Objective In recent decades, the excessive development and continuous expansion of urban rivers and their surroundings have led to a series of ecological issues such as habitat fragmentation and loss, environmental pollution, invasion of alien species, and a sharp decrease in biodiversity. Urban rivers, as the interlace zones of urban aquatic and terrestrial ecosystems, play a crucial role as key ecological corridors and important habitats for biodiversity. They not only provide outdoor activities and recreational spaces for city residents, but also significantly contribute to the integrity and stability of urban ecosystems. River corridors serve as vital habitats for spontaneous vegetation, which are profoundly affected by urban development and human activities, leading to the formation of highly heterogeneous habitats. Spontaneous vegetation is an excellent subject for studying the feedback mechanisms between urbanization and urban ecosystems, and holds great potential for addressing issues such as urban biodiversity loss, pollution control, ecological restoration and rewilding, and for creating low-maintenance and sustainable plantscape. Based on this, this research takes the native plants in herbaceous layer in the central urban sections of the Hejiagou and Majiagou river corridors in Harbin as the research object, analyzes the compositional characteristics of spontaneous vegetation across different urbanization levels and habitats, elucidates the distribution patterns of spontaneous vegetation diversity and their influencing factors, and reveals the strategies for spontaneous vegetation to adapt to highly heterogeneous habitats.

Methods The research period is from June to September 2022. In this research, a combination of uniform and typical sampling methods are employed to conduct a survey of spontaneous vegetation in herbaceous layer in 951 quadrats along the Hejiagou and Majiagou river corridors in Harbin. The river corridor habitats are classified into three major categories of river channels, revetments, and uplands, which are further divided into 11 microhabitats such as river beaches, concrete revetments, and stone revetments. The species composition and diversity distribution of spontaneous vegetation in herbaceous layer in these habitats and microhabitats are analyzed. Concurrently, based on the urbanization level index and the division of urbanization gradients, the differences in α-diversity of spontaneous vegetation among different urbanization levels and habitats are examined. Finally, from the perspectives of habitat creation and species selection, strategies for enhancing biodiversity in urban river corridors and creating low-maintenance and sustainable plantscape are discussed.

Results Research results are summarized as follows. 1) Harbin’s urban river corridors are rich in spontaneous vegetation species, with a total of 151 species recorded, belonging to 112 genera under 36 families. The life forms of spontaneous vegetation are mainly annuals and biennials; native species account for 71.52%, and alien invasive species account for 18.54%. In terms of reproduction, seed reproduction dominates, accounting for 96.03%. Regarding dispersion, the types of spontaneous vegetation featuring autogenic dispersal, wind dispersal, animal dispersal and water dispersal respectively account for 47.02%, 34.44%, 29.80% and 13.91%. 2) The composition of spontaneous vegetation varies with different levels of urbanization. The α-diversity of herbaceous spontaneous vegetation and native spontaneous vegetation species is significantly higher at medium to low levels of urbanization (I – III); significant differences in diversity characteristics are observed among different habitat types, with invasive species showing a homogenized distribution pattern. 3) Such factors as slope aspect, distance from water body, vegetation structure, and management intensity significantly impact the life forms, occurrence modes, and dispersal methods of spontaneous vegetation in herbaceous layer. 4) Two strategies are proposed to enhance biodiversity and create low-maintenance and sustainable plantscape in urban river corridors. One is reducing the channelization of some river sections while ensuring the flood prevention and safety functions of urban rivers, protecting habitat continuity and integrity, and increasing the diversity of vegetation structure types within habitats; the other is preferentially selecting native plants and fully considering the life habits such as life forms, reproduction methods, and dispersal modes of native plant materials, while also focusing on monitoring invasive species along the edges of river corridors.

Conclusion The spontaneous vegetation in urban river corridors is an important component of urban vegetation. It holds great potential for addressing issues such as loss of urban biodiversity, pollution control, ecological restoration and rewilding, and for creating sustainable plantscape with low maintenance requirements. This research analyzes the composition characteristics of spontaneous vegetation in different habitats under varying levels of urbanization, elucidates the causes of diversity distribution patterns, and proposes the strategies for habitat creation and spontaneous vegetation application for river corridor landscape. This research may help enrich the urban vegetation database of Harbin, provide a new perspective for the landscape creation of urban river corridors, and offer theoretical support for the conservation of urban river corridor biodiversity, the development and application of spontaneous vegetation, and the creation of low-carbon and sustainable green landscape. Ecological researches suggest that urban ecosystems and their spontaneous vegetation communities are dynamic. This research only conducts surveys during the summer season, which may impose certain limitations on the results. In subsequent work, the distribution characteristics of spontaneous vegetation in urban river corridors should be further explored through surveys conducted in multiple seasons and a community-level perspective should be formed.