Risk assessment for nonindigenous pests: 2. Accounting for interyear climate variability

The paper firstly discusses the importance of accounting for interyear variability when assessing the likelihood of establishment of an alien pest. The potential establishment of Colorado beetle (Leptinotarsa decemlineata) is used as an illustration within the geographical context of England and Wales. An aggregate risk index is introduced as a probabilistic representation of the likelihood that a pest might complete a single generation over a 30-year period (1961-90). Data for individual years were used to compute, objectively, the interyear distribution of risk across the landscape. The standard deviation in area at risk (26 800 km2) was high relative to the average proportion of the landscape potentially at risk (95 700 km2). In 40% of years, the area at risk was estimated to be higher than 'average'. Secondly, the paper demonstrates multiple indices of risk that reflect different aspects of pest risk assessment. Viewing risk from a variety of perspectives provides a means of gauging the consistency and therefore reliability of the results. This contrasts with current practice, where a single mapped output is commonly presented to decision makers. Modelling using a daily time step allowed the use of indices to investigate the long-term probabilities of biotic and abiotic events of short duration. These indices include estimates of pest activity and flight potential.