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Oxalis is spreading fast in SF Bay and its toll is just beginning to be recognizedPhoto: Margo Bors

The Innocuous Looking Weed Saturating the Bay Area

It's spring, and the hills are alive with the sounds of … oxalis.

It's everywhere.

Yellow oxalis, Oxalis pes-caprae, appears after the onset of autumn rains. It persists through the wet season, then disappears until the next season. Perhaps your awareness has unconsciously become part of the shifting baseline syndrome—it is so much a part of the landscape that it is part of your baseline view of the world. You can't remember a time when it wasn't here.

Yet oxalis has not always been here; it was not common a mere 20 years ago. The fact that it has increased dramatically and that there are some areas where it is the only kind of plant—what does this tell you? It says that it is displacing what was there before. In many cases, what was there was what co-evolved with the landscape—that is, the native animals and the plants they depended on.

And, because its increase is surreptitious, your baseline view is likewise gradual—and may lack awareness of the damage it is doing.

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That is bad news for us but a tragedy for all the foragers whose lives depend on the native plants: myriads of insects and other creepy-crawlies, the birds and others that feed on the insects and other hunters higher up the food chain—coyotes, hawks, owls and the like. These charismatic hunters are loved by people who count them and who log their comings and goings. These folks are not aware of the coming danger posed by this pretty plant.”

The shifting baseline syndrome anesthetizes us to the assault on California's biodiversity by its insidious spread. The grasses and wildflowers—and the animals needing those plants—will be surreptitiously transformed into a flash of yellow in winter/spring months, and then we're left with bare ground the rest of summer and autumn. No birds, no foragers.

And no solution in sight.

Biodiversity is not easy to define and is poorly understood. A quick and dirty attempt: The greatest number of biological organisms in an interacting biological community persisting over time. You may introduce a plant—like this oxalis—and that temporarily increases the diversity. However, if it expands and displaces the other plants and animals it drastically decreases diversity.

1. As with many introduced plants, the organisms that kept it in check in its native range are missing here, so the indigenous plants and animals native lack defenses against it, not having evolved in its presence. For a discussion of this and two other problem plants—Cape ivy and ehrharta grass—see Triple Threat From South Africa in the October 2003 Fremontia, online at:

Cape Ivy
Cape Ivy another invasive species from South Africa chokes trees in San Francisco's Sutro Forest

Worldwide, biologists and land managers are gravely concerned that the balance that provides the necessary stability to ecosystems is falling apart, and plants and animals that formerly provided the balance have weakened or displaced.

2. No other plant, in my experience, has occupied new territory and so much of it in such a short time. This mystery deepens when we learn that it doesn't set seed and produces exclusively by bulb-offset. That is highly unusual in nature—I know of no other plant doing this—and not a recipe for success in natural competitive situations.

Some plants, such as quaking aspen, seldom flower or set seed because aspen is so good at spreading via root runners that it has little need for seed. However, nature doesn't carry all its eggs in one basket, and aspen retains the ability for sexual propagation—it flowers and sets seed on rare occasions.

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It took eons to create these intricately-woven balanced communities—and we carelessly let them disappear overnight. We stand in the grim prospect of losing nearly all our grasslands in San Francisco - and many other coastal areas in California. ”

3. How do oxalis bulbs get around to new territories? How does it jump a hundred feet, or colonize new places miles away? How does it get to all the window boxes?

We do know that gophers cache bulbs. But more numerous, harder to explain, and more damaging are the single plants that pop up in the middle of a grassland—how did that happen? Finding this out is valuable information we need, and surprisingly, no botanists or ecologists I know of have ever remarked on it, much less researched it.

One credible witness said he had seen scrub jays deliberately move a bulblet from an above-ground mother plant and plant it in another part of his garden, so we have a beginning to solving this mystery. Two native (!!) animals promoting an exotic plant that displaces a native plant they co-evolved with? What irony. Did nature make a mistake? This deserves scientific research.

