My late mother, a schoolteacher in rural South Africa, always carried a large knife in the glove box.  We called it the Alien Killer.

Driving home from school with a bunch of sweaty kids and a supportive Staffordshire Terrier she would often stop suddenly and reach for the knife.

We and the dog knew the drill.  Follow her to a nearby tree.  Wait for her lecture on the debilitating effect on the ecosystem of invasive alien plant species (especially those from Australia!).  And then, with the deft strokes of a trained butcher, watch her ring-bark the tree. The landscape was dotted with evidence of her kills.

My mother is badly needed along the northern coast of California where the Australian blue gums (Eucalyptus globulus) grow in great profusion.  They rise tall in lonely clumps along Highway 101, occupy valleys near the sea, and mass in city parks and university campuses in the Bay Area.

Controversy

Like all invasive aliens, the trees create controversy and division. There are many who want to follow my mother’s path and rid the sunshine state of its Australians.  And there are others, nature lovers too, who want to protect the trees. The divisive issues may not be as incendiary as those, like abortion and immigration, that divide the great nation in its current culture wars.  But eucalyptus does certainly inflame emotions, especially when it comes to fire.  Twenty-five people lost their lives and around 3,000 homes were burned in the 1991 Oakland Hills firestorm, fuelled, some say, by gum trees close to the houses.

But the tragedy provided insufficient evidence to change the minds of eucalyptus defenders.  In 2015, about 75 respectable citizens of various ages and lumpiness stripped naked and clung to a group of mature gum trees on the University of California, Berkely campus. They were protesting plans to use government funds to remove nearby trees to create a wide fire break.

Their arguments continue to be championed by The Hills Conservation Network, a largely crowd-funded conservation organization that fights (mainly through the courts) for “species-neutral risk mitigation strategies” to prevent fires in the Bay Area. The Network argues that all tree species provide valuable ecological services and are needed to combat climate change.

Origins

In a State that has a wide variety of beautiful native trees, such as majestic redwoods and dark green coastal oaks, why bring eucalyptus all the way from Australia?  Explanations abound.  Gold diggers brought seeds from Australia during the California gold rush in 1849 to plant much needed timber. The trees grew fast but not quick enough to outrun the decade-long rush.

Horticulturists liked the blue gum for its ornamental leaves and fascinating bark, planting it in parks and rich people’s gardens.  Landscapers and farmers used them for wind breaks and shade.  And scammers persuaded investors to plant the trees for lumber with the false promise that they would provide a quick financial return.  This did not happen because the trees produce low-quality timber, good mainly for burning.

The net result is a State where the coastal landscape is largely defined by the eucalyptus rather than native species.

Those who want to wield the Alien Killer point to the gums’ many negative traits: invasive because of few natural pests (as with most exotic plants); a fire hazard because of their inflammable oils (menthol) and piles of tinder-dry bark that surrounds their base; and their terrible thirst which depletes ground water reserves.

Blue gum lovers say that the mature specimens are statuesque, even regal.  They provide habitats for wildlife and don’t burn any easier than a pine.  They lock up carbon and must be protected to combat climate change. And they are seen by many as iconic, creating many Instagram moments.

Art

A worthy Instagram site is the 400-meter Andy Goldsworthy sculpture called “Wood Line” in San Francisco’s vast Presidio park.  The work is an extended zig-zag formation of eucalyptus trunks laid end to end on the ground, created in 2010 within a eucalyptus glade using redundant gum tree logs from the park.

The piece is showing signs of (intended) decay and will eventually fade away as the wood rots, returning the earth to its original state, to the time before the 1800s when the glade was planted by the US army which was based there.

The sculpture — one of four by Goldsworthy in the Presidio — encourages you to look at the ground as you follow its line.  For me, this evokes a range of emotions about our relationship with nature, the eroding quality of our soil and, yes, the need to protect the diversity of native landscapes.

Quagmire

A recent Guardian article summarised the Californian eucalyptus issues well: “ …the eucalyptus may well be the most salient arboreal symbol of the state: a stupid business idea that grew out of control, reshaped the landscape forever, and become an eco-political quagmire”.

For me, the only escape from the quagmire demands a purist line.  While it’s sometimes hard to differentiate the native from the alien because so many imported species have become an integral part of our landscapes — as with Californian eucalyptus — it is important to favour the native over the alien.  Being species neutral is not an option if we want to protect ecosystems – the flora, the fauna, and the water.

That’s why I support my mother’s attitude. In her homeland of South Africa, the local ecosystems have been ruined by invasive Australian species which multiply fast and displace native plants. This has transformed the landscape and confined the indigenous species to valleys. The ever-increasing number of wildfires has only encouraged aliens many of whose seeds are stimulated by fire, leading them to germinate ahead of native plants after fire has passed through.

Because the blue gum self-seeds relatively easily in California (the species is classified as “moderately invasive”), it’s time for California to open the glove box and reach for the Alien Killer. Of course, that’s not going to happen any time soon.  Not until the American people begin to find a path of compromise through their self-made culture wars quagmire.

It looks likely Australia’s eucalyptus globulus will remain a Californian icon for some time to come.