News reports about wildfires in California—currently battling its largest fire ever—and Portugal, which has also been battling huge fires in recent years, highlight the dangers posed by eucalyptus trees. But why, when nearly all eucalypts are native to Australia and neighboring islands?
Fire certainly wasn’t on the minds of those who spread eucalypts around the world. As geographer Robin Doughty details it, eucalypts were taken from Australia after Europeans first arrived in the late eighteenth century. He describes a combination of “push” and “pull” factors. The pull was the appeal of exotic, ornamental plants by botanists, royals, and other estate owners. The push factor was originally a single individual. The German-born botanist Ferdinand Jacob Heinrich von Mueller migrated to Australia in 1847. Within a decade, he was the world’s leading evangelist for eucalypts. Through books, correspondence, and, rather more to the point, the mailing of seeds, this Johnny Eucalyptus helped spread the tree around the world.
The best place to see eucalypts in the United States is in the southern half of California. One of von Mueller’s correspondents was the president of Santa Barbara College, who joined the eucalyptus cult in the 1870s. The region between San Diego and the Bay Area was the locus of a veritable boom in Australian trees. The re-forestation was sold as a get-rich-quick scheme, harvested as lumber for fuel and furniture, with a sideline in miraculous eucalyptus oil. By the early 1900s, Berkeley had fourteen species growing within its boundary; another one hundred and fifty species were being tested in the state. But the speculative boom, as so many others, went bust. For one thing, petroleum was the up-and-coming fuel. And it turned out that the best lumber was from mature trees, not the quickly harvested plantation types. A glut of eucalyptus oil meant that if often went rancid before marketing.
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Brett M. Bennett, a historian of forest management, discusses the “globalization of eucalypts” from 1850 through the end of the twentieth century. In his case studies (India, South Africa, and Thailand), the trees “changed local ecologies and encouraged a movement towards market-based capitalism…at the expense of indigenous groups living in or near forests.” Traditional land use systems and habitats were replaced with monoculture for the benefit of local and/or international elites.
The flip side of this industrial expansion of eucalypts is that these trees burn really well. Also known as gum trees, they produce gummy resin and oily leaves. The oil is what makes eucalypts toxic to most herbivores, excepting koalas, who can munch away because of their gut bacteria, unique intestines, and twenty-two hours of sleep a day. Long used for medicinal purposes, this remarkable oil has been tested in ethanol and petroleum mixtures and as a fuel in its own right. So when it comes to eucalyptus canopies, wildfires burn through them furiously; the thin, burning bark can be blown over a mile in the wind.
So now, more than a century later, eucalypts grow tall throughout a lot of California, waiting for the next fire. These once exotic trees have become a potent fuel in this new era of megafires.