The Very Long Life of Eucalyptus Trees

This article is republished with permission and minor changes from Death of a Million Trees, a website that fights unnecessary tree killing in the San Francisco Bay Area.

 

 

PUTTING ANOTHER MYTH TO REST: LIFESPAN OF BLUE GUM EUCALYPTUS

When the native plant movement began in earnest, about 25 years ago, its proponents weren’t expecting blowback from those who value the existing landscape.  As far as they were concerned, the trees had to be destroyed solely because they “don’t belong here.”

When they started destroying our predominantly non-native urban forest, they learned that it wasn’t going to be as easy as they thought.  They began to defend their destructive projects with cover stories to convince the public who didn’t share their devotion to native plants that it is necessary to destroy non-native trees because they are a threat to public safety and to wildlife.

One by one, we have debunked the myths that were used to justify the destruction of our urban forest:

Great horned owl in eucalyptus. Courtesy urbanwildness.org

  • About 20 years ago, one of the first myths was that eucalyptus trees kill birds. It is an absurd claim that is completely unsupported by reality.  With a lot of careful research, we were eventually successful in convincing the public that birds are not harmed by eucalyptus.  In fact, many bird species are dependent upon the trees for safe nesting and winter nectar.   That myth is dead.
  • The claim that eucalyptus and other non-native trees are more flammable than native trees was a powerful narrative that was more difficult to kill. As wildfires have increased in frequency and intensity in California, that claim is no longer credible because every wildfire occurs in native vegetation.  Again, this myth was eventually disproved by reality.
  • More recently, we have finally put to rest the claim that “nothing grows under eucalyptus.” This myth was based on a theory that eucalyptus emits allelopathic chemicals that prevent the growth of plants in the eucalyptus forest.  Thanks to a recent, rigorous study done at Cal Poly, we know with confidence that the allelopathy story is another myth.

It was not surprising that the nativists, having run out of bogus justifications, created a new narrative.  In parks that the East Bay Regional Parks District had been planning to thin, we began to see clear cuts.  When we inquired about why it was necessary to destroy ALL of the trees, we were told they were hazardous.  Then, in the minutes of a meeting of East Bay Regional Park District Park Advisory Committee , we saw the claim that eucalyptus lives only 50-60 years.  Simultaneously, this claim was made in San Francisco by proponents of destroying all eucalyptus trees there.

We eventually tracked down the source of that lifespan estimate to a website called SelecTree, which originally said that the longevity of blue gums is only 50-150 years.  We knew that isn’t an accurate estimate because of how long blue gums live in Australia and how long they have already lived in California.  We provided that information to the authors of SelecTree and were able to get the estimate corrected to “greater than 150 years.”  That’s not nearly long enough, but it is the longest lifespan estimate available on that website and it corresponds with many other trees, including native Coast Live Oak.

In the process of researching the lifespan of eucalyptus, we learned several interesting stories about blue gums that have lived in California for 150 years and are still going strong.  We would like to share some of this information with our readers today.

BLUE GUM EUCALYPTUS IN AUSTRALIA LIVES 200-400 YEARS

Blue gum eucalyptus and all other species of eucalyptus are native to Australia.  They were brought to California shortly after the Gold Rush of 1849.  Since they haven’t been in California 200 years, we don’t know how long they will live here.  But how long they live in Australia is obviously relevant to answer that question because longevity is specific to tree species.  We can expect some variation by climate, but not much, and the climate of Australia is similar to the climate in California with wet, mild winters and hot, dry summers.

We know that blue gums live in Australia about 200-400 years because Australian scientists tell us that:

Growth Habits of the Eucalypts by M.R. Jacobs, (Institute of Foresters of Australia, 1955, 1986): Blue Gum eucalyptus lives in Australia from 200-400 years, depending upon the climate.” In milder climates, such as San Francisco, the Blue Gum lives toward the longer end of this range.

That reference was corroborated by John Helms, Professor Emeritus of Forestry at UC Berkeley and an Australian who said in response to our question about blue gums in California, “Blue gums would commonly live for 200 – 400 years, although I presume that some might live longer.”

We also asked the Australian National Botanic Gardens.  They said, “It’s possible that the average lifespan of a native species growing in the wild in Australia would differ to the average lifespan of the same species introduced in northern California, since introduced plants can often “escape” their natural predators when such introductions occur.”

