The Tasmanian blue gum, Eucalyptus globulus, is a magnificent tree. That is perhaps the only thing that everyone agrees on. It is, as Jake Sigg puts it, “a big, grand, old tree.” Tall, gnarled, stripey-barked, with white flowers like sea anemones, blue gum eucalyptus are characteristic of the San Francisco Bay area, despite being native to an Australian island half a world away. They just happen to thrive in the Bay climate, and many were planted either for timber or for scenery from the 1850s onwards.

There is, to put it mildly, widespread disagreement about what to do with these trees. The argument is as complex and tangled as the bark streamers that hang from the blue gum’s trunks. In the most general terms, there is a faction of environmentalists that want to see many of these eucalyptus trees removed, because they are a fire hazard close to homes, or because they are non-native and make poor habitat for native species, or both. In this group, place native plant enthusiast Sigg (who nevertheless loves the species and would like to see more of them planted in landscaped, irrigated parks). This faction also includes the local chapter of the Sierra Club.

There is another faction of environmentalists that dispute that the trees are more of a fire hazard than what might replace them, see them as decent or even very valuable habitat, and want to retain them to sequester carbon, provide shade, beauty, and recreation, and to avoid the use of the herbicides that are generally necessary to thoroughly kill them off. This faction includes a longtime correspondent of mine, Mary McAllister, and allies in different groups, including the Hills Conservation Network and the small-but-fierce Forest Action Brigade.

Those are the basic contours, but getting a fuller understanding requires a walk deeper into the woods.

This fight is many years old. There have been lawsuits and there have been letters to the editor pro and con. There have been protests and postcard campaigns and blog posts and newsletters and lots and lots of official public comment on management plans for various eucalyptus forests and groves. It is a classic Bay Area dispute: greens vs. greens, experts vs. experts, and committed amateurs vs. committed amateurs. And it has gotten very hot.

One recent summary of the dispute was this feature in Bay Nature by Zach St. George. The piece seemed pretty even-handed to me, but McAllister sent me a four-page memo with counter arguments against a hypothetical fire scenario described in the article. And that’s not surprising. McAllister, a retired university administrator, is very much engaged in the eucalyptus debate and always ready to rumble. And she and her allies can chalk up some recent wins. The Hills Conservation Network recently settled with the Federal Emergency Management Agency, who, as a result of the settlement, cancelled grants to remove eucalypts in the East Bay.

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I became interested in the Great Eucalyptus Debate several years ago. In 2011, I wrote a book, Rambunctious Garden, that reported on new exciting directions in conservation. Among these was a reassessment of non-native species. Maybe not all of them were terrible. In fact, maybe we had been spending too much time and money removing non-natives in a quest for an unobtainable purity, money we could have spent on something else, like land acquisition or climate change mitigation. McAllister read my work and got in touch. People were trying to cut down all the eucalyptus trees just because they were non-native, she said. All the talk about fire risk was just “a cover story.” Recently we spoke on the phone. “They learned that the public is not interested in killing trees or eradicating plants just so it can look like it did 250 years ago,” she says. “They learned that they have to use fear tactics, and their main response is fire.”

McAllister has “reams” of studies that she says shows that the trees aren’t a fire hazard—or any more of one than the native shrubs and trees. She points in particular to the “fog drip” that these large, lanceolate-leaved trees collect and retain making them, in her opinion, a lovely defense against fire.

Sigg actually agrees that fire isn’t the main reason to remove eucalyptus. His central motivation has always been “the importance of saving natural ecosystems”—in this case the oak woodland-grassland that predated the eucalyptus at many sites around the Bay.

Sigg and McAllister have tried to remain cordial over the many years that they and their allies have disagreed about the blue gums. They haven’t always managed to stay on speaking terms. And both sides naturally see science as supporting their own position.

So which side does science support? Well, it is complicated.

According to Doug Johnson, executive director of the California Invasive Plant Council, whether the Tasmanian blue gum deserves to stay depends a lot on one’s goals for a particular site. That is, much of the disagreement is not on how to achieve a shared goal, but what the goals should be. And that’s an issue of differing values. “There are a number of competing visions for the wildland-urban interface,” he says. And then he ticks off just a few: “the safety aspect of wildfire protection, the cultural and recreational aspect of the beauty of large trees, the practical greenhouse gas storage aspect, the habitat aspect.”

It is Johnson’s belief that while “intelligent people and well-meaning people” are working on each side, positions have unfortunately become calcified, unbending no matter what any new study says.  “People fit the information to the narrative,” he says.

Over the course of his career, Johnson has seen interest in native plants move from a hip, counterculture movement to becoming the establishment position. These days, questioning “nativism” has become hip itself—and much of the questioning is led by scientists. Even invasive species conferences now feature panels on how to work with exotics to achieve restoration goals, Johnson says. The embrace of eucalyptus may be part of this pendulum swing.

As far as the public perception is concerned, the herbicides used to kill exotics certainly don’t help sell the idea of removing the trees. “When it comes to using herbicides to control invasive plants, there is a strong underlying narrative of fighting authority and any kind of synthetic product, especially something made by a large corporation and especially if that company is Monsanto,” Johnson says.

As we talk, I ask Johnson whether having an independent third party weigh in on some of these questions might be useful, and he perks up. When it comes to working with the horticultural plant trade—often the entry point for non-natives that go on to spread beyond home gardens—he’s had luck with using research by botanical gardens as a “trusted messenger” for science that all sides can believe. “We trust them to be scientifically based and horticulturalists know they love plants and don’t think they will be overly cautious and restrictive without good reason.”

So who would the trusted independent third party be on issues like the relative fire danger posed by eucalyptus vs. whatever would grow up where they were removed vs. a complete native restoration? Or the danger posed by herbicides used to remove eucalyptus? Johnson thinks universities are perceived as tainted by industry ties. But what about the National Academy of Sciences (NAS)? Could a study on the relative risks and benefits of removing, thinning, or retaining these Australian giants be explored for a number of different goals, from safety to habitat to beauty? (Most NAS studies are paid for by federal agencies, but a California state agency could fund a study, or the NAS could use some of their internal funding to take it on themselves.)

Macalister isn’t 100 percent sure she could trust a NAS report, but she likes the idea better than charging a local university with studying these issues. “I would say it is a roll of the dice, but if you must put the dice in particular hands, the Academy is certainly better than local options,” she says.

Science can’t tell us what to do, whether to hone the axe and ready the glyphosphate or simply spread a picnic blanket under the canopy and relax. But in an ideal world, there would be an agreed-upon set of facts. From there, the differences of opinions would flow from different values, and there’s always hope that opposing values can expand and melt into each other—that compromise and compassion can be achieved. Until then, the magnificent Tasmanian blue gum is, in some sense, a prisoner of dueling realities.

This post appears courtesy of Last Word on Nothing.