Warming Could Dramatically Alter South Australia's Weed Map

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June 18th, 2010

	Wheel cactus (Opuntia robusta). Image source

Another seven decades of climate change could see substantial changes in South Australia’s weeds, with olives, Coolatai grass and wheel cactus among those likely to spread further south as the climate warms and dries.

CSIRO researchers Darren Kriticos and others examined the likely climate change impacts on weeds for the South Australian Government. Using mid-range predictions for global warming by 2080, they considered 13 weeds in detail and modelled likely distributions (using the CLIMEX program).

In general, the state’s northern regions face a lower threat from current prominent weeds, but may be vulnerable to invaders from Western Australia, the Northern Territory and Queensland.

However, SA’s more southerly regions can expect an increase in weed threats. Cold boundaries that currently limit the spread of many weeds will shift south and to higher elevations.

While olives (Olea europaea ssp. europaea) are expected to lose suitable climatic conditions in the north but gain them in the south, Coolatai grass (Hyparrhenia hirta) is expected to survive in northern areas where it currently invades, and much further south to Kangaroo Island and the southern tips of the Eyre and Yorke peninsulas.

The movement of this grass into new areas could significantly increase fire risks in urban and peri-urban areas.

The researchers contrast the likely capacity of weeds and native plants for dispersal and warn that corridors established for native vegetation could serve as conduits for weeds:

Weeds have considerable capacity for dispersal, and in contrast, many terrestrial native vegetation communities are effectively islands, in a sea of weed-infested agricultural land.

The ability of species to move to areas of changed, but suitable climate will depend on the existence of a pathway for introduction, and dispersal ability.

Weed species that are dispersed effectively by animals may be especially effective at tracking their climatically-suitable range as it shifts.

Native vegetation corridors established to facilitate the movement of native species in response to changing climatic conditions may also serve as landscape conduits for the movement of weeds, and may well suffer from the presence of weeds.

This problem is likely to be most poignant whenever these corridors or their surrounds are disturbed, by such means as fire or prolonged drought.

Some native species also have this weedy characteristic and will respond to climate change in a similar manner to weeds.

They also note that agricultural weeds are more likely to adapt to climate change than the crop species they invade, with the widespread presence of herbicide resistance “strong evidence of the ability of weeds to evolve to cope with environmental stresses”. This adaptability will ensure that weeds remain a significant cropping problem.

Kriticos and colleagues make the following recommendations:

1. Maintain or establish long-term monitoring plots or procedures in key environmental and agricultural areas so that changes in distribution and abundance of weed flora can be detected early enough to apply appropriate management strategies.
2. Introduce climate change considerations into South Australian weed risk assessments:
        a. to incorporate expected changes in distribution and abundance
            into strategic management plans for priority weeds; and,
        b. to develop an alert species and sleeper weeds list for South Australia.
3. Use climate change considerations to identify for NRM regions the future risks posed by weed species that may either not be present, or may be currently present as benign (sleeper) populations.
4. Encourage NRM regions to undertake a programme of surveillance and local eradication of possible climate change sleeper populations.
5. Consider the placement of quarantine barriers or strategic containment lines within South Australia in anticipation of weed species range expansion as climates change.
6. Use the climate analogue analyses (section 5) to identify potential weed species that presently occupy climates that are similar to South Australia’s recent historical or expected future climates. The list of potential weeds can then be used to investigate the presence of these species in Australia (e.g. in horticulture) and to undertake weed risk assessments.
7. Maintain or establish ongoing monitoring of biological control of weeds, especially for currently successful programs, so that the trends in changes can be detected early and acted on accordingly.
8. Develop strategic research priorities for South Australia in the area of climate change and invasive plants.

References

Kriticos DJ, Crossman ND, Ota N & Scott JK. 2010. Climate change and invasive plants in South Australia. Report for the South Australian Department of Water, Land and Biodiversity Conservation. CSIRO Climate Adaptation Flagship, Canberra, Australia.

 

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