Contrasting Associations of Urbanization and Lateral Hydrological Gradients With Functional Structure and Rarity of Spontaneous Plants in River Corridors: Evidence From Changde, China

ABSTRACT River corridors play an important role in maintaining the diversity and ecological functions of spontaneous plants. Within urban river corridors, spontaneous plant communities are exposed to both urbanization in the surrounding landscape and lateral hydrological variation between water and land. However, the relative contributions of the surrounding urban matrix and the lateral hydrological position to these community properties have rarely been examined within a common framework. Functional rarity was included because it complements conventional diversity metrics by identifying uncommon functional strategies. We surveyed spontaneous plants along six rivers and one lake in the central urban area of Changde, China, and combined analyses of plant functional traits with structural equation modeling to evaluate the associations of urbanization gradient and lateral hydrological gradient with species diversity, functional structure, and functional rarity. The results showed that species diversity (Shannon–Wiener) and functional diversity (FDis) showed unimodal patterns across urbanization levels, with the highest values at intermediate urbanization. Functional trait space was more clearly separated among lateral habitat types than among urbanization levels. Functional rarity increased with ISA but declined with WD. The structural equation models showed contrasting associations of the two gradients with community properties: higher ISA was associated with greater community‐weighted mean plant height and functional rarity but lower species diversity and FDis, whereas greater WD showed the opposite pattern. Functional rarity was positively associated with FDis in both models. This study provides a transferable framework for comparative research across urban river systems. The framework integrates urbanization at the landscape scale, lateral habitat variation within river corridors, and complementary species, functional, structural, and rarity metrics. The framework is helpful in identifying community patterns that assessments based on a single gradient or a single metric may overlook.