of poisoning nature is something not studied. And the cost of this “cure” is pretty staggering.
Nature expands into environments where it can adapt, and you can’t stop that. It is like Boyle’s law about gas – it expands to fill a vessel. Trying to hold back the tide of species is pointless and fruitless (pardon the pun) as nature will sneak around at every turn, as soon as you let your guard down.
Yes, it is bad there are Boas in the Everglades. It is also irrelevant whether they got there as escaped pets or were dropped from an airplane or swam over from South America. They are there, and trying to extinguish them is going to be a long, difficult, and expensive job that will never get done.
Here on the island, a couple runs a program that captures and neuters cats and then releases them. It has been effective as the cat population has plummeted from the 1990’s until today. (They did a similar thing in Key West, and now there is no cat problem, just a chicken problem).
But on the other hand, we are being overrun by deer – and not in the sense that “the deer ate my flowers” nonsense. We simply have more deer than the island can support, and they are becoming smaller and more sickly as a result (and more brave, as they are not afraid of humans at all). New breeding stock was brought in to try to reverse the trend, but it has not really helped. Talk of managing the deer population or relocating deer is shouted down as “inhumane”.
But apparently, it is open season on cats.
(Disclaimer: I do not presently own any cats. I like them, but don’t like cleaning out litter boxes. Hence I have no cats).
The deadline for sending comments to the California Invasive Plant Council (Cal-IPC) about their draft reassessment of blue gum eucalyptus is Thursday, July 31, 2014 (send to info@cal-ipc.org). We are hoping to inspire you to write your own comment by sharing our personal favorites of some of the goofy statements Cal-IPC uses to justify its classification of blue gum as “moderately invasive.”
Eucalyptus trees do NOT kill birds!
Our regular readers have heard the absurd claim that eucalyptus trees kill birds by “gumming” up their noses or beaks with the nectar of the eucalyptus flowers. We have published detailed critiques of this claim, so we won’t repeat them because you can visit those posts by clicking HERE and HERE.
Of course, all of this detailed information was provided to Cal-IPC when the original request to reconsider their classification of blue gum was submitted in December 2013. In their draft reassessment, Cal-IPC now sinks to a new low by claiming Ted Williams as the source of the claim that eucalypts kill birds. Mr. Williams writes an opinion column published by Audubon magazine, which is appropriately entitled “Incite.” In 2002, Audubon magazine published Mr. Williams’s opinion of eucalyptus, which he called “America’s Largest Weed.”
Ted Williams is not a scientist or a journalist. He is a commentator. His column in Audubon magazine is not entitled “Insight,” because it is intentionally inflammatory. It engages in rhetoric and hyperbole in support of Mr. Williams’s opinion. In an article in High Country News, Mr. Williams describes “Incite” as a “muckraking column” and he calls himself an “environmental extremist.” Citing Mr. Williams as a source of information undermines the credibility of Cal-IPC’s draft reassessment. Quoting Mr. Williams on the subject of eucalyptus is a bit like quoting Rush Limbaugh on the subject of immigration.
But let’s be more specific with examples of the absurd statements Mr. Williams makes and the evidence that these statements are not factually correct.
The truth about Anna’s hummingbirds
Hummingbird in eucalyptus flower. Courtesy Melanie Hofmann
Cal-IPC’s draft reassessments says, “Williams reported that PRBO found that 50% of the Anna’s hummingbird nests [in eucalyptus] are shaken out by the wind, while only 10% of nests are destroyed by wind in native vegetation.”
Cal-IPC’s quotes from Williams are not found in any publication of the Point Reyes Bird Observatory (PRBO), which Williams claims as the source of the information. Statements about the nests of Anna’s hummingbird are explicitly contradicted by Cornell Ornithology Laboratory, America’s preeminent research institution of bird biology and behavior:
“In the first half of the 20th century, the Anna’s Hummingbird bred only in northern Baja California and southern California. The planting of exotic flowering trees provided nectar and nesting sites, and allowed the hummingbird to greatly expand its breeding range.”
“Anna’s Hummingbird populations increased by almost 2% per year between 1966 and 2010, according to the North American Breeding Bird Survey…The Anna’s Hummingbird is the most common hummingbird on the West Coast, and it has thrived alongside human habitation. Its range has increased dramatically since the 1930s, when it was found only in California and Baja California. Thanks to widespread backyard feeders and introduced trees such as eucalyptus, it now occurs in healthy numbers all the way to Vancouver, Canada.”
“Females choose the nest site, usually a horizontal branch of trees or shrubs 5-20 feet off the ground (occasionally higher) near a source of nectar. They often build nests in oak, sycamore, or eucalyptus trees…”
“They [Anna’s Hummingbirds] are notably common around eucalyptus trees, even though eucalyptus was only introduced to the West Coast in the mid-nineteenth century.”
In other words, the nation’s most prestigious ornithological research institution tells us that Anna’s Hummingbirds have benefited greatly from eucalyptus trees, which provide both winter sources of nectar not otherwise available in California as well as safe, secure nesting habitat. Since Anna’s Hummingbirds nest preferentially in eucalyptus, their populations would not be increasing if 50% of their nests were destroyed, as Mr. Williams claims.
Red-tailed hawk nesting in eucalyptus. Courtesy urbanwildness.org
Furthermore, the implication that eucalypts provide a less stable nest site than native trees is also explicitly contradicted by a study that Cal-IPC cites elsewhere in its draft reassessment. Stephen Rottenborn studied the nesting choices and reproductive success of red-shouldered hawks in Santa Clara County. He found that the hawks prefer eucalypts to native trees and that their nests were more successful when they made that choice.He attributes that greater success rate to the fact that eucalypts are “large, sturdy trees” that provide “greater stability and protective cover.”
“Fourteen of 27 nests in 1994 and 38 of 58 nests in 1995 were in exotic trees, predominantly eucalyptus. Nesting and fledging success were higher in exotic trees than in native trees in both years, owing in part to greater stability and protective cover. Most nest trees in upland areas were exotics, and even in riparian habitats, where tall native cottonwoods and sycamores were available, Red-shouldered Hawks selected eucalyptus more often than expected based on their availability. Of the habitat and nest-tree variables measured at each nest, only nest-tree height and diameter were significantly associated with reproductive success, suggesting that large, sturdy trees provided the best nest sites. Red-shouldered Hawk populations in the study area have likely benefited from the planting of exotic eucalyptus and fan palms.” (1)
Magic! Turning 2 dead birds into 300
Cal-IPC’s draft reassessment says, “Stallcup reported finding two dead warblers and ‘about 300 moribund warblers with eucalyptus glue all over their faces’ over the years, including ‘a large number of gummed-up Townsend’s warblers, yellow-rumped warblers, ruby-crowned kinglets, Anna’s and Allen’s hummingbirds, and a few Bullock’s orioles. Anyone who birds around eucalyptus trees sees it all the time’ (Williams 2002).”
This particular quote from Ted Williams is easily discredited because Rich Stallcup published his theory about birds being harmed by eucalyptus trees (available HERE). In this publication, Mr. Stallcup reports seeing just two dead birds (one hummingbird and one ruby-crowned kinglet) in the eucalyptus forest during his long, illustrious career as an amateur birder. He says nothing about seeing “300 moribund warblers” in his publication. A small measure of common sense enables the reader to evaluate Mr. Williams’s claim: If Mr. Stallcup had seen 300 dying birds, why would he say he had only seen 2 dead birds in his published article in which he is trying to make the case for removal of eucalyptus?
Overwintering monarch butterflies use predominantly eucalyptus
Monarch butterflies roosting in eucalypus tree.