In other words, since eucalyptus trees have more predators in Australia than they do in California, we should expect them to live longer here.  This is called the “predator release” hypothesis.  Ironically, that hypothesis is used by nativists to support their claim that eucalyptus is invasive in California.  (California Invasive Plant Council rates the “invasiveness” of blue gum as “limited.)  It’s only logical to apply that hypothesis to the question of how long blue gums will live in California.

MANY HEALTHY BLUE GUMS IN CALIFORNIA ARE 150 YEARS OLD

However, using actual experience in Australia to predict the future of blue gums in California requires some speculation.  Therefore, we turned to the question of how long they have lived in California for guidance.  We found several interesting local stories about blue gums that were planted in California 150 years ago and remain healthy and vigorous today.

There are many examples of blue gums being planted as street trees in California about 150 years ago.  One of the most well-known examples is the city of Burlingame on the San Francisco peninsula. When the City was founded in the 1870s, John McLaren was hired to plant trees to provide a much needed windbreak because the City was nearly treeless, as was the entire San Francisco peninsula.  McLaren planted over 500 eucalyptus (blue gum and manna) along the main highway through Burlingame, along with a row of English elms.  John McLaren was subsequently hired by the city of San Francisco, where he planted many more eucalypts while serving as superintendent of the parks department for 53 years.

The eucalypts in Burlingame are still thriving, but the elms have been dead for about 60 years.  SelecTree says the longevity of English elms is “greater than 150 years,” the longest category of longevity published by SelecTree and completely open-ended.

El Camino Real bordered by Eucalyptus trees. Burlingame, SF Bay area, California, USA

The people of Burlingame greatly value their eucalypts and designated them as “heritage trees” in 1975 under a local ordinance.  That local legal status did not protect them from several attempts by Caltrans to destroy the trees.  The people of Burlingame came to the defense of the trees and were eventually successful in getting permanent legal status to protect 2.2 miles of the trees.  That section of El Camino Real in Burlingame lined with eucalyptus was listed on the National Register of Historic Places in 2012.

Caltrans is now working cooperatively with the people of Burlingame to address safety concerns while “also keeping an eye to the prized grove of eucalyptus trees along the street.”  A task force was formed in 2018 to discuss these issues.  The City of Burlingame remains committed to the preservation of these trees, which suggests that they have a future there. (1)

The life span of street trees is generally much shorter than trees planted as forests because they are subjected to more wind and polluted air of heavily traveled roads, such as El Camino Real.  Although blue gums have passed the test of those challenging conditions with flying colors, they have not been planted as street trees for decades.  Their out-sized scale makes them unsuitable for that purpose.  If blue gums can survive as street trees on heavily traveled roads, they can surely survive longer in the protection of their neighbors in forests.

BLUE GUMS AT STANFORD UNIVERSITY

The blue gums on the campus of Stanford University are another example of 150 year-old blue gums that are very much alive.  Although blue gums were included in the campus landscape design of Frederick Law Olmsted in the 1880s, many of the blue gums actually predate his design:  “Several hundred mighty giants on the campus date back prior to 1870 when Leland Stanford acquired several farm properties, one of which already had avenues of gum trees.  They are mostly Tasmanian blue gums and red gums with a sprinkling of manna trees.”

Eucalyptus on Stanford campus

That description of the old blue gums was written in 1971.  The trees are still alive and well.  I worked on the Stanford campus for 10 years and walked among those trees at every opportunity.

AN EVEN OLDER OLMSTED DESIGN IN OAKLAND

Mountain View Cemetery in Oakland, California was designed by Frederick Law Olmsted in the 1860s.  Like most of the East Bay, the site was treeless.  Olmsted’s design was an eclectic collection of mostly non-native trees, including blue gums.  The cemetery is on steep, windward facing hills, where the windbreak provided by blue gums is particularly valued.

Eucalyptus in Mountain View Cemetery, planted on an unirrigated windward facing hill. 2017

Olmsted designed a straight avenue through the cemetery lined with magnolia trees.  Many of the magnolia trees have died and those that remain are in poor condition.  SelecTree claims that the life span of Southern magnolia is “greater than 150 years,” which is contradicted by our local experience.

