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.