19 February 2006

Damn Acorns

It's that time of year again, and the oak trees in Canberra are dropping their acorns. I crunch them while walking across the back patio. Occasionally I slip on the roly-poly hard round objects that dig uncomfortably into my bare feet. Oaks are only one of Australia's many imports, and, despite my inconvenience, one of the less pernicious ones.

The first year I moved here I thought the local oaks must have been mutants. I grew up in the middle of Long Island. Long Island's mature forest was dominated by oak. I can recall one white pine at the top of the block and a birch and a peach tree my parents had planted. We had a weeping willow that I climbed when I was four. I cried when it was cut down in my seventh year after an unfortunate storm caused one massive branch to dangerously overhang my neighbour's kitchen. Every other tree in my memory is an oak. And in spite of their overwhelming numbers, I knew I had never seen quite so many acorns as I did that day crossing the street to my mum-in-law's. Trying to maintain my balance across a lawn could have been injurious. The carpet of round hard acorns providing no traction.

It took me a while to realise that the missing ingredient in all this was squirrels. Upon my realisation, I suggested to Shane that Australia could import some, in the interest of public safety. He pointed out that foreign imports had often been disastrous. "What can go wrong? They're only squirrels," I protested feebly.

Indeed. Australia's history is filled with equally naive people importing flora and fauna that have some major evolutionary advantage and wind up completely filling a niche, ousting the former inhabitants of that niche and often damaging local habitats. Off the top of my head, I can easily think of half a dozen:
  • blackberries - one of twenty Australian Weeds of National Significance(WONS), blackberries were originally introduced into Australia as a horticultural plant. The tale goes that an itenerant hobo, desiring to be the Aussie Johnny Appleseed, spread blackberry seeds throughout Australia so the hungry traveller would always have a meal. The weed grows in dense thickets, reducing movement and the diversity of vegetation and wildlife habitat.

  • rabbits - You've probably seen "Rabbit-Proof Fence", a moving real life tale about three little girls who escape mandatory enculturation as part of the "stolen generation". They find their way home by tracing the rabbit-proof fence for 1500 miles.

    That Australia built more than 2000 miles (3200 km) of fence in toto is testimony to the recognition of rabbits as a serious pest. According to Wikipedia:
    rabbits are responsible for serious erosion problems as they eat native plants which would have retained soil. One eighth of all mammalian species, and many species of plants, in Australia are now extinct due in a large part to the rabbit infestation.
  • the cane toad - Sugar cane was introduced to Australia with the first fleet in 1788. Cane beetles and frenchie beetles probably came soon afterwards or were introduced as larvae with that first shipment. The Cane Toad (Bufo marinus) was introduced to Australia in 1935 in order to control these pests. Some of Australia's smarter predator animals, such as crows, have learned to eat the toads' soft bellies and avoid the poison sacs. Others are not so lucky, and cane toads have been responsible for poisoning, displacing and/or predating indigenous species. Oh, and by the way - they were completely ineffective against the beetles.

  • Patterson's curse - "Ooh, pretty!", I exclaimed the first time I saw the fields of purple flowers carpeting the otherwise drought-ridden valleys around Canberra's bushland. "Patterson's curse," was the reply. Intrigued that such a pretty plant could have such a negative name, I researched and found that Echium plantagineum is devastating because it is so successful in Australia's dry, mineral-poor topsoil that it will easily displace most difficult-to-grow cultivates.

    Ironically, where native vegetation is healthy and undisturbed, Patterson's is less successful. But Australia's soil is already degraded by human-related activities such as overgrazing and the introduction of rabbits.

    In addition, Patterson's contains alkaloids that taste sweet, but are deadly to livestock. The alkaloid quickly builds up to toxic quantities in horses' and cattle's livers and eventually cause death.

  • Indian Mynah birds, wild dogs, foxes and feral cats - the same old story. Extremely successful species displacing natives, generally by competition or predation.

And then of course, there's the most dangerous import of all: modern westernised H. sapiens. The impact of this species can include complete degradation of natural habitats, degraded water and air quality and most recently intense climate change. Finally, this is not simply an Australian problem. It remains a world-wide concern.


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