Cal-IPC’s draft reassessment says, “Natural experimental evidence from mixed stands (native trees mixed with eucalyptus) show that Monarchs do not consistently cluster preferentially on eucalyptus, and at times, appear to prefer native trees in some seasons and locations. (Griffiths & Villablanca 2013)”
This is a misleading statement because it implies that monarchs have the option of overwintering in native trees. In fact, the reference cited by Cal-IPC is speaking specifically of three species of native trees with small native ranges: Monterey pine, Monterey cypress, and redwoods. The study is reporting observations of monarchs within the native ranges of these three tree species. These tall trees provide a similar microclimate to overwintering monarchs. However, the native ranges of these tree species are small.
Monterey pines are native in “three disjunct populations in San Mateo and Santa Cruz counties, Monterey County, and San Luis Obispo County. The native population of Monterey cypress is significantly smaller: “The native range of the species was confined to two small relict populations, at Cypress Point in Pebble Beach and at Point Lobos near Carmel, California.” Where Monterey pine and cypress have been planted outside their native range, they are being eradicated by the same public land managers who are eradicating eucalyptus.
For example, when UC Berkeley destroyed approximately 18,000 non-native trees over 10 years ago, many were Monterey pines. Their plans to eradicate 80,000 more trees include all Monterey pines in the project area. In San Francisco, the plans (SNRAMP) of the Natural Areas Program propose to destroy many Monterey cypresses on Mount Davidson. The GGNRA has destroyed about 500 Monterey pines on Hawk Hill in Marin County and many Monterey cypresses throughout their properties.
Furthermore, both Monterey pine and Monterey cypress have much shorter lives than eucalyptus. Monterey pine lives at most 150 years and Monterey cypress about 250 years, compared to E. globulus, which lives in its native range from 200-500 years. Therefore, even where they are not being eradicated, they will die long before E. globulus and are unlikely to be replanted outside their small native range by public land managers who are committed to a “natives-only” policy.
We are unaware of any attempts to eradicate redwoods outside their native range, in the few locations where they still exist. They seem to have escaped the wrath of nativism. However, the range of redwoods is very narrow: “The redwoods occupy a narrow strip of land approximately 450 miles (724 km) in length and 5 to 35 miles (8-56 km) in width. The northern boundary of its range is marked by two groves…within 15 miles (25 km) of the California-Oregon border. The southern boundary of redwood’s range is marked by a grove…Monterey County, California.”
Although native plant advocates may be willing to plant redwoods outside their native range, they do not have that option because of the horticultural requirements of redwoods. Redwoods require more water than Monterey pine and cypress and they do not tolerate wind, which prevents them from being successful in many coastal locations, where monarchs overwinter. Redwoods cannot be successfully grown south of Monterey County where the climate is warmer and drier than its native range.
In other words, monarchs do not have the option of roosting in native trees in most of the places in California where they overwinter. This is a more accurate description of the behavior of overwintering monarchs and the alternatives that are available to them in about 300 locations along the entire coast of California, where they have overwintered in the past:
“Three types of trees were used most frequently by roosting monarchs: eucalyptus (75% of the habitats primarily Eucalyptus globulus), pine (20% of the habitats; primarily Pinus radiata), and cypress (16% of the Cupressus macrocarpa). Twelve other tree species were identified…with a combined prevalence of only 10%…The negative sign for this indicator means that habitats had smaller populations when the roosting tree type was a species other than eucalyptus, pine, or cypress…our long-term analysis showed that abundance has historically been greater at habitats dominated by eucalyptus, pines, or cypress than at those with ‘other’ species. Stands of these three signature taxa may be more likely to produce a community structure and associated microclimate that increases the residence time of monarchs. Furthermore, these taxa may produce a more attractive landscape architecture in terms of sensory cues to migratory monarchs arriving in a certain region.” (2)
For the record, we will add that we would be happy to have more Monterey pines and cypress and if public land managers would quit destroying them, we would consider them attractive alternatives to eucalyptus. However, for the moment, we must assume that the crusade against all non-native trees will continue unabated.
What is your personal favorite?
We have shared our personal favorites with you, but everyone comes to this issue from a different place. We have been flabbergasted by the unfounded claims that the eucalyptus forest is devoid of life. We wonder if the people who say that, really believe it. Or is it just one of the many strategies used to justify their demands that our non-native landscape be destroyed?
Please choose your own personal favorite and write your own comment by Thursday, July 31, 2014. Are you primarily concerned about the herbicides that are needed to prevent the trees from resprouting when they are destroyed? Are you concerned about the loss of your protection from wind or noise? Or do you value eucalyptus as a sight screen or for shade in an otherwise treeless environment? Are you concerned about the carbon loss that will contribute to climate change? Please help us to save our urban forest from being needlessly destroyed by telling Cal-IPC why they should take blue gum eucalyptus off their “hit list.”
Thank you for your help to save our urban forest.
Update:On March 13, 2015, the California Invasive Plant Council published its final reassessment of Blue Gum Eucalyptus (available HERE). Cal-IPC has downgraded its rating of invasiveness and ecological impact from “moderate” to “limited.” Although the detailed assessment is less than perfect, the over all rating itself is an improvement. Thanks to those who sent comments to Cal-IPC.
(1) Stephen Rottenborn, “Nest-Site selection and reproductive success of urban red-shouldered hawks in Central California,” J. Raptor Research, 34(1):18-25
(2) Dennis Frey and Andrew Schaffner, “Spatial and Temporal Pattern of Monarch Overwintering Abundance in Western North America,” in The Monarch Butterfly Biology and Conservation, Cornell University Press, 2004.
Last week, we told our readers about the California Invasive Plant Council’s (Cal-IPC) draft reassessment of blue gum eucalyptus, Eucalyptus globulus. (available HERE) Cal-IPC is accepting comments on its draft until July 31, 2014 (send to info@cal-ipc.org). Although Cal-IPC now acknowledges that blue gum has “low invasive potential” and its population is stable in California, it proposes to maintain its over-all classification of “moderately invasive.” You might wonder how Cal-IPC manages to accomplish this sleight of hand, so we will tell you how its scoring system enables it to maintain its overall rating of blue gum.
Cal-IPC has three main evaluation categories: “Impact,” “Invasiveness,” and “Distribution,” which are combined to produce an over-all rating. Cal-IPC’s draft lowers the rating of “invasiveness” to “limited,” but it has changed its rating of “impact” from “moderate” to “severe.” These changes cancel one another, enabling them to reach the same over-all rating of “moderately invasive.” In this post, we will focus your attention on Cal-IPC’s opinion of the “impact” of blue gum so that you can see how they arrived at their conclusion.
Drought is on our minds
Epicormic sprouts on trees in Glen Canyon Park, June 2014
As we told our readers recently, the drought in California is making water use an important issue that is getting a lot of attention, as it should. Native plant advocates have not hesitated to jump on that band wagon. For example, they now claim that eucalypts in San Francisco are dying of drought. With the help of a highly qualified arborist, we evaluated that claim in a recent post and reported that the trees are reacting to the loss of their understory and their neighboring trees, as well as the herbicides used to kill the understory and prevent their former neighboring trees from resprouting from their stumps.
Given this recent experience, we weren’t surprised to find that Cal-IPC has introduced accusations of extreme water use into their assessment of blue gum for the first time, and this new issue helps them to claim that blue gums have a “severe” impact on the environment. Now let’s drill down into this claim, examine the source of the claim and tell you why we believe this is another bogus issue used to vilify eucalyptus.
Tracking down the truth about water use by blue gums was a bit like a game of gossip. Starting with the final version of the rumor in Cal-IPC’s draft reassessment, we tracked that version back to its original source. We found exaggeration at each iteration of the rumor, from its source to its landing in the Cal-IPC draft. The final version bore little resemblance to the original version. The original version is over 100 years old and therefore describes circumstances that have since changed substantially.
Exaggerated and outdated description of root structures
Cal-IPC’s draft assessment of “impact on hydrology” is: “Eucalyptus globulus is adept at tapping into deep groundwater, even under drought conditions (DiTomaso & Healy 2007), altering water availability to depths of 45 feet and distances of 100 feet from the trunk.”
