关键词: 韩江三角洲, 红树林, 区系, 群落, 立地条件, 保护与恢复

Abstract: [Objective]As one of the six major estuaries in China, the Hanjiang River Delta (HRD) is of significant importance for conserving wetland biodiversity and guaranteeing ecological safety. Hence, conducting a detailed survey on the mangrove communities and their sites conditions in this area could provide a basis for mangrove conservation and restoration.[Method]The current mangrove communities at the HRD were surveyed by means of route investigation and plot sampling to collect data of communities and site conditions. Multivariate statistical methods were performed for comprehensive evaluation of the communities.[Result]Totally, 13 species of true mangrove and semi-mangrove plants which belonged to 10 families were recorded, including 4 introduced species. Compared with the records in 1964, the species composition was not changed significantly. However, the natural mangrove populations have declined generally, especially characterized by the extinction of natural population of Bruguiera gymnorrhiza. The natural mangroves were retreated, fragmented, and subjected to an area loss of almost three fourths. The flora similarities of mangrove between the HRD and Futian, Zhangjiang Estuary, Jiulongjiang Estuary were higher than those between the HRD and other mangroves of southern China. The species diversity as Shannon-Wiener index (H') ranged 0.168~1.318, and evenness as Pielou evenness index (J) varied between 0.242~0.896. The H' and J indices of artificial mangroves were both higher than those of natural mangroves, indicating a more diversified and well-proportioned state in artificial mangroves. Oppositely, due to the massive dominant population of Aegiceras corniculatum, the natural mangrove communities had lower H' and J indices. The site of Liuhewei had the maximum value of biomass at 106223 kg·hm^-2, which was 14.9 times of the biomass value at the site of Aotou. The environmental factors were statistically significantly different among communities. Salinity and Eh value were significantly correlated, while pH value and other nutrient factors were highly related. The salinity of sediment, salinity of pore water, and Eh of sediment were affected by the sites' locality, which referred to the horizontal distance from estuaries to inlands. Nutrient factors and sediment pH were closely related to each site factor, and their changing trends are related. The results from PCA showed that the site conditions in this area were significantly different among sites. Generally, the sites with lower salinity, higher Eh and higher nutrients values were preferable. Especially for site of Xiangkou, which is bordered in a freshwater dominated intertidal river channel, particularly suited the growth of lower saline preferring species as Sonneratia apetala and S. caseolaris.[Conclusion] It is suggested to perform key conservation of the natural communities at Aotou. Besides, the mangrove at the HRD had limited distribution and population sources. To restore biodiversity rapidly, enforcing the introduction and reintroduction of native semi-mangroves and associates, monitoring the dispersal of introduced mangroves are necessary. Moreover, expanding the area of mangroves through improvement of the existing mangrove plantations was recommended. Based on a comprehensive evaluation of site conditions, the mangroves at the HRD were classified into categories as priority, suitable and unsuitable for development. Restoration of plant communities needs to be implemented according to the local conditions.

Key words: Hanjiang River Delta, mangrove, flora, community, site conditions, conservation and restoration