Distribution drivers in a globally invasive plant: Climate dominates at large scales, human presence at local scales

Abstract The occurrence patterns of invasive species are shaped, on the one hand, by the availability of suitable habitat, and, on the other hand, by how dispersal has progressed since their introduction to the new region. This complicates attempts to understand and predict their distributions, especially if the relative importance of these factors differs between spatial scales. Here, we investigate environmental and dispersal‐linked patterns in the distribution of the globally invasive plant Lupinus polyphyllus . For this purpose, we created a uniquely extensive and high‐resolution occurrence dataset for the entire country of Sweden by surveying 2100 km of roadside, collected density and size data from 152 populations, and analyzed global distribution patterns using citizen science data. Analyses revealed that at the regional scale (>50 km), lupine occurrence was best explained by climate, with some effects of soil chemistry. However, at smaller scales, both lupine presence and density were best explained by the presence of nearby buildings, suggesting a large role of human‐aided dispersal. Furthermore, the results depended on road type: environmental variation (especially soil chemistry) only weakly limited lupine occurrence along highways, suggesting that large roads may act as dispersal corridors across otherwise unsuitable habitat. When integrating modeling results for Sweden with observations from the global range of L. polyphyllus , further northward expansion in Scandinavia appears possible even under the current climate regime, but likely with limited maximum abundance in northern regions. Our results illustrate how a nested study design and a combination of data sources enable a more comprehensive assessment of the factors influencing a biological invasion.