Saving our Urban Forest: A small step forward

 The San Francisco Forest Alliance (SFFA) has announced (see below) the successful conclusion of a year-long process of developing a policy for the management of San Francisco’s urban forest by the city’s Urban Forestry Council (UFC).  If you have not been closely following the development of this policy it may be difficult to appreciate the importance of this accomplishment. Native plant advocates made every effort to prevent the UFC from adopting a policy that would make a commitment to the preservation of the urban forest.  As our readers know, native plant advocates want the entire urban forest to be destroyed because it is non-native, so they can attempt to recreate native grassland and scrub that existed at the end of the 18th century, prior to the arrival of Europeans. Native plant advocates tried several different strategies to make the case to the UFC for the destruction of the forest.  This is the sequence of the many bogus narratives they attempted to sell to the UFC:

  • They started with the claim that the forest is diseased and dying and must be destroyed.  With the help of arborists and our usual independent research, we were able to disprove this particular story line.
  • Then they claimed that forest health would be improved by radical thinning of the forest.  Again, our research was able to prove that mature forests do not benefit from thinning because mature trees are unable to respond positively to increased light and wind.  The trees that remain are actually more vulnerable to windthrow because they are not adapted to increased wind.
  • Then they claimed that the forest is dying of drought and must be destroyed to prevent the dead trees from becoming a fire hazard.  Again, our research was able to prove that our eucalyptus forest is drought-tolerant and is actually more likely to survive the drought than the native plants which will not precipitate as much fog drip as tall trees.  However, the final document contains an erroneous claim that the drought has “serious negative effects to mature trees.”  In fact, young trees require more water than mature trees.

In December 2014, after listening to six months of these horror stories, it seemed that the UFC was headed in the wrong direction.  Their questions and comments, as well as the meetings we were able to arrange, seemed to indicate they were prepared to endorse the destruction of our urban forest.  In January 2015, the first draft of the UFC policy confirmed our worst fears.  They endorsed “land conversion” from forest to native grassland and scrub and the use of herbicides to prevent the resprouting of the forest.

Having done everything we could to prevent this outcome, we despaired.  And then the UFC produced a revised draft in April 2015 which was a 180-degree turn from the first draft.  We will never know what turned the UFC around, but we surely had a hand in it.  Even if there was some unseen influence operating in the background, our viewpoint was confirmed and vindicated by the final outcome.

The UFC then postponed approval of their document, saying they were waiting for public comments from one of the stakeholders.  I presume this delay was requested by the Recreation and Park Department, because the final revision of the document accommodated its so-called Natural Areas Program by stating that “management priorities and decisions for some of the mature and historic tree stands [within the “natural areas”] may be different from management practices for other areas of the urban forest.”  However, written comments from the Recreation and Park Department were not visible to us.

We are taking the time to tell you about this accomplishment because we hope you will be encouraged by it.  Sometimes the odds seem overwhelmingly against our efforts to save our urban forest.  But with tenacity and commitment, it is possible to prevent bad things from happening.  We are deeply grateful to those who participated in this successful effort to prevent the development of an official city policy that could have endorsed the destruction of our urban forest.

Much remains to be done.  Do not give up hope that we can save our urban forest.  Please renew your commitment to our efforts


SFFA UFC policy

Greetings to SFFA Supporters and Members

This week the Urban Forestry Council of the Dept. of Environment accepted a document now called “Guidelines for Managing Mature and Historic Tree Stands,” which had originally been called “Best Management Practices for Urban Forests.” It was written largely by John Leffingwell of HORT Science who sits on the Council, with assistance from Mei Ling Hui, staff member from Dept. of Environment; John Flanagan, Chair of the Council; and Igor Lacan, who also sits on the Council and works for the San Mateo-San Francisco Cooperative Extension service.

The document went through several iterations, starting back with its first draft in January 2015, which followed six months of meetings and presentations in 2014. By April 2015 it had been completely revised and had moved away from its earlier endorsement of restoration ecology and the native plant agenda of destroying blue gum eucalyptus forests. Unfortunately, it was passed including one section called “Competing Land Use Priorities” that provides a disclaimer for the Natural Areas Program to treat its trees differently than other urban forests in the name of “protecting San Francisco’s ‘remnant fragments’ of its original landscape.” That section could, at some later date, be used by Rec and Park as endorsement of their destructive plans in the Natural Areas.

However, there is much in the document that would mitigate against that destruction, including a section called “Protect and sustain iconic forest stands.” This section argues that our mature and historic tree stands “are character defining features of the city that provide unique experiences to those who enjoy them” and should be “protected and managed for their cultural and social benefits to residents and visitors.” Their importance is “evidenced by community groups formed around the protection and management of these sites” [Note: that would probably mean the SF Forest Alliance and Concerned Citizens for the Maintenance Alternative.] Although this document may not sound important, it is. It will be used as a guideline by the Urban Forestry Council whenever issues or plans related to the urban forests are brought before them. Potentially, the Board of Supervisors might refer to it as well when there is an appeal of the EIR for the Natural Areas Program’s management plan.

