A Study On CA Model Of Population Expansion For Spartina Alterniflora At Jiuduansha, Shanghai

The Jiuduansha shoals holds mainly Phragmites australis community, Scirpus mariqueter community and Spartina alterniflora community. The Jiuduansha shoals have never been colonized by humans and have been in a natural condition since they were formed. The Jiuduansha shoals provide an ideal setting for analysis of the sequence of events associated with the initial colonization, lag time, rate of geographic spread and features of geographic spread of the exotic S. alterniflora and the native P.australis. Nowadays, more attentions are focused on their classification surveying and describing qualitatively dynamics based on RS images interpreted, rather than on simulating and predicting their dynamics quantitatively, which is of greater importance for managing and planning the salt marsh vegetation. So the characteristic of the cellular automata was analyzed and a conclusion indicated that it was necessary for a Cellular Automata (shortened form, CA) model to be extended geographically under varying conditions of space-time circumstance in order to make results matched the facts accurately.This study investigated an ecological model based to simulate the population expansion pattern of an exotic species of S.alterniflora and a local species P.australis for a period of 7 years after being introduced to the neonatal shoals, Jiuduansha in the Yangtze River Estuary, Shanghai. Based on the CA methodology, in conjunction with Remote Sensing (RS) and Geographical Information Systems (GIS), this model was used to simulate the population dynamics and competition patterns of S.alterniflora and P.australis on Jiuduansha shoals. This model was based on the hypothesis of space pre-emption theory between S.alterniflora and the native P.australis, and the smoothly expanding range with simple advancing wavefronts was supposed to be the main expansion way of invasive S.alterniflora in the model in order to explain the infection factors and succession laws of population dynamics for the plant community on Jiuduansha shoals.Firstly, the author introduce the biology and ecology characteristics of S.alterniflora, and review the study of the plant community dynamics and population models at home and abroad. Secondly, the concept,composing, principle, characteristic, classification and application of the standard cellular automata were introduced detailedly in the paper. Thirdly, the author set up a CA model for simulating the dynamics of S. alterniflora and P.australis after the satellite images classification of Jiuduansha shoals were analyzed. Then the author simulate the population dynamics of S.alterniflora and P.australis on Jiuduansha shoals from 1997 to 2004 using this CA model and assess the simulation accuracy. Finally, the population dynamics of S.alterniflora and P.australis on Jiuduansha shoals from 2006 to 2008 were predicted.The results of this research indicate the potential of this approach to obtain insight into the interaction and mechanism between expansion patterns and ecological process, as well as to predict the expansion trend of exotic S.alterniflora. The CA model are compatible with the field observations and interpreted data from the satellite images, they are also corresponding to the spread theory of smooth expanding range with simple advancing wavefronts. This research of CA model based on S.alterniflora population dynamics provides a theoretical foundation to decision-make of control and management in Shanghai region. Due to the competition capacity and space-preemption theory, which was tested by the CA model in this study, the range expansion of S.alterniflora will last for a rather long time in future, and also more native species on the Lower Shoal such as S.mariqueter will be out-competed. Therefore, our further studies will focus on modeling different control strategies on S.alterniflora. Application of these results in control programs for S.alterniflora and similar invasive species could greatly reduce the costs of control work and improve the likelihood of local or complete eradication.