Anthropogenic modifications of river systems mainly happen in riparian ecosystem, especially in the flora. It is well-known that alterations of the hydrological regime and its interactions with natural environmental parameters determine the riparian vegetation composition. This study was conducted in riparian zone of the Yongding-Haihe river system, which is about 270 km long, with a drain catchment about 3600 km², strongly anthropogenically impacted river flowing into the capital Beijing and Tianjin, China. Several sections of this river have been dried-out for several years due to water abstraction in the catchment. Streambed elevation ranges from 10 m to 300 m (above the sea level). The study area is characterized by a semi-arid continental climate in the warm temperate zone and has an annual temperature of 12-13 ℃. The long-term mean annual precipitation ranges from 400 to 600 mm. It is dominated by the Asian summer monsoon from July to September that accounts for about 70% of annual precipitation.
This study aims to identify the flora characteristics of riparian vegetation in Yongding-Haihe river system and the differences of flora between three river sections. Plant composition has been surveyed in 17 experimental sites along Yongding-Haihe river system. 5 sites were selected in the mountain section and 5 sites were selected in Haihe section, other 7 sites were located in the plain section. In each site, we used transect to set plots following the line from riverside to the highland, the distance is 5 m between two plots nearby. In this study, the size of herb plots is 1m×1m, while 5 m×5 m for shrub plots and 10m×10m for tree plots, which are typical sampling sizes for vegetation survey in Northern China. The native plants and alien plants have been also indentified from the species list in each plot based on the Flora of China and Flora of Beijing. The flora composition of the entire river and different river sections were analyzed. In order to better describe and reflect the flora characteristics of wetland plant species, we preferred to analyze the flora composition on the species level rather than genera level.
There are 134 vascular plants from 100 genera and 37 families, including 1 fern species and 133 spermatophyte species. The major families are Gramineae and Compositae and the major genera is Artemisia. The flora of riparian vegetation in Yongding-Haihe river system had 16 geographical components falling into 4 main component categories (i.e. temperate, tropical, cosmopolitan, and Asian). 50% of the species are of the temperate type. It indicates that the flora of riparian vegetation is mainly characterized by temperate components. In addition, the results also show that the flora is different among the three river sections. Yongding Mountain and Haihe river section have similar composition: Temperate > Cosmopolitan > Tropical > Asian; whereas Yongding Plain section which has been cut off from river flow for many years shows a different composition: Temperate > Tropical > Cosmopolitan > Asian. We conclude that the flora of riparian vegetation in Yongding-Haihe river system has a temperate characteristic. Our results also highlight that the differences of flora composition in Yongding plain section due to the displacement of native plant species.