Aims Xixi wetland is located at the outskirt of Hangzhou, eastern China. Under the influences of human residents, farming and fishing activities for more than one thousand years, Xixi has changed to secondary farming wetland with 70% of the area covered by open water interfaced by narrow dikes and large islets. Urbanization and industrialization during the last 20 years has rapidly shrunken Xixi. We investigated species composition of vascular plants in Xixi to explore: 1) relationships between species composition and habitats, 2) species which should be protected in the restoration of Xixi and methods for their protection, 3) favorable habitats for native and wetland species, and 4) occurrence and effects of invasive exotic species in different habitats and methods for their control.
Methods The herbaceous habitats of Xixi were classified into five types based on plant composition, water level, and solar radiation: blazing high dike (BHD), shading high dike (SHD), blazing low dike (BLD), blazing high islet (BHI), and blazing low islet (BLI). Community composition of the five habitats was studied by quadrat sampling method. Important values (IV) were used to calculate diversity indices and DCA ordination. A total of 26 sites with 234 m² quadrats were sampled in this study.
Important findings There were 119 vascular species belonging to 103 genera and 44 families. Among them, 108 species were native, 11 were invasive exotic; 50 were wetland plants; 6 were legumes, and 35 were grasses or grasses relatives. Results showed that BHD, SHD, BLD, BHI had greater plant species richness than BLI, and BHD had the greatest native species and woody species richness. Invasive exotic species and wetland plant species were prevalent in BLI, and common in BHD, SHD, BLD and BHI. BHD may be in favor of the protection of native species, and may be good for resisting the invasion of exotic species, but may be an unfavorable habitat for wetland plants, BLI was reversed. BLD could maintain moderately native plant species richness and had higher proportions of herbs and wetland plant species. Therefore, well-managed BLD should be emphasized in Xixi for protection and enhancement of native vegetation diversity and wetland plant species richness. The invasive exotic species, such as Alternanthera philoxeroides, which were harmful to the landscape or harmful to maintain native species diversity, must be removed periodically.