Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2009
Publication Date: 12/1/2010
Citation: Hardegree, S.P., Moffet, C.A., Roundy, B.A., Jones, T.A., Novak, S.J., Clark, P., Pierson Jr, F.B., Flerchinger, G.N. 2010. A comparision of cumulative-germination response of cheatgrass (Bromus Tectorum L.) and five perennial bunchgrass species to simulated field-temperature regimes. Environmental and Experimental Botany. 69:321-327.
Interpretive Summary: Cheatgrass has invaded and now dominates millions of hectares of public and private rangeland in the Intermountain region of the western United States. Rapid germination and establishment during periods of cold temperature in the fall, winter and early spring may contribute to the ability of this species to out-compete native bunchgrass species after wildfire. In this study, we evaluated cheatgrass and 5 different native bunchgrasses by simulating potential germination response as if they had been planted on any day during the last 38 years. In addition to evaluating their performance over a long time period, we evaluated over 70 different seedlot collections to ensure that we could account for variability that may be present within a given species. By comparing potential response over such a long time period, we confirmed that over the long-term, cheatgrass is from 2-5 times faster than these other species in early germination. The modelling techniques developed in this study, however, can also be used in the future to identify just what type of weather conditions are necessary to establish desirable native plant species even after taking measures to control cheatgrass competition. By identifying climatic requirements for establishment of different species, we can make better and more cost-effective decisions about species selection for revegetation and restoration in a given year.
Technical Abstract: Cheatgrass (Bromus tectorum L.) has come to dominate millions of hectares of rangeland in the Intermountain western United States. Previous studies have hypothesized that one mechanism conferring a competitive advantage to this species is the ability to germinate rapidly at low temperatures in the fall, winter and spring and, therefore, initiate growth and establishment more rapidly than more desirable perennial bunchgrass species. In this experiment, we developed thermal-germination-response models for multiple seedlots of cheatgrass and five perennial grass species. We conducted sensitivity analysis on potential-cumulative-germination response to a 38-y simulation of field-variable conditions of seedbed temperature and moisture. Cheatgrass uniformly germinated at a higher rate, and required significantly less time to complete germination than any of the perennial species for all but the slowest seed subpopulations. A germination-rate-sum index was used to integrate relative response characteristics over time. This index showed that germination rate of the most rapidly-germinating subpopulations of cheatgrass were 2-5 times higher than for the other species tested. Model simulations of this type provide a more ecologically relevant basis for seedlot evaluation as they allow comparisons across a wide range of potential conditions that may be experienced in the field.