Abstract:

The invasion of Eupatorium adenophorum has caused serious damage to natural ecosystems by suppressing native species populations in disturbed forests and pastures in southwest China. In this study, the age structure dynamics of E. adenophorum populations were examined in 20 plots (10 m × 10 m) using the Greig-Smith grid method, in Panzhihua Prefecture, Sichuan Province of China. There is no standard method for identifying the age of an E. adenophorum plants, but through careful observations of the growth characteristics of E. adenophorum over several years in Panzhihua, we found a reliable method for aging individual plants. During the coldest season of every year, the apical half of branches grown in the current year wither and die, and a pair of opposite branches expand out from the lignified half that is below the wilted top. Although it can turn out clone genet alone once the branch touches the ground. At the same time sexual propagation and vegetative reproduction of radicicolous branches carry through from year to year. That is to say, the most number of branching ranks of the same branch is likely to indicate the real age of the plant. We dug out the entire plant in each grid and counted the grade rank of each branch to determine the age of each individual plant. The results showed that the age structure of the 4 populations were similar with most individuals in the infancy (92.3%) and youth (6.4%) periods. The analysis of life tables and survival curves showed that chronological sequence of an E. adenophorum invasion was as follows: first, invasion occurred along roadside fields, followed by invasion into the margins of broad-leaved forest, then deep into broad-leaved forest, and finally into Pinus yunnanensis forest. Even under different environmental conditions, survival curves of all E. adenophorum populations belonged to the Deevey type Ⅲ pattern, and mortality of all populations showed a peak in 1-2 years old with mortality rates of 97.3%. The degree to which a population deviated from a typical curve related to the intensity of human disturbance. In general, mortality during infancy period and mature period were high (93.1% and 92.0%). The invasion time-sequence model predicts that young and mature individuals will dominate the populations at 3 and 5 years from the present. Therefore, in the Panzhihua Prefecture, we predict that E. adenophorum will become a serious problem in 3 to 5 years. Compared with populations of other invasive plants, the population of E. adenophorum has a similar break out pattern among populations. Traits promoting weediness included the ability to reproduce sexually and asexually, rapid growth from seedling to sexual maturity, and, most importantly, adaptation to environmental stress (phenotypic plasticity) and high tolerance to environmental heterogeneity.

Key words: Eupatorium adenophorum, Life table, Survival curve, Population dynamics, Time sequence