Mission Bells and oxalis
Oxalis crowds our indigenous Mission Bells, next year there will be no Mission Bells in this field.Photo: Margo Bors
mission bells
Mission bells or chocolate lily, Fritillaria affinis usually
comrd back every year from a bulb, is probably in its last
year as oxalis moves in for the kill Photo: Margo Bors

4. This oxalis not only spreads quickly, but it displaces other vegetation. Once it invades a grassland, the reproduction of existing plants slows, and by the second year will show stress. By the following year, it is in dramatic decline, subsequently becoming an oxalis monoculture. A 100-year-old native bunchgrass clump (bunchgrasses tend to live a long time, sometimes centuries) succumbing to this invasion says one thing: chemical warfare.

To my knowledge there has been no research on chemical warfare (aka allelopathy) by oxalis. There is no question in my mind but that's what is happening.

Oxalis is active only in the rainy season. When rain stops in April the plant dies down to the offset bulblets, producing a dozen or more bulblets before dormancy. That is how it multiplies.

5. Once it forms a monoculture when the rain stops and it dies down to the bulb, the soil is bare until the next rain season. People who rejoice at its cheerful beauty must consider this.

6. When native grasslands/wildflowers are displaced, they cannot be recreated; they are gone forever. It took eons to create these intricately-woven balanced communities—and we carelessly let them disappear overnight. We stand in the grim prospect of losing nearly all our grasslands in San Francisco - and many other coastal areas in California. Here is a scene from Glen Canyon in 2016, on its way to becoming a monoculture:

Oxalis in Glen Canyon
Oxalis in Glen Canyon

That is bad news for us but a tragedy for all the foragers whose lives depend on the native plants: myriads of insects and other creepy-crawlies, the birds and others that feed on the insects, and other hunters higher up the food chain—coyotes, hawks, owls and the like. These charismatic hunters are loved by people who count them and log their comings and goings. These folks are not aware of the coming danger posed by this pretty plant.

Miner's Lettuce
Miner's Lettuce Claytonia perfoliata
Photo: Margo Bors

7. Controlling oxalis is a Herculean challenge. Hand removal, even on a small scale, is difficult, perhaps impossible. The deeply-set bulb must be killed, and that is challenging. The best long-term hope is control by biological agents: researching how nature keeps it as part of a balanced community in its native range. This research is expensive, rigorous, and time-consuming, and not without risk. It is already late to start research, and today US Department of Agriculture is not convinced it should be a priority. But it may be our only hope, and I will approach USDA again in view of the biological crisis oxalis has created.

There are presently no large-scale technologies other than herbicides for addressing this frightening weed. As a consequence, the City's Natural Resources Division—charged with responsibility of preserving our biological heritage—must spray in order to save our grasslands; there is no other technology. The choice is to save a whole biological community or knowingly let it perish, an intolerable thought.

8. Some waifs of the plant world survive in marginal orphaned pockets of land, like along sidewalks. These are being monopolized by oxalis. The native miner's lettuce has survived here, but is losing out to oxalis. Miner's lettuce, so numerous—even weedy—is being displaced by this oxalis. That would be tragic. Unseen, many native animals need this plant.

Blue-eyed Mary
Blue-eyed Mary

9. The United Nations, the United States, California, and San Francisco have all passed Biodiversity Resolutions because it is now recognized that this diversity is intimately related to climate warming, and you can't have one without the other. As for San Francisco, our native biological communities are under assault from this one oxalis—an arresting statement that deserves close attention. The San Francisco Recreation and Park Department's Natural Resources Division is understaffed and under extreme challenge from this plant, on top of assault by other invasive plants.

Blue-eyed Mary
Kids viewing the single plant of Franciscan blue-eyed Mary, Collinsia multicolor. This annual wildflower, rare in San Francisco (Bayview Hill), must reproduce from seed. Oxalis will prevent its germination, so this formerly numerous patch is doomed. The City's Natural Resource Division is working hard to grow seed for reintroduction if they can control the oxalis.

Each oxalis leaf has three leaflets, and the leaflet is like the imprint of a goat's foot, hence the specific epithet, pes-caprae.

