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“Drought-Adapted Eucalyptus NOT Dying by the Thousand”

June 23, 2015

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.

16 Comments leave one →
  1. June 23, 2015 7:46 am

    Makes good sense! Appreciate, as usual, these interesting and informative posts.

  2. j struthers permalink
    June 23, 2015 10:21 am

    Even if they do not die, they are sucking up the water needed for the native trees in the area. and they are so fire adapted that if burned down the seeds are ready to sprout and there will be a million more of them.. The area was not planted with trees originally. It was dunes. McLaren had them planted and they have multiplied. It would be a good idea to thin them out so all could live on the sadly diminishing water. If they are not dying , they are shedding and the litter is a fire hazard. jean struthers cnps-scv

    • June 25, 2015 3:40 am

      Ms. Struthers notes that eucalyptus was planted where there were no native trees, yet she expresses concern that they are taking water needed by native trees. Since there were no native trees where eucalyptus was planted, how could they be “stealing” water from native trees? In fact, native trees will not grow where most eucalyptus have lived for over one hundred years. That’s why they were planted by people who wanted trees. Ms. Struthers is also mistaken about eucalyptus sprouting from seeds after a fire. The seeds of eucalypytus are not viable long after they fall from the tree. They will sprout from the trunk after a fire unless they are repeatedly poisoned with herbicides to kill the roots. Thinning mature eucalyptus does not benefit the trees. It merely exposes the trees that remain to more wind and makes them more vulnerable to the wind to which they have not been subjected while they grew. So many myths…more myths than there are hours in the day.

    • June 25, 2015 7:35 am

      Eucalyptus and other exotics should be exterminated, if possible, so they don’t waste our time & money in perpetuity. Thinning is a political “solution”, and makes no biological sense.

      • June 25, 2015 8:07 am

        Leaving our urban forest alone will save far more “time and money” than destroying it. Aside from the cost of the destruction, there will be repeated applications of herbicides to prevent their re-generation as well as the cost of the environmental damage caused by erosion, loss of windbreak, damage to the soil, loss of fog drip, etc. We have heard many absurd justifications for destroying our urban forest, but this is more ridiculous than usual.

        • June 25, 2015 8:34 am

          “Leaving our urban forest alone will save far more “time and money” than destroying it”. Yeah, and we could have saved a lot of money by not entering WW II, right? Luckily, our park managers aren’t that stupid.

          “There will repeated applications of herbicides”. Nonsense. You know that I have always opposed the use of chemicals. You aren’t paying attention.

          • June 25, 2015 10:46 pm

            Your personal opinion of herbicides does not prevent those who manage our public lands from using them, as I have said before. Whether you like them or not, they will be used. You are the one who is not paying attention. Reality trumps your personal opinions.

  3. June 23, 2015 3:45 pm

    Correction:

    http://forums.gardenweb.com/discussions/1799841/eucalyptus-and-nothing-grows

    gardenguru1950(SunsetZ16)

    There is no real evidence that shows that Eucalyptus are “allelopathic” (exuding soil toxins). It seems to be a myth.

    The real problem with Eucalyptus is threefold:

    1. The roots suck water and nutrients from the surrounding soil, so much so that new plants have a hard time competeing.

    2. The trees (mostly Eucalpytus globulus) cas dense shade and but a few plants grow in such shade.

    3. Shear biomass — large Eucs drop great quantities of leaves, burying little guys, and often great quantities of larger bulk (whole branches) that break even big stuff planted below.

    There are some plants that do better than others other a Euc:

    Large Shrubs, Small Trees–

    Acacia longifolia SYDNEY WATTLE
    Arctostaphylos MANZANITAS
    Callistemon citrinus LEMON BOTTLEBRUSH
    Cotoneaster COTONEASTER
    Escallonia ESCALLONIA
    Heteromeles arbutifolia TOYON
    Melaleuca nesophila PINK MELALEUCA
    Myoporum laetum COAST SANDALWOOD
    Myrica californica PACIFIC WAX MYRTLE
    Nerium oleander OLEANDER
    Pittosporum undulatum VICTORIAN BOX
    Rhamnus californica COFFEEBERRY
    Xylosma congestum SHINEY XYOLOSMA

