Differing effects on dicots and monocots by Centaurea maculosa.

Abstract

The purpose of our study was to test the effects of the invasive species spotted knapweed (Centaurea maculosa) on plant community. Being efficient at competing for nutrients and water, and for producing offspring, C. maculosa is an aggressive invader of dry pastures and native rangelands. We predicted that knapweed would more negatively affect dicots than monocots in terms of plant abundance, species richness, and height. Our study site was located in a field in Harbor Springs, MI. We set up plots with and without knapweed and measured species richness, abundance, and height for the plants within the plots. We found a marginally significant effect on total and dicot species richness between the two treatments, with lower species richness in plots with knapweed, while monocot species richness did not vary in plots with and without knapweed. There was not a significant difference in total plant abundance between the two treatments. We also did not find significant differences between dicot or monocot abundance or height in plots with and without knapweed. We could not conclude that knapweed impacted dicot species more than monocot species, or had an impact on the plant community. It is possible that C. maculosa must be at higher densities in order to have a large impact on plant communities.