Objective In cities, there is a category of plants given little attention, the so-called spontaneous plants. Although being “indigenous urban inhabitants”, such plants are often seen as targets for removal due to their rough and messy appearance, strong breeding and settlement capabilities, and competitive advantage over cultivated plants. However, in the current context of ecological sustainability, people are gradually realizing that large-scale homogenized landscapes are not the optimal solution for the healthy development of urban ecosystems. It is necessary to explore other beneficial solutions, and spontaneous plants, the inconspicuous “urban weeds”, may be the “key” to such new solutions. Urban industrial wasteland is one of the important habitats for spontaneous plants. Revealing the species composition and diversity characteristics of spontaneous plants in such special habitats may guide the construction of low-maintenance plantscape.
Methods This research focuses on the central urban area within the Fourth Ring Road (Chengdu Ring Expressway) in Chengdu City, Sichuan Province. The area is divided into the four parts of southeast, northeast, northwest, and southwest parts, based on the lines connecting the four entrances and exits of the Chengdu Ring Expressway to Tianfu Square. Through stratified random sampling, the research determines the potential for reusing wasteland as green space based on land use planning, surrounding water systems, and people’s usage needs. Subsequently, the research selects from within the Fourth Ring Road 10 typical industrial wastelands, including the lands for both light and heavy industries, based on their distribution, size, and industrial type. In total, 584 quadrats are recorded, and the habitat types of spontaneous plants are categorized into four major types: abandoned habitat, semi-hard habitat, wetland habitat, and building habitat. Furthermore, 14 micro-habitat types including spontaneous grassland, spontaneous shrub grassland, and spontaneous underwood are classified based on different stages of plant succession and environmental substrates, and the species composition and diversity characteristics of spontaneous plants in different habitats and micro-habitats are analyzed.
Results This research records a total of 237 spontaneous plant species, belonging to 183 genera within 70 families, with 84.9% thereof found in the built-up areas of Chongqing. In terms of dominant families, Asteraceae and Poaceae are prominent, and perennial herbaceous plants constitute 30.80% of the total species. Significant differences are found in the frequency of species among wastelands varying in abandonment duration and area, while the species richness of habitats and micro-habitats show no significant differences. The absence of clear boundaries between different habitats in unmanaged abandoned areas may promote species exchange, resulting in little variation in spontaneous plant species among different habitats. However, there are significant differences in community diversity between habitats and micro-habitats, with the diversity of communities along channels, water edges, industrial structures, and factory edges being higher in micro-habitats. Despite the limitations of sample size, it can be found that heterogeneous habitats can promote community diversity. In undisturbed industrial wasteland, spontaneous plants tend to settle and grow in areas beyond obvious hard surface. With the change in the duration of disuse of wasteland, spontaneous plants in different succession stages form a multi-layered wild vegetation structure, thus creating abandoned habitats in various “soft” areas of wasteland. In areas formed after the demolition of roads, pavements, and buildings, a small amount of soil can provide rooting space for spontaneous plants, which can gradually cover most of the original hard grounds, forming a semi-hard habitat. In addition, despite the small number of quadrats recorded in wet habitats formed in depressions, ditches, and ponds, such habitats support a diverse range of species. There are more typical quadrats along the edges of factories and industrial structures, which are important building habitats in industrial wastelands.
Conclusion This research is a rare exploration focusing on the distribution pattern of spontaneous plant species and the diversity characteristics of communities on urban industrial wastelands. Spontaneous plants are the most natural component of urban biodiversity, making them ideal material for studying the interaction mechanism between urbanization and urban ecosystem. Urban industrial wastelands, as urban wilderness, are important habitats for spontaneous plants, which can preserve natural wilderness forms and maintain rich biodiversity. In spring alone, 237 species of spontaneous plants were recorded on 10 industrial wastelands within the Fourth Ring Road of Chengdu, showing extremely high species richness. Species frequency varies significantly with the abandonment duration and area of wastelands, reflecting the dominant characteristics of different species. In terms of community diversity, different habitats present significantly different and distinctive communities, forming natural and interesting plantscape with various ornamental benefits. In future planning and design, it is necessary to scientifically preserve and utilize dominant species and spontaneous plants in industrial wastelands, and formulate reasonable plant zoning plans according to the different levels of pollution in the wastelands. Furthermore, it is essential to appropriately plant cultivated plants based on the distribution patterns of different species and the structure of community components in various habitats, in order to construct a habitat that supports the survival of diverse species while maximizing aesthetic and ecological benefits. However, further research is needed to provide more comprehensive and scientific guidance for low-maintenance plants, predominantly spontaneous plants.
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