Objective The relatively low level of human interference in most of the vacant lands allows natural succession and ecological processes to take place to a certain extent, thus forming wilderness landscapes dominated by spontaneous plants and enhancing the stability of urban ecological functions. Therefore, revealing the community characteristics and growth pattern of spontaneous plants in such special habitats can provide some support for ecological restoration of vacant land and guide the construction and renewal of wilderness landscape.
Methods Taking the Xiyuhe Village construction and demolition site in Beijing as an example, this research comprehensively adopts the satellite image analysis method and the field survey method to visually interpret and statistically analyze the trend of vegetation coverage and the change of vegetation growth distribution before and after the construction and demolition as shown in eight historical satellite images spanning the period from 2009 to 2022. Using the grid distribution sampling method, the research area is divided into native forest area, primitive river area, and construction and demolition area. During the period from March to May in 2023, the investigation of spontaneous plants was repeated 10 times targeting the 39 quadrats selected, and the evaluation indexes such as relative frequency, relative cover, relative density, relative dominance, and importance value were calculated using SPSS 26.0.
Results 1) In terms of vegetation coverage, before construction and demolition and within one year of demolition (2009–2018), the vegetation coverage did not change significantly, with coverage change mainly concentrated in the vacant open space at the forest edge on the west side of the research site and in the area of building demolition on the south side, and newborn plants mainly appearing in the vicinity of the primary vegetation. While after construction and demolition (2018–2022), the vegetation coverage increased significantly, with an average annual increase of about 8%. It is clearly observed that during this period, a large number of plants began to grow at the gaps left by hard paving, in which woody plants grew and spread rapidly, most of the secondary trees grew in the area with more fertile soil and no hard concrete block residues near the primary trees, and the growth range of herbaceous plants was enlarged. 2) In terms of spontaneous plant species, a total of 44 species of plants classified into 24 families under 41 genera are recorded at the research site, including 39 species of spontaneous plants, of which herbaceous plant species are the most numerous, accounting for 69.23%, mainly dominated by Asteraceae (11 species in total), accounting for 28.95% of the total number of spontaneous plants. In addition to the Asteraceae family, the rest families mostly comprise 1 – 2 species each, such as Zygophyllaceae, Gramineae, Labiatae, Cheloniaceae, Coriandrum, Ledebouriaceae, Cruciferae, and Syzygium. 3) In terms of the propagation type of spontaneous plants, wind propagation serves as the dominant propagation type, accounting for 43.59%, which can achieve long-distance propagation of plant seeds by the action of wind, making plant seeds more widely distributed. In addition, animal propagation accounts for 17.95%, autochthonous propagation accounts for 5.13%, the combination of animal propagation and wind propagation accounts for 10.26%, and the combination of wind propagation and autochthonous propagation accounts for 17.59%. In terms of dominant species of spontaneous plants, the dominant species include Chenopodium album, Artemisia annua, Crepidiastrum sonchifolium, Setaria viridis, Humulus scandens, Ulmus pumila, Lactuca indica, etc. The distribution of spontaneous plants in different regions varies locally, with a total of eleven dominant plant communities being formed, such as Ixeris chinensis, Lactuca indica, Humulus scandens, Ulmus pumila, Broussonetia papyrifera, Salix matsudana, Chenopodium album, Salix matsudana, Broussonetia papyrifera, Crepidiastrum sonchifolium, and Artemisia annua. 4) In terms of the ornamentality of spontaneous plants, the herbaceous spontaneous plants typically sprout in March, and bloom in April, with the blooming period of some plants extending to May. Of these spontaneous plants, those with more obvious ornamentality include Rehmannia glutinosa, Taraxacum mongolicum, Lactuca indica, etc. For spontaneous herbaceous plants with unremarkable ornamentality, such as Ixeris chinensis, Crepidiastrum sonchifolium, and Viola philippica, they often also have ornamental flower organs, but due to the small flower volume and sparse inflorescences, it is difficult for them to form an outstanding ornamental effect. Generally, such herbaceous spontaneous plants have strong ornamentality when arranged together, which may compensate for their poor individual ornamentality, and they also play a more important role in autochthonous plant community landscapes. 5) In terms of competition among spontaneous plant species, Humulus scandens, Chenopodium album and Crepidiastrum sonchifolium acuminata show obvious competition. Humulus scandens grows rapidly from March to April, with their number of leaf blades, plant height, and fluffy diameter growing to the maximum extent then, while Chenopodium album and Crepidiastrum sonchifolium still maintain rapid growth from April to May, with Chenopodium album performing best.
Conclusion The scientific retention and use of spontaneous plants may provide a new idea for creating wilderness landscapes in unused land. In the future, we still need to carry out in-depth research on the reduction of human interference, the ecological balance of wilderness landscapes, and the management measures in the early stage of vegetation restoration.
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