The first distortion of evidence occurs with Cal-IPC’s exaggeration of its cited source. Here’s what DiTomaso & Healy actually said about the roots of blue gum: “In deep soils with high water tables or other deep soil water source, lateral roots grow toward the moisture source and can deeply penetrate soil to 14 m deep.” In other words, DiTomaso and Healy say that such deep roots occur only in certain conditions of “deep soil,” “high water table,” or a “moisture source.”
The source of DiTomaso & Healy’s description of the roots of blue gum is a similar statement in Bean & Russo, who wrote an evaluation of blue gum for the Nature Conservancy in 1989: “Large roots have been discovered at a depth of 45 feet below the surface, and surface roots frequently spread over 100 feet away from the trunk. (Sellers 1910)”
Bean & Russo provide a reference for their statement, which takes us to the original version of this rumor. A book about eucalyptus in California by C.H. Sellers was published in 1910. Here is what Sellers actually says about the roots of E. globulus, grown in the State of California:
“The root system consists mostly of numerous strong laterals; the tap root rarely penetrates to a depth of more than 10 feet. Abundant supply of moisture is demanded and as the roots grow quickly toward water Eucalyptus globulus should never be planted near wells, cisterns, water pipes, irrigating ditches or similar water impounding structures. In loose, sandy or gravelly soils the large lateral roots penetrate to great depth, and extend almost incredible distances. In digging wells large roots have been discovered at a depth of 45 feet below the surface and the surface roots of large trees frequently spread over 100 feet from the trunk of the tree.” (1)
In other words, the extreme root lengths reported by DiTomaso & Healy are an anomaly, only found in specific conditions and unusual cases. The roots of E. globulus are “rarely” deeper than 10 feet, according to this original source of information regarding the roots of E. globulus.
Contemporary sources which are not trying to make a case against E. globulus describe its roots in a less extreme manner: “Bluegum eucalyptus generally does not form a taproot. It produces roots throughout the soil profile, rooting several feet deep in some soils.” (Esser 1993) Also: “Bluegum eucalyptus generally does not form a taproot. It produces roots throughout the soil profile, rooting several feet deep on soils that permit it, or shallowly otherwise.” (Skolmen & Ledig 1990) Esser and Skolmen wrote their evaluations of blue gum for the US Forest Service.
Bringing Sellers up to date
We will assume that Sellers’s observations are accurate, but we will now consider the possibility that an observation that is over 100 years old may not be relevant to present conditions. For a more contemporary perspective on blue gum, we turn to R.G. Florence, an Australian academic scientist who studies eucalyptus and was also a visiting professor at UC Berkeley. R.G. Florence helps us to understand why the observations of Sellers may be very different from more recent observations: “As a tree develops through the sapling and pole stages it will tend to form a main root which penetrates vertically downward, but this main root is rarely significant in a large tree.“ (2) Florence reports that E. globulus uses more water during early stages of growth, when it is growing quickly, than it does as a mature tree. Sellers was reporting in 1910 at a time when most eucalypts in California were young. Their roots may have been longer during these early stages of growth. Since E. globulus has not been planted in California for decades and is no longer available for planting, its root structure at early stages of development is irrelevant to evaluating its behavior in California presently.
Is blue gum drought tolerant?
Cal-IPC denies that blue gum is drought tolerant: “E. globulus is able to withstand prolonged dry summers by tapping into deep water reservoirs; they do not economize in the use of water but have far-reaching root systems and can extract water from the soil at even higher soil moisture tensions than most mesophytic plants (Pryor 1976, Florence 1996).”
Once again, Cal-IPC misquotes its cited sources. R.G. Florence does not make the statement that Cal-IPC attributes to him. Rather, this is how Florence describes the water needs of eucalypts: “…the eucalypt might be generally characterized as being a drought-tolerant mesophyte, that is, it tends to maintain transpiration and cell metabolism under conditions of developing drought.” (2)
Florence says drought tolerance and water use varies by species of eucalyptus. He places E. globulus in this category of drought tolerance: “coastal zone species with high rates of growth and water use, but with somewhat wider environmental [drought] tolerance.” He makes these observations about water use by E. globulus:
Water use is greatest when the trees are young and generally tapers off as the tree grows, between 10-15 years of age. As we have said, only mature E. globulus exists in California presently or will in the future.
E. globulus has been observed to regulate water use by opening and closing its stomata in response to temperature and moisture: “Water use may be regulated in this way.” (2)
Pryor’s description of drought tolerance of eucalypts was published 20 years earlier than Florence at a time when variations in drought tolerance of different species of eucalyptus had not yet been studied. He therefore, does not report on the ability of E. globulus to withstand drought, as Florence does in 1996. He acknowledges some variability with respect to drought tolerance in genus Eucalyptus, which is consistent with Florence’s later report specifically about E. globulus, although Pryor says nothing specifically about E. globulus.
Self-watering blue gums
Sutro forest on a typical summer day. Courtesy Save Sutro Forest.
E. globulus was planted most widely along the coast of California. Most of the coast of California is foggy during summer months, when there is little if any rainfall. Tall eucalypts are known to condense the moisture in the fog which has been measured to double annual rainfall. (3) In these regions, eucalyptus is essentially self-watering. Ironically, Cal-IPC acknowledges this self-watering feature of eucalypts: “The volume of water channeled down the stem is about eight times more than that of falling rain, so soil at the base of trunks receives relatively large quantities of water…” (May & Ash, see “allelopathy” section of Cal-IPC draft).
A recent study conducted in 24 parks in San Francisco measured moisture in the soil in the late summer months (August to September), when the soil would be driest in the absence of fog condensation. That study reported that the greatest amount of moisture (15%) was found in the parks with eucalyptus forests. Soil in parks vegetated with grassland or scrub contained significantly less moisture. In other words, even late in the dry season mature eucalypts were not draining all available moisture from the soil. Their water needs were met by the condensation of moisture from the fog during the dry summer season. (4)
Please come to the defense of our urban forest!
We hope that we have made the case that the draft reassessment is not a fair evaluation of the predominant tree in our urban forest, blue gum eucalyptus. We ask that you write to Cal-IPC by July 31st about their biased reassessment. Tell them why you think our urban forest is important to the environment and the people and animals living in it. Ask them to remove blue gum eucalyptus from their “hit list” which is being used by managers of our public lands to justify the destruction of our urban forest.
Eucalyptus forest, Lake Chabot
Thank you for your help to save our urban forest from being needlessly destroyed.
Update:On March 13, 2015, the California Invasive Plant Council published its final reassessment of Blue Gum Eucalyptus (available HERE). Cal-IPC has downgraded its rating of invasiveness and ecological impact from “moderate” to “limited.” Although the detailed assessment is less than perfect, the over all rating itself is an improvement. Thanks to those who sent comments to Cal-IPC.
(1) C.H. Sellers, Eucalyptus: Its history, growth and utilization, published by A.J. Johnston, Sacramento, CA, 1910
(2) R.G. Florence, Ecology and Silviculture of Eucalypt Forests, CSIRO, 1996
(3) Page 37, Weather of the San Francisco Bay Area, Harold Gilliam, 2002
(4) Kevin M. Clarke, et.al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst., 11:317-334, 2008
Some of the folks who are opposed to the use of pesticides in our public lands have written the following comment on the draft reassessment of blue gum eucalyptus by the California Invasive Plant Council. Their organization is named Communities United in Defense of Olmstead [CUIDO) for a 1999 Supreme Court decision which affirmed the rights of disabled Americans.
We are publishing their comment at their request and extending their invitation to our readers to sign their comment. The deadline for comments is due by July 31, 2014. They are planning to send their comment on July 29th. Please let them know if you would like to add your name and/or organization to their comment. Contact them at: sismhall1@aol.com or 510-654-1366.
Our next two posts will make more suggestions for possible comments. So, our readers will have several options of topics to cover. And you are free to sign as many comments as you wish. It’s still a free country. Exercise your rights to free speech. That’s what makes them strong.
