Enhancing early detection of exotic pests in agricultural and forest ecosystems using an urban-gradient framework

In the United States, exotic plant pests cause estimated economic losses of 37.1 billion dollars per year in agricultural and forest ecosystems. Most of these pests are unintentionally introduced by humans during transportation of goods and travel. Urban areas are major hubs of international transport, thus providing convenient gateways for exotic pests. This paper assesses whether ecosystems near more urbanized areas are at greater risk of invasion. The authors applied an urban gradient for both agricultural and forest ecosystems in the United States in order to analyze the pathways and determine the ecological processes involved in human-mediated invasions. Two high-risk zones are proposed to demonstrate the function of using an urban gradient framework to predict the locations of future invasions. Risk Zone A accounted for the part of cropland and forestland where 75% of the selected agricultural and forest pests were found. Risk Zone B represented the part of cropland and forestland where an additional 15% of the selected agricultural and forest pests were found. The results revealed that Risk Zone A, which encompassed 21% of forestland and 26% of agricultural land, accounted for 70% of the invaded counties and 90% of the 39 selected pest species. The authors also found strong associations between higher numbers of exotic pest occurrences and the urban end of the urban-rural gradient. These findings suggest that agricultural and forest areas at the urban end of the urban-rural gradient are at greater risk of invasion and highlight the important role that humans play in both pest introduction and dispersion. Based on this research, national monitoring programs should allocate resources to prioritize surveillance of agricultural and forest areas in Risk Zone A, as this could potentially serve as an advantageous and efficient solution for early detection of exotic invasive pests.