Eucalyptus Trees - Myths and Facts
There’s been a lot of fear and conversation in the community about eucalyptus trees. It's understandable. Wildfire is a real concern.—It is also important to look at the facts and the other side of the story about these trees. Misinformation can spread quickly, so let’s take a closer informed look at their impact on our environment.
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FALSE
Quick Answer
They can live for 200-400 years.
We live in USDA Hardiness Zone 10A, which is similar to Temperate Southern Australia where the same eucalyptus trees live 400-500 years.
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The Long Answer
This myth is used to justify eucalyptus removal. Precipitating marine air keeps them cooler and less likely to fail or burn, which has been confirmed by local fire authorities.
The Forest Action Brigade requests correction of the public record regarding lifespan of eucalyptus
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YES and NO
Yes, our local Fire Chief says it is highly flammable just like pines and scrub brush. Some sources say Eucalyptus are not more flammable than other vegetation. See our references below.
No. They do NOT fuel most California wildfires. They are part of some of the fires. Lots of fires are being blamed on Eucalyptus trees. Even our local fire fighters have said they do NOT explode.
References:
Fire scientist says, “…eucalyptus did not burn with high intensities leading to home destruction”
The Atlantic, The Great Eucalyptus Debate
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FALSE
Quick Answer
Soil temperatures and fire danger increase from tree removal. All Trees keep the ground wet and cool, and help drive the water cycle.
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Long Answer
A large tree can push 150 tons of water into the atmosphere each year, which then returns as rain. With a vast reduction of trees, the ground will heat up and dry out, resulting in unpredictable wildfires.
Reference
To Protect Our Water Sources, Plant A Tree
Using Trees and Vegetation to Reduce Heat Islands (all trees cool the planet)
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MAYBE, IT'S BEING DEBATED
Quick Answer
While Eucalyptus may absorb more water than other trees, where would all that water go? That would mean the tree is made of a large percent of water….
The Long Answer
They are, in fact, 75-80% water and less flammable than our homes made of dried wood petroleum materials.
Moisture Absorption and Release: Eucalyptus, Monterey pines, and cypress trees absorb up to 50% or more of their needed moisture directly from the marine layer through their leaves.
Cooling Effect: These trees release water into the air and soil maintaining a dense, damp, and cool environment—including their root systems and the surrounding soil—which helps sustain groundwater.
Stormwater Management: By soaking up stormwater, the trees increase the soil’s capacity to store additional water. The roots hold the soil and place and prevent erosion as all vegetation and trees do.
Improved Groundwater Recharge: Their root systems break up compacted soil, allowing water to penetrate more easily into the groundwater table.
References:
To Protect Our Water Sources, Plant A Tree
Water is vital. We manage our water with trees/plants/forests
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FALSE
Quick Answer
Some plants may not grow under them, but many herbaceous plants, ground covers, shrubs and woody plants do grow in eucalyptus forests. For proof just look what grows in Quarry Park, San Bruno Mountain or Pacific Grove Monarch Butterfly Sanctuary.
… “blue gum extracts had no effect on germination of the native species studied.”
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The Long Answer
A study by Kristen Nelson for her 2016 Master’s Thesis at CalPoly explored the impact of field-collected soils on the germination of native plant species using blue gum leaf extracts. She concluded that blue gum extracts had no effect on germination of the native species studied. The concentration of the extracts was matched to what would normally be found in a field environment.
A 2021 study published in the National Library of Medicine/National Center for Biotechnology Information found eucalyptus globulus soil supported germination and early seedling growth of native species equal to or better than coastal scrub soil with variable species responses.
EVALUATING THE MYTH OF ALLELOPATHY IN CALIFORNIA BLUE GUM PLANTATIONS:
Testing an invasion mechanism for Eucalyptus globulus: Is there evidence of allopathy?
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FALSE
Over 40 species of birds have been identified in Sutro Forest in San Francisco, which mimics the Coastside eucalyptus forests. Our coastal area is part of the Great Pacific Flyway zone where many birds and even Monarchs stop to rest and nest in our trees.
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The Long Answer
Over 100 species of birds use the trees either briefly or as a permanent habitat.
The high branches of eucalyptus trees are filled with songbirds every morning. Without raptor and owl habitat, we will likely experience an increase in rodent populations. Eucalyptus are a favored roosting place for Great-Horned Owls and nesting place for many species of raptors. Numerous red-tailed hawks and other raptors are commonly seen in other median trees.
These birds keep rodent populations at bay without the use of pesticides which can kill our pets and wildlife, including apex predators. An adult male and female owl and their young eat three to four rats a day. In one year, this owl family can catch more than 1,000 rats.
References: