Microtopography Enhances Surface Runoff Regulation and Plant Growth in Urban Relocation Green Spaces: Evidence from Shanghai Expo Cultural Park

Urban microtopography plays an important role in regulating soil processes and vegetation performance in newly constructed green spaces, yet its effects on surface runoff, soil nutrients, and plant growth remain insufficiently quantified in urban relocation sites. This study investigated how slope gradient, slope position, and slope curvature influence surface runoff, soil nutrient distribution, and tree growth in Shanghai Expo Cultural Park. Field monitoring was conducted in 36 plots planted with Cinnamomum camphora and Ginkgo biloba in 2017, 2020, and 2024. Microtopographic characteristics were quantified using terrestrial and handheld three-dimensional laser scanning, point-cloud processing, and digital elevation models (DEMs), and plant growth, calculated runoff, and soil physiochemical properties were analyzed using analysis of variance (ANOVA) and regression analysis. Annual DBH increments were greatest on meso slopes (mean = 0.558 cm), followed by gentle slopes (0.513 cm) and abrupt slopes (0.511 cm). Growth was also greater at slope-tail positions than at slope-head positions and greater on concave slopes than on convex slopes. The mean calculated runoff increased from gentle to meso and abrupt slopes, and soil organic matter, total nitrogen, hydrolysable nitrogen, available phosphorus, available potassium, and cation exchange capacity were generally higher at slope-tail positions. These results indicate that micrographic design affects tree growth mainly through runoff-mediated redistribution of water and soil nutrients. These findings provide practical guidance for optimizing microtopographic design, tree species selection, and soil management in urban green spaces established on relocation sites.