This article is from the free e-mail newsletter Nature News from Jake Sigg. Jake Sigg is an unabashed tree-hugger who lives on the Westside. Subscribe: NatureNews/JakeSigg

February 23, 2023

Environmental Review: Reversing Mount Davidson's Long Decline

Jake Sigg
Jake Sigg

The Recreation and Parks Department'smanagement plan for its natural resources was sent to the Planning Department for environmental review in 2006. After an extraordinarily long time the review is finished, and it, plus the possibly modified management plan, arenow slated for public hearing in November before a joint meeting of the Planning Commission and Recreation and Park Commission.


Bottom line the November hearings are not the end of the process; they are the beginning of the next phase, implementation of the management plan, and the public will have ample opportunity to express its opinions."

There is confusion and much misinformation surrounding the management plan, much of it deliberately created by people with agendas. For readers of this newspaper, a salient topic is the part of the Plan pertaining to the tree plantation on Mount Davidson. With that in mind, I wrote a series of articles for the Westside Observer in the September, November, and December 2015 issues. They are online (below), andI recommend that you read them because basic problems with Mount Davidson are clearly explained. Although given the opportunity, writers of "rebuttals" were unable to rebut any of the statements. I especially urge you to read the December article explaining what this plan does and doesn't call for, and how the ensuing processes work. Read it carefully and don't listen to voices that tell you differently. The planning and regulatory information in that December articlewas written by Linda Shaffer, recently retired from eight years on the Parks, Recreation, and Open Space Advisory Committee. She has taken training in CEQA (California Environmental Quality Act), has double-checked everything said with RPD staff,and speaks precisely.


If the two Commissions certify the environmental review (Planning) and approve the management plan (Recreation and Park), there will almost certainlybe appeals, and possiblylawsuits. Eventuallythere will be further planning processes in which public participation is invited. All this is explained in the December article, and it will save wear and tear on your emotions if you read it. Bottom linethe November hearings are not the end of the process; they are thebeginningof the next phase, implementation of the management plan, and the public will have ample opportunity to express its opinions. By no means will approval of the management plan in November mean approval of the specific proposals for Mount Davidson; that will go through its own public process.

USF employes environmentally friendly weed whackers Photo: John Dunbar

Delay in implementation of the management plan will serve no useful purpose, and will increase dangers inherent in a century of neglect in addressing dangers now shouting for attention. These include fire--early rains have almost assured we got through this year safely, but the danger may return next summer--and dropping limbs or toppling trees, both of which are already happening. Beyond that, this wonderful piece of land can become much more pleasing and welcoming to the public. Its long decline should be reversed, the sooner the better.

Jake Sigg is an unabashed tree-hugger who lives on the Westside.

November 2016

Golden Violet (Viola pedunculata) - host for Callippe Silverspot butterfly, formerly abundant on Mount Davidson, is now virtually gone, a victim of the chemical warfare of yellow oxalis, Oxalis pes-caprae

Oxalis Uber Alles

The brash yellow of Oxalis pes-caprae can almost break the sound barrier. And—have you noticed?—there is more and more of it every year?  The damage yellow oxalis is doing to our wildflower fields is huge and increasing.

quotes practices chemical warfare by exuding chemical compounds that prevent germination of seeds of other plants and inhibit growth of existing plants.  Advent of oxalis in a given area is followed by decline and elimination of other plant species in a short time."


This short article is an attempt to draw attention to the consequences of the massive takeover of our land by this pest plant. We should be taking it far more seriously, and I ask the public to focus attention on its behavior and rate of spread. Where it grows, the public may see masses of pretty yellow, but perhaps they don't think of what until very recently occupied that same space. Lacking any natural controls—it left those controls in its native South Africa—there is nothing to stop it here. To boot, it is allelopathic; that is, it practices chemical warfare by exuding chemical compounds that prevent germination of seeds of other plants and inhibit growth of existing plants. Advent of oxalis in a given area is followed by decline and elimination of other plant species in a short time. The endgame is a monoculture.

quotes takes over and excludes soil-binding perennial grasses and forbs.  That means there is nothing to hold the soil against erosion.  Worse, it means there will be nothing for wildlife, nothing for foragers such as hawks, owls, and coyotes, nothing for bees and butterflies to pollinate or lay their eggs on."

