This study clarified the root growth of trees in a demonstration of a green infrastructure method using rainwater storage materials to improve the planting bases and protect roots for street trees. Comparing the root system diagrams of the construction areas, root growth was clearly observed in 2023 (one year later) compared to 2022 (before construction), indicating the effect of improving the planting base. Furthermore, in 2024 (two years later), more roots branched, and long fine roots less than 2 mm were prominent. The relationship diagram and distribution diagram of root length and thickness showed that in all construction areas, root growth and root thickness increased in 2024 (two years later) compared to 2023 (one year later), with an increase in lateral roots and an expansion of the root system. The annual growth rate of root length and thickness was about 1 to 2 times. The results of a two-year survey showed that roots were growing every year within the construction area, demonstrating the usefulness of this green infrastructure method for improving the planting base and protecting the roots. As a construction method that allows pavement and street trees to coexist, it can contribute to providing a good environment for street trees to grow. It was also thought that the improved planting base could be used as a temporary rainwater storage space.