To: California Invasive Plant Council
Re: Public Comment, Draft Reassessment of E. globulus
July 29, 2014
We understand that you are now reassessing your listing of blue gum eucalyptus as an “invasive species” in California, and that you are inviting public comments.
We represent some of the thousands of people who live near and recreate in East Bay area parks and who vehemently oppose the massive removal of eucalyptus trees in our urban forests. These trees are not “invasive” as you yourselves have conceded; their population is stable. (“It is reasonable to conclude that there is no significant net change in cover statewide.”) Instead you now raise concerns about fire danger and water shortage as pretexts for continuing to scapegoat this species of tree.
Climate change is upon us, and deforestation (which contributes to climate change) in the name of mitigating fire and drought (which are exacerbated by climate change) makes no sense and is counterproductive. We observe every summer that these tall trees capture significant moisture from fog. We witness intense fires all over the west, mostly in areas that do not contain eucalyptus. The scapegoating of this species is a false solution to a very big problem. You are not seeing the forest for the trees.
Furthermore, as people with disabilities, including chemical sensitivity caused by exposure to pesticides, we object to the use of herbicides, which inevitably follow attempts to remove “invasive species.” We are alarmed by the recent dramatic increase in the application of poisonous pesticides to our public parks. This threatens our health and violates our right to access public spaces, a right which is guaranteed by the Americans with Disabilities Act.
Finally, as human beings who love the earth, we cannot allow to go unchallenged the hubris and ethical failings embedded in the idea that we humans have a right to destroy ecosystems. (If any species belongs on a list of “invasives,” it is homo sapiens!) Such destruction is the inevitable consequence of your decision to continue with this listing. The science does not justify keeping eucalyptus on your list of “invasive” species. It is rooted in xenophobic prejudice, and like all bigotry, will cause untold damage.
Additional organizational and individual supporters:
Update:On March 13, 2015, the California Invasive Plant Council published its final reassessment of Blue Gum Eucalyptus (available HERE). Cal-IPC has downgraded its rating of invasiveness and ecological impact from “moderate” to “limited.” Although the detailed assessment is less than perfect, the over all rating itself is an improvement. Thanks to those who sent comments to Cal-IPC.
In December 2013, one of our collaborators in the effort to save our urban forest from pointless destruction submitted a request to the California Invasive Plant Council to reconsider its evaluation of blue gum eucalyptus (Eucalyptus globulus) as “moderately invasive.”
The California Invasive Plant Council (Cal-IPC) has responded to that request with a draft reassessment which is available here: http://www.cal-ipc.org/ip/inventory/eucalyptus.php. Cal-IPC’s draft maintains the same over-all rating of blue gum as “moderately invasive.”Cal-IPC is inviting “substantive comments and questions” by July 31st toinfo@cal-ipc.org.
Today we are publishing with permission the cover letter of a public comment that will be submitted by one of our collaborators. We hope it will inspire you to write your own public comment by the deadline of July 31,2014.
From the perspective of humans, there are pros and cons to most species of plant and animal. E. globulus is no exception to this general rule. Cal-IPC reaches a negative conclusion regarding blue gum by exaggerating negative issues and de-emphasizing or omitting positive issues. Cal-IPC now acknowledges that blue gum has “low invasive potential” only in specific conditions and that its population in California is stable, but it has introduced new issues and intensified others so that it can maintain its overall rating of “moderately invasive.” I remind Cal-IPC that its name is InvasivePlant Council, not fire council or hydrology council.
Cal-IPC also fails to take into consideration the negative side-effects of attempting to eradicate eucalyptus. There are environmental benefits associated with leaving blue gums alone. These damaging consequences of eucalyptus removal should appear on the “asset” side of the ledger:
When eucalypts are destroyed, repeated applications of herbicide to stumps are required to kill the roots of the trees to prevent them from resprouting multiple trunks. If the resprouts are not aggressively managed, the result will be more eucalypts than presently exist, which has been the result of some past projects.
The herbicides used to kill the roots (usually Garlon) are known to damage mycorrhizal fungi and microbes in the soil. Therefore, the growth of whatever plant succeeds the eucalypts is hindered by the damage that is done to the soil.
It is also not in Cal-IPC’s strategic best interests to continue to advocate for the eradication of eucalyptus in California:
As the eradication projects get progressively more destructive, the public’s negative reaction to the destruction becomes progressively more aggressive. There are now thousands of us all over the State and all over the country, working to stop this destruction and we are often effective in preventing these projects from being approved or funded. An op-ed in the New York Times in September 2013, expressed support for our opinion that the word “invasive” has become a destructive tool and is inappropriately applied to eucalyptus in California.
Since blue gum eucalyptus is no longer available in nurseries in California and has not been planted for many decades, it has no long-term future in California. To the extent that eucalyptus is a problem, it is a problem that will resolve itself in time.
Cal-IPC’s continued support for these projects is no longer in the mainstream of scientific or public opinion. Removing eucalyptus from Cal-IPC’s “hit list” would significantly improve Cal-IPCs chances of success with the plants that remain on its inventory of invasive plants. The public is unlikely to expend the same amount of energy opposing the eradication of broom, for example.
Cal-IPC has an opportunity to defuse a controversy that is handicapping the success of its venture. Cal-IPC would be wise to abandon its crusade aganst blue gum eucalyptus.
Update:On March 13, 2015, the California Invasive Plant Council published its final reassessment of Blue Gum Eucalyptus (available HERE). Cal-IPC has downgraded its rating of invasiveness and ecological impact from “moderate” to “limited.” Although the detailed assessment is less than perfect, the over all rating itself is an improvement. Thanks to those who sent comments to Cal-IPC.
A new front has opened in the relentless war on eucalyptus in California. The drought has given native plant advocates an opportunity to develop a new narrative to justify their demands for eradication of eucalyptus. The opening gambit in this new strategy is an item in Jake Sigg’s “Nature News” of May 16, 2014:
“The prolonged drought of the last 2-3 years seems to be taking its toll. The Tasmanian blue gums in Glen Canyon along O’Shaughnessy Boulevard strongly show drought stress. The stress is more evident from the high cliffs above O’Shaughnessy than it is at ground level. Thinning crowns and discolored foliage was striking. And that was before the recent heat wave.
Barring substantial rains–unlikely, but not impossible–the trees are in serious trouble. The City could have an emergency situation and no money to address it.”
Recap of the war on eucalyptus
When public land managers began the war on eucalyptus in the 1980s it did not occur to them that the public would object. So deep was their prejudice against eucalyptus, that they assumed the public shared their opinion. The first two massive projects in the 1980s on National Park Service and State Park properties were greeted with angry public protests. Land managers quickly learned that it was not going to be as easy to eradicate eucalyptus as they had thought. They developed a series of story-lines to justify their projects, which were designed to convince the public that the eradication of eucalyptus is both necessary and beneficial. This is a summary of some of their cover stories with links to articles that debunk them:
Based on our experience, we were immediately suspicious of the new claim that San Francisco’s eucalyptus forest is dying of drought. We know that our predominant species of eucalyptus—Tasmanian blue gum—grows successfully throughout California, all the way to the Mexican border in climates that are much hotter and drier than the Bay Area. We also know that the central and north coast of California is foggy during the dry summer months, which doubles the amount of annual precipitation in the eucalyptus forest. All reliable sources of horticultural information describe blue gumeucalyptus as drought tolerant. Frankly, we couldn’t see how our eucalyptus could be dying of drought.
What is wrong with our eucalyptus forest in Glen Canyon?
The picture became clearer when Jake Sigg posted the following on his “Nature News” on June 12, 2014:
“The June 10 newsletter [see below*] included an editorial on an evolving catastrophe, mostly involving our numerous plantations of Tasmanian blue gums. The editorial focused primarily on the plantations on O’Shaughnessy Blvd in Glen Canyon and on Mt Sutro, and included a photo of a grove of Mt Sutro dying trees. Here is a photo of the Glen Canyon plantation, taken from above the high cliffs on O’Shaughnessy. The damage is most visible from high, looking down.
