Investigation into Community Characteristics and Interspecific Association of Erigeron sumatrensis in the Three Gorges Valley

Erigeron sumatrensis is an exotic noxious weed, which is a serious threat to agricultural biodiversity and ecosystem function. In order to effectively observe and evaluate the invasion degree of Erigeron sumatrensis at different elevations, 180 quadrats were set up in the Three Gorges River Valley. The interspecific association and community stability were studied by test statistics, variance ratio, association coefficient, matching coefficient and Gordon M community stability measurement method. The results indicate that: (1) A total of 149 species of parasitic plants were found in the invasive community, ranging from 56 species at low-altitude to 97 species at high-altitude. The changes of altitude significantly increased the species diversity of invasive communities, the important values of species were generally higher, and the aboveground biomass increased. (2) The dominant degree and niche width were the largest in the low and high-altitude communities, and Stellaria aquatica was the largest in the intermediate-altitude communities. Compared with the low-altitude, the dominance of the intermediate-altitude and high-altitude communities increased by 1.09% and 8.32%, respectively. (3) The χ² test and association coefficient show that there was no significant negative association between the species of low-altitude invasive communities, while significant positive association existed between the species of intermediate-altitude invasive communities, and significant negative association existed between the species of high-altitude invasive communities. The invasive community generally showed no significant negative association, and the interspecies association was loose and the independent distribution was strong. The data of community stability show that the intersection coordinates of low altitude and middle altitude communities were (39.85, 59.98) and (35.79, 63.91), respectively, and the distance between the two intersection coordinates was (20, 80), indicating that the invasion community of Erigeron sumatrensis was in an unstable state. The stability ratio of high-altitude communities is (26.82, 72.28), which is close to the stable point coordinates and shows high community stability.