Branching Structure and Fractal Patterns of Urban Forest Plants in Shanghai, China

Plant branching is a complex biological trait that reflects plant adaptation to light, temperature, water, and other environmental factors. Branch architecture and patterns shape canopy morphology and physiological activities, and further affect plant growth and development. In this study, we investigated the branching structure and patterns of eight species in an urban forest in Shanghai, including four tree species (Cinnamomum camphora, Ginkgo biloba, Metasequoia glyptostroboides, Cedrus deodara), two shrub species (Prunus cerasifera f. atropurpurea, Phyllostachys nigra), and two herb species (Medicago sativa, Equisetum ramosissimum). We compared branch number and length across four horizontal directions (east, south, west, north) and two vertical directions (south, north), fitted canopy morphology models, and calculated fractal dimensions based on branch diameter distribution. For the six woody species, branch length and quantity showed no obvious horizontal asymmetry, while the two herb species had better-developed southward branches. Canopy shapes were mainly fitted with quadratic (parabolic) functions. By contrast, coniferous trees and E. ramosissimum presented linear relationships. Fractal dimension increased with plant height in woody species, whereas no such trend was observed in herbs. This study aims to address the following questions: (1) Are there quantifiable differences in horizontal and vertical branching characteristics among trees, shrubs, and herbs? (2) Can fractal dimension serve as a reliable indicator to distinguish such differences? (3) Is there a correlation between fractal dimension and plant height? This is a descriptive and exploratory study, and no biological mechanisms are examined herein.