The Conservation Decisions Team

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.

Which threatening processes should be research priorities to save more threatened species?

Our latest paper is out in Nature Communications! Read on for the details (TL;DR= we show that the value of information from resolving threat uncertainty is much bigger than we thought, and that priority threats for uncertainty reduction are high frequency fire, invasive predators and dieback).

*Note that the following text is reblogged from Nature Ecology and Evolution‘s “Behind the Paper” blog*

Managing threatened species requires making tough decisions. The lists keep getting longer, and management agencies globally are increasingly required to prioritise limited resources to save species. With limited resources, it’s important to use resources efficiently. Unfortunately, species management outcomes are often uncertain, so we rarely know where to target efforts to improve management efficiency, nor how many additional species could be saved by more efficient management.

To understand the potential gains from removing uncertainty about threatening processes, we undertook a value of information analysis. Value of information is a decision-science technique that measures the potential gains from the collection of new information. In our case, it allows decision-makers to prioritise the investment in improving knowledge about management effectiveness of threatened species. Working with the New South Wales government’s innovative Saving our Species program in Australia, we analysed almost 1,000 threatened species and threatened ecological communities affected by 20 key threatening processes including some of the big threats impacting species globally, such as fire, invasive species, and diseases. Calculating the value of information for such large numbers of species and threats is challenging and hasn’t been attempted before. One of our biggest challenges was to evaluate the gains in reducing two sources of uncertainty: the effectiveness in management of threats and the response of the species to that management. To collect the data for our analysis, we asked species experts to estimate the effectiveness of best practice management and the expected persistence of species with and without each threat.

We analysed the impacts of threats to almost 1000 listed species and threatened ecological communities in NSW, including (clockwise from top left): Grey-crowned babbler, koala, and Major Mitchell’s cockatoo. Photos: May-Le Ng.

Across all threats, we found that the average gain in species persistence if managed under current uncertainty would be 3% per species. If uncertainty could be removed, the gains would jump to 12% per species. The potential gains from removing uncertainty about threat management effectiveness could quadruple the gain in persistence achieved by managing under current uncertainty.

The implications of this finding are that uncertainty is far more influential than we thought for some threats and there are big opportunities to improve species management if we target research investment towards particular threats. We found that managers were confident about controlling invasive plant threats, but very uncertain about the benefits of managing high frequency fire, invasive predators and the plant dieback pathogen Phytophthora cinnamomi. Uncertainty about how species respond to threats had greater value than uncertainty about management’s ability to reduce the threat itself: i.e. it’s always better to attempt management than to do nothing even when the effectiveness is uncertain; but there are large potential benefits from better understanding how species will respond to threat reductions.

Our study quantifies the opportunities from better understanding how threat management influences species persistence but also creates new questions about how to best capitalise on these opportunities. When we looked at the interactions between threats, we found that the threats with the greatest potential gains from management (fire, invasive predators, dieback) were also those that interacted most with other threats. How to disentangle these interactions to reduce uncertainty is an ongoing challenge. Our next project will use adaptive management algorithms from artificial intelligence to strategically learn how to improve threat management over time while managing the system.

Our study is the first to quantify the value of information about threat management at such a broad scale. While many previous value of information studies have focused on single species and found minor benefits from removing uncertainty, our approach showed that when small benefits are aggregated across the many species impacted by threats, there can be large potential gains to management from reducing those uncertainties.

The paper citation:

Nicol, S., Brazill-Boast, J., Gorrod, E., McSorley, A., Peyrard, N. & Chadès, I. (2019) Quantifying the impact of uncertainty on threat management for biodiversity. Nature Communications, 10, 3570.

Come and do a PhD with us!!

Together with Dr Kate Helmstedt and Dr Mike Bode from the Queensland University of Technology (QUT) School of mathematical sciences, Dr Sam Nicol from our team is offering a PhD scholarship to study optimal sampling and control of spatial populations in real time. It’s a great opportunity for someone with an interest in applied mathematics and ecology to come and work with our team. On top of the QUT PhD Scholarship, we’re offering a CSIRO top-up of A$7000/year to the successful candidate. If you’re interested to discuss more, get in touch! Applications close September 30, 2018.

The PhD advertisement is here:

Optimal monitoring and control of spatial populations in real time