Environmental Drivers and Seasonal Dynamics of Spontaneous Plant Communities on Urban Walls: A Case Study in Nanjing, China

As urbanization increasingly compresses ecological spaces, traditional urban greening faces dual challenges of high maintenance costs and diminished ecological functions. Within this context, urban walls-characterized by their widespread distribution, diverse microhabitats, and relatively low levels of human intervention-are gaining recognition as valuable components of urban green infrastructure. Spontaneous wall vegetation, with its strong local adaptability and ecological functions, aligns well with emerging concepts of low-intervention, nature-based urban restoration. This study investigates the composition and environmental drivers of spontaneous wall plant communities across 321 plots on 100 urban walls in central Nanjing, China. Standardized vegetation surveys recorded species composition, cover, and wall-related environmental variables. Variance partitioning, canonical correspondence analysis, and multiple linear regression were applied to elucidate the relationships between plant diversity patterns and environmental factors. Results revealed high species diversity on urban walls, with 163 vascular plant species across 125 genera and 60 families. Retaining walls and spring plots exhibited more complex community structures. Environmental factors collectively explained 58.1% of the variation in plant communities, with wall inherent attributes contributing 23.1%. Diversity indices indicated a moderate level of richness and evenness, with an average Shannon index of 1.3 (0.6-2.5), Simpson index of 0.6 (0.02-0.9), and Patrick index of 1.9 (0.3-3.8). Microstructural attributes such as joint degradation and surface roughness facilitated colonization, highlighting the critical role of microhabitat heterogeneity in community assembly. As one of the first systematic studies on spontaneous vegetation of urban vertical structures in the Yangtze River Delta, this research provides foundational data on urban wall biodiversity and offers valuable insights for integrating native species into green infrastructure planning.