The current owner of the cemetery destroyed many of the blue gums about 5 years ago, in the middle of the extreme drought.  He replaced many of the blue gums with redwoods.  The redwoods are irrigated and are still surviving.  I did not object to the removal of the blue gums because they are on private property.  I confine my advocacy to healthy trees on public land.

LONG LIVE THE BLUE GUMS!

SelecTree has revised its listing of blue gum longevity based on the information we provided.  The myth that our blue gums are dying of old age will not die as easily.  We will have to repeat this information many times and in many different venues, just as we did for every other myth.  If and when that particular myth dies, we can be sure there will be another waiting in the wings.  Ideologies stubbornly persist, despite contradictory evidence.  And yet, we just as stubbornly persist in defense of our urban forest.


(1) Here is the public record, on which my report about the trees in Burlingame is based:

https://burlingameproperties.com/articles/1607-burlingame-s-heritage-trees

https://www.smdailyjournal.com/news/local/future-plotted-for-burlingame-s-el-camino-real/article_a27c43c4-1dd1-11e8-8a5d-b31dfaa94144.html

http://www.burlingamevoice.com/2012/03/nationally-historic-100-years-of-protection-rewarded.html

https://tclf.org/landscapes/howard-ralston-eucalyptus-rows

http://articles.latimes.com/2003/aug/10/local/me-sbriefs10.1

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The Myth that Nothing Grows Under Eucalyptus

Eucalyptus haters are fond of saying “Nothing grows under eucalyptus.” This refers to “allelopathy” of eucalyptus trees – a defense mechanism in some plants that uses chemical means to prevent other plants growing in the same area. This is empirically a myth, as laid out in this article: Eucalyptus Myths.

When confronted with the tangles of diverse vegetation thriving in the eucalyptus forests on Mt Davidson and Mt Sutro, they amend it to “No native plant grows under eucalyptus” – assuming that native plants as a class have particular characteristics that make them susceptible.  Recent scientific research shows that’s a myth too

 

ABSTRACT: EVALUATING THE MYTH OF ALLELOPATHY IN CALIFORNIA EUCALYPTUS GLOBULUS PLANTATIONS (NELSON, RITTER, YOST)

Here’s the abstract from a paper presented at recent conference of the California Native Plant Society (Feb 2018):

“14.05 Evaluating the myth of allelopathy in California Eucalyptus globulus (Myrtaceae) plantations
Kristen Nelson, Matt Ritter, Jenn Yost, California Poly, San Luis Obispo, CA

It is widely accepted that allelopathy is not only significant, but more or less singular, in the inhibition of understory vegetation in California Eucalyptus globulus (Myrtaceae) plantations. However, there is no published documentation of allelopathy by blue gums against California native species despite continuous references in the literature since the late 1960’s. Previous studies on allelopathy have been inconclusive and criticized for their lack of meaningful, ecologically relevant controls, test species, and test conditions.

We tested the effect of blue gum soil, volatile leaf extracts, and water-soluble leaf extracts on germination and early seedling growth of five California native species that are common components of native habitats typically found adjacent to blue gum plantations. We conducted greenhouse and laboratory experiments to compare the effect of blue gum extracts to ecologically-relevant controls including water, a non allelopathic native plant control (Quercus agrifolia [Fagaceae]), and a native allelopathic plant control (Salvia apiana [Lamiaceae]).

In these experiments, we found that germination and seedling growth of the species tested were not inhibited by chemical extracts of blue gum foliage, either at naturally-occurring or artificially concentrated levels. These results are significant because they are the first to test an allelopathic effect of blue gums against ecologically-relevant species. These results may have significant implications for management and restoration of land historically occupied by blue gum.”

In other words – they looked for allelopathy and they didn’t find it.

The picture below, incidentally, shows Pacific Reed Grass – a native plant – growing under eucalyptus. It’s often found growing under eucalyptus because the water precipitated from the fog provides its preferred growing conditions.

 

 

Photographic evidence that eucalyptus is NOT invasive

Photographic evidence that eucalyptus is NOT invasive | Death of a Million Trees

Guest Post: Death of a Million Trees

Our subscribers have probably noticed that we are studying the case the California Invasive Plant Council (Cal-IPC) has made to classify Blue Gum eucalyptus (Eucalyptus globulus) as “invasive.”  We have reported to our readers that Cal-IPC has made speculative claims about harm to wildlife that are unsupported by scientific evidence:

Is Blue Gum eucalyptus invasive?

