Two Kinds of Turnover: Contrasting Drivers of Beta Diversity Between Cultivated and Spontaneous Plants Along a Coastal Island-to-Mainland Gradient

Urban park plant communities comprise cultivated and spontaneous species, but whether their beta-diversity drivers differ and whether urbanization homogenizes or differentiates composition remains unclear. We surveyed 102 plots in 21 parks along a coastal island-to-mainland gradient in Fuzhou, China. We partitioned taxonomic, functional and phylogenetic beta-diversity into turnover and nestedness, related them to environmental, anthropogenic and spatial predictors using Mantel tests, variation partitioning and db-RDA, and modeled local contributions (LCBD) using mixed models and structural equations. Turnover dominated both groups, with higher turnover and lower nestedness in cultivated plants. Cultivated functional and phylogenetic nestedness rose with distance (p < 0.01), whereas spontaneous nestedness fell across all dimensions (p < 0.05); the slopes differed significantly in all three dimensions. Taxonomic beta-diversity exceeded functional and phylogenetic, and LCBD synchronization was taxonomic only. Landscape configuration and anthropogenic factors drove cultivated beta-diversity, whereas spontaneous beta-diversity related to spatial structure, park area and elevation. Marine exposure lost significance for most responses once space was controlled. Composition varied among regions; island plots the most concentrated; LCBD depended on park area for spontaneous plants and on landscape configuration for cultivated ones. The two kinds of turnover reflect different processes, ecological replacement and planting decisions, and require parallel management.