Abstract: Biological invasions increasingly reshape ecosystems, yet the mechanisms linking climate, plant functional traits, herbivore communities, and the occurrence of invasive alien plant species (IAPS) across environments remain poorly resolved. We used region-wide IAPS occurrence data, combined with measurements of herbivore communities and plant functional traits, to investigate how these drivers jointly structure the relative IAPS frequency across two climatically contrasting regions in the mountainous landscapes of western Sichuan, China. We quantified direct and indirect pathways connecting climate, plant traits, and herbivore assemblages to invasion outcomes. Herbivore abundance and richness exhibited strong but site-dependent associations with the relative IAPS frequency, with negative effects emerging in the humid region but not in the drier valley. In contrast, functional traits—particularly leaf thickness and the C:N—showed consistent positive associations with IAPS occurrence across sites. Elevation and precipitation further reorganized these relationships: several trait and herbivore effects reversed direction across gradients, indicating that the roles of plant traits and herbivores shift from limiting to facilitating invasion depending on climatic context. Path analyses confirmed that climate shaped the relative IAPS frequency primarily through its effects on plant trait axes and herbivore communities, and that the influence of herbivore richness on invasion was opposite in the two regions. Our findings demonstrate that plant invasions are governed by climate-mediated trait-trophic interactions rather than single-factor effects, and that invasion processes are fundamentally context-dependent. These insights highlight the need to incorporate coordinated plant-trait and biotic interactions into invasion forecasting across increasingly heterogeneous and changing environments.

Key words: Climate change, Herbivore insects, Leaf traits, Plant invasion, Regional pattern