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.