Exotic plant invasion in agricultural landscapes: A matter of dispersal mode and disturbance intensity

Question: Does dispersal mode and/or disturbance intensity affect the spread of exotic species across agricultural landscapes? Location: Friuli Venezia Giulia, NE Italy. Methods: We analysed α- and β-diversity of native and exotic plants in 128 plots distributed in four habitats (viz. woods, hedgerows, field boundaries and meadows), in four agricultural areas in northeast Italy, along a gradient of increasing cover of arable land in the landscape. We used a multi-model inference approach to explore the relationships between species diversity and landscape variables (i.e. agricultural disturbance), testing the role of dispersal mode (i.e. biotic, abiotic) for both native and exotic plants. For each habitat and plant trait combination, distance-decay of similarity was assessed by regression on distance matrices. Results: Species diversity of exotic and native plants was related to the degree of disturbance (cover of crop) and proximity to disturbance (distance to crop), with different responses according to dispersal mode and habitat type. In most of the habitats, the number of species dispersed by biotic vectors decreased when disturbance was higher. We further found that in woods and hedgerows the interaction between disturbance and dispersal mode drove the exotic richness. Exotic species were less dispersal-limited than native species showing a weaker distance-decay of similarity. Conclusions: The spread of exotic species in semi-natural habitats was driven by agricultural disturbance at the landscape scale. The effect of disturbance on exotic species richness was further shaped by species dispersal mode. Most initiatives related to preventing and controlling invasions are conducted at the local scale, whereas the influence of the land-use dynamics in the landscape is seldom explored. Our contribution provides useful information to identify the most susceptible semi-natural habitats to exotic plant invasions according to intrinsic local resistance and large-scale processes such as invasiveness from the surrounding landscape. © 2018 International Association for Vegetation Science.