Bridging Ecology and Perception: Context-Dependent Relationships Between Plant Communities, Ecological Benefits, and Perceived Restorativeness in Open-Rooftop Green Spaces

Open-rooftop green spaces can integrate ecological function with restorative experience in high-density cities, yet whether plant configurations that deliver ecological benefits are also restorative remains unclear. This study examined plant-community structure, ecological benefits, and perceived restorativeness across 80 plots within ten publicly accessible ORGSs in Chengdu, using i-Tree Streets and the Perceived-Restorativeness Scale with 380 on-site participants. Annual modeled ecological benefit totaled 284,524 CNY, with carbon sequestration contributing 78.5%. Plant communities were systematically miniaturized (93% of stem < 7.6 cm DBH; 90.55% of individuals < 2.5 m). Perceived restorativeness was highest on ornamental roofs (M = 0.64) and lowest on sports-oriented roofs (M = −0.56); conifer–broadleaf mixed forest ranked first among community types (M = 0.33), and pure bamboo ranked last (M = −0.72). Bivariate associations between ecological benefits and PRS were positive, but this relationship became context-dependent when plant-community characteristics and roof function were jointly considered. Simplified structure was negatively associated with PRS on ornamental roofs (β = −0.52, p < 0.01), yet positively associated on sports-oriented roofs (β = 0.54, p < 0.05). High stem density on sports roofs (β = 0.25, p < 0.05) and tall plants under simplified structure (β = 0.40, p < 0.01) showed positive associations in both dimensions, whereas single-species planting on sports roofs was associated with lower outcomes in both (β = −0.34, p < 0.01). The findings indicate that ecological and perceptual outcomes depend on the fit between planting configuration and functional context, and that ORGSs’ design should coordinate vegetation composition and structure with the intended use of the space.