Impacts of the invasion of Alternanthera philoxeroides on the species composition and diversity of native vegetation community

The influence of invasive Alternanthera philoxeroides on local vegetation community composition and biodiversity was systematically studied in the suburb of Shangrao city, Jiangxi province. 20 plots which were invaded by A. philoxeroides, were established. One plot which was none or a few A. philoxeroides individuals selected as control plot with a distance of 5 m from others. The pattern of local community biodiversity was analyzed by Simpson index, ShannonWiener index，Pielou index, and Alatalo index. The results showed that: 1) There were totally 59 species in all plots which were subordinated to 29 families. The numbers of species in tested plots were lower than those in the control; 2) There were significant differences of the importance value distribution between the tested and control plots, indicating that the patterns of the species in the local vegetation community changed under the invasion of A. philoxeroides; 3) Analysis of relationship between importance value and biodiversity indices of the local community revealed that Simpson index, Shannonwiener index, Pielou index and Alatalo index were all increased before the importance value of A. philoxeroides reached 29.7, then reduced when the importance value was higher than 64.3, all the indices decreased sharply. This indicated that the invasion of A. philoxeroides had the positive effect and negative effect on the local vegetation community biodiversity. The local community biodiversity could reduce when the invasion of A. philoxeroides reached a threshold.