Modelling vehicles as vectors of forest pest and pathogen spread

Abstract Invasive pests and pathogens cause immense damage globally, costing an estimated US$ 248 billion to the agricultural industry alone. Vehicles, such as farming and timber harvesting machinery and transportation trucks, can facilitate the rapid spread of biological invaders over distances far greater and more quickly than their natural dispersal ability. Understanding how frequent trips by these vehicles increase the spread of invasive agricultural and forestry pests can help inform effective biosecurity procedures before, during, or after an incursion. We used a case study of timber transport trucks in Aotearoa New Zealand to examine whether and how vehicles facilitate the spread of soil-borne pathogens between commercial forest plantations. Our results show that long-distance dispersal associated with truck movement facilitated the introduction of oomycete-like pathogens in 97% of forest sites within only one year, with pathogen loads within infected sites predicted at 84% of the sites’ carrying capacity. Implementing preventative management strategies to reduce the transportation of infected soil by logging trucks, however, can reduce the spread by up to 50% after one year and reduce the pathogen load within infested sites by more than three times. Mitigating other human-assisted dispersal pathways can also help reduce spread. Reducing movement of forest visitors not involved in forestry activities, for instance, by closing forest sites to the public, can help to further reduce spread in addition to management related to harvesting activities. These results highlight the benefits of preventative management strategies in reducing the spread rate of novel soil pathogens through a high-intensity commercial forestry network but show that pest spread is still likely even with significant investment.