Ranking biodiversity risk factors using expert groups - Treating linguistic uncertainty and documenting epistemic uncertainty

Sound planning is vital to ensure effective management of biodiversity, particularly where there is a high risk that management goals may not be achieved. This is the case at Toolibin Lake, an internationally recognised wetland, where changed hydrology as a result of agricultural development has detrimentally affected the quality and quantity of water entering the lake. Although management actions have slowed or halted degradation of the lake's biological assets, goals have not been fully achieved and management is under review. To rank the hydrological risk factors threatening the lake's biota as a foundation for more detailed planning, a structured elicitation process was used with an expert, cross-disciplinary group. Techniques used were explicitly aimed at minimising and documenting uncertainty. These included calibration questions to assess the accuracy of experts, and tightly specified goals and terms to minimise vagueness, ambiguity and redundancy. Surface water salinity, groundwater salinity and drought were the only factors identified as having a high probability of causing goal failure. Importantly, the majority of risk factors were evaluated as having a low probability of causing goal failure, enabling these factors to be rapidly eliminated from short-term consideration. The experts, acting anonymously when estimating probabilities, varied considerably in the assessment of one risk. This underlines the importance of rigorous processes to identify knowledge gaps and assess the likelihood that proposed management will be successful. The elicitation process provided low cost, rapid assessment of large numbers of risk factors with explicit assessment of uncertainty.