Weed risk assessment: a way forward or a waste of time?

Hulme, P. E. (2012). Weed risk assessment: a way forward or a waste of time?. Journal of Applied Ecology, 49(1), 10-19. PDF.

Summary

Weed risk assessments are a common strategy for identifying the next wave of invasive plants. But we rarely measure the success of risk assessments, and it is unclear how effective they are for novel, potentially invasive species. Therefore, Hulme (2012) evaluates the weaknesses of three approaches to weed risk assessments: statistical models, semi-quantitative scoring, and expert assessment. Problems with weed risk assessments include lack of measures of uncertainty, inability to predict across scales, difficulty measuring impact, biases based on the user’s priorities, and varying descriptions of species traits. Additionally, considering how few introduced species become invasive, weed risk assessments must be highly accurate to be effective. Although the possibility of successfully identifying and banning a weed likely outweighs the cost of doing a risk assessment, weed risk assessments must increase consistency between approaches to be effective. Therefore, Hulme (2012) suggests other strategies, such as EDRR and field tests, may be more effective for identifying invasive species. 

Take home points

  • The errors, biases, and unmeasured success of week risk assessments suggest this may not be an accurate or effective strategy to identify potentially hazardous species.

  • Adaptive management using early detection and rapid response or scenario planning between stakeholders is an alternative strategy to managing invasive species.

Management implications

  • If using weed risk assessment, be careful in your choices and be aware of the pitfalls.

  • Consider asking these questions when choosing a risk assessment tool: What are my priorities and consequent biases (e.g. economic, conservation etc.)? Does the tool account for uncertainty and/or variability? What prior knowledge do we have (e.g. about the species, the introduction pathway, and the current established species pool) and how does the tool incorporate it?

  • Continue with early detection and rapid response (EDRR) efforts through regular monitoring, which may be more effective than risk assessment frameworks.

Keywords

Novel Introduction Pathways; Shifting Seasons; Range Expansion; Review; Invasive Plant; Risk Assessment