Abiotic Gradients and Grazing Effects on the INteractions of Dominant Meadow Grasses, Deschampsia cespitosa, a Native, and Poa pratensis ssp. pratensis, a Non-Native

MASTERS THESIS: Competition between native and introduced species for resources has been hypothesized as a primary factor behind the success and failure of an invasion. However, few studies have analyzed the effects of long-term competition, which may result in the establishment of environmental niches, between native and introduced species. Poa pratensis, a persistent introduced species in the meadows of the Sierra Nevada mountain range, and Deschampsia cespitosa, a native bunch grass in these meadows were examined for evidence of interspecific competition and niche partitioning, using both field and greenhouse experiments. I tested each species performance across soil moisture and light gradients, as well as their response to simulated grazing. In the field, Poa grows better in relatively drier sites, whereas Deschampsia is found in more mesic environments. When grown in the greenhouse using a range of simulated meadow environments, Poa competitively dominated Deschampsia under xeric conditions. For field and greenhouse studies, phytomass of both species decreased significantly and similarly after clipping, suggesting no clear role for differential grazing response. Results suggest that these species partition resources into separate niches according to meadow hydrology, allowing coexistence. Thus, meadow hydrology is a primary factor when considering conservation of habitat for endemic meadow flora such as Deschampsia, as Poa may more easily invade drier sites.