In this post, we will look at the “evidence” provided by Cal-IPC that Blue Gum eucalyptus is invasive in California.  Here is how Cal-IPC described the “local rate of spread with no management” of Blue Gum eucalyptus:

“Once a tree matures and produces seed, it can produce a profusion of progeny within a few years; doubling of stand area within 10 years possible but not well documented Without quantitative data, this response is conservative; stands have certainly expanded far beyond initial plantings in many locations, based on unpublished photodocumentation (1, 2) and personal observations (3)”  [numbers refer to cited “references”]

And here is the “evidence” Cal-IPC provides in support of this rather dire prediction of the invasiveness of Blue Gum in California:

 “Potts, Michael. 2003. About this edition. Caspar News. Online @http://casparcommons.org/Press/News0305.htm. 2. Site Stewardship Program, Parks Conservancy. Unpublished photographs of Oakwood Valley, Marin Headlands, Golden Gate National Recreation Area. 3. Warner, PJ. 2004. Personal observations from 1980-2004 working in and adjacent to Eucalyptus stands in Marin, Sonoma, and Mendocino Counties, CA. 707/937-9172; pwarner@mcn.org.”

With the exception of an article in “Caspar News,” all evidence provided by Cal-IPC is unpublished.  Although the one written source is described as “Caspar News,” in fact its title is “Caspar Newsletter.”  The edition of this newsletter that is cited is the first unprinted edition of the “Caspar Newsletter.” Some of the unpublished “evidence” cited by Cal-IPC is described as “personal observations” of Peter Warner, who is the author of the Cal-IPC assessment for Blue Gum eucalyptus. 

Therefore, the only source of information about the invasiveness of Blue Gum that we can evaluate is the one that is available on the internet HERE.

First a word about the town of Caspar, which is located 4 miles north of Mendocino on the coast of California.  According to the 2010 census, it has a population of 509 souls.  We celebrated New Years Eve there many years ago in a rocking bar, so we have fond memories of it.  It is a lovely little town.  We mention its small size to put its newsletter into perspective.  It’s hardly mainstream journalism.

The article in the “Caspar Newsletter” starts with the recommendation of Peter Warner to eradicate all eucalyptus in Caspar:

“In this newsletter you find several articles written by strong advocates of dire means, including the authoritative Eucalyptus indictment written by State Parks’ expert on managing exotics Peter Warner, who advocates a draconian solution:  cutting and then careful application of a dire chemical to eliminate every tree.”

In other words, the “Caspar Newsletter” is merely a repetition of Peter Warner’s agenda to eradicate eucalyptus and poison them with herbicides to prevent them from resprouting.  It’s not an independent source of information.

Photographic evidence of invasiveness?

The only photographic evidence of the invasiveness of Blue Gum eucalyptus provided by Cal-IPC’s assessment is in the article in “Caspar News:”

"Eucalyptus encroaching on the ocean view"

“Eucalyptus encroaching on the ocean view”

There are three problems with this photograph with respect to the claim that it is evidence of the invasiveness of eucalypts:

  • We are asked to trust the memory of the photographer about the history of this eucalyptus grove.  Credible evidence of spread of the eucalyptus grove would provide dated photographs taken at each period of time represented in this photo, i.e., 1989, 1994, 1999, and 2003.
  • We see the ocean in the far distance, west of this grove of trees.  As the forest approaches the ocean, we see that the trees are smaller.  This is as we would expect, because the wind from the ocean has suppressed the growth of the trees on the windward side of the grove.  The fact that wind suppresses the growth of trees was established by Joe R. McBride in his study of trees in the San Francisco Presidio which the Presidio contracted with him to conduct:  “Wind at the Presidio affects tree growth, form, and mortality. Exposure to winds in excess of 5 mph usually results in the closure of the stomata to prevent the desiccation of the foliage (Kozlowski and Palhardy, 1997) Photosynthesis is thereby stopped during periods of moderate to high wind exposure resulting in a reduction in tree growth…Eucalyptus showed the greatest reduction in growth with trees at the windward edge being only 46 percent as tall as trees on the leeward side.” (1) (emphasis added)
  • The photographer asks us to believe that the eucalyptus forest is spreading towards the ocean.  Given that the seeds of eucalyptus are dispersed by gravity and wind and that the wind is coming from the ocean, we would not expect the eucalypts to spread towards the ocean, but rather on the leeward side of the forest.

