Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/3/2007
Publication Date: 11/1/2007
Citation: Roundy, B.A., Hardegree, S.P., Chambers, J.C., Whittaker, A. 2007. Prediction of cheatgrass field germination potential using wet thermal accumulation. Rangeland Ecology and Management, V60, 613-623. Interpretive Summary: Cheatgrass has invaded millions of acres of public and private rangeland in the Intermountain western United States that were formerly dominated by native sagebrush and bunchgrass species. This weed has greatly decreased ecological values and increased the frequency of catastrophic wildfires in this region. We investigated the potential impacts of alternative management treatments on cheatgrass germinability in order to better understand why this species is such a successful competitor with native plant species. We found that ecologically significant germination was predicted for most field sites and treatments in the spring and fall. This suggests that cheatgrass invasion and dominance is best limited by maintaining high density and cover of perennial herbaceous species in big sagebrush communities to compete with cheatgrass seedlings.
Technical Abstract: Invasion and dominance of weedy species is facilitated or constrained by environmental and ecological factors that affect resource availability during critical life stages. We compared the relative effects of season, annual weather, site, and disturbance on potential cheatgrass (Bromus tectorum L.) germination in big sagebrush (Artemisia tridentata Nutt.) communities to test the hypothesis that disturbance was not necessary for potential germination. Soil water status and temperature in the seedbed were measured continuously for 4 years on 9 big sagebrush sites in Nevada and Utah. Field plots at lower, middle and upper-elevation sites were either undisturbed, or were burned, sprayed with herbicide, or both sprayed and burned. Spraying removed perennial herbaceous vegetation, while burning removed sagebrush. We used thermal-germination data from laboratory-incubation studies of 18 cheatgrass seedlots to model and predict potential germination in the field plots for periods when seedbeds were continuously wet (above -0.5, -1, or -1.5 MPa) and across intermittent wet and dry periods. Season had the greatest effect on potential cheatgrass germination, followed by annual weather, and site variables (elevation and location), while the effects of disturbance were minimal. Ecologically significant germination was predicted for most sites and years in spring, a majority of sites and years in fall, and few sites or years in winter. We conclude that disturbance is generally not necessary for potential cheatgrass germination in similar big sagebrush communities.