Research on Reconstruction Patterns and Maintenance Strategies of New Natural Habitats Under the Shade of Urban Viaducts: A Case Study of Shanghai City

Objective Urbanization has led the development of cities in the direction of “high population density” and “high-rise buildings”, causing social and environmental problems. The improvement of urban carrying capacity and the mixed use of public space become the main strategies for solving “urban diseases” such as heat island, waterlogging, and biodiversity loss. Nature-based Solutions (NbS) are proposed for urban greening by using modern technologies to enhance the adaptability of plants in cities and increase the comfort of urban environments. Urban viaducts can provide convenient transportation and efficient travel for high-density cities, but at the same time generate ecological and spatial problems. A three-dimensional greening system of “plant screening – habitat construction – sustainable operation and maintenance” for viaducts is constructed to explore the feasibility of reconstructing urban viaducts into a network of new natural habits, aiming to improve the habitat of urban hard space and enhance urban biodiversity.

Methods Shanghai Censhan Botanical Garden develops a planting plan from three dimensions of species selecting, habitat optimization, and commercial development, to achieve the construction of a new nature in the city. Based on field investigation, this research has established a resource base of 120 plant candidates that may be adapted to three-dimensional greening in low-light areas. We set up a three-factor and four-level test of shading, drought, and low temperature, counted the survival rate of different plants, and recorded the phenological and physical appearance characteristics with a focus on the testing and calculation of plants. The research focuses on testing and calculating plants’ photosynthetic indexes, and assisting in testing physiological indexes, so as to establish a three-dimensional greening plant evaluation model for low-light areas.The research applies a three-layer filtering sieve of ecological adaptability, ornamentality, and functionality to screen suitable plants. The research establishes an integrated greening facility system using PP resin. The load of the system can be reduced by improving the shape and size of planting modules. The research explores the stability of the irrigation system with a focus on the stacked base cultivation containers and the water storage and infiltration watering integration module. With acrylic acid and kaolin as raw materials, high water-absorbent materials are prepared by the aqueous solution polymerisation method and then mixed and co-mingled with other matrix materials in different forms. Additionally, a four-factor and three-level orthogonal test is adopted to prepare lightweight and high-quality media formulations, which satisfy the soil conditions required for long-term growth of plants. The research also explores the relationship between rainwater volume of viaducts and the supply and demand of water for three-dimensional greening in the shade of viaducts, and realizes the rapid purification of rainwater from viaducts through the triple purification steps of “pre-processing – core processing – enhanced processing”. The screening results of comprehensive resistant plants suitable for low-light areas, research and development of new lightweight containers, formulation of new and superior media, and integration technology are demonstrated in the 1,012.6 m² demonstration project, which integrates various technologies to give full play to the functionality of the overall system.

Results After nearly three years of teamwork, 27 species of shade-tolerant plants are screened, which extends the single replacement cycle of plants to more than 5 years. The 2nd generation of modular support facilities can help increase the rainwater interception and storage utilization rate to 45%, and realize multiple goals such as rainwater resource utilization, source pollution control and urban flooding alleviation. In terms of landscape form, plane greening is expanded to three-dimensional greening, which is expected to increase the per capita greening area of Shanghai by 0.3 m². Meanwhile, based on the construction of a technology system for iterative greening of special habitats, the commercial development of three-dimensional greening, the research makes it possible to promote business through greening, thus realizing the goal of complementation between business development and greening management.

Conclusion In combination with NbS, this research establishes an integrated three-dimensional greening module through the research and development of three-dimensional greening technology suitable for typical low-light urban areas, the utilization of strongly resistant plants and lightweight containers and media, and the adoption of a complementary commercial mode for integrated long-term greening, making it possible to transform the narrow and long pollution lines under urban viaducts with wide coverage and strong connectivity into life landscape lines and biodiversity corridors, thus providing important ecological, social and economic benefits for sustainable urban development.