| Roger L. Sheley and Larry L. Larson |
| Authors are assistant professor, Department of Plant, Soil, and Environmental Sciences, Montana State University, Bozeman, 59717; and associate professor, Department of Rangeland Resources, Oregon State University, Corvallis stations at OSU-EOSC Agriculture Program, Eastern Oregon State College, La Grande 97850. At the time of the research, the senior author was graduate research assistant, Oregon State University, Corvallis 97331. |
Abstract |
| Cheatgrass (Bromus tectorum L.) and yellow starthistle (Centaurea solstitialis L.) have invaded over 250 thousand hectares throughout the Pacific Northwest. Future management of rangelands dominated by these species will require an understanding of the plant-plant interactions which contribute to the regulation of community dynamics and the establishment of desirable plants. Addition series experiments, with total stand densities ranging from 20-20,000 plants m-2, were used to quantify the interference between cheatgrass and yellow starthistle in unrestricted soil depths on 12-day intervals throughout the growing season and in soil depths restricted to 0.2- and 0.5-m. Intraspecific interference was nearly twice as important as interspecific interference when plants were grown in unrestricted soil. Resource partitioning by cheatgrass and yellow starthistle was associated with rooting depth. When restricted to a 0.5-m depth, resource partitioning did not occur and intra- and interspecific interference were similar for both species. Restriction to a 0.2-m depth resulted in cheatgrass density being twice as important as yellow starthistle density for predicting yellow starthistle shoot weight. Yellow starthistle density was not important for predicting cheatgrass shoot weight. Cheatgrass appeared to have a competitive advantage over yellow starthistle in shallow soils, but the rooting depth and seed production capacity of yellow starthistle was greater than cheatgrass in deep soil. |
| Key Words: Centaurea solstitialis, Bromus tectorum, addition series, community dynamics, competition, rangeland weeds |