What the report is about

This project focuses on the weed risk in relation to climate change in the Northern Agricultural Region (NAR) of Western Australia. The region was chosen because it is predicted to experience considerable environmental impact from climate change. It is also one of Australia's highly productive agricultural regions, generating approximately $1 billion annually.

This project aimed to assess the impact of climate change on agricultural weed spread by building on the distribution data collected from field surveys of the NAR and neighbouring areas.

Based on the feasibility of containment scores generated by this report, it is possible to determine what course of action could be taken for control of the 20 riskiest weeds as in the NAR.

Where are the relevant industries located in Australia?

In the future, potentially large reductions in rainfall will reduce agricultural yields markedly. Experience has also shown that increased temperatures during the growing seasons of crops are likely to negatively affect yield. In such an eventuality, cropping will become more challenging at the current dry margins of regions with Mediterranean climate, such as south-west Australia, but may expand into areas currently generally too wet for regular cropping. A significant part of the challenge will be the weed regime, which will increase the level of stress faced by crops.

Aims/objectives

This project aimed to assess the impact of climate change on agricultural weed spread by building on the distribution data collected from field surveys of the NAR and neighbouring areas. The research objectives included:

• Applying a weed risk assessment (WRA) model to determine the relative weed threats posed by 20 high-priority species in the survey.
• Developing CLIMEX models for the five ‘riskiest' species.
• A prediction of the distribution of each weed species in 2070 under an IPCC4 scenario relevant to Australia.
• Developing recommendations for adaptation responses to manage the changed weed threat.

Methods used

Several field surveys and databases were used to develop a complete list of plant species present within the NAR and buffer zones. Each species was then categorised according to its weed risk.

Weed risk assessments on the region's 20 riskiest weeds were conducted using criteria based on the South Australian weed risk management guide, and a final five species were selected for CLIMEX modelling. The land use chosen for each WRA was a crop-pasture rotation within the NAR.

Results/key findings

Based on the feasibility of containment score, a course of action can be determined for control of each weed. For example, species that are currently widespread and difficult to control have a negligible rating, which suggests that containment is very unlikely and control should be based on ongoing management. Species which are not currently present within the NAR have a very high chance of containment; therefore, the course of action is to restrain the spread.

Implications for relevant stakeholdersr:

Under a future climate change scenario of annual temperature increases of 1.7-2.5°C and rainfall decreases of 5 mm (16%) in summer and 40 mm (23%) in winter, it is expected that each of the 20 species selected for detailed WRAs would have a significant impact on the crop-pasture rotation systems of the NAR.

Recommendations

The main priority for future research is to extend this study to include an assessment applicable to the whole cropping region of Western Australia.

The risk assessments are based on the ability of weeds to grow in different climates. Each risk assessment could be augmented by overlays of the weed's response to different soil types, agricultural practices and other non-climatic factors. However, research would be needed to establish the relevance of those factors to the growth and survival of each weed species.