Assessing the role of plant trade networks in the vulnerability of forest nurseries to plant pathogens

Pathogen damage is responsible for a considerable reduction in profit to the New Zealand forest industry. An assessment of pathogen prevalence, propagation and production methods, and phytosanitary/biosecurity protocols at the forest nursery level was conducted in order to identify predictor variables for pathogen acquisition and potential spread. Higher pathogen incidence within a nursery was found to be positively correlated with the use of copper oxychloride and a higher number of biosecurity protocols implemented by nurseries (presumably due to an increased interest in pathogen management) as well as the presence of a plantation forest within 1 km of the nursery. Information on seed purchases and seedling sales were used to produce directional transport networks describing product movement within the industry. The subdivision of these transport networks into modules can be used as a tool for forecasting the likelihood of movement of product from seed orchards to nurseries to plantation forests. These networks identify the regional association of a network module as the best predictor for product movement through the New Zealand forest industry. In addition, the network analysis highlights that the industry is most vulnerable to any new pathogens contaminating seed and can be used to assess potential transmission routes.