The discoloration of leaves was very dramatic, but the foliage color and condition is not fully conveyed in the photograph. Some trees defoliated entirely in the prolonged winter dry spell. Look very closely at the juvenile blue leaves of the coppice shoots; anything that appears faintly bluish are new coppice shoots which grew in response to the late rains we had in February and March. Once you see coppice shoots on old trees you know the trees are in trouble. These trees are in double jeopardy, as they invested energy in new shoots, but were betrayed by another dry spell which, under normal circumstances, will last until autumn. Note that you can now see the grassland through the trees; that slope was not previously visible. Even a casual inspection of these groves reveals dead, dying, and stressed trees, and under normal circumstances we will have four or five months of dry. The fire situation is serious right now and is likely to become worse.”
View of west side of Glen Canyon Park from Marietta Drive, June 2014
With more specific information in hand about what Jake Sigg is looking at, we went to see for ourselves. We could see what he was describing from a vantage point on Marietta Drive, west of Glen Canyon Park. We could see lighter colored leaves, but they were more localized than Jake Sigg’s description implied. We didn’t feel qualified to speculate about why the leaves were lighter colored so we recruited an arborist to help us figure out what is happening there. We were fortunate to enlist the help of a certified arborist who has been responsible for urban forests on public lands in the Bay Area for several decades. This is what we learned.
Epicormic Sprouts
Looking through binoculars from our vantage point on Marietta Drive, the arborist said immediately, “Those are epicormic sprouts.” The leaves of epicormic sprouts are distinctively lighter colored than the darker green of mature eucalyptus leaves. They are also a more rounded shape than the long, pointed mature leaves of eucalyptus. This is how Wikipedia describes epicormic sprouts:
“Epicormic buds lie dormant beneath the bark, their growth suppressed by hormones from active shoots higher up the plant. Under certain conditions, they develop into active shoots, such as when damage occurs to higher parts of the plant. Or light levels are increased following removal of nearby plants.”
Epicormic sprouts on trees in Glen Canyon Park, June 2014
The remaining question was why some of the eucalypts, were producing these epicormic sprouts, when most were not. We went down to O’Shaughnessy Blvd to get a closer look, hoping to answer that question. This is what we learned:
The understory of non-native shrubs between O’Shaughnessy Boulevard and the trees with epicormic sprouts has been cleared in the past year. We could see the dead brush piled up next to the trees. We had to wonder how people who claim to be concerned about fire hazard could think such huge piles of dead brush were nothing to be concerned about.
Remains of dead non-native brush destroyed along O’Shaughnessy Boulevard, June 2014
We could see the stumps of some of the dead brush and we wondered if the stumps had been sprayed with herbicides after they were cut. Pesticide use reports for Glen Canyon indicate that O’Shaughnessy was sprayed several times in the past year, twice with products containing imazapyr. Imazapyr is known to be harmful to trees if sprayed in proximity to their roots. The trees with epicormic sprouts were downhill from the understory shrubs that were destroyed, in the probable direction of water and herbicide flow.
We found several trees that had been girdled in the past and are now dead.
Girdled tree in Glen Canyon Park, now dead, June 2014
The trees in Glen Canyon Park
Then we walked into Glen Canyon Park from its southern end. It’s not a pretty sight. Many huge, old eucalypts have been destroyed. When they were destroyed, their stumps were immediately sprayed with herbicide to prevent them from resprouting. The stumps are simultaneously painted with dye so that workers can tell which trees have been sprayed. The dye is no longer visible, but regular visitors took photos of the painted stumps before the dye faded. The spraying of the stumps do not appear on the pesticide use reports of the Recreation and Park Department. We assume that’s because the spraying was done by the sub-contractors who destroyed the trees.
Poisoned and dyed eucalyptus stump, Glen Canyon Park, 2013. Courtesy San Francisco Forest Alliance
The arborist who walked in the forest with us said, “The painting of stumps with RoundUp or Garlon in proximity to trees that are being preserved can kill the neighboring preserved tree. Stumps near living, residual (preserved) trees should not be painted with RoundUp or Garlon if the stumps are within 40’ of mature, blue gums that are slated for preservation.” If the remaining trees are damaged by herbicides, their mature leaves fall and epicormic sprouts will then emerge as the tree recovers.
Some of the stumps of the trees that were destroyed in Glen Canyon Park in 2013. Taken June 2014
We saw a lot of epicormic growth in the Canyon, sprouting from stumps that must be cut back and resprayed with herbicides. It usually takes several retreatments to successfully kill the roots of eucalypts that are destroyed. We also saw epicormic growth from eucalypts that had been severely pruned and were also exposed to a great deal more light because they had lost the shelter of their neighboring trees.
Epicormic growth, Glen Canyon Park, June 2014
Wrapping up
The trees in Glen Canyon are reacting to the traumas to which they have been subjected: the loss of their neighbors that were either girdled or cut down thereby exposing them to more light and wind, the loss of the shelter of their understory, the application of herbicides known to be harmful to trees.
The good news is that there are still plenty of trees in Glen Canyon that have not yet been destroyed and they are in great shape. Here is the view of the tree canopy in Glen Canyon taken from the east side of the park near Turquoise Way. The first picture was taken in December 2012 (before the current round of tree destruction in Glen Canyon Park) and the second picture was taken in May 2014.
Eucalyptus canopy on east side of Glen Canyon Park, taken from Turquoise Way December 2012, before tree destruction began. Courtesy San Francisco Forest AllianceSame perspective of Glen Canyon tree canopy, taken May 2014. Courtesy San Francisco Forest Alliance.
These trees are doing just fine because the Natural Areas Program has not yet gone that deeply into the park. But NAP intends to destroy many more trees in Glen Canyon (and elsewhere) when the Environmental Impact Report (EIR) for their management plan (SNRAMP) is finally approved. Then we will see more consequences of the destructive practices of the Natural Areas Program and we will probably hear more bogus explanations for that damage.
We expect the EIR to finally be considered for approval at the end of 2014. [Update: now predicted for fall 2015] We will do whatever we can to convince San Francisco’s policy makers that they should approve the “Maintenance Alternative” which would enable NAP to continue to care for the native plant gardens they have created in the past 15 years, but prevent them from expanding further. We hope that our readers will help to accomplish this important task.
*Jake Sigg’s Nature News of June 10, 2014, introduced the theories of Craig Dawson about the health of the Sutro Forest. Mr. Dawson’s speculations are different from Mr. Sigg’s and we will not address them in this post. You can find an analysis of Mr. Dawson’s theories on Save Sutro Forest HERE.
This is a guest post by Mark Spreyer, Director of the Stillman Nature Center in Barrington, Illinois. He can be reached at: stillmangho@gmail.com
We publish his article about mulberries as our July 4th gift to our readers.
Thy stout heart
Now humble as the ripest mulberry
That will not hold the handling
–Coriolanus, Shakespeare
For those of us of a certain age, mulberries and childhood went hand in hand. Whether it was singing “Here we go round the mulberry bush” or reading Dr. Seuss’ And to Think That I Saw It On Mulberry Street, the word mulberry was all around us.
I was an adult before I learned that actual mulberry trees were all around us as well. We have two species, one red and one white, one native and one introduced. Both are wildlife favorites, and both grow here at Stillman. So, let’s take a walk down our local Mulberry Street.
Mulberry Leaves
The variously lobed red and white mulberry leaves look but don’t feel alike. White mulberry leaves are smoother to the touch than red mulberry leaves. Creative Commons Attribution 3.0
I have often had students, from elementary school to college, identify trees by looking at their leaves. Some have teeth, some have lobes, and some have neither.
Those that have lobes often have a set number. Sugar maple, for example, usually has five lobes.
