Background complexity affects landscape aesthetic quality: Evidence from subject evaluations and fractal dimension analysis

Small green spaces on campus (SGSc) possess irreplaceable aesthetic and ecological values. However, studies combining both qualitative and quantitative approaches to improve landscape aesthetic quality remain unexplored. Both subjective questionnaires and fractal dimension values using the box-counting method were used to evaluate SGSc under four background types: buildings, sky, evergreen conifers, and broadleaf foliage. Results showed that: (1) The sky background exhibited the highest fractal dimension value in summer (1.332 ± 0.024), while the value of coniferous background peaked in winter (1.199 ± 0.014). The building background had the lowest fractal dimension values in both summer and winter (1.057 ± 0.002 and 1.053 ± 0.005, respectively). (2) The broadleaf background received the highest subjective evaluation scores in both summer (5.444 ± 0.182) and winter (5.526 ± 0.158), while the building background scored the lowest scores in the two seasons (3.433 ± 0.110 and 2.811 ± 0.113). (3) A significant correlation was observed between fractal dimension values and subjective evaluation scores, which increased significantly as fractal dimension values rose to 1.225 but declined significantly beyond this threshold. Effects of fractal dimension on scenic beauty appeared to have an optimal threshold. This study provided foundational data for intelligent SGS C design and renewal, as well as offered scientific support for the quantitative and qualitative evaluation of scenic beauty.