This is a more serious situation than people credit. If it kills off all competitors, what is to clothe the ground during oxalis's dormant period during the summer and autumn months? Nothing.  

When its takeover is complete, hillsides will be bare, without vegetation. This is a tap-rooted plant which lacks a network of fibrous roots; it takes over and excludes soil-binding perennial grasses and forbs. That means there is nothing to hold the soil against erosion. Worse, it means there will be nothing for wildlife, nothing for foragers such as hawks, owls, and coyotes, nothing for bees and butterflies to pollinate or lay their eggs on. It will be an ecological tragedy: the ecosystem, once gone, cannot be recreated. What was once a rich and diverse area sustaining grasses, wildflowers and a large and varied wildlife community now becomes a biological wasteland. Public assumption that the pretty mixed flowers and grasses of our wild areas will always be there will be shocked when this monoculture happens. That realization will be too late.

Are we really ready to be deprived of these animals and wildflowers?

To refer to work that preserves the diversity of plants and animals that have lived here as a community for thousands of years we use the term restoration, for lack of a better word. It consists primarily of removing aggressive invasive plants like thistles, broom, and oxalis that are displacing our natural heritage. If this heritage is once gone it cannot be re-created. The fabric consisting of a complex relationship between above-and below-ground organisms (including large animals) is gone, and humans are unable to recreate them..

How can we prevent this loss of our wildflowers and wildlife? We don't have many tools in our toolbox. It is necessary to kill the bulb, and the only current technology we have for killing the bulb is herbicide. The reason we still have a few grasslands and wildflowers on Mt Davidson is because the Natural Areas Program has prevented the takeover by employing herbicides. There is no other way presently known, and it is acting in the interests of the public, which values its natural heritage.

Jake Sigg is an unabashed tree-hugger who lives on the Westside.

April 2016

Mount Davidson and the Natural Areas Management Plan – what happens next?

Ivy choking trees
Hundreds, perhaps thousands of Mt. Davidson trees have similar problems Photo: Randy Zebell

Sometime in the next year or so, Mount Davidson (and Mount Sutro for that matter) will cease to be the laissez-faire woods they have been for 130 years. They will begin to go through a process of change, as problems that have been evolving and clamoring for attention are addressed. The problems of the two mountains are identical, but different landowners have devised different approaches to address them. Here the focus is Mount Davidson and the document of concern has the lengthy tongue-twister name Significant Natural Resource Areas Management Plan, or SNRAMP (pronounced sin-ramp).

These Mount Davidson trees are dying; the thinning foliage is due to drought and the ivy is increasingly choking off light needed to photosynthesize, as well as competing with tree roots. Even a winter of heavy rain can only delay death, and they should be considered dangerous to hikers and workers. The number of such trees on the mountain is in the hundreds, possibly thousands. Mount Sutro offers identical scenes.


All the green you see in this picture is ivy. Large blocks of dead trees around Aldea Housing are being clearcut, as they are a clear and present danger.”

Some people are understandably apprehensive about what changes will occur, and about whether concerns they have will be heard. The purpose of this article is to explain processes a bit, and, the authors hope, alleviate some unnecessary stress.

It should help to understood that the process of approving and implementing a management plan is lengthy and goes through stages, at each of which the public is able to offer comments. There are two upcoming stages to explain.

First stage: The Final Environmental Impact Report (EIR, which has taken almost 10 years to produce and which takes into account massive amounts of public input) is currently expected to come before the Planning Commission and Recreation and Park Commission (probably in a joint meeting) early next year. The Planning Commission decides whether to certify the EIR as being sufficiently accurate and complete, and the RecPark Commission votes whether to approve the management plan. This latter Commission can make changes to the plan, but only changes that conform to options that have already been subjected to the CEQA analysis done in the EIR. There will be ample opportunity for public comment at the joint hearing.

Second stage: If the Commission approves a management plan, that just means a twenty year Plan has been approved. Next the Plan must be implemented, which involves more planning because, with one exception (a project at Sharp Park in Pacifica) the SNRAMP EIR is a programmatic EIR — a sort of complicated road map. Yes, the SNRAMP contains what looks like detailed information about the management plans for each of the city’s 31 Natural Areas. But it should be understood that these area plans are based on estimates, and include the maximum amount of possible change envisioned. (This is a necessary part of planning: while RPD is under no obligation to do every single thing mentioned in the area plans, they cannot take actions that were not been subjected to environmental impact analysis. So it’s best to over-estimate.)

