Sweetness and light

On our shady south-west facing hillside (who went house hunting without a compass, then?) there’s just one spot that gets plenty of light year round: not a bad place for some solar panels on the top of a pole. But right in that spot there’s a native tree, sweet pittosporum or pittosporum undulatum.  And there’s a healthy specimen of the same species dead to the north of our kitchen windows, right where the winter sun might otherwise beam through.

Hornsby Council is pretty proud of its status as a leafy north shore suburb – “The Bushland Shire” – and dissuades its rate-payers in the strongest of terms from cutting down trees.  But not this one.  Until 2011, despite its status as a native, gardeners had a licence to kill sweet pittosporum, along with a select few imported nasties – cotoneaster, camphor laurel, privet and coral trees. But now it’s a different story.  You can chop down quite a lot in Hornsby these days – pretty much any non-native tree.  You can even gaily hack down Australian natives that don’t hail from this part of the Hawkesbury.  But put that saw down!  Pittosporum is now right there on that not very lengthy list of protected local trees, shrubs, grasses and vines.  It’s a dramatic turnaround, from big-league environmental weed to local hero, all in the space of a single year.

So what’s going on here?  Tim Low’s immensely readable book, “The New Nature: Winners and Losers in Wild Australia” (Viking, 2002), a fat but fascinating volume filled with stories about birds and trees, insects and frogs and their complex inter-relationships with human beings, has a lot to say about weeds and natives, and in fact quite a bit to say about sweet pittosporum.  The essential argument of the book is that any quest to preserve untouched wilderness or to maintain nature free from human interference is not just doomed, but essentially ill-conceived.

Human influence has been making plant and animal winners and losers in Australia for many thousands of years, and Low documents not only the way some pragmatic species capitalise on urban environments (think peregrine falcons nesting in high rise buildings) but the way many others rely on continuing human intervention (like firestick farming or stock grazing) to survive.  Sydney’s green and golden bell-frog survives at the Brickpits in Homebush, a location described as “one of the most industrially polluted in the Southern Hemisphere” (24) because these frogs are tolerant of high levels of heavy metals, while the frog-killing chytrid fungus is not. Low points out the limitations of the distinction between “native” and “exotic” as a way of gauging the impact of animals and plants on biodiversity, and argues that decisions about what to conserve and how to do it, are in short, very very complicated.  Koalas can be forest killers and cows can step into the gap left by extinct megafauna in maintaining diverse grassland.  As a greenie and a gardener, I found the anecdotes and ideas in “The New Nature” provoking and intriguing, making me take a good hard look at my weed anxieties and my fantasies of a bird-friendly, local provenance garden.

Hornsby Council’s change of heart about sweet pittosporum illustrates Tim Low’s arguments beautifully.  Don Burke, the Australian Native Plants Society of Australia, Grow Me Instead (The Nursery and Garden Industry Association) and the Queensland Government all agree that it’s an invasive weed. “The New Nature” with its ambivalence about such terms calls pittosporum “our worst native weed” (250), “replacing diverse systems with monoculture” (201).  While a canopy of eucalypts allows a rich understory, pittosporum shades out nearly everything else (although that nasty garden escape, privet, apparently copes well).  Birds enjoy the pittosporum’s orange fruits and disperse its sticky seeds.  Not needing fire or light to germinate, and tolerant of richer soils than many other natives, pittosporum is a native to this neck of the woods, flourishing on the shale ridgetops on Hawkesbury sandstone – most of which are now built on.  Run off from houses and gardens has enriched the sandstone soils on the slopes and pittosporum has moved on in.  According to Low, “If you take eucalypt forest, add fertiliser and water and take out fire, you have a recipe for rainforest.  The pittosporum invasion is really a takeover by rainforest” (248).

Pittosporum undulatum has its defenders.  Jocelyn Howell from the Royal Botanical Gardens suggests that pittosporum can shade out and outcompete other more troubling weeds (although Tim Low would argue that even invasive weeds like lantana can play their own role as a habitat).  Others argue for it in terms of the food supplies it offers and the fact that it *is* a local really. Obviously, Hornsby Council has plumped for this point of view.  Most of the advisories suggest that it’s a weed only outside its home range, using provenance to distinguish true locals from native invaders.

But according to Low’s arguments, its home range isn’t the home it once was.  His book gives poignant examples of Sydneysiders talking about the impact of pittosporum (“pittos”) in terms of solastalgia, the sense of homesickness you have when you haven’t left home, but your home has changed forever.  Orchids and grasses gone, along with the smell of eucalyptus (248).  There are no easy answers here: it’s “a hard one”, “one of the most sensitive issues around” (249).  Are the eucalypt forests of the Hawkesbury slowly morphing into (monocultural) rainforest?  Will the catastrophic fires I expect and dread drive it back?

From a more selfish point of view, it seems like my kitchen windows will remain gloomy and my solar panels a dream, even as my fantasy as a kid growing up in the arid lands of the South Australian mallee, of coming home to a rainforest seems to be coming true…

4 thoughts on “Sweetness and light

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  4. Very interesting. We used to live in Queensland where the borders between the rainforest and the dry forest are a battle zone of competing plants, battles fought out over decades, or even centuries. Round here the invasive native is a tea-tree which has formed some big areas of monoculture. I keep reminding myself – biodiverse, resilient, that’s what we’re aiming for. It’s hard enough. Good luck with your window.

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