Simon A. Lei


Interactive effects of red brome grass (Bromus rubens) density and time of establishment on the early survival and growth of blackbrush (Coleogyne ramosissima) seedlings were quantitatively investigated. Seeds of Coleogyne and Bromus were collected from Cold Creek of the Spring Mountains in southern Nevada. A series of pot trial experiments were conducted in a controlled environmental glasshouse. In mixed culture pots when Coleogyne seedlings planted four weeks later than Bromus at medium and high density levels, survival of Coleogyne seedlings (experimental populations) was greatly reduced compared to single Coleogyne seedlings that grew alone (control population). Significant interactions were detected between neighboring Bromus density and time of planting for shoot height, root/shoot ratio, leaf length, and shoot water potential of experimental Coleogyne populations. When Bromus density was examined independently, all measured growth parameters of experimental Coleogyne populations were significantly reduced compared to the control population. When time of planting was examined independently, shoot height, root/shoot ratio, shoot biomass, leaf length, and water potential of experimental Coleogyne populations were significantly reduced. Results of this study revealed that some Coleogyne mortalities occurred in the absence of interspecific competition, and that growth among surviving seedlings were significantly reduced under conditions of increased density of neighboring Bromus and early Bromus establishment.