Skip to main content Skip to navigation

Pastures and environmental weed risk assessments

To minimise the negative environmental impact of introducing new agricultural species to WA, the department uses a risk assessment procedure based on widely accepted scientific standards. 

Field of tall grass

Introducing new plants to an area may have both positive and negative effects on the environment, economy and community. To minimise the negative environmental impact of introducing new agricultural species, we use a risk assessment procedure based on widely accepted scientific standards. 

Agriculture in Australia is based largely on exotic or non-indigenous plants, however there is a well-documented history of introduced plants becoming environmental weeds. 

A number of plants introduced for agriculture have spread from sown areas and become serious environmental weeds. For example, Gamba grass (Andropogon gayanus) was introduced into the Northern Territory as a pasture species but has subsequently become a serious environmental weed as the large biomass greatly increases the intensity of fires (note: Gamba grass is a prohibited import into Western Australia (WA)).

Species in the pastoral zone

All landholders in the pastoral zone of WA (Kimberley, Pilbara, Gascoyne-Goldfields) are encouraged to be aware of the potential of species they sow or cultivate to become weeds of the natural environment and to take appropriate measures to minimise the risk.

On pastoral leasehold land, a diversification permit from the Pastoral Lands Board is required to grow any species that are not indigenous to WA. Diversification permits for species that are endemic (i.e. native) to WA are not required. The status of species (native or exotic/alien) can be checked using Florabase. 

The environmental weed risk ratings for a wide range of species for the Kimberley, Pilbara, and Gascoyne-Goldfields regions in the pastoral zone of WA have been assessed. 

Weed risk assessment process 

To minimise the negative environmental impact of introducing new agricultural species, DPIRD use a weed risk assessment procedure based on widely accepted scientific standards. 

The environmental weed risk assessment (WRA) of a species is assessed for 3 regions in the pastoral zone of WA (Kimberley, Pilbara, Gascoyne-Goldfields) using a 3 step process (Figure 1). 

Weed risk score calculation 

The first 2 sections of the protocol contain a series of questions that will generate a weed risk score depending on the response given. The scores for each question are then summed and standardised (maximum score of 10 for each section). 

The adjusted scores for each section are then multiplied by the potential distribution score (maximum score of 10) to arrive at the overall weed risk score (equation 1). 

Equation 1: Weed risk score = Invasiveness (0–10) x Impacts (0–10) x Potential distribution (0–10) 

The weed risk category is then determined from the weed risk score (Table 1). 

Example: For species X with an invasiveness score of 6.2, an impacts score of 3.2 and a potential distribution score of 4.4, the risk score equals 6.2 x 3.2 x 4.4 = 87.3, which equates to a medium risk rating. 

Table 1 Weed risk scores and corresponding risk rating 

Weed risk score 

Risk rating 

Possible conditions on a diversification permit 

>236 

Very high 

In general, unlikely to be approved, however if approved the PLB may include additional conditions. 

112 – 235 

High 

If approved, the PLB may include additional conditions. 

50 – 111 

Medium 

Standard conditions 

0 – 49 

Negligible to low 

Standard conditions 

Source: Future Farm Industries (FFI) CRC; Stone et al. (2012)

Environmental weed risk ratings for the pastoral zone of WA

References  

Moore G, Munday C, Barua P (2022) ‘Environmental weed risk assessment protocol for growing non-indigenous plants in the Western Australian rangelands’, Department of Primary Industries and Regional Development, Bulletin no. 4924, Perth. 

Stone L, Munday C, Bettink K (2012) ‘Environmental weed risk assessment protocol’ Future Farm Industries CRC Weed Risk Assessment. 

Contact us