Impact of urbanization on vegetation functional diversity across typical urban areas in China

Vegetation diversity in urban areas is crucial for maintaining urban ecological security. Rapid urbanization significantly affects vegetation diversity. However, the absence of effective regional-scale monitoring methods makes quantitative assessments challenging. This study used the remote sensing-based Rao's Q index to assess both the direct and indirect effects of urbanization on vegetation functional diversity in Suzhou, China, in 2021. Our results showed that the modified Rao's Q method effectively captured the spatial distribution patterns of urban vegetation functional diversity. Urban cores showed a 76.9 % reduction in functional diversity (Rao's Q = 0.003) compared to suburban areas (Rao's Q = 0.013), underscoring the substantial impact of urbanization on vegetation diversity. Direct effects increased with urbanization intensity (β); for every 1 % increase in β, Rao's Q declined by 1 %. Indirect effects displayed threshold behavior: they promoted diversity when β < 0.2, but became detrimental when β > 0.2 due to heightened environmental stress and human activities. In 2021, indirect effects mitigated the loss of functional diversity by an average of about 10 % in suburban areas. Partial correlation analysis revealed land surface temperature (LST) and urban greening (UG) as key factors influencing positive indirect impacts. LST enhanced functional diversity in low-urbanization zones, while intensive human activities accelerated its decline. UG was identified as a vital strategy for enhancing vegetation diversity in highly urbanized areas. These findings deepen our understanding of the impact of urbanization on vegetation functional diversity and offer valuable insights for developing adaptive policies to safeguard ecosystem services and improve urban living quality.