Submitted to: Ecological Modelling
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2003
Publication Date: 5/13/2003
Citation: Hardegree, S.P., Flerchinger, G.N., Van Vactor, S.S., Hydrothermal germination response and the development of probabilistic germination profiles. Ecological Modelling 2003, v. 167, p. 305-322. Interpretive Summary: Millions of acres of rangelands in the western United States have been taken over by annual weeds that proliferate after wildfire. Revegetation and restoration of these lands is difficult because of the high variability in available soil moisture from year to year. If we could predict soil moisture requirements for establishment of desirable plant species, it would be possible to devise more cost efficient strategies for rangeland rehabilitation efforts. In this study, we calibrated a soil moisture and temperature model to predict seedbed microclimate for the last 38 years at our experimental field site in southern Idaho. We also developed a germination response model to predict potential germination response of two native grass species and the dominant annual weed in the region. From this data, we were able to estimate the probability of successful plant establishment under a wide range of potential climatic regimes in the region. This information can be used to evaluate, rank and select plant materials relative to their ease of establishment; and can also be used in conjunction with long- and medium-term weather forecasts to make decisions about allocation of limited revegetation and restoration funds.
Technical Abstract: Millions of acres of rangeland in the western United States are now dominated by introduced annual weeds such as cheatgrass (Bromus tectorum L.). The ability to germinate rapidly at low temperatures has been proposed as one of many mechanisms that confer a competitive advantage to this species. Previous studies of this phenomenon, however, have been limited to relatively simple comparisons of total germinability and germination rate under selected constant-temperature treatments. In this study, we germinated seeds of cheatgrass and two native perennial bunchgrass species, bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Löve] and big squirreltail [Elymus multisetus (J.G. Smith) M.E. Jones], over the temperature range of 0 to 36 °C and water potential range of 0 to -2.5 MPa. A hydrothermal-germination model was constructed to predict germination rate response for the 10, 25 and 50th percentile seed subpopulations. Germination rate estimates were predicted for each species, seedlot and subpopulation for every hour of a 38-year simulation of seedbed temperature and water potential. The seasonal and annual distributions of germination-rate summation were used to integrate relative seedlot response across a wide-range of seasonal and annual patterns of seedbed microclimate. The analysis supported the hypothesis that cheatgrass germinates more rapidly than the other species tested. The absolute magnitude of this effect, however, is small relative to expected differences in seed numbers between cheatgrass and planted species in the field. Historical patterns of seedbed microclimate and predicted germination response may be useful in assessing and optimizing alternative field planting scenarios. Inclusion of weather forecasting and seedbed modeling may provide real-time management options for improving rangeland seeding success.