Relative Competitive Ability of Bulbous Bluegrass (Poa bulbosa) and Cheatgrass (Bromus tectorum) with Perennial Grasses

Invasive grasses often negatively impact desirable vegetation. While the interactions and impacts of some species have been widely studied, land managers know little about other invasive species. This research compares the relative competitive abilities of bulbous bluegrass, a largely unstudied invasive grass and cheatgrass – arguably one of the most impactful invasive species in North America. We compared growth of these two grasses using a replacement series design in a greenhouse setting. Light and water were readily available, and plants where grown in a clay-loam field soil with five replicates. Focal species (cheatgrass and bulbous bluegrass) were grown alone, with one another, and with five perennial grasses at focal plant:competitor ratios of 8:0, 6:2, 4:4, 2:6, and 0:8. Twelve weeks after planting, we collected above ground biomass, dried it at 60°C for 72 hours, and weighed it to the nearest mg. Cheatgrass biomass exceeded expected values in mixtures, and bulbous bluegrass competitive response was neutral. As a group, perennial grasses were suppressed more by cheatgrass than by bulbous bluegrass. Idaho fescue was suppressed equally by both bluegrass and cheatgrass. Western wheatgrass was clearly suppressed by cheatgrass, but not by bluegrass. Cheatgrass was smaller with Idaho fescue than with western wheatgrass. Competitive response of bottlebrush squirreltail was superior to other native grasses and was most similar to the non-native crested wheatgrass. Cheatgrass suppressed bulbous bluegrass in direct interaction, and was a stronger competitor in this study. More research is needed to understand the potential impacts of bulbous bluegrass in Wyoming's rangelands.