Assessing local and global ecological impacts of the alien plant Senecio inaequidens across different environmental conditions in Northern Italy and applying EICAT

To understand the impacts of invasive alien plants on native ecosystems, it is crucial to assess their effects across different scales. Most studies only focus on assessing the impacts of plant invasions on plant communities and disregard the context-dependency of their effects at a local and global scale. This research investigates the ecological impacts of the alien plant Senecio inaequidens in Northern Italy, combining field observations in different habitats with a global impact assessment applying the Environmental Impact Classification for Alien Taxa (EICAT) framework. We examined S. inaequidens effects on soil chemistry, plant, and soil bacterial communities across high- and low-productivity habitats. Our results showed no significant changes in soil chemistry following invasion. Yet, both plant and, marginally, bacterial diversity increased in invaded plots (GLMMs plant richness: p < 0.001; GLMMs bacterial richness: p = 0.056), with more pronounced effects in low-productivity habitats, suggesting a potential facilitative role of S. inaequidens in harsh environments. The global EICAT assessment, including our findings, assigned S. inaequidens to the Moderate impact category, indicating negative effects on native taxa without causing local extinctions. Our study highlights the context-dependency of invasion impacts and the importance of considering both above- and below-ground effects. These findings contribute to a nuanced understanding of S. inaequidens ecological impacts and emphasise the need for comprehensive, long-term studies to inform invasive species management strategies.