It took a year’s worth of volunteer hours from SF Forest Alliance leaders who attended meetings, made comments and presentations. Additionally, others, including Dr. Joe R. McBride and members of the Hills Conservation Network made presentations before the Council supporting our point of view. We see it as a small step in the right direction. 

Thanks for your continued support!

San Francisco Forest Alliance

STAYING IN TOUCH

1) We encourage you to visit our Blog at http://sfforest.net.  Enter your email address as the top right (“sign me up”) in order to receive our updates directly to our email.

2) If you’re on Facebook, please “Like” our page http://www.facebook.com/Forest Alliance.  We currently have 424 “likes.”  Help us to take it over 450!

3) We can be reached at this email address:  sfforestnews@gmail.com

We welcome your interest and support!

“Drought-Adapted Eucalyptus NOT Dying by the Thousand”

Native plant advocates in the Bay Area have always had trouble convincing the public and their elected representatives that it is necessary to destroy every non-native tree in our urban forest.  They have therefore resorted to fear-mongering to convince the public that it is necessary to eradicate all non-native trees for public safety. 

Fear of fire has been effective in the East Bay where there have been fires, although claims they were caused by non-native trees are a distortion of the facts.  For the past year, native plant advocates in San Francisco have been using a variation on that theme to support their demands to destroy all non-native trees.  They now claim our eucalyptus forest is dying of drought and must be destroyed before it causes a disastrous fire.  You can read that story line in Jake Sigg’s Nature News (here) or in his recent public comments to San Francisco’s Urban Forestry Council (here), which is in the process of developing Best Management Practices for San Francisco’s urban forest.

It is our pleasure to republish this post from Save Mount Sutro Forest, responding to those claims.  As usual, it is meticulously researched and documented.  We only wish to add this small bit of common sense: The drought is hard on all plants.  If the drought were capable of singling out one species of tree to kill, it would not be the drought-tolerant eucalyptus. 


Jake Sigg, retired San Francisco Recreation and Parks Department (SFRPD) gardener who is considered the doyen of the Native Plant movement in San Francisco, has a widely circulated email newsletter. In it, he has been pushing the argument that thousands of eucalyptus trees in San Francisco are dying of drought, as evidenced by epicormic growth on these trees: “2015 is the year of decision, forced upon us by 20,000 to 30,000 dead trees.” He is suggesting they will be a fire hazard and that SFRPD must act, presumably by cutting down the trees. In a recent post, he published a picture of a tree covered in young blue-green leaves, and predicted it would be dead within a year.

But he’s mistaken.

Eucalyptus trees are drought-adapted, and the shedding of mature leaves followed by sprouting of juvenile leaves (epicormic sprouting) is one of their defense mechanisms. These trees survive in areas far drier than San Francisco, where fog-drip provides an important source of summer moisture.

2015-05-27 ab eucalyptus with epicormic growth wordEUCALYPTUS RESPONSE TO DROUGHT

Eucalyptus trees are adapted to drought. They shed mature leaves and twigs so they don’t lose water through transpiration (the tree version of breathing, which takes place mainly in the leaves.) Later, they can replace the lost branches and leaves through “epicormic sprouting.”

Blue gum eucalyptus trees have buds buried deep under their bark. When the tree is stressed, they may shed adult leaves and later sprout new leaves along their branches. When you see a eucalyptus tree that seems to have shaggy light bluish-green new leaves along its branches or trunk – that’s epicormic sprouting.

Here’s what Jake Sigg said in a recent newsletter: “According to arborists, the trees produce these abnormal shoots from epicormic buds when their lives are seriously threatened. In this case, the tree is expected to be dead by the end of 2015. On Bayview Hill, barring heavy unseasonal rain, hundreds of the trees will be dead this year. Yet the City continues to not see a problem.”

We asked UC Berkeley Professor Emeritus Joe McBride and California’s leading expert on eucalyptus for his opinion. He’s observed this condition in trees along the edge of the Presidio forest and explains, “This response is common in blue gum as a mechanism to reduce transpiration rates in order to survive drought years.”

He continues: “I am not convinced that the trees will die in large numbers.

bayview-hill-2010 smTHE GIRDLED TREES OF BAYVIEW HILL

As an aside, we find it ironic that Mr Sigg should be so concerned with dead trees on Bayview Hill, given that’s where nativists girdled hundreds of healthy eucalyptus trees to kill them. Two girdled trees

(This is done by cutting around the tree, thus starving it of nutrients that are carried only in the outer layers of the tree-trunk.) It’s clearly visible in the two photographs here, both taken on Bayview Hill.

EUCALYPTUS ADAPTS

In fact, one of the reasons eucalyptus is so widely planted – including in climates both hotter and drier than in San Francisco – is that it adapts to a wide range of conditions.

Eucalyptus globulus thrives in Southern California, Spain, Portugal, India – all places hotter and drier than San Francisco.

