Pest risk assessment and invasion pathways: invasive weeds.
For pathogens and insect pests, risk assessments are carried out to determine to what extent they are likely to enter accidentally, as passengers on an imported commodity. By contrast, risk assessments of potential weeds are typically conducted on plants that people actually want to introduce, either as ornamentals, or for agriculture. Here, the focus is on determining whether a species, unknown elsewhere as a weed, could become invasive in the country of proposed introduction. A proper assessment of risk here, therefore, requires us to understand what triggers a species to become invasive. Such understanding still eludes us, and indeed is at the frontier of ecology, yet weed risk assessment systems are already being implemented or adopted all over the world. I present concepts from the epidemiological literature, that are relevant to the assessment of such systems.