Invasion of Silky Bush Clover (Lespedeza Cuneata) in Midwest Prairies

Lespedeza cuneata is a non-native legume, introduced as forage crop and cover from Japan, that forms thick, dense stands, letting very little light through. Many hypotheses explain how and why invasion by plants occur, but my research will focus on the refuge-mediated apparent competition hypothesis, which posits that a plant species can indirectly reduce growth of potential competitors, and thus invade, by providing refuge for herbivores of these surrounding plants. This hypothesis assumes that the invader is less suitable as a food resource than its neighbors. I hypothesize that Lespedeza cuneata indirectly competes by sheltering arthropod species that are herbivores of the surrounding plant species. This is likely because its dense stems provide better protection from predators of these herbivores and better foraging habitat. Further, L. cuneata is likely not a food resource of most arthropods because its foliage is chemically defended. If this hypothesis is correct, I predict: (a) higher percent herbivory on the plants surrounding L. cuneata than on L. cuneata itself, indicating it is not a food source. (b) higher abundance of arthropods in areas where L. cuneata is present, indicating that it provides more suitable habitat. I also predict (c) removal of L. cuneata in experimental plots will reduce herbivory on neighboring plants, compared to control plots. Last summer, I tested prediction (b) in a field experiment to determine how removing L. cuneata would affect the diversity and abundance of arthropod species. I continuously removed L. cuneata throughout the field season from 20 1-m2 plots and left another 20 plots unmanipulated. Arthropods were collected monthly using a variety of methods including pan traps, observations, pitfall traps, and sweep nets. So far, results indicate that Popillia japonica, an invasive beetle, have higher numbers in plots with L. cuneata, supporting prediction (b). This summer I will test predictions (a) and (c) by evaluating the intensity of herbivory of plant species in plots, including L. cuneata, over the field season. A better understanding of the direct and indirect effects of L. cuneata on native communities can inform management decisions intended to limit the spread of L. cuneata, which could then increase arthropod and plant community diversity