Environmental weed risk assessments

Why assess environmental weed risk for introduced plants?

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).

The information on this page is of particular relevance to pastoralists as a diversification permit from the Pastoral Lands Board (PLB) is required to grow any non-indigenous (exotic) species on pastoral leasehold land. However, the weed risk is not confined to certain land tenures, so all landholders in northern Western Australia (WA) 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.

In this context, ‘non-indigenous’ refers to any species not indigenous to WA. There is no need to apply for a diversification permit for species that are endemic (i.e. native) to WA. This can be checked using Florabase.

How we assess environmental weed risk

The environmental weed risk assessment of a species is assessed for three regions in the pastoral zone of WA (Kimberley, Pilbara, Gascoyne-Goldfields; Figure 1) using a three-step process (Figure 2).

Step 1: Species prerequisites for WRA

Non-indigenous species or specific varieties may undergo post-border weed risk assessment after checking that each of the proposed species is:

• permitted entry into Australia
• not a Weed of National Significance (WoNS)
• not listed as a WA prohibited organism (s12) or a declared pest (s22) on Western Australian Organism List (WAOL).
• either listed as a permitted organism (s11), or a permit has been granted for its import (r73) on WAOL.

If a proposed species is not listed as a prohibited organism, declared pest or permitted organism on WAOL, the applicant/importer can lodge an ‘Application for Import Permit’ with DPIRD.

Step 2: A filter

The second step is a ‘filter’ to identify species which are:

• recorded as environmental weeds in similar environments in Australia or overseas and,
• likely to persist in the given environment without management.

Species with a ‘negative’ response to both filters represent a negligible to low environmental weed risk in the pastoral zone.

Step 3: Full environmental weed risk assessment

For all other species, an environmental weed risk assessment (WRA) is undertaken using the ‘Environmental weed risk assessment protocol for growing non-indigenous plants in the Western Australian rangelands’ (Moore et al. 2022) which is based on the methodology developed by the Future Farm Industries Co-operative Research Centre (FFI CRC) WRA for southern Australia (Stone et al. 2012). DPIRD Bulletin 4924

Figure 1 The three regions within the pastoral zone of Western Australia plus the agricultural area

Figure 2 Flow diagram showing the three-step assessment process

Note: *For all organisms listed on WAOL under s11 of the Biosecurity and Agriculture Management Act 2007 or r73 of the Biosecurity and Agriculture Management Regulations 2013.

**The ‘environment’ can be considered in the context of the WA Rangelands and the three regions (Kimberley, Pilbara, Gascoyne-Goldfields), or for a specific application within a single Region.

***Without management, means without any fertiliser, Rhizobia, irrigation, grazing management or control of competition from other species.

The WRA protocol is subdivided into three sections where:

• invasiveness – assesses the ability of a species to spread beyond agricultural systems or grazed native vegetation into intact native vegetation
• impacts – assesses the potential detrimental impacts a species may have on intact natural ecosystems
• potential distribution – assesses how widely adapted is the species to the novel environment based on the climate and soils of the target area.

Weed risk score calculation

The first 2 sections of the protocol contain a series of questions that will generate a 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.

The environmental weed risk assessment scores for the Kimberley, Pilbara and Gascoyne-Goldfields (includes Gascoyne, Murchison and Goldfields) regions are listed in Table 2.

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

Environmental weed risk ratings for species for three regions within the pastoral zone of WA

Plants are listed alphabetically in ‘species’ order:
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Note: The species name hyperlink opens a PDF of the weed risk assessment for that species. Blank cells means that an assessment has not been done or is currently in preparation.

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.