Exotic grasses are a large and important component of Australia’s weed flora. They are emerging as one of the greatest threats to tropical savannas, for both the environment and the pastoral industry. There are approximately 200 species of naturalised grasses in northern Australia, and several have already been identified as serious weeds. In addition to recognised weedy grasses, many grasses have been introduced and spread by various sectors including the mining, pastoral and nursery industries that perceived them as beneficial.
However, some of these exotic grasses are now emerging as environmental weeds with the potential to dramatically alter savanna function. Weedy grasses are particularly difficult and costly to manage, especially in less closely settled regions of Australia. It is therefore important to be proactive to prevent the spread of these grasses and other species which have the potential to become a problem. This will require a tool to assess the weed risk posed by naturalised grasses.
Weed risk assessments already exist but they have been developed either for point of entry quarantine and may not be as relevant when dealing with species already naturalised. Furthermore such systems have proven to need refinement for application in tropical locations. Other weed risk assessments have been developed specifically to prioritise management effort for naturalised species. These have been developed in southern Australia so there is a need to test these methods, and possibly refine them, for use in tropical savannas.
This project recognises that there are savanna users who need to use exotic grasses for grazing and rehabilitation. There are also users, such as conservation managers, who do not want exotic grasses on the lands they are responsible for, such as parks and reserves. While weed risk assessment has been used principally to identify species of weed risk, this project will explore its potential to identify exotic grasses with a lower risk of becoming weeds.
There has been relatively little weed research into either native or exotic grasses in the tropical savannas and a lack of such information currently hinders weed risk assessment which requires information on:
- Potential distribution,
- Invasiveness,
- Impacts and
- Response to management.
Some information on the first two criteria has been compiled in databases developed by the Weeds CRC. There is still a need for more information on the impacts on savanna function following colonisation by exotic grasses. Information on impacts at larger spatial scales and over longer time periods can be predicated by using empirical data to develop simulation models such as Flames and Savanna AU.
This project will use a weed risk assessment (WRA) approach to identify the grasses mostly likely to become important weeds and their likely effects. This approach will also be used to identify species that pose less of a weed risk and to make recommendation on the management actions required to prevent the unwanted spread of grassy weeds. This information can also be used by managers to prioritise weed management activities.
To maximize the impact of the WRA developed by this project, we have included stakeholders in its development and testing. The project includes staff in government agencies that are developing policies regarding the use and management of exotic grasses. These relationships will be instrumental in ensuring maximum impact of the project outcomes.
Major recommendations from the project workshop held in April 2003 were
- to modify and then test the appropriateness of the AQIS (Pheloung ) and Virtue (Virtue ) WRA tools for savanna grassy weeds
- to increase the level of knowledge on the control of grassy weeds increasing rehabilitation success.
These two recommendations were incorporated into activities for 2004-2006.