In other words the “evidence” provided by the Cal-IPC assessment that E. globulus is very invasive is not supported by the evidence that is provided.

It is possible to document invasiveness with photographic evidence.  We have provided our readers with two such examples that indicate that Blue Gum eucalyptus is not invasive in the San Francisco Bay Area:

  • In “Vegetation Change and Fire Hazard in the San Francisco Bay Area Open Spaces,” William Russell (USGS) and Joe McBride (UC Berkeley) used aerial photos of Bay Area parks taken over a 60 year period from 1939 to 1997, to study changes in vegetation types.  They studied photos of 3 parks in the East Bay (Chabot, Tilden, Redwood), 2 parks in the North Bay (Pt Reyes, Bolinas Ridge), and one on the Peninsula (Skyline).  These photos revealed that grasslands are succeeding to shrubland, dominated by native coyote brush and manzanita.  Eucalyptus and Monterey pine forests actually decreased during the period of study.  In those cases in which forests increased in size, they were native forests of oaks or Douglas fir.  In other words, they found no evidence that non-native trees are invading native trees or shrubs.
  • Another example of photographic evidence that E. globulus is not invasive is from Mount Davidson in San Francisco.  Adolph Sutro purchased Mount Davidson in 1881.  He planted it—and other properties he owned in San Francisco—with eucalyptus because he preferred a forest to the grassland that is native to the hills of San Francisco.  Here are historical photos of what Mt. Davidson looked like in 1885, 1927 and 2010:

Mt Davidson 1885

Since Sutro didn’t own all of Mt. Davidson, there was a sharp line between the forest and the grassland when this photo was taken in 1927.

MD 1927 RPD presentation

Over 80 years later, in a photo taken in 2010, there is still a sharp line between the forest and the grassland.  We see more trees in the foreground where residential areas have been developed and home owners have planted more trees, but the dividing line on the mountain is nearly unchanged.

MD 2010 RPD

There is one well-documented case of significant expansion of planted E. globuluson Angel Island.  Using historical records of planting of E. globulus on 23.6 acres as well as observations of uniform spacing of those plantings, McBride et. al., determined that E. globulusspread to 86.1 acres.  The trees were planted starting in the mid-1870s to 1933 and their spread was measured in 1988.  The authors of the study reported that most spreading occurred in areas of high soil moisture, such as swales, and in disturbed areas such as road cuts.  This is also the only documented case of significant expansion of planted E. globulus mentioned in the US Forest Service plant data base. (2)

The one exception to the general rule that Blue Gum eucalyptus has not been invasive in California is consistent with what we know about Angel Island and about the limitations of seed dispersal and germination rates of Blue Gum eucalyptus:

  • Angel Island is an extremely windy and foggy place because it is located in the San Francisco Bay, close to the Golden Gate to the Pacific Ocean, where wind and fog enter the bay.
  • Eucalyptus seeds are dispersed by gravity and wind.  Therefore we can expect seeds to travel further in a very windy place.
  • Optimal soil moisture increases the success of seed germination.  Fog drip increases soil moisture and spreading of the eucalyptus forest on Angel Island occurred in drainage swales, where moisture would be greatest.

How invasive is Blue Gum eucalyptus?

Blue Gum eucalyptus is rarely invasive.  The only documented case of significant spread of eucalyptus forest occurred in ideal conditions for seed dispersal and germination.  Therefore,Cal-IPC’s claim that Blue Gum eucalyptus is extremely invasive is exaggerated at best and fabricated at worst. 

If our readers are aware of any other documented cases of spreading of eucalyptus, we invite them to inform us.  We are committed to accurately informing ourselves and our readers of the reality of invasiveness of Blue Gum eucalyptus.

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(1)	“Presidio of San Francisco, Wind Study, First Phase,” Joe R. McBride, circa 2002, page 6.  (unpublished, contracted study) 
(2)	“Focused Environmental Study, Restoration of Angel Island Natural Areas Affected by Eucalyptus,” California State Parks and Recreation, July 1988, pg 47 & 51.