Perversity in the pastureGuarding against new pasture varieties becoming tomorrow's environmental disasters

Hundreds of the invasive plant species that now inflict major environmental and economic damage in Australia were originally developed and distributed as pasture species. What a perverse outcome. What's worse, we don't seem to have learnt from these mistakes.

Consider African lovegrass. It was used to 'improve pasture' in Australia for almost 100 years, but is now declared a weed in four Australian states and the ACT. It has been of little value in pastures, poses a substantial fire risk and threatens a range of native species.

Similarly, Gamba grass was widely promoted in northern Australia by the cattle industry and government. It is now listed as a Weed of National Significance. Gamba grass increases fire intensity five-fold, which transforms native woodlands into exotic-dominated grassland and increases the cost of fire management by an order of magnitude.

Agricultural weeds cost Australia an estimated $4 billion every year, and the environmental damage is thought to be of a similar magnitude. Introducing these pasture species was a big mistake that Australians will continue to pay for indefinitely. We face increased fire risks, increased management and weed control costs, as well as ongoing loss of our natural heritage.

So, we've learnt our lesson, right? The problem of deliberately introduced plant species going rogue is both well known and well documented. Well, as incredible as it seems, we don't seem to be learning at all. Agribusinesses still develop and promote new varieties of species that are known invasive weeds.

A global survey of pasture plants by researcher Don Driscoll and Jane Catford has revealed that over 90% of plant species developed and sold by agribusinesses are weeds somewhere in the world, and on average 30% are weeds in the country in which they are promoted. In Australia, species promoted by agribusiness include orchard-grass (Dactylis glomerata), canary-grass (Phalaris species), tall fescue (Schedonorus arundinaceus), and sub-terranean clover (Trifolium subterraneum). These species are all recognised weeds in Australia, weeds that degrade native communities such as threatened box-gum woodlands.

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Image: Jane Catford and Don Driscoll in dense sward of canary grass.  This species is a known invasive plant but new varieties are still being developed for pasture. Phot: Stuart Hay

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