Abstract: Plant invasions are a major component of global change and an important driver of biodiversity loss and ecosystem transformation. Yet, why only some alien plants establish, spread, and become dominant remains unresolved. This review uses community assembly and modern coexistence theory to integrate mechanisms commonly studied in isolation. Propagule supply initiates invasion; functional traits, phenotypic plasticity, and evolution modify passage through abiotic and biotic filters; density dependence and ecological feedbacks govern persistence and dominance; and repeated dispersal and establishment generate spread. We synthesize evidence for plant–plant competition, kin recognition, allelopathy, interactions with enemies and mutualists, plant–soil feedbacks, cross-trophic pathways, environmental matching, and resource change. These mechanisms alter vital rates by shifting stabilizing niche differences and average fitness differences, with outcomes contingent on invasion stage, spatial scale, population density, exposure history, and environmental change. Once abundant, an alien may shift from a target to a source of filtering by pre-empting resources, restructuring interaction networks, and conditioning soils against later arrivals. Abiotic and multitrophic filters also interact, making invasion outcomes poorly represented by single-process explanations. Progress requires life-cycle studies estimating population growth and conspecific versus heterospecific limitation, long-term and native–introduced range comparisons, and factorial experiments spanning trophic groups and environmental drivers. Comparisons among invasive aliens, non-invasive naturalized aliens, unsuccessful introductions, and successful natives will distinguish invasion-specific mechanisms from attributes of plant dominance generally.

Key words: alien, coexistence, non-native, global change, invasion risk, species interactions