The Ecological Studies On Succession Process And Sustainable Management Of The Vegetation Communities On Jiuduansha Wetland

Jiuduansha wetland is a newly formed intertidal wetland, covering three parts: Shangsha, Zhongsha and Xiasha. The ecosystem of Jiuduansha wetland is comparatively vulnerable because of its consistently growing. During the previous studies, some found that Jiuduansha wetland was enduring some external disturbance. The introduction of Phragmites australis and Spartina alterniflora in Zhongsha and Xiasha which took place in 1997 have brought serious and impactive influences on the future succession tendency of the vegetation communities in Jiuduansha.We investigated seasonal changes of the 3 main vegetation communities by monitoring their dynamic growth; Based on the present results, we studied the change of total area and biomass of all vegetation types with remote sensing data from 1998 to 2004 and survey on the spot to find out vegetation communities' succession process and developing tendency in last 8 years after the introduction experiment. Furthermore, we studied the ecological functions and economic worth of the 3 vegetation types with results of avian investigation, and then we discussed what influence was brought to local vegetation and avian communities by the eco-engineering which called "planting to attracting birds". At last, primary management strategies aimed at vegetation were raised.After continuous investigation in 18 months, we get results as follows:The status of ecosystem in Jiuduansha is very unstable as it's consistently changes. The simple vegetation communities consist of Phragmites australis, Spartina alterniflora (introduced species), Scirpus mariqueter & S. triqueter. In Shangsha, P. australis, S. mariqueter & S. triqueter are the main vegetation types. P. australis dominates a majority of Shangsha from the south edge to central section. S. mariqueter & S. triqueter grow in north section mostly; in south section, they grow in long and narrow edges along the alluvion. In 1997, the introduction experiment took place in Zhongsha and Xiasha. Nowadays, P. australis or S. alterniflora or their mixed communities occupy most area of Zhongsha and S. mariqueter & S. triqueter grow in peripheral zone. Because of the lower altitude, it has a high percentage of mudflats in Xiasha. P. australis or S. alterniflora occupy the area from north to central section and S. mariqueter & S. triqueter also grow in peripheral zone. In fall 2004, the areas were occupied by 3 main vegetation communities as follows: 1516.42hm² by P. australis; 1458.08hm² by S. alterniflora; 6662.87hm² by S. mariqueter & S. triqueter.Through annual investigations, we understand that P. australis grows well in summer (biomass per m²: 2336.49±1737.19g/m²) and bad in spring (1221.61±974.21g/m²); S. alterniflora grows to the top in autumn (4554.87±889.02g/m²) and in the lowest status in winter (2083.98±1184.87g/m²). S. mariqueter & S. triqueter grow stablely, just a little higher in summer (561.86±256.39g/m²). S. alterniflora gets least affects from season-change and growing condition and it holds highest biomass among the 3 main vegetation communities in Jiuduansha, with 3.033×10⁷kg in autumn 2004.Among the 3 alluvions, average annual speed of vegetation pervasion in Xiasha is 38%, much higher than in Shangsha (17% annually) and Zhongsha (22% annually). S. alterniflora outspreads fastest; its percent of total vegetation area rose from less than 1% in 1998 to 21.88% in 2004. P. australis, S. alterniflora invade more growing space formerly occupied by S. mariqueter & 5. triqueter. From 1998 to 2002, 381.18hm² of S. mariqueter & S. triqueter area in Zhongshana and Xiasha were invaded by S. alterniflora, and another 366.90hm² in entire Jiuduansha was invaded by P. australis. The area occupied by S. mariqueter & S. triqueter community decreased from 89.35% to 55.36% because of the invasion form S. alterniflora. Although invaded and occupied, area of S. mariqueter & S. triqueter still grows up because it takes the place of the external mudflat-zone about 1459.62hm². P. australis community took 22.76% percent of the total vegetation area. It has formed a single and stable community in Shangsha.All vegetation types in Jiuduansha have some ecological functions and economic worth. In P. australis community, 43 kinds of birds of 4 orders were recorded in the research. The avian group is composed with Passeriformes mainly so that P. australis is very important habitats for Passeriformes birds. P. australis can bring 9,442,500 Yuan (RMB) through absorbing CO₂. It also has functions of the clime-adjustment, water purification, paper making, etc. Based on the characteristic of its growth, a management plan just like "furrowing in turns" applied in agriculture produce about 1,500,000～2,300,000 Yuan (RMB) in the practice. S. alterniflora has the highest value of absorbing CO₂ in three vegetation types, which can be calculated as high as 12,359,500 Yuan (RMB) , however only hold only 39 species of birds (G-F index: 0.29), which kept lowest bird diversity among 3 vegetation communities. In a conclusion: S. alterniflora community could not provide a good habitat for avian communities.The value of CO₂- absorbing of S. mariqueter & S. triqueter community is about 3,291,800 Yuan (RMB). There were 104 bird species in the sites of S. mariqueter & S. triqueter community. Its G-F index is 0.62, higher than the other two.Currently, both structure and functions of the ecosystem of Jiuduansha wetland seems to be in health condition generally. However, the conservation actions need to be undertaken in the future, particularly in the: scientific management on S. alterniflora community in this area. Furthermore, we need to understand how to use sustainably the wetland resources, and then maintain the healthy status of the native ecosystem of Jiuduansha directed by scientific view of sustainable development...