    Medium Shrubs–

    Abelia x grandiflora ABELIA
    Arctostaphylos MANZANITAS
    Cistus ROCKROSES
    Correa AUSTRALIAN FUCHSIAS
    Cotoneaster COTONEASTER
    Escallonia ESCALLONIA
    Fatsia japonica JAPANESE ARALIA
    Galvesia speciosa ISLAND SNAPDRAGON
    Juniperus JUNIPERS
    Mahonia aquifolium OREGON GRAPE
    Nandina domestica HEAVENLY BAMBOO
    Nerium oleander OLEANDER
    Pittosporum tobira TOBIRA
    Rhaphiolepis umbellata INDIAN HAWTHORNE
    Ribes sanguineum glutinosum PINK-FLOWERING CURRANT
    Rosmarinus officinalis ROSEMARY
    Viburnum tinus LAURUSTINUS
    Westringia COAST ROSEMARY

    Small Shrubs–

    Cistus ROCKROSE
    Correa AUSTRALIAN FUCHSIA
    Escallonia ESCALLONIA
    Mimulus aurantiacus and hybrids BUSH MONKYFLOWER
    Nandina domestica HEAVENLY BAMBOO
    Pittosporum tobira WheelerÂs Dwarf DWARF TOBIRA
    Rhaphiolepis umbellata INDIAN HAWTHORNE
    Sollya heterophylla AUSTRALIAN BLUEBELL CREEPER

    Large Perennials–

    Acanthus mollis BEARÂS BREECH
    Dietes vegeta FORTNIGHT LILY
    Elymus condensatus BLUE WILDRYE
    Phormium tenax NEW ZEALAND FLAX

    Small to Medium Perennials–

    Agapanthus LILY-OF-THE-NILE
    Aristea ecklonii BLUE STAR IRIS
    Asparagus (many) ASPARAGUS “FERN”
    Bergenia cordifolia PIGÂS SQUEAK
    Clivia miniata KAFFIR LILY
    Dianella tasmanica FLAX LILY
    Helleborus lividus corsicus CORSICAN HELLEBORE
    Hemerocallis DAYLILIES
    Heuchera maxima CORAL BELLS
    Liriope LILY TURF
    Muhlenbergia rigens DEER GRASS
    Nephrolepis cordifolia SOUTHERN SWORD FERN
    Pelargonium GERANIUMS
    Penstemon BEARDTONGUES
    Phormium tenax (dwarf cultivars) NEW ZEALAND FLAX

    Ground Covers–

    Aptenia cordifolia RED APPLE
    Arctostaphylos TRAILING MANZANITAS
    Coprosma kirkii TRAILING COPROSMA
    Cotoneaster TRAILING COTONEASTERS
    Duchesnea indica MOCK STRAWBERRY
    Hedera IVIES
    Juniperus TRAILING JUNIPERS
    Mahonia repens CREEPING BARBERRY
    Myoporum parvifolium TRAILING SANDALWOOD
    Ophiopogon japonicus MONDO GRASS
    Vinca major TRAILING PERIWINKLE

    Vines–

    Distictis TRUMPET VINES
    x Fatshedera lizei BOTANICAL WONDER
    Hardenbergia violacea WINTER WISTERIA

    Hedges/Screens–

    Acacia longifolia SYDNEY WATTLE
    Callistemon citrinus LEMON BOTTLEBRUSH
    Hakea suaveolens SWEET HAKEA
    Juniperus JUNIPERS
    Ligustrum japonicum JAPANESE PRIVET
    Myoporum laetum COAST SANDALWOOD
    Myrica californica PACIFIC WAX MYRTLE
    Nerium oleander OLEANDER
    Pittosporum eugenioides WAVY-LEAF PITTOSPORUM
    Pittosporum tobira TOBIRA
    Prunus ilicifolia HOLLYLEAF CHERRY
    Rosmarinus officinalis ROSEMARY
    Viburnum tinus LAURUSTINUS
    Westringia COAST ROSEMARY
    Xylosma congestum SHINEY XYLOSMA

    Joe
    Like Bookmark August 8, 2007 at 8:35PM
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    bahia(SF Bay Area)

    I would second Joe’s explanation of root and water competition, heavy debris being shed constantly by some species such as E. globulus, and shade. I would put the most emphasis of the root competition and drying out of soil, but the piling up of debris over time can also be considerable… Don’t forget that in Australia where Eucalyptus are native there are many, many understory plants that are part of a diverse plant community.

    in my experience locally, Toyon seems to be one of our California natives that best tolerates growing under dense Eucalyptus globulus, as does Poison Oak. Dianella tasmanica is also well adapted to root competition, and is a native understory plant to Euc. globulus in habitat.