Here’s a quote from R.G. Florence’s textbook, Ecology and Silviculture of Eucalyptus Forests:

florence quoteFrom p.121 of the same book: “… they regulate their water usage in hot dry summers by closing their stomata [breathing pores in the leaves] during the day and lowering their rates of gaseous exchange. They adapt by their elastic cell structure to water stress.”

EPICORMIC SPROUTING IS IMPORTANT IN EUCALYPTUS

Mr Sigg describes “how to identify a dying blue gum” as follows: “Look for trees with thinning foliage and copious juvenile leaves (called coppice shoots) hugging the main stems. These coppice shoots are easy to see because of their blue color and tight clustering, as opposed to the adult leaves, which are 6-8 inches-long, dull-olive-colored and sickle-shaped and which hang from the ends of long branches. These coppice shoots are the give-away that the tree is in trouble and is destined to die soon…” (He later corrected “coppice shoots” to epicormic growth.)

But again, this is not actually true.

In fact, epicormic sprouting allows eucalyptus to survive not only drought, as described above, but even fire. The epicormic sprouting grows into new branches to replace the ones that have been damaged in the fire. This is from Wikipedia: “As one of their responses to frequent bushfires which would destroy most other plants, many Eucalypt trees found widely throughout Australia have extensive epicormic buds which sprout following a fire, allowing the vegetative regeneration of branches from their trunks.[4][5] These epicormic buds are highly protected, set deeper beneath the thick bark than in other tree species, allowing both the buds and vascular cambium to be insulated from the intense heat.[4]”

(The references are: [4] “Effects of fire on plants and animals: individual level”. Fire ecology and management in northern Australia. Tropical Savannas CRC & Bushfire CRC. 2010. Retrieved 27 December 2010. [5] “Learn about eucalypts”. EUCLID – Eucalypts of Australia. Centre for Plant Biodiversity Research. Retrieved 27 December 2010.)

And sometimes, dead branches and leaves and epicormic growth don’t even indicate stress – it’s part of the normal growth cycle. R.G. Florence’s book on eucalyptus says: the “mature crown of a eucalypt maintains itself by the continual production of new crown units, which die in turn. There will always be some dead branches in a healthy mature crown.” He goes on to say an “undue proportion of dead branches is an unhealthy sign” but a “reasonable proportion of death of crown units should be accepted as normal.” He also discusses the “epicormic shoots from dormant buds on the top and sides of the branch develop into leaf-bearing units of the mature crown.” (p.13) Eucalypts go through stages of development that include extensive self-thinning, particularly in younger trees. (p. 194)

Another reason for epicormic sprouts on eucalyptus is increased light. From Wikipedia, with references: “Epicormic buds lie 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 plant. Epicormic buds and shoots occur in many woody species, but are absent from many others, such as most conifers.” [The Wikipedia article references the Encyclopedia Britannica.]

We have seen these epicormic sprouts in eucalyptus trees around the clubhouse in Glen Canyon after many trees were removed.

epicormic sprouts on eucalyptus when nearby trees removed

We also saw them on Mount Sutro near where 1,200 trees were removed for “fire safety.”

MISTAKING DEFENSES FOR DEATH THROES

In summary, then, epicormic sprouting does not indicate that the tree is near death. It may indicate that the tree is responding to drought (or even to other stresses like pesticide use or damage to its root systems) with defensive measures. It’s like declaring that everyone who has a fever is bound to die of it. The trees below are the same ones featured in the picture at the start of this article – one year later, they’re surviving, not dying.

Epicormic sprouting on eucapyptus 2014In some cases, epicormic sprouting may indicate nothing at all, except that the tree is going through a normal growth phase, or changed light conditions following removal of nearby trees.

LIVING WITH A FEW DEAD TREES

We asked Dr McBride if it made sense to cut down these trees. “I do not think the city would be justified in cutting trees down as a fire prevention action,” he says. “Cutting down drought-stressed trees at this point would be much more costly, sprouting would be difficult to control without herbicides, and the litter on the ground would have to be removed to decrease the fire hazard.”

“The problem as I see it is the accumulation of leaves, bark, and small branches on the ground. This material presents a serious fuel problem when it dries out sufficiently.” However, he points out that “In many eucalyptus stands in San Francisco the eucalyptus ground fuel (leaves, bark, and small branches) seldom dries to a point that it can be ignited because of summer fog and fog drip.” In dry areas, the best course is to “launch a program of ground fuel reduction by removing the litter from beneath eucalyptus stands.”

The eucalyptus-tree nest hole of the red-shafted flicker - San Francisco. Janet Kessler
Eucalyptus-tree nest hole of red-shafted flicker – San Francisco. Copyright Janet Kessler

A few trees may indeed die, with the drought or without it. If you think of a forest as a normal population, you expect to find some trees that are thriving and some that are hanging on, and some that are dying – just like in any population. And dead and dying trees are very valuable to wildlife: They’re more likely to have cavities that are suitable for nesting (and are easier to excavate for woodpeckers and other cavity-building species). They also have bugs that come to feast on the decaying wood, and that’s bird-food.

Tracking down the truth about blue gum eucalyptus

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
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.
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
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