The bottom line: it is our understanding that before any of the plans for individual natural areas can be implemented, those plans have to be turned into specific projects, with budgets and timetables, etc. There have to be community meetings, similar to those held when bond-financed capital projects are carried out in individual playgrounds or parks. For example: the area plan for Mount Davidson includes the possibility that an estimated number of trees will be removed. An implementation project would state how many and which trees are to be removed from what location, when, why, and how much it would cost to do so. The public will have an opportunity to weigh in on all this information.

It is also good to be reminded that this is a plan to be carried out over 20 years, and that only about one-third of the area planted in trees is even covered by the Plan — those areas designated as Management Area 1 (MA1). There are also MA2 and MA3 areas, which will have to be covered by a separate plan yet to be proposed.

There was initial public concern about the number of trees proposed for thinning. Ironically, due mostly to severely dry weather, there are at least that number of trees which are either dead or dying, meaning in retrospect the Plan may seem overly conservative. Be that as it may, the Plan is what it is and cannot be substantially changed, so other exigencies must be attended to under a different document.

Discussion so far has focused on thinning trees. Perhaps the largest changes likely will be the understory. This has been dominated by ivy and blackberry almost to the point of exclusion of other kinds of plants, leading to large stretches of trail that are dreary and monotonous. This is unfortunate, because there are a huge number of native plants to be planted that are a delight to the eye and provide rich support for wildlife and that thrive under these conditions. Imagine trails graced by red columbine, five different kinds of ferns in profusion, fringe cups, self-heal, scarlet monkey flower, carpets of strawberry, robust native bunchgrasses, rushes, and sedges. The present condition of the plantation is unsatisfactory from all points of view, and the increasing danger from tree failure—aggravated by extended dry periods—is creating an intolerable situation.

It may be as well that nature is forcing the City’s hand in coming to terms with a difficult problem. Proposed changes promise to make the tree stands healthier, and to make the experience of walking its trails more diverse and exciting to humans while also being supportive for a wider variety of wildlife.

Linda Shaffer is is completing her 8th year of service on PROSAC (Park, Recreation and Open Space Advisory Committee).

Jake Sigg is an unabashed tree-hugger who lives on the Westside.

December 2015

Evolving Eucalyptus Wrangle Escalates

Eucalyptus Sprouts
Disagreement about the growths at the top of these trees sparks concerned arborists Photo: Craig Dawson

The response of Nancy Wuerfel et al to my article in the September Westside Observer on the dangers of the blue gum plantations in the city is rife with errors that are too numerous to correct here. I will select a few of the more egregious ones; a full rebuttal would necessitate an article longer than the editor would accept. The subject is of great import to the city, as there are issues of public safety as well as recreation. A few of the errors, in no particular order:

1. Some people want to cut down our healthy forests simply because the trees are not “native.”

Cutting down trees simply because they are not native has never been a part of City policy or operations, nor is it a valid reason for removing them. My article, and the City’s draft management plan, calls for managing the Mount Davidson plantation, which includes selective tree removal where they constitute a problem. Their being nonnative is not especially relevant.

2. The City’s Natural Areas Program has plans to convert existing habitat (including eucalyptus forests) in one-quarter of the city’s parkland to native plant gardens, and that it would cut 18,000 healthy, mature trees to accomplish this.

No such conversion is proposed by the City. The Natural Areas Program works to preserve the biological systems surviving on the pieces of original landscape (those which have never been plowed, bladed, or built on). Most of the world’s cities have similar programs to accomplish just this, as people recognize their heritage is something worth saving.

3. Sometimes epicormic sprouts are a response to stress, but other times they’re just part of the normal growth cycle.

These sprouts are always in response to stress or injury, and the reason they are not part of the normal growth cycle and why they are a danger was clearly explained in my September article. Production of these shoots is a desperation move to save the tree’s life and even if successful it leaves the tree misshapen, aesthetically displeasing, and unsafe, and likely an intermediate stage on the way to ultimate death.

