Landscape Heterogeneity Drives Plant Assemblage Dynamics and Invasibility of Semi-Natural Grasslands Under the Long-Term Invasion of Ageratina adenophora

Grassland degradation is a critical ecological problem worldwide that threatens ecosystem integrity and functional services. Although previous studies have documented the drivers of climate change, overgrazing, and anthropogenic perturbation, research concerning the impact of invasive alien plants on grassland ecosystems remains limited. The present study, integrating pairwise field investigation of Ageratina adenophora invasion and non-invasion plots across heterogeneous grassland types (tropical grasslands [TG]; tropical shrub-grasslands [TS]; warm-temperate grasslands [WG]; and warm-temperate shrub-grasslands [WS]) and A. adenophora indigenous plants phytotoxicity bioassay, aims to assess the invasibility and resilience of heterogeneous grassland landscapes to A. adenophora invasion. The field investigation demonstrated the greater vulnerability of TG and TS to A. adenophora invasion, whereas WG and WS possessed higher resilience. In addition, regression analysis revealed significant reductions of the Shannon–Wiener index and the Pielou index as the A. adenophora’s important value reached the threshold 0.36. Bioassay showed that A. adenophora aqueous extracts inhibit seed germination and seedling growth of recipient plants, with Saccharum arundinaceum exhibiting the highest tolerance to A. adenophora stress. In summary, our findings not only highlight the flora communities’ dynamics and invasibility of diverse grasslands driven by A. adenophora invasion in subtropical regions but also verify S. arundinaceum’s potential for A. adenophora replacement management.