Enter the mulberry. Whether red or white, mulberry leaves can be unlobed to variously lobed. No, they aren’t about to be limited by a set number!
Yet some tree books seem desperate to quantify the number of lobes. One source writes that mulberry leaves are “sometimes 2-lobed, sometimes 3-lobed, often unlobed….” Well, isn’t that helpful?
There is a pattern to the location of the different leaves. Multiple-lobed leaves are more likely to be found on young trees and root sprouts while unlobed leaves are found in the crowns of mulberry trees.
Red Mulberry (Morus rubra)
This is our indigenous mulberry. It ranges from southern Vermont down to southern Florida across to central Texas and back north to southeastern Minnesota.
Red mulberry. USDA
In Illinois, red mulberries can be found growing in almost every county.
These trees prefer moist woodlands and deciduous bottomlands rubbing branches with American elm, hackberry, silver maple, and box elder.
Red mulberry is a medium-sized tree that can reach a height of fifty feet with a diameter of two feet. Its broad rounded crown makes red mulberry a useful shade tree.
Both red and white mulberry trees are named after the color of their fruit but be forewarned: when red mulberries are red, they are NOT ripe.
Mulberries. Courtesy Kristi Overgaard
The tasty mulberries are ripe when they are purple-black, like a blackberry. When reaching for that first juicy handful, do remember that Shakespeare (as usual) was right. A ripest mulberry easily crumbles in your soon-to-be purple palm.
Not just humans enjoy a handful of sweet mulberries, but wildlife dines on mulberry street as well. A partial list of birds enjoying a midsummer meal of mulberries would include eastern kingbird, American robin, gray catbird, wood duck, starling, Baltimore oriole, northern cardinal, cedar waxwing, brown thrasher, plus red-bellied and red-headed woodpeckers.
Some mulberry munching mammals include opossum, raccoon, fox, skunk, an assortment of squirrels, plus a few dogs I know!
Simply put, red mulberry is one of the best summer fruit trees for wildlife.
White Mulberry (Morus alba)
Now that I think of it, it doesn’t matter to hungry animals if the berries are red or white. This brings us to white mulberry.
Like its red counterpart, white mulberry is a medium-sized tree with variously lobed leaves. It was introduced to N. America during colonial times (see below). It can now be found growing from Maine to Minnesota, south to Texas and east to Georgia. It also is naturalized across most of Illinois.
When white mulberries are ripe, they are indeed white or sometimes pink. The closer you look, though, the more confusing it gets since red and white mulberries freely hybridize. The resulting hybrid fruits come in a variety of colors between white and purple.
White mulberries will grow in almost any upland habitat being particularly at home in urban environs.
Silk Road to Mulberry St.
If you break the leafstalk of a white mulberry, milky sap exudes. This Elmer’s goo is the foundation of a multi-cultural exchange that dates back thousands of years.
Take white mulberry leaves and add the domesticated Chinese silkworm caterpillar (Bombyx mori) and the result are large cocoons spun of the finest silk.
Unwrap that silk and one can weave it into garments that were desired by traders around the world.
What comes next? The ancient and famed silk road (trade routes actually) that crossed Asia from China to Europe.
Others thought there might be an easier way to get their silk. After it was discovered that imported silkworm caterpillars found native red mulberry leaves to be too tough, tens of thousands of white mulberries were being raised by nurserymen in colonial Virginia.
Some of those who planted these promising saplings were Ben Franklin, George Washington, and Thomas Jefferson.
While a few American entrepreneurs succeeded in this labor-intensive silk business, the growing textile industries soon found ways to make quicker profits.
The neglected white mulberry trees fed birds and mammals that, in turn, spread white mulberry seeds around a good chunk of the continent.
Back on Mulberry Feet
Mulberries are indeed good street trees. Once established, they can withstand salt, drought, air pollution, and soil compaction. Some will say, there is little need to plant mulberries as wild animals are doing a fine job at that.
However, when the berries fall thick from the trees they can make you feel like you have double-sided tape on the soles of your shoes. Your gooey shoes pick up bits of gravel and so it goes.
Keep in mind that mulberries are dioecious meaning there have separate male and female plants. Planted male mulberries, of course, won’t bear fruit.
With apologies to Dr. Seuss– perhaps you like sticky feets or just want handfuls for eats, either way visit Stillman for treats along our Mulberry Streets.
Mulberry Jam Recipe
Mr. Spreyer’s note: This recipe comes from the Illinois Department of Natural Resources. In particular, the cooking credit belongs to Deb Singer and Kathy Andrews.
I expect that red mulberries are used more often than white mulberries in this recipe.
I say this because I think we are used to ripe berries being red or darker in color (i.e. blackberries, blueberries, strawberries, raspberries). However, I bet if you hybridize your jam with some white mulberries, it would taste just as good.
Oh yes, a mulberry pie would also be a nice summer treat.
3 cups crushed mulberries
½ cup lemon juice
1 package (1.75 ounces) powdered pectin
6 Cups sugar
Bring berries, lemon juice and pectin to a rolling boil. Add sugar. Return
to a boil and boil for 1 minute. Skim off foam. Ladle into prepared jars and process in a water bath for 10 minutes
A new study reported changing public and scientific interest in biodiversity compared to climate change. Using reports in the media and scientific journals in the United Kingdom and the US, as well as funding of scientific studies by the World Bank and the National Science Foundation, the study reports that the interest in climate change has increased and the interest in biodiversity has decreased in the past 25 years.
This analytical approach seems to suggest that these two environmental issues are mutually exclusive, that the interest in one is at the expense of the other. We find this both unfortunate and unnecessarybecause we consider these two issues intimately related. Climate change is increasingly the biggest threat to biodiversity. If plants and animals are unable to adapt to climate change, they are doomed to extinction.
Therefore, we believe that science should study these topics together. In fact, the study on which we are reporting acknowledges the relationship between these topics: “Dual-focus projects are being funded more often, but… ‘this is relatively small and does not mitigate the plateauing expenditure on biodiversity research.’” (1)
Conservation in a changed climate
As long as conservation and “restoration” projects are devoted to replicating historic landscapes, they are likely to be unsuccessful. The climate, atmosphere, and soil conditions are no longer suited to a landscape that existed hundreds of years ago, particularly in urban environments. Therefore, if biodiversity is to be preserved by conservation and restoration, such projects must look forward, not backwards.
We have been watching the Nature Conservancy closely for signs that it is adapting to climate change. We look to the Nature Conservancy to lead the way because they employ hundreds of scientists. In contrast, many mainstream environmental organizations employ more lawyers than scientists.
Unfortunately, the old guard of conservation biology has engaged in a vigorous campaign to silence the Conservancy’s new approach. This conflict between the old guard and scientists who have proposed a more realistic approach to conservation was recently reported by the New Yorker. (2) According to that article, Peter Kareiva has made a commitment to the old guard to quit publishing anything regarding the Anthropocene and its implications for conservation practices.
The Nature Conservancy has responded to the article in the New Yorker in its on-line blog. It doesn’t explicitly address the question of whether or not a commitment has been made to quit advocating for a more realistic approach to conservation. However, it implies that the Conservancy plans to continue on a course of scientific innovation and experimentation, which it describes as “practical.” Here is a specific choice made by the Conservancy that typifies this approach:
Monarch butterflies roosting in eucalyptus tree.