The prodigious sprouting of these stricken trees has been mistakenly interpreted as evidence of vigorous recovery. The dying tops are the result of the breaking of the hundreds of capillary water columns resulting from the trees’ inability to supply sufficient water to keep the water columns intact. Sprouting in this case is a desperation move by the tree to keep the lower part of the column intact. If sufficient water becomes available it may have a precarious hold on life for awhile, but even the best scenario would leave us with a bunch of short, leafy, weakly-attached sprouts clothing what was formerly a smooth, clean bole—one of the traits that endears the tree to us. Those sprouts are subject to coming loose in winds, and will always be there because they lack the deep anchoring of naturally-formed limbs.


These sprouts are always in response to stress or injury, and the reason they are not part of the normal growth cycle … Production of these shoots is a desperation move to save the tree’s life and even if successful it leaves the tree misshapen, aesthetically displeasing, and unsafe, and likely an intermediate stage on the way to ultimate death

4. Mount Davidson is half covered in a eucalyptus forest.

The thousands of trees on Mount Davidson do not constitute a forest; it is a plantation, and the difference is important.

Inappropriate language creates confusion and obscures proper management. A forest is a self-managing biological community which appears similar over time; a plantation is essentially a garden. This is not playing with words—it cuts to the core of the matter.

To manage, we need to understand the difference between a forest and a plantation. To illustrate, let’s take a glance at a forest: When you drive across the Sierra Nevada the scene you see is similar to what the American Indians saw 500 years ago: forests of pines and firs punctuated by grassy wildflower meadows, lakes, and bogs. You see a community of plants and animals, as well as organisms from other kingdoms that are used to living with each other, as they have for thousands of years, tightly-knit into a fabric. That scene is stable and doesn’t change much over time.

A plantation, on the other hand, is artificially imposed on a land that didn’t normally support those plants and it is in a constant state of disruption as the plants are forced to compete with others they are not accustomed to, and lacking the animals and other components that serve to keep the system in balance. The result is chaotic, with usually two or three species eventually predominating. Ivy and blackberry have claimed the understory to the exclusion of other species—and they account for the dreary monotony of large stretches. They even prevent regeneration of the blue gums, something that never happens in forests. The plantation, therefore, contains the seeds of its own destruction because smothering blankets of ivy and blackberry prevent germination of blue gum seeds. Ivy crawls 150-200 feet into the crowns and deprives the trees of light needed to photosynthesize. The results are visible today with trees dying and toppling from light deprivation and the heavy burden of tons of ivy. This tangled mess does not require expertise to diagnose; it is obvious even to a layperson. In fact the plantation’s problems are horticultural, and academic expertise is of little use.

5. I am personally identified as “a native plant advocate [who] has called for cutting down blue gum eucalyptus in city parks for over a decade.”

Not so. I love blue gums and ask for removal only when there is compelling reason. I do advocate for preservation of our indigenous plants and encourage their use in gardens as a means of attracting and supporting wildlife, many of which are dependent on native plants, with which they co-evolved. Because nature has served notice that this tree is not suited to our changing climate, this represents an opportunity to diversify the overstory to make it more friendly to wildlife—part of the mission of the City’s Natural Areas Program. At present it is a biological wasteland, with only generalist species present.

About 50 years ago I became smitten with the genus Eucalyptus, and in 1977 toured Australia for six weeks specifically to learn more about this huge genus—at the time considered to contain over 600 species. Part of that time was in the field in the company of the world’s top eucalyptologists. In 1979 I wrote my first article in praise of the Tasmanian blue gum, and have written several since, including in the February 2014 Miraloma Life. I love this tree and have been in conversation with the Recreation and Park Department to plant them in our irrigated parks, where they can thrive. Did you know that it has abandoned planting blue gums and hasn’t planted them for several decades? The grand old specimens in the eastern end of Golden Gate Park and its Panhandle—a de facto arboretum that should be declared a heritage site—are over 130 years old and won’t live forever. That means there will be a period of several decades when park visitors will be unable to be inspired by these majestic, clean-limbed behemoths.

