A model of vegetation dynamics of Spartina alterniflora and Phragmites australis in an expanding estuarine wetland: Biological interactions and sedimentary effects

Spartina alterniflora (Smooth Cordgrass) and Phragmites australis (Common Reed) are dominant types of vegetation in Jiuduansha Shoals in the Yangtze Estuary of China. Each species has advantages in terms of growth and competition in different tidal zones. The vegetation types are dynamic due to the variation in the extension and position of different elevation zones due to the deposition of the sediments carried by river runoff. A model was constructed to simulate the vegetation changes over time due to the changes in sediment loads and zonation. A structurally dynamic model was built using Stella software which based on: (i) S. alterniflora and P. australis biological interaction at different elevation; (ii) the morphometric changes of the island which are increasing based on sediment disposition and the sediment trapping effect of plants. The model simulations predict that the areas of P. australis will continue to increase; it will be reach to 1100 ha in 2028. S. alterniflora areas will decrease after the areas slightly increasing to maximum 712 ha in 2015.