KAIKOURA, NZ. After addressing my postcard to Julie, I read the caption one last time. “Mountain lupin is a beautiful, but highly damaging, introduced weed,” it began, describing the purple flowers forming the foreground of the card’s mountain scene.

 

When I first found the card, I’d debated its purchase. As an ecologist, shouldn’t I be sending images of native New Zealand species? But Kaikoura is a tiny town with limited gift shops, each with a limited postcard selection. Plus it was a beautiful photo, and representative of what I’d seen in New Zealand.

 

Honestly, I was impressed the card even mentioned lupin’s foreign nature. Despite how often non-native species feature in representative images of a place, we rarely acknowledge that they really shouldn’t be there.

 

Sometimes introduced species even become iconic. Hawaii’s guava trees are nasty weeds; plumeria comes from Central America. Although we expect pork at luaus and shade from palm trees, we forget that pigs (introduced by native Hawaiians more than 1,000 years ago) demolish the native forest floor and that coconut palms probably accompanied the first human settlers.

 

Back home, I associate California with the smell of eucalyptus trees, and I think iceplant (which carpets the coast) is beautiful. I find it hard to accept that these two species are among our worst weeds, and that I should revile them accordingly. Imprints of sight and smell are hard to shake.

 

Now, here in New Zealand, a new twist: Some of my favorite North American conifers — Douglas-fir, Monterey pine and Lodgepole pine — are nasty invaders. Pines in particular are taking off through New Zealand’s grasslands like wildfire.

 

Except that there’s hardly any wildfire in New Zealand. Indeed, that’s why pines are so successful. When the Maori burned parts of the native forests to clear the land, the original trees, having evolved in a nearly fire-free environment, were slow to return. The grasslands that replaced them are now iconic: They’ve persisted for 500 years or more, predating European settlement and acquiring a novel set of human-introduced plants and self-introduced birds.

 

Enter the foreign pines, many of which were planted to stabilize the steepest slopes in the wake of the Europeans’ wave of fire clearing. But once the pines started creeping into grasslands, they became species non grata.

 

Never mind the human origins of those very grasslands: They’ve been ingrained into the Kiwi sense of place, and must therefore be defended.

 

The practical ecologist in me wonders how much I’d be willing to pay to clear whole hillsides of pine, as New Zealand’s Department of Conservation is doing now. If the area was originally forested, why not let pines settle there? Pines are fire-followers — their seedlings grow fast but require high light and all but absent tree cover. So the pine forests will last only for a single generation. Perhaps, though, they’ll form a sheltered steppingstone back to native forest.

 

Fortunately, this decision isn’t mine to make. I’ll happily avoid the mess of conflicting practical matters, scientific opinions and cultural identities. Still, such issues raise questions for all of us who grew up in a human-modified world that’s changed perceptibly within our own lifetimes.

 

Often, managers marshal crews of weed whackers and brigades of rodent trappers to chase an idealized image of a place that’s neither practical nor appropriate. Sometimes the goal is the most “natural-looking” system; other times aesthetics favor charismatic species. Recently, we’ve begun managing for “functional” ecosystems, which cycle nutrients or photosynthesize or interconnect in ostensibly “ideal” ways.

 

There seems to be a common theme, though, and that’s the desire to reproduce some fixed vision of how things “should” be. We want to restore places to match a glorified memory, and hold them unchanged indefinitely. What could be more human than wishing to hold the places dearest to our hearts constant?

 

What could be more human than wanting something we can’t have?

 

As Ben Franklin quipped, nothing’s certain in life but death and taxes. Everything else changes — including our natural systems. Plants and animals evolve — sometimes unpredictably. They adjust their behaviors and ranges according to shifting environmental conditions (with a new twist thrown in by climate change). And as we know from Hawaii, California and New Zealand, our views change too. We form new baselines from our observations as we grow up, and as we travel to places outside our former experience.

 

So we are confronted with two extremes: to fight desperately and in vain for constancy, or to surrender to global homogenization, accepting the attendant waves of species invasion and native extinction.

 

Obviously, the answer lies somewhere in between. And it’s different in every case, depending on how you feel about the smell of eucalyptus.

 

Send first, changing or lasting impressions to Holly at hollyvm “at” stanford “dot” edu. No foreign plant seeds, please!