In 1990, long before the City created a Natural Areas Program, I talked to the Miraloma Park Improvement Club about the state of the Mt Davidson plantation; there are some who remember that event. My aim was to save the “forest”, as most called it. I loved its atmosphere—especially in fog or rain—evocative of the mood created in redwood forests, and as a gardener I knew that ivy and blackberry could destroy it. In addition—and of great concern to me—was that the understory, consisting mostly of native plants that were able to survive the shade and extra moisture from fog drip, would be decimated, and with it the wildlife community. It was primarily the understory that concerned me at the time. Alas, nothing was done and the health and attractiveness of the grove continued to deteriorate, and we see the result in the present unruly tangle and dead and dying trees.

I see this unfortunate situation as bordering on the tragic. A potentially prize area that can enrich the city is left to stagnate, is yearly becoming less attractive to humans, is of little use to wildlife, and is a safety hazard to not just visitors but to the entire city. Urgent action is called for.

These trees can never assume a “tree” shape again even if they should live, as they may for two-three years should they get the promised heavy rain this winter. Scenes like this are common in the blue gum plantations throughout the city, including Mount Davidson.

Ms Wuerfel et al have tried to comfort the public on a subject that is dangerous and needs full exposure and debate. That debate of necessity would be contentious because it is about a subject that is very expensive and that stirs strong emotions. Facts must trump emotions if the public is to be served.

In December I plan to write about the City’s proposed draft management plan.

Jake Sigg is an unabashed tree-hugger who lives on the Westside

November 2015

Too Late for the Eucalyptus?

Eucalyptus in Drought
Eucalyptus in Drought

Most of the California eucalyptus groves, including the Tasmanian blue gum (Eucalyptus globulus)—the tree synonymous with the word eucalyptus in the Bay Area—were planted in the late 19th century, meaning the older trees are around 130 years old. That may not seem old in a state boasting coastal redwoods, giant sequoias, and bristlecone pines, whose ages are in the thousands of years, but it is impressive enough, especially for a tree of such enormous proportions, majesty, and strength. For those and other reasons they command the affection of large numbers of people, including the writer. Two separate and overlapping problems have arrived that must be dealt with.

eucalyptus knots -drought.

One subject is how to manage the lands, and there is a draft management plan due to come out of environmental review soon that is part of a process to address these problems. We will go into this aspect in the October issue of this newspaper. For this article, the focus will be on the more immediate concerns resulting from four dry years: the potential for out-of-control fire, and the danger of falling trees and limbs. There are extensive plantations of blue gums scattered over the city, concentrated in groves of thousands of trees (there are >11,000 on Mt Davidson alone, and the city total must exceed 50,000 in areas without irrigation). To hikers accustomed to mucky trails with streams running down them in mid-summer (exclusive to the west sides of the peaks) they must think talk of fire is laughable. But to those working in them (I volunteer with the San Francisco Recreation and Park Department’s Natural Resources Division, as well as with the Sutro Stewards on Mt Sutro) it is a subject to be taken seriously. Even in wet years there are dry periods, and clearing ivy or blackberry reveals large quantities of organic matter—bark, leaves, branches, seed pods, whole limbs, whole trees, plus the buildup from ivy and blackberry debris. Once while working on Mt Sutro the ground gave way beneath me and I plunged into such debris up to my armpits. Don’t be fooled by all that green ivy and blackberry; all that debris can burn. And what was just described was before the current four-year dry spell.


The dense knots of foliage are epicormic shoots. Even if heavy rain comes soon, it is too late to save these trees. Just four years ago these mature eucalyptus trees were so dense there was no sky visible through their canopy. On Johnstone, Mount Sutro’s East Ridge, August 2015. Photos: Craig Dawson

