One of native plant advocates’ favorite justifications for eradicating eucalypts is the claim that they are invasive. But are they? In one of our early posts (“ALIEN INVADERS!! Another Scary Story”) we reported a scientific study, based on photographic evidence over a 60 year period, that eucalyptus and other non-native trees have not invaded public lands in Marin, Alameda and San Mateo counties. In fact, the non-native forests in these public lands decreased in size, while native forests increased in size.
Now we have photographic evidence that eucalyptus has not been invasive when planted in San Francisco. Adolph Sutro purchased Mt. Davidson in 1881.(1) 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 is a historical photo of what Mt. Davidson looked like in 1885:
Sutro foretold the future of his property:
“…people… will wander through the majestic groves rising from the trees we are now planting, reverencing the memory of those whose foresight clothed the earth with emerald robes and made nature beautiful to look upon.”(2)
Since Sutro didn’t own all of Mt. Davidson, there was a sharp line between the forest he planted and the grassland when this photo was taken in 1927.
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. The eucalyptus forest has not invaded the grassland.
Adolph Sutro would be saddened by a walk in the forest on Mt. Davidson to see over 50 dead and dying trees that have been girdled by native plant advocates. And the Natural Areas Program’s management plans for Mt. Davidson also announce the intention to destroy 1,600 more trees over 15 feet tall. Smaller trees to be destroyed are not quantified by the plan.
Despite the lack of evidence, the California Invasive Plant Council (CIPC) has designated both the eucalyptus and the Monterey pine as “moderately invasive.” There is even less evidence that Monterey pine grow where not intentionally planted. These trees and many of the nearly 200 plants on the CIPC “hit list” are on that list because they aren’t native, not because they are invasive. Few of these plants are truly invasive, but CIPC designates them as such so that their eradication can be justified.
Conservation Sense and Nonsense 
Nice photos. This is interesting, and does suggest that the locally planted eucalypt forests do not invade neighboring grassland. I haven’t seen much evidence elsewhere for eucalypts invading other areas; I’m not opposed to them sharing space in our forests.
However, I’m not about to start “reverencing the memory of those whose foresight clothed the earth with emerald robes and made nature beautiful to look upon”. Does nature need a white man’s engineering to look beautiful? Apparently Sutro thinks so, and is fixated on large, towering trees. I find a lot more of nature’s complexity and beauty in healthy native scrub and grasslands, and I think the wildlife is with me.
Webmaster: While we respect your aesthetic preference, we also hope you will read our post which compares the biodiversity of the eucalyptus and oak-bay forests: “Biodiversity: Another myth busted.” Professor Dov Sax finds that our wildlife does not prefer the native to the non-native forest.
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