Sorghum halepense (L.) Pers. (Johnson grass, Poaceae) is a worldwide problematic alien species, rapidly expanding its alien range in Europe. This study reconstructed the spread history, and assessed the current distribution, ecological traits, and invasion potential of this species in the Insubric region of northern Italy and southern Switzerland. Herbarium and occurrence data showed that its spread began in the late 19th century and has accelerated recently in the foothill zone, progressing northward and upward. High-cover populations occurred in anthropogenic habitats, especially ruderal and agricultural areas. Morphological analyses revealed statistically significant site-dependent differences in plant height (140–292 cm) and specific leaf area (12.32–1077.59 cm2/g−1). CCA analysis linked species occurrence to lower levels of soil phosphorus and calcium. The species shows medium-high invasive potential in the Insubric region due to the combination of high reproductive (sexual and vegetative) and spread potential, combined with medium impact potential on native biodiversity (competition, allelopathy) and medium-high impact on agriculture (severe crop losses and pathogen host). According to impact classification schemes, S. halepense falls under ‘Moderate’ (environmental) and ‘Major’ (socioeconomic) impact categories. Because S. halepense can develop herbicide resistance, other control measures should be preferred. Ongoing climate warming and land use changes are expected to further facilitate its spread across and beyond the Alps.
Gentilini et al. (Thu,) studied this question.