    • June 25, 2015 3:51 am

      The eucalyptus forest condenses fog moisture which supplies its needs for water during the dry season. In San Francisco’s eucalyptus forest, fog drip has been measured at over 16 inches per year. The soil moisture in eucalyptus forest in San Francisco’s so-called “natural areas” has been measured at over 10% during the driest summer months, compared to less than 4% for scrub vegetation and 2% for herbaceous vegetation. Destroying the tall trees will not provide more water to other plants. In fact, it will deprive other plants of water.

      There is an excellent example of toyon thriving in the eucalyptus understory on Albany Hill. The vegetation “management plan” for Albany hill observes that the toyon does not pre-date the eucalyptus forest. It is there BECAUSE of the eucalyptus forest.

      As for casting shade and adding leaf letter which depresses other forms of the vegetation, such is the case with any tree whether it is native or non-native. There is far less understory in the redwood forest because the shade is denser. Oak-bay woodland produces just as much leaf litter as the eucalyptus forest and we won’t find significantly more understory there either.

      Virtually any argument against eucalyptus, is equally true of similar types of native plants and trees.

      • June 25, 2015 7:38 am

        “Virtually any argument against eucalyptus, is equally true of similar types of native plants and trees.” Not true. Native species naturally provide more value for native species, due to their long association.

        • June 25, 2015 8:03 am

          This is a nativist myth which is contradicted by many empirical studies which consistently report that introduced plants are equally valuable for native species and some are essential to them.

          • June 25, 2015 8:29 am

            That’s patently false! If they were “essential”, they could never have lived there prior to the introduction of the exotic. Therefore, we have to assume that your other statements are equally flawed. Care to retract your statement? …

          • June 25, 2015 10:58 pm

            There are many examples of exotic plants that are essential to our fauna. Honeybees require the winter nectar provided by eucalyptus at a time when there are no native sources of nectar. For the same reason, the population and range of Anna’s hummingbirds has expanded significantly in California because of the nectar provided by eucalyptus. Hawks and owls require the tall non-native trees for their nests. The Anise swallowtail lays its eggs multiple times because of the year-around availability of introduced fennel. It was confined to only one brood per year when its native host died back during winter months. Seventy-five percent of monarch butterflies in California use eucalyptus trees as their winter roost. There is no record of a monarch migration in California prior to the introduction of eucalyptus.

            Nature has moved on. It is not frozen by your xenophobic perspective. Nature is opportunistic. It uses what is available. It is not influenced by nativist prejudices.

  4. February 15, 2016 12:15 pm

    We have a Eucalyptus that suffered greatly from the drought. My hope is that is is not dead. It does seem to have growth on it toward the bottom 8-10 feet (it’s a very large tree) that could be epicormic sprouting. My dilemma is in having it evaluated by an ‘arborist’, e.g., tree cutting company, and trusting their opinion. Any suggestions? Would anyone be able to evaluate pictures of the sprouts and know if it is epicormic growth?

    • February 15, 2016 12:34 pm

      Where are you located? I can recommend an arborist in the East Bay and one in San Francisco who can be trusted to evaluate eucalyptus appropriately.

      Eucalyptus is nearly indestructible because of its ability to resprout from the trunk after any type of damage, including cutting it down. You may need to prune dead growth, but you will want to do so carefully so that the regrowth is structurally sound. A tree that resprouts from the stump after it is cut down will grow multiple trunks with a low fuel ladder unless it is coppiced. You definitely have options and it would be best if you were advised by someone who is knowledgeable about eucalyptus and is not anxious to just cut it down.

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