The giant ragweed(Ambrosia trifida L.), originated from the North America, has designated as an invasive alien species in South Korea. With fast growing and abundant seed production, this species can dominate invaded area in a short time. This could lead decrease of species diversity which could threaten certain innate ecosystem process, and consequentially may have negative impact on biodiversity. In this study, we have investigated the effects of invasive species, Ambrosia trifida L., and management activities on species diversity in old field ecosystem to find out what makes the giant ragweed more invasive in South Korea. To figure out the impact on species diversity and how the species diversity can change after management, we have established control plots (intact plots) and treatment (giant ragweed stems were periodically cut at 10 cm above the ground) plots in May, 2015 in the study area.
In control plots, average coverage of giant ragweed was more than 90%, and the number of other plant species were few. The reason for this seemed that the giant ragweeds take dominant position and the result of shading effect caused by giant ragweed’s leaves. The number of species recoded in control and treatment plots was 14 and 28, respectively, which is two times greater in treatment plots than in the control plots. Average species diversity index (H′) from June to September in control and treatment plots was 1.73 and 2.45, respectively. The size of giant ragweed community in the treatment plots was smaller than the control plots in 2016. Besides, many other plant species were appeared in the treatment plots. The results showed that the physical control should be conducted at least before seed production because it could prevent the increase of the soil seed bank. Our results suggested that post management activity such as revegetation with native species, and long-term monitoring should be performed to recover the native ecosystem in this area.