The tree’s vulnerability to drought has caught us by surprise, so we have no management experience to guide us—and no maintenance or capital funds to pay for what is certain to be very expensive. Up to now rainfall was fairly reliable, and summer’s copious fog drip met the tree’s water needs in our cool climate, simulating the year-round rain the tree gets in its native Tasmania. It’s a tough tree and its endurance in a four-year dry spell is remarkable. However, even a casual look at the groves reveals all is not well when winter rains are deficient: dying tops, thinning and premature shedding of leaves, and epicormic shoots along the main stem all signal plants in crisis. This became apparent in the spring of 2014, and has worsened since. If we get the hot days we usually get in autumn and/or dry winds from the north that sometimes occur in October/November (think Oakland, 1991) the condition could become dangerous indeed. One hard fact: long strips of blue gum’s shedding bark have been documented carrying fire 12 miles. That could set fires across the city, leapfrogging from, say, Glen Canyon to the groves in McLaren Park, Bayview Hill, and Yerba Buena Island, each consisting of several thousand stressed blue gums—and even carrying the fire to the East Bay. Worst-case scenarios do happen, and this mere possibility is too awful to contemplate. From the perspective of fire, we are entering the most dangerous time of year—and worse, the state’s beleaguered firefighters may not be able to assist our firefighting personnel.

Moving to another problem—the danger of falling tree limbs—it helps to understand the blue gum’s response to water stress. When a mature tree loses a large limb, or when a tree is cut down, or injured by fire or freezing, it responds by producing epicormic shoots with blue-green juvenile leaves (as opposed to the long, sickle-shaped adult leaves). This is a survival adaptation, and it responds to water stress the same way: when the capillary columns transferring water to the treetop become broken, it responds by producing epicormic shoots lower down the trunk or limbs. It is a desperate measure to keep the water column moving—once the column taking water and nutrients from the ground upwards is broken, it cannot be reestablished and the tree dies from that point on up. If the tree doesn’t die it still creates a problem, described in the next paragraphs.

Some background on the physiology of woody plants is helpful here. Limbs originate at the center of a plant stem or other branch. Both the main stem and the branch expand in diameter as successive layers of xylem are laid down annually. That means that when a limb becomes really large it is securely anchored deep in the main stem or trunk. It is like a tapered, deeply embedded bolt or screw. A limb produced in an epicormic shoot doesn’t have this deep anchoring; it is weakly attached only in the outermost layer. Every year it survives the sprouted limb gets bigger and heavier. Although the attachment also gets slightly stronger, it does so only proportionate to the limb getting heavier, so the young limb, lacking deep anchoring, is forever subject to tearing off and falling. The attachment is weak throughout its life and can never be beyond danger of sudden failure. Ask an arborist about the difficulties of pruning large blue gums.

Many of these attachments don’t survive even the first year; they are vulnerable to even a gust of wind. Look at the trees bearing these new shoots. Some of the shoots have broken already and are just hanging on the trunk; others will tear off in winter storms. Some of the limbs may live several years and become large enough they could come loose and fall on someone . There is no way around it: they will be hazards as long as they live.

At time of writing, news reports are rife with speculation that the coming rain season will be wet, perhaps very wet. If we are lucky and get rain before a catastrophic fire, and if the rain season is heavy, that will bring temporary relief, but not an end to worries, as much damage has already been done. When a tree’s limbs die there is a corresponding death of its roots, meaning the tree’s stability is compromised and it is subject to toppling. And you still have all those weakly-attached sprouts that will forever be unsafe to walk under.

What to do? Getting the public to agree on a plan of action, even for its own safety, is difficult. There are always those who don’t want any tree cut down anywhere, anytime, for any reason, and they are not amenable to reasoned argument. Government becomes hamstrung and finds itself unable or unwilling to act. Add that much of the public distrusts government, is not fully aware of the novel danger, and is confused regarding what to do, and what you get is not a recipe for quick action to protect life and property. Our normal means of address—the political process—is not likely to be effective when the body politic is uncertain and divided.

All we have left is to spread information—and to hope; hope that the worst doesn’t happen and we are allowed a little more time to muddle our way through. But as Peanuts’ Linus says “Hoping to goodness is not sound theology”. Better to remind elected representatives that these lands are in the middle of the third densest city in the U.S. and management should weigh heavily on the side of protecting life and property.

Jake Sigg is a long time Westside plant advocate and unabashed tree-hugger.

* I wrote a tribute to the Tasmanian blue gum in the February 2014 issue of Miraloma Life.

September 2015

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