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Australian Plants now Outnumbered!
Introduced plant species now outnumber known Australian native species
About 27,500 introduced plant species have made their way into the country; and we know of 24,000 native species.
Around 10% of the invaders have become ‘naturalised’, meaning they now grow and thrive in the wild. Each species introduced to Australia needs to be considered as potentially dangerous for our biodiversity. The seemingly harmless introduced plants of today could become the devastating weed of tomorrow.
Invasive plants a threat to natives
Four of Australia’s native plants have already been wiped out by weeds choking them,and another 57 are under threat of the same fate. Not all weeds are foreign plants but most were introduced in fields and gardens from abroad.
In agriculture, useful foreign plants such as wheat or barley don’t seem to naturalise and need to be re-sown each year; others grow out of control and overrun grazing and crop fields, costing the sector about $3.5 billion a year, excluding the environmental cost.
Horticulture is by far the main source of plant introduction.
Exotic species imported to gardens sometimes jump the fence and invade the countryside, depleting the soil and harming other plants. Garden escapee arum lily (Zantedeschia aethiopica), for example, competes with pasture for nutrients and space, and may replace pasture species in grazing areas. It is also toxic to stock, especially cattle.
Arum lily, like many other foreign plants known to be invasive, is still available for sale in Australia.
Long-term problem of invasive weeds
It’s difficult to assess whether an introduced plant will thrive in Australia. Some can live in the wild for years before becoming a problem. The Australian Quarantine and Inspection Service manages invasive species effectively at our national borders. But plants can be easily transferred between states, and cause as much havoc.
So before you buy a foreign plant species for your garden, do your homework. Better still, favour local species as much as possible.
For more information see C Thuilier,
Introduced plants outnumber natives,
Australian Geographic, August 2012
RH Groves, R Boden & WM Lonsdale’s 2005
CSIRO report, Jumping the Garden Fence
for WWF-Australia www.wwf.org.au
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