Distribution Patterns and Environmental Correlates of Invasive Plants Along an Urbanization Gradient in a Medium-Sized Mountainous City of Southwest China.

Against the backdrop of ongoing urban expansion, alien plant invasions are closely linked to the stability of urban ecosystems. However, few studies have documented invasive plant distribution and their statistical associations with landscape variables in mountainous medium-sized cities, which serve as critical urban-rural transition zones. This study selected Anning City, a representative mountainous medium-sized city in Yunnan, Southwest China, as the research case. We established 63 standard sampling plots spanning urban, suburban, and exurban zones along an urbanization gradient. Canonical Correspondence Analysis (CCA) and Monte Carlo permutation tests were adopted to quantify statistical associations between six major macro-environmental variables and invasive plant spatial distribution, and to characterize the distribution features of invasive plants for reference in targeted monitoring work. The main observations are summarized as follows: (1) A total of 66 alien invasive plant species belonging to 24 families and 51 genera were recorded. Asteraceae was the most abundant family, accounting for 25.75% of all taxa; 68.18% of species originated from the Americas, and annual and biennial herbs dominated the community (75.75%), which tend to occur abundantly in frequently disturbed habitats. (2) This local dataset captured a site-specific trend where invasion abundance declines as urbanization intensity rises: the total number of invasive species increased from urban to suburban and exurban zones, yet significant gradient differentiation only existed in plant abundance rather than species richness. Suburban and exurban plots had similar abundance values (p > 0.05), and both presented significantly higher invasive abundance than urban plots (p < 0.001). Dense invasive aggregations were frequently detected along transportation corridors and rural land, while forested areas generally corresponded to lower invasive plant coverage. (3) Invasive plant distribution displayed combined statistical associations with multiple environmental variables. Building density presented the strongest correlation with community composition (p = 0.004), while urbanization gradient, terrain attributes, and population density also showed significant associations; no meaningful statistical links were detected for road network density and land-use type. Widespread and common species exhibited significant correlations with macro-environmental predictors, whereas rare species showed no such associations. Collectively, this paper describes the site-specific distribution features of invasive plants and their correlated landscape variables in mountainous medium-sized cities of Southwest China. This work supplements case evidence for invasion ecology research in moderately urbanized mountainous regions and offers empirical references for invasive plant surveillance in comparable subtropical mountainous medium-sized cities globally.