Two winters ago, I visited California's central coast for the first time since I was a teenager. Back then, I paid little attention to botany or landscaping. But this time, I spent the trip gripped by plant envy. In Santa Cruz, lemon trees littered yards with ripe fruit, and multi-colored aloes with fleshy leaves as big as my leg grew outdoors. I was equally taken by the soaring trees with white-striped bark and sea-colored leaves I saw in forests along highways and in coastal parks. They seemed to come from a different world.
As it turns out, they do. These tall beauties, I later discovered, are eucalyptus trees. Eucalypts of various species were shipped to California from Australia in the 1800s and planted in great numbers – for their beauty, for timber, as wind barriers, even to fight malaria. For Californians, it was the beginning of a fraught relationship.
Eucalyptus trees are now so common that it's easy to assume they belong. Many Californians believe that they do, regardless of how they got here, and passionately defend their right to persist on the landscape. By the middle of the 20th century, environmental historian Jared Farmer writes, "the immigrant plant had been naturalized in the cultural sense: Californians adopted the genus as an honorary native."
For others, however, the eucalyptus has fallen from grace. They would like many of the trees removed, especially blue gums, one of the most common – and problematic – species. Blue gums can shade out native plants or bury them in leaf litter, and can be hazardous to humans, sometimes dropping big limbs and stoking destructive fires.
Some exotic species are easy to hate. Take cheatgrass, the Great Basin's ruthless conqueror, an archetypal invasive. Since its introduction from Eurasia, it has spread aggressively, crowding out native grasses, reducing biodiversity, and offering little in return to people, plants or animals.
But the blue gum is no more than moderately invasive, making it harder to agree on its management. As Madeleine Nash reports in this issue's cover story, many eucalyptus species haven't spread beyond where they were planted, some native plants will grow in their presence, and they help sustain the annual migration of monarch butterflies. Eucalyptus trees have ecological virtues as well as vices.
Still, the rhetorical jabs traded between their fans and foes often ignore such nuance. "Either blue gums are noble trees deserving of every protection," as Nash puts it, "or they are invasive interlopers overrunning indigenous ecosystems." Yet a radical middle ground does exist: According to scientists like Matt Ritter, being prejudiced against a tree simply because it is a eucalyptus is shortsighted. Blue gums are troublesome, but many of their relatives aren't. "(Those) should be grown way more because they're drought-tolerant, and they're beautiful," Ritter says, adding: "I love our native flora, too. I try to shy away from species bias."