The Impact of Ambrosia trifida (giant ragweed) on Native Prairie Species in an Early Prairie Restoration Project

As the ecological importance of prairies is becoming more recognized, the number of prairie restoration projects is increasing worldwide. One of the major challenges in restoring any disturbed ecosystem is the successful establishment of native species at the expensive of invasive species. While some weedy species are gradually replaced as other, more desired, species become established, there are invasive species that, due to their level of dominance, may out-compete native species indefinitely. The objectives of this study were 1) to quantify the impact of Ambrosia trifida (giant ragweed) on the plant community of a newsly established prairie, 2) to assess any difference in effectiveness between management practices (cutting versus pulling) of A. trifida, and 3) to establish a baseline vegetation survey to be used in future evaluations and research of the prairie. In March of 2011, 30 plots (each 3 m2) were established within the 20 acre prairie including 10 control plots [C], 10 plots where A. trifida was selectively cut approximately 10 cm above ground level [Rc], and 10 plots where A. trifida was selectively pulled [Rp]. Treatment (cutting/pulling) was applied three times (April, June, and August) during the study, and in order to compare the effectiveness of the treatments, the number of removed A. trifida was recorded for the first two applications. Between April and June, the number of A. trifida decreased by a mean of 34.9 individuals in the cut plots, and increased by a mean of 12.4 individuals in the pulled plots suggesting (albeit, not significantly) that pulling may disturb the ground and promote the germination of more seeds from the seedbed. Final biomass data collection was conducted in mid August by removing the above ground biomass of all plants excluding A. trifida from four subplots within each of the 30 main plots, followed by drying and weighing of all biomass. A total of 172 plants from 30 species were removed for a total biomass of 1735.10 grams. In the control plots the mean biomass was 6.73g and the species diversity (H\u27) was 0.037. In the treatment plots, the corresponding values were 83.39g, and 2.093. This twelve-fold difference in biomass suggests that the presence of A. trifida has a remarkable impact on the overall community of this newly established prairie and that the correct management of A. trifida could expedite the restoration process