The dual role of native plant diversity in shaping plant invasions: scale and habitat dependence in urban-rural ecotones

Introduction Urban–rural ecotones are characterized by high habitat heterogeneity and intense anthropogenic disturbance, are recognized as high-risk areas for alien plant invasions. To explore the differences in diversity patterns between native and invasive herbaceous plants, as well as their relationships, across various habitat types, and to determine the major environmental factors facilitating invasion, we conducted a comprehensive field survey in Jiangdong New District, Haikou City, Hainan Province, a rapidly urbanising ecotone in southern China. Methods A total of 537 herbaceous plant quadrats were established across six representative habitat types selected according to in situ habitat heterogeneity at 220 sampling sites. We recorded a total of 229 herbaceous plant species, including 155 native and 74 invasive species. Results Analyses revealed significant differences in diversity indices and total cover between native and invasive assemblages among habitats. Invasive herbaceous plant diversity was highest in roadside habitat, whereas native herbaceous plants were dominant in landscape green space. Native species diversity was positively associated with invasive species richness, but negatively associated with their total cover and invasion intensity. Suppressive effects of native diversity were strongest in abandoned land and depression wetland habitats. Trampling intensity promoted invasive species richness, whereas proximity to buildings, proximity to water bodies, and higher relative humidity facilitated the formation of high invasive plant cover. In contrast, active management, such as artificial removal, consistently suppressed invasion across all metrics. Discussion This study clarifies the scale and habitat-dependent dual role of native herbaceous diversity in regulating invasions, providing scientific support for the development of habitat-targeted management approaches in urban-rural ecotones.