“We know it was worth spending millions of dollars to rid Santa Cruz Island of non-native pigs. But we are pretty sure it would not be worth spending what could be hundreds of millions of dollars to rid California of non-native Eucalyptus trees (which also happen to harbor wildlife and monarch butterflies.)” (3)
Although the Nature Conservancy’s Chief Scientist may have agreed to “shut up,” we see signs of the Conservancy’s new approach in its latest magazine. In a brief article entitled “Forests of the Future,” the magazine reports that they are no longer planting the species of trees that existed in the past in one of their properties in Minnesota, because they don’t believe that species is adapted to current or predicted future conditions. Instead they are actively engaged in reforestation of the land with new species:
“Over the past two springs, the team planted 88,000 tree seedlings across 2,000 acres in the northeastern corner of the state. The seedlings consisted of species that should survive better in a warmer and drier climate—trees, such as red oak, found in higher numbers just south of the area. For a team accustomed to restoring forests to match historical landscapes, helping the North Woods [of Minnesota] adapt to a predicted future climate is a new but necessary idea. [The Conservancy’s science director in Minnesota] says, ‘All of our modeling is saying the same thing,’ she adds, ‘We needed someone to actually go out and start trying some of this stuff.’” (4)
Looking forward not back
We are very encouraged by the Conservancy’s new approach and we hope that other land managers will be inspired by it. We are also reminded of a recent visit to a nature reserve near San Luis Obispo managed by the local chapter of the Audubon Society. We reported about this reserve in a recent article because the land managers had planned to destroy all eucalyptus trees on that property but were forced to scale back their plans in response to a noisy negative reaction from the public.
Dying oak tree, Sweet Springs Nature Reserve
On our recent visit, we learned that this was a wise choice because many of the oak trees that were planted on this reserve by those who wish to “restore” it are quite dead despite the fact that the reserve has an extensive irrigation system. These land managers looked back and the result of that retrospective thinking is a landscape of dead native trees.
Climate change requires land managers to wake up to the realities of what will grow where. Land managers in the San Francisco Bay Area appear to be blind to that reality. They repeatedly plant species where they grew hundreds of years ago and we are forced to watch the plants die repeatedly.
Ants are important members of the ecosystem. They improve the fertility and consistency of the soil. They distribute plant seeds. They are both predators of and food for other insects as well as birds and omnivorous mammals. Therefore, their abundance in an ecosystem is often considered an indicator of its health.
Today we will report on a study of ant populations in San Francisco’s “natural areas,” parks that were designated over 15 years ago for restoration and preservation of native plants. This study reaches this conclusion:
“The results of this study indicate that natural areas within urban parks play a critical role in supporting ant biodiversity. Many habitats in the natural areas of San Francisco’s parks support healthy, diverse ant communities. Areas of non-native forest, however, reduce this diversity. Maintaining open grasslands, reducing tracts of non-native forest, removing the invasive understory, and thinning forest canopy may all help support a healthier ant community and ecologically valuable parks.” (emphasis added) (1)
Could this ant study be the first example we have found of evidence that native plants benefit wildlife and conversely that our non-native urban forest is less valuable for wildlife? We have examined this study to determine how it reached this conclusion. We have compared this study to similar studies that report different findings. We reached the conclusion that this study does not support its conclusion that “reducing tracts of non-native forest…may…help support a healthier ant community and ecologically valuable parks.”
The relationship between ant communities and soil moisture
The ant study used pitfall traps to survey the abundance and diversity of ant populations in 24 “natural areas.” It also measured the moisture of the soil in proximity of the traps. The ant study found that soil moisture and ant abundance and diversity were positively correlated at low levels of moisture, but that high levels of moisture found in eucalyptus forest were negatively correlated with abundance and diversity of ants:
We will tell you how this ant study used this empirical observation of the relationship between soil moisture and ant populations to reach its conclusion that non-native forests must be “reduced” to achieve “ecologically valuable parks.”
Generalizing about “urban forests”
This study of San Francisco’s ant population asks us to believe that its negative assessment of San Francisco’s urban forest applies to all urban forests: “Urban forests are structurally different than natural forests. Besides being smaller, fragmented, and more isolated than non-urban forests, urban forests also show increased canopy cover, greater disturbances due to human traffic and pollution, and differences in leaf litter accumulation.” (1)
We don’t think it is possible to generalize about all urban forests. Here are two sources which suggest that the ant study has over-generalized about urban forests and ants found in them:
According to the US Forest Service survey of urban forests, San Francisco has one of the smallest tree canopies in the country. Only 11.9% of San Francisco is covered by the tree canopy, compared to 20.9% of New York City. According to that survey, San Francisco’s urban forest removes 141 tons of pollutants per year compared to 1,677 tons of pollutants removed by New York City’s urban forest.
Ants are found in some urban forests. A study in Toledo, Ohio and Detroit, Michigan compared ant populations in urban habitats (forests in city parks, community gardens, and vacant lots). (2) The study found greater diversity of ant species in forests than in other habitat types, but fewer ants. They found 26 species of ants in the forest, 20 in vacant lots, and 14 in gardens. They found no correlation between various characteristics of vegetation and ant diversity or abundance. Soil moisture was not measured by this study. Generalizations about urban forests derived from one study in San Francisco clearly do not apply to Toledo and Detroit.
More soil moisture in forest with a closed canopy
The ant study in San Francisco predicts greater soil moisture in a forest with a closed canopy and dense understory:
“A combination of high soil moisture, dense canopy cover, and dense understory (habitat complexity) may help explain the lack of ground-foraging ants in urban forests.” (1) The study associates those characteristics specifically with the eucalyptus forest: “Within forest types examined, eucalyptus forests contained significantly more soil moisture than other forest types and also had lower ant richness and abundance.” (1)
We don’t think these generalizations can be applied neither to all eucalyptus forests nor solely to eucalyptus forests:
The density of eucalyptus forest in the San Francisco Bay Area varies widely according to data presented recently by Professor Joe McBride to the Commonwealth Club:
Location
Average Number of Trees per Acre
Presidio, San Francisco
163
Land’s End, San Francisco
364
Tilden Park, Berkeley
540
East Ft Baker, Marin County
1795
In other words, not all eucalyptus forests have closed canopies.
The density of understory in the eucalyptus forests of the Bay Area also varies widely. One of the densest understories exists on Mount Sutro, which is the location of the Interior Greenbelt, where the ant study reports finding no ants. In drier locations, such as Bayview Hill, there is little understory in the eucalyptus forest, which may be why the ant study reports finding ants there. Bayview Hill is on the east side of San Francisco and therefore receives much less fog than Mount Sutro, which is closer to the ocean.
Eucalyptus forest is not unique in often having a closed canopy. Native redwood forest also has a closed canopy:“Many meters above the ground, the branches of trees, especially those of redwood, merge to form a ceiling, or canopy.” (3)
Fog and soil moisture
The ant study describes the relationship between fog and soil moisture in San Francisco: “The increased moisture in eucalyptus is due to the fact that summer fog tends to condense on eucalyptus leaves and branches and drip down to the soil below. Such fog drip can add as much as 42 cm of water to eucalyptus forest during a single summer.” (1)
Fog in San Francisco is unrelated to the fact that its forest is predominantly eucalyptus:
Redwood forest. NPS
Although redwoods did not live in San Francisco when Europeans arrived in 1769, they lived there in the distant past. Native redwoods now exist only on the coastal fog belt of California. Fog is essential to their survival: “During the study period, 34%, on average, of the annual hydrologic input was from fog drip off the redwood trees themselves. When trees were absent, the average annual input from fog was only 17%, demonstrating that trees significantly influence the magnitude of fog water input to the ecosystem…The results presented suggest that fog, as a meteorological fact, plays an important role in the water relations of the plants and the hydrology of the forest.” (4)
Fog exists along the northern coast of California because the interior is hot and the ocean is cool. When the cool ocean air meets the hot air from the interior, fog forms. The existence of fog has nothing to do with the species composition of the forest. Any tall tree is capable of condensing the fog, which then drips to the forest floor, providing water to both the trees and their understory. The eucalyptus forest is not to blame for this sequence of events.
The nativity of the urban forest is irrelevant to the ants
The ant study implies that there are few ants in San Francisco’s urban forest because the forest is not native to San Francisco: “…reducing tracts of non-native forest…may all help support a healthier ant community and ecologically valuable parks.”
Soil moisture is the operative variable in predicting abundance and diversity of ant populations. The nativity of the vegetation is irrelevant to the ants:
If the urban forest in San Francisco was native redwoods, it would precipitate equal amounts of fog, resulting in equal amounts soil moisture. The ant population would probably be similar.
