Australasian Science: Australia's authority on science since 1938

Perversity in the Pasture

By Don Driscoll and Jane Catford

Hundreds of the invasive plant species that inflict environmental and economic damage in Australia were originally developed and distributed as pasture species, yet we don’t seem to have learnt from these mistakes.

African lovegrass 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.

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? 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.

When we undertook a global survey of pasture plants we revealed that more than 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, canary grass, tall fescue and sub clover. These species are all recognised weeds in Australia that degrade native communities such as threatened box gum woodlands.

Although these weed species already occur throughout much of Australia, the environmental risk escalates when new varieties of these species are released. They may belong to the same species, but these varieties can be quite distinct from their parents – just think of the differences among dog varieties like chihuahuas and wolves.

New varieties can be created by cross-breeding different varieties or different species. Engineering plants in this way can lead to varieties with higher reproduction, higher growth rates, better resistance to disease and higher tolerance of environmental extremes. Unfortunately, these are the same characteristics associated with invasive species. They are bred to grow great pasture, but at the same time they are inadvertently bred to be superweeds.

Once these souped-up plants have been bred, they are matched to the environments in which they are most likely to succeed. To make matters worse, because of the nature of pasture production, these new varieties will likely be planted widely across the landscape. Because they can be planted very quickly over massive areas, it will be very expensive to try to control invasion once a weed has got away. Pre-emptive action makes sense.

Risks from new pasture varieties are not considered by current regulations. At the moment, Australia only considers the weed risk of new exotic species that may be imported. Exotic species that are already present in Australia are not assessed but are permitted ongoing entry, even if they are known to cause harm.

This is a major flaw: it suggests that if a species is already here then the damage, if any, is done, and ongoing use is a reasonable course of action. New varieties of these permitted exotic species can be developed, released and spread widely across Australia’s pastoral areas without any scrutiny of their potential to become new weeds, increase the impacts of existing weeds or spread into new areas.

But there are solutions. We need to:

  • account for full environmental, social and economic benefits and costs of new varieties;
  • produce a list of prohibited and permitted species based on varieties;
  • apply weed risk assessment to new varieties; and
  • monitor new varieties and respond rapidly if they become invasive.

While government must play a lead role, the solutions are not up to government alone. Agribusiness could take up opportunities to integrate weed risk assessment into their development programs, with the aim of developing varieties with low weed risk. Farmers could also improve stewardship of their land by refusing to buy new pasture varieties that have a high weed risk.

As our tropical savannahs succumb to gamba grass fires, as our arid woodlands vanish under buffel grass wastelands, and as native species vanish from the few remaining box gum woodlands degraded by introduced pasture plants, it seems like common sense to stop making these kinds of problems worse.

Don Driscoll and Jane Catford are members of the Environmental Decisions Group. Don is based at the Australian National University and Jane is based at the University of Melbourne.