The luxury effect under environmental filtering: Drivers of residential plant diversity in 15 high-altitude cities

Urban biodiversity theories, such as the luxury and legacy effects, have been developed mainly in low-altitude, temperate, and long-urbanized cities. Whether these frameworks hold under extreme high-altitude conditions remains unclear, and the rapidly advancing urbanization on the Qinghai-Tibet Plateau (QTP), one of the world's most climatically constrained and ecologically sensitive regions, provides a critical setting to test their applicability. Against this backdrop, residential areas-as critical components of urban ecosystems-provide an important lens for understanding how natural and anthropogenic factors jointly shape urban plant diversity. To investigate these dynamics, we conducted field surveys of 598 plant species across 34 residential areas in 15 plateau cities and assessed the influence of architectural, climatic, socioeconomic, and landscape variables at both residential and plot scales. The flora was dominated by native and spontaneous herbaceous plants, indicating strong environmental filtering associated with high elevation. Socioeconomic indicators, particularly GDP, exhibited the strongest significant positive relationships with diversity indexes, demonstrating the relatively pronounced luxury effect despite severe climatic constraints. By contrast, both residential age (time since construction) and historical land use types showed limited explanatory power for current plant diversity, indicating no detectable legacy signal given current data. Climatic gradients and landscape fragmentation further limited plant diversity, especially in higher-altitude and structurally complex residential environments. Overall, the results show that socioeconomic investment and landscape configuration outweigh architectural attributes in shaping residential plant diversity. These findings underscore the need for context-specific greening strategies and equitable resource allocation to support biodiversity in rapidly transforming high-altitude cities.