## 3 Results
### Classification and Distribution of Vegetation Communities  
From a longitudinal perspective, the plants of the 11 floodplains were clustered and analyzed using complete-linkage clustering (Figure 2a). The classification of plant communities was based on selecting level 4, which allowed the plants of the floodplain to be categorized into five distinct types. The communities were named based on the dominant species found within them. 1. _Bidens pilosa_ L.--_Centella asiatica_ (L.) Urban community. This community contains 83 sample points, accounting for 17.8% of the total sample points. This group is commonly found and evenly distributed across the 11 floodplains in the upper, middle, and lower reaches of the river. 2. _Cynodon dactylon_ (L.) Pers.--_Conyza candensis_ (L.) Cronq. community. This community contains 185 sample points, accounting for 39.7% of the total sample points. The dominant species in this community is _Cynodon dactylon_ (L.) [PERSON], and the companion species is _Salvia japonica_ Thunb. This community is mainly distributed in the middle and lower reaches of the river, such as the Meicun floodplain (Z2), the Jiangxiyan floodplain (X1), and the Gaotieqiao floodplain (X4). It is commonly found in the near-water area. 3. _Avena fatta_ L.--_Inula japonica_ Thunb.--_Clinopodium gracile_ (Benth.) Matsum. community. This community contains 89 sample sites, accounting for 19.1% of the total sample sites. This community is widely distributed in eight floodplains, which are mostly located in the midstream of the river. 4. _Cicuta virosa_ L.--_Alternanthera philosercoides_ (Mart.) Griseb. community. This community contains 72 sample sites, accounting for 7.7% of the total sample sites. This community is distributed in ten floodplains, and most of the community is concentrated in the upstream of the river, such as the Xikousiqao floodplain (S1). The majority of the _Alternanthera philosercoides_ (Mart.) Griseb. is distributed in the near-water area of the floodplains. 5. _Humulus scandens--Vicia seipium_ L. community. This community contains 36 sample sites, accounting for 15.7% of the total sample sites. This community is relatively evenly distributed, and is common at both the near-water and far-water area, occurring at the Shangyang floodplain (X3), the Xiaux floodplain (S3), the Meicun floodplain (Z3), and the Caihongqiao floodplain (X5). From a lateral perspective, the plants in the near-water area were classified into four communities using complete-linkage clustering (Figure 2b). The analysis focused on species with importance values exceeding 5% in the 31 sample points located at 0 m from the water. 1. _Polyprogon fugax_ Nees ex Steud.--_Alopecurus aequals_ Sobol.--_Artemisia argyi_ Levl. et Van. community. This community contains 21 sample sites, accounting for 67.7% of the total number of sample sites. It is a dominant community in the near-water area. 2. _Conyza canadensis_ (L.) Cronq. community. This community includes 13 sample sites, or 41% of the total number of sample sites, with companion species of _Runex acetosa_ L. and _Cicuta virosa_ L.
3. _Humulus scandens--Avena fatua_ L. community. This community comprises 10 sample sites, or 33% of the total number of sample sites, with no obvious companion species. 4. _Marsilea quadrididia_ L. community. This community is a dominant species endemic to the near-water area, which contains three sample sites, or 10% of the total number of sites, with no obvious companion species. The plants in the far-water area were classified into three clusters using complete-linkage clustering (Figure 2c). The analysis focused on species with importance values exceeding 5% in the 32 sample points located at a distance of 15 m from the water.