Evaluating the risk of invasive plant species in Queensland

Invasive plant species threaten both agriculture and biodiversity globally and require ongoing management to minimise their impacts. However, the large number of invasive species means that prioritisation is required to ensure that limited resources are directed to managing species with both a high risk of impact as well as a good chance of management success. In our latest two collaborative papers, we used an expert-driven, risk-based approach to generate a State-wide priority list of invasive species for Queensland, Australia. Both papers were led by Dr Olusegun Osunkoya (Biosecurity QLD-DAF) and involved a number of other co-authors, including Dr Jens Froese (CSIRO Health and Biosecurity).

In our first study, we asked experts to assign risks to ~100 species considered by practitioners to pose significant risks across regions and likely to be management priorities. Risks were assessed using an impact metric that combined a measure of invasiveness (measured using the proportion of local government areas containing the species that also listed the species as a priority for management) and expert-generated severity scores. We found that the 5 invasive plants with highest impacts were: Parthenium, prickly acacia, rubber vine, Parkinsonia, and bellyache bush. We also carried out some regional analysis: while the invasive plant communities of most coastal regions were similar, the regions in western Queensland and the Torres Strait Island region had distinctly different invasive communities. This suggests that while there are many opportunities for common invasive species control plans, distinct approaches may be required in the west of the State and in the Torres Strait Island region.

Bellyache bush, Jatropha gossypiifolia, was one of the top 5 invasive plants with highest impact but also had relatively low management feasibility. Image from: Wikipedia Commons

While our first study prioritised species according to impacts, our second study estimated the feasibility of management for 63 of the species prioritised in the first study. We used an expert elicitation approach to estimate the feasibility of three management approaches (biocontrol, mechanical and chemical control) in terms of cost, effectiveness and practicality. Across all species, chemical control was consistently rated highest on all three criteria, followed by biocontrol and mechanical control. Feasibility varied by life form: control of succulents and shrubs was generally rated more feasible than control of trees, vines and grasses. Experts were more confident about the feasibility of chemical and mechanical control than biocontrol.

To combine our two studies, we created a risk plot that mapped the 63 invasive plant species onto an impact/management feasibility plot, enabling managers to identify and target species with high impact and high management feasibility (good candidates for immediate site-specific control, e.g. Parthenium, Parkinsonia, Giant rat’s tail grass), as well as species with high impact but poor management feasibility (good candidates for research to improve management options, e.g. Prickly acacia, bellyache bush).

Read the papers:

Osunkoya, O. O., Froese, J. G., Nicol, S. , Perrett, C. , Moore, K. , Callander, J. and Campbell, S. (2019), A risk‐based inventory of invasive plant species of Queensland, Australia: Regional, ecological and floristic insights. Austral Ecology. doi:10.1111/aec.12776

Osunkoya, O.O., Froese, J.G. & Nicol, S. (2019) Management feasibility of established invasive plant species in Queensland, Australia: A stakeholders’ perspective. Journal of Environmental Management, 246, 484-495. https://doi.org/10.1016/j.jenvman.2019.05.052.