Study On The Mosaic Distribution Pattern Of Phragmites Australis And Spartina Alterniflora Populations Along Tidal Gradient And The Relationship With Habitats

Alien species Spartina alterniflora spreads quickly in Dongtan wetland, Chongming, Shanghai, China, after being introduced, and competes with native species Phragmites australis intensively, forming a mosaic distribution pattern. Using the methods of GIS and field investigation, the distribution pattern of the two populations along tidal gradient and the relationship with habitats were studied.The results shown that:1) S. alterniflora population distributed concentratively in the form of large patches with close interconnection, while P. australis population distributed in the form of obvious fragmentation, which was caused by the successful difusion of S. alterniflora population in the distribution area of P. australis population.2) Certain environmental factors in microhabitats did not show exactly relevance with the tidal level, which reflected the environmental characteristics was obvious at whole gradient and complex in local microhabitats of Dongtan wetlands. Environmental factors in microhabitats such as elevation, soil salinity, and soil P, locally and complicatedly influenced on the spread and distribution pattern of the two populations. The distribution patterns of the two speices reflected their adaptability to the characteristics of local microhabitats.3) P. australis population and S. alterniflora population competed most fiercely for space resources in the habitats at middle tidal level. Meanwhile, S. alterniflora population had the tendency to spread into the area presently occupied by P. australis population at high tidal level. The distribution characteristics of P. australis population and S. alterniflora population at every tidal level reflected their adaptability and choice for the space, time and resources in Dongtan wetlands. Suitable blank patches and the patches presently occupied by P. australis or S. alterniflora loosely might become potential areas for the spread and competition of S. alterniflora or P. australis populations, respectively. 4) The interaction between P. australis and S. alterniflora populations with small-scale microhabitat environmental factors further affected their distribution patterns. The different effects between P. australis and S. alterniflora in shading soil, reducing soil evaporation and affacting soil salinity may lead to the difference of competitive advantage of P. australis and S. alterniflora in different habitats. These characteristics might affect the competitive strategies of the two species in the habitats.The results provided scientific basis for the understanding and analysis on the situations of the spread of S. alterniflora and its relationship with P. australis, as well as the protection of biological diversity and Dongtan wetland ecosystem management.