Spatial Distribution Heterogeneity of Riparian Plant Communities and Their Environmental Interpretation in Hillstreams

In plant ecology and environmental remediation, the characterization of riparian plant communities and the influence of environmental factors have been widely discussed. However, the delineation of plant communities from different spatial perspectives is often overlooked, especially in hillstreams. In this study, the Lingshan River is taken as the research area, which is a quintessential hillstream and is characterized by a plethora of hydraulic structures lining its course by 20 weirs. We aim to investigate the multidimensional spatial distribution of riparian plants and their main environmental factors through plant field surveys combined with cluster analysis and redundancy analysis (RDA). The main findings are as follows: (1) In this study, a total of 104 herbaceous species were investigated, distributed among 12 families, in which Poaceae (16.67%) and Compositae (9.65%) showed significant dominance. (2) Plant community delineation was based on the complete linkage clustering. Five plant communities were classified along the longitudinal scale of the river, four plant communities were in the near-water zones, and three plant communities were in the far-water zones. (3) Riparian plant diversity and community distribution in longitudinal and lateral dimensions exhibits significant differentiation. Longitudinally, there was a significant decrease in plant diversity from upstream to downstream. Laterally, the plant biomass in the near-water zone was higher than in the far-water zone, while diversity demonstrated a reverse trend in the midstream. (4) The main environmental factors influencing plant distribution varied for different spatial dimensions. Longitudinally, the physical factor of soil is domination, particularly soil texture, which exhibits the strongest correlation with plant communities. Laterally, the chemical factor of soil is domination, such as soil organic matter and soil nitrate nitrogen content. This study enhances our understanding of the riparian area's ecology, and provides a scientific basis for plant cover restoration and ecological environment protection, and their management.