Distribution of Asian knotweeds on the Rhône river basin, France: a multi-scale model of invasibility that combines biophysical and anthropogenic factors.
Biotic and abiotic factors are important drivers of the introduction, dispersal and establishment of an invasive species in fluvial corridors. In this study, we propose to better understand the spatial distribution of Asian knotweeds and to model their invasibility at the river basin scale in the Rhône Mediterranean and Corsica regions, France. We implemented a multiscale analysis of biophysical and anthropogenic factors related to the presence of knotweeds. Subbasins were sampled (50-600 km2), a large dataset on knotweed occurrence and biotic/abiotic factors was collected, and logistic regression was applied. A robust logit model (accuracy: 90%; false positive rate: 13%) estimated the probability of the occurrence of knotweeds at the river basin scale. We found clear evidence of: (i) spatial scale-dependent water availability for knotweed implantation (e.g., summer vs. winter rainfalls > 250 mm); (ii) an important role of hydrogeomorphic forces in dispersal; and (iii) interspecific competition in riparian areas. The occurrence of knotweeds is also closely related to human-derived pressures. The management of knotweeds on roads and railways in the vicinity of rivers may be a major source of propagules. Hydraulic infrastructures (dikes and mill weirs) may also have served as locations of knotweed introduction since the end of the nineteenth century and may play a major role in the propagule transfer of knotweed; to date, these infrastructures have provided favourable conditions for knotweed establishment. Despite local water authorities' increasing awareness of invasive plants, local management practices for flood mitigation, low awareness of roads/railway managers, and negative representations of knotweeds have probably largely contributed to their dispersion over decades. The final model intends to integrate these biophysical and human factors by providing an operational tool to help river managers determine the sensitivity of their river basins to knotweed invasion.