Percent cover is commonly used to assess the effectiveness of potential control strategies for invasive plant species. Other measurements may also be used but tend to be more time- and labor-intensive. In the present study, percent cover and biomass were measured to assess the effects of herbicide and prescribed burning on Lygodium japonicum (Japanese climbing fern), an invasive exotic species found throughout the southeastern United States. In a randomized block design, eight 3m x 3m plots in eight blocks were established in Lygodium-infested areas at the Joseph W. Jones Ecological Research Center in southwest Georgia. In September 2008, each plot was treated with one of seven herbicide treatments or used as a control. Four of the blocks were burned in prescribed fires in winter 2009. Prior to and at one year following herbicide treatment, overall species richness and percent cover of L. japonicum and non-target vegetation were assessed. Fourteen to sixteen months following herbicide treatment, above- and belowground biomass samples were collected from two 0.1 m2 subplots within a subset of the treatment plots. Samples were sorted, dried to constant mass, and weighed. ANOVA was used to test for significant differences between treatments.
Results/Conclusions
One year after herbicide treatment, percent cover of L. japonicum was reduced but did not vary significantly among herbicide treatments. Prescribed burning did not significantly affect percent cover. Similarly, belowground biomass did not vary significantly with herbicide or fire treatments. However, aboveground biomass was significantly lower in plots treated with glyphosate and a glyphosate/imazapyr mix than in imazapyr-treated and control plots. Across all herbicide treatments, L. japonicum aboveground biomass was significantly greater in unburned plots than in burned plots. Percent cover of non-target vegetation generally increased in burned plots and decreased in unburned plots treated with herbicide. However, above- and belowground biomass of non-target vegetation did not vary significantly with herbicide treatment or burn treatment. In this study, vegetation response to different treatments varied depending, in part, on how the response was measured. Other factors such as stress dormancy and seasonality may have contributed to this variation. In addition, biomass measurements may better capture the three-dimensional structure of species like L. japonicum, which often has a vine-like growth habit. The results suggest that the use of alternate and/or multiple response variables, while more resource-intensive, may provide a more complete picture of treatment effects and their implications for restoration.
