Turnover-dominated β diversity of urban spontaneous flora and its associations with park landscape and management

Spontaneous flora is an important but often overlooked component of urban biodiversity, especially in rapidly urbanizing landscapes where habitat fragmentation and intensive management may affect community composition. However, it remains unclear whether differences among urban park spontaneous plant communities mainly reflect species and lineage replacement or ordered species loss, and how these patterns are associated with landscape structure and maintenance intensity. We surveyed spontaneous plants in 51 urban parks in Zhengzhou, China, and partitioned both taxonomic and phylogenetic β diversity into turnover and nestedness components. We further examined their relationships with geographic distance, landscape structure, and maintenance intensity using Mantel tests, multiple regression on distance matrices, and adjusted R²-based variation partitioning. A total of 348 spontaneous plant species from 255 genera and 80 families were recorded. Both taxonomic and phylogenetic β diversity were high and dominated by turnover (Tβ SIM = 0.86; Pβ SIM = 0.80), whereas nestedness contributed relatively little (Tβ NES = 0.08; Pβ NES = 0.11). Landscape distance and maintenance intensity distance were significantly associated with total β diversity and nestedness components, while geographic distance was mainly related to nestedness. Variation partitioning showed that the measured predictor groups explained 24.16% and 24.98% of total taxonomic and phylogenetic β diversity, respectively, with higher explanatory fractions for nestedness than turnover. These findings indicate that urban parks support complementary spontaneous plant assemblages, while park-scale landscape structure and management are more closely linked to ordered differences in species and lineage retention. Conserving spontaneous flora therefore requires maintaining heterogeneous park networks and retaining low-intervention microhabitats within urban green spaces.