A study of ant populations in the central Appalachian Mountains found the same relationship between soil moisture and ant populations in native forests: “Fewer ants, lower number of species, and lower ant diversity were found at sites with higher elevation and soil moisture.” (5)
A study of ant populations in Northern California grasslands found that the characteristics of the soil were better predicators of ant populations than the types of vegetation: “Plants were less important than soil attributes in explaining variation in overall ant species richness and abundance…” (6) Chemical composition and consistency (sand vs. clay) of soils were evaluated by this study, but not soil moisture
“Science” in the service of nativism
We consider this ant study a classic demonstration of nativism. In this case, soil moisture was confounded with the non-nativity of forest in San Francisco. The nativity of San Francisco’s forest is irrelevant to the amount of soil moisture.Any closed canopy forest of tall trees would precipitate equal amounts of fog and have a similar impact on ant populations.
The study speculates that the allelopathic properties of eucalyptus may have a negative impact on the ants, but offers no evidence. We have found no evidence of allelopathic properties of eucalyptus. Nor do we think that the existence of ants should be the sole criterion for “ecological health.” Would we demand the destruction of redwood forests so that we could have more ants? We doubt it.
However, we must also give credit where credit is due. The ant study reports that the existence of the non-native Argentine ant does not have a negative impact on the populations of native ants. They report that the Argentine ants occupy the perimeter of the “natural areas” where native ants generally are not found. This is a refreshing departure from the usual nativist claims that all non-native plant and animal species have negative impacts on native species.
(1) Kevin M. Clarke, et. al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst, 11:317-334, 2008
(2) Shinsuke Uno, et. al., ”Diversity, abundance, and species composition of ants in urban green spaces,” Urban Ecosyst, 13:425-441, 2010
(4) T.E. Dawson, “Fog in the California redwood forest: ecosystem inputs and use by plants,” Oecologia, 117-4:476-485, December 1998
(5) Changlu Wang, et. al., “Association Between Ants and Habitat Characteristics in Oak-Dominated Mixed Forests,” Environmental Entomology, October 2001
(6) April Boulton, et. al., “Species Richness, Abundance, and Composition of Ground-Dwelling Ants in Northern California Grasslands: Role of Plants, Soil, and Grazing,” Environmental Entomology, February 2005
One of the persistent questions in our interminable debate with native plant advocates is whether or not native vegetation provides superior habitat for wildlife compared to existing non-native vegetation. At the heart of that question is the closely related question of whether or not more insects are found in native vegetation than in non-native vegetation. That’s because insects (and other arthropods) are near the bottom of the food web. If there are fewer insects, there are probably fewer birds and other animals that eat insects. We have told our readers about many studies that find equal abundance and diversity of insects in native compared to non-native vegetation, so we won’t repeat them, but here’s a brief list of those studies and links to them for new readers:
Does “restoration” of native vegetation increase insect populations?
Arthropods – Creative Commons Share Alike
In this post we will consider this issue from a slightly different angle: can insect population or diversity be increased by “restoration” of native vegetation? Even if we accept the premise of native plant advocates that native vegetation supports greater abundance and diversity of insects, can that population be “restored” by eradicating non-native vegetation and replacing it with native vegetation? That question is answered with a resounding “NO” by a study that compared arthropod abundance and diversity in undisturbed (predominantly native vegetation), disturbed (predominantly non-native vegetation), and disturbed sites 5 and 15 years after restoration. (1) Restoration methods described in the study are mowing followed by disking and seeding, disking and seeding, planting of container stock, and clearance by hand. All sites were irrigated initially. No mention is made of herbicide use or prescribed burns to eradicate non-native vegetation. The vegetation type in all 15 sites in Southern California was coastal sage scrub. This is the dominant vegetation type along the coast of California and is the goal of many restoration projects in the San Francisco Bay Area. Many species of both native and non-native vegetation in the study sites also exist in the Bay Area.
Coastal sage scrub in Southern California – Creative Commons Share Alike
The study used pitfall traps to collect arthropods in these sites. Arthropods are invertebrates that include insects, arachnids (spiders), and crustaceans (aquatic species not relevant to this study). Arthropods are further divided into guilds such as herbivores, predators, scavengers, and parasites. Because of the method of collecting in pitfall traps, few herbivores were found. Here are some of the findings of this study:
“Arthropod diversity at undisturbed and disturbed sites was greater than at sites that were 5 and 15 years following restoration.”
“Number of arthropod species was not significantly different among undisturbed, disturbed, and restored sites.”
“Vegetation at disturbed and undisturbed sites differed significantly; older restorations did not differ significantly from undisturbed in diversity, percent cover, or structural complexity.”
“Vegetation characteristics did not differ significantly between the newly restored site and disturbed sites.”
“…arthropod communities at all restored sites were, as a group, significantly different from both disturbed and undisturbed sites.”
“As found in other studies of other restoration sites, arthropod communities are less diverse and have altered guild structure.”
Here is the concluding discussion of this study:
“Of the restoration sites sampled, none had developed an arthropod community that resembled undisturbed or disturbed native coastal sage scrub. Restoration sites in general exhibited lower arthropod diversity and a preponderance of exotic arthropod species. The time elapsed since revegetation effort had no discernible effect on arthropod community structure; there was no gradual return of the community to a more natural structure over time”.
“Restorations” do not improve arthropod abundance or diversity
This study found that arthropod population and diversity was the same in disturbed (non-native) and undisturbed (native) vegetation. When disturbed vegetation was “restored” arthropod population was maintained but the composition of the arthropod community was significantly changed even 15 years after the restoration was completed. There were more “exotic” species of arthropods in the restored sites even though the vegetation was similar to the undisturbed sites of native vegetation. The restored vegetation was native, but its arthropod occupants weren’t.
However, the birds and other animals that prey on those insects don’t care if the insects are native or non-native. Much like humans, animals are not concerned with the nativity of their food. The non-native apple you are eating is just as tasty whether you are eating it in its native range in Central Asia or where it has been introduced. If you have an apple tree, you know the birds and squirrels enjoy the apples too and the bees and other pollinators enjoy the apple blossoms. Most of what we eat is not native, yet many people are obsessed with the nativity of vegetation, claiming that animals require native vegetation even though humans don’t.
An important caveat
The predominant vegetation type in the San Francisco Bay Area is coastal scrub, which is also the vegetation type in the study of arthropod populations. This suggests that if a similar study were conducted here, the results might be similar. However, there is one very important difference between the restorations studied in Southern California and the restorations in the Bay Area. Land managers in the San Francisco Bay Area are using large amounts of herbicides to destroy non-native vegetation. The study in Southern California reports no herbicide use in restoration sites.It seems likely that herbicides sprayed in restoration projects in the Bay Area would decrease the population of arthropods. We would like to see a study that tests that hypothesis.
There is more to an ecosystem than plants
The veneration of native plants has become a national obsession. Demands for eradication of non-native plants are supported by many fictions to justify these destructive projects. One of those fictions is that wildlife requires native vegetation. We have found no empirical evidence to support that assumption. The study we are reporting today is yet more evidence that restoring native plants does not restore an ecosystem. In this case, after 15 years of effort, land managers were eventually successful in establishing a population of native plants. However, these “restored” native landscapes did not support a population of insects and spiders that were comparable to either the undisturbed native landscape or the unrestored non-native landscape. We have been looking for some legitimate reason to engage in these destructive projects for over 15 years. We have yet to find any justification for spraying our public lands with herbicides or destroying hundreds of thousands of healthy trees. We will keep looking.
(1) Travis Longcore, “Terrestrial Arthropods as Indicators of Ecological Restoration Success in Coastal Sage Scrub (California, USA),” Restoration Ecology, December 2003, Vol. 11 No 4, pp.397-409
Conservation Sense and Nonsense 