Postplanting microclimate, germination, and emergence of perennial grasses in Wyoming big sagebrush steppe

Authors: Hardegree, Stuart; Sheley, Roger; JAMES, JEREMY - California Polytechnic State University; Reeves, Patrick; Flerchinger, Gerald; Moffet, Corey

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2022
Publication Date: 6/21/2022
Citation: Hardegree, S.P., Sheley, R.L., James, J., Reeves, P.A., Flerchinger, G.N., Moffet, C. 2022. Postplanting microclimate, germination, and emergence of perennial grasses in Wyoming big sagebrush steppe. Rangeland Ecology and Management. 84:63-74. https://doi.org/10.1016/j.rama.2022.05.008.
DOI: https://doi.org/10.1016/j.rama.2022.05.008

Interpretive Summary: The Intermountain Western U.S. has been increasingly invaded by annual grasses and degraded by frequent and intense wildfires. Restoring these rangelands, however, is very difficult given the general aridity of these systems and the extremely high variability in annual and seasonal weather patterns. In this study, we planted 4 perennial grass species at 15 cites in the central Columbia Plateau over two years to examine site and year specific weather effects on seedbed microclimate, and resulting germination and emergence in the spring. In both years and all sites, seeds were planted late enough in the fall that they survived the winter as seed and were not killed by freezing temperatures after premature germination. Emergence, however, was relatively low, although was correlated with post-germination microclimatic favorability in the seedbed. Mechanistic models for seedling germination and emergence, of the type tested in this study, are critical for designing new strategies for improving restoration outcomes in these difficult ecosystems. This information supports recommendations for management agencies to both plant later in the fall season, and to diversify their seed mixes to increase the probability that at least some seedlots will successfully establish in all but the worst weather scenarios.

Technical Abstract: It has been hypothesized that post-germination and pre-emergence microclimate has a major impact on spring emergence of seeded perennial grasses in the Intermountain Western U.S. In this experiment, we measured germination and emergence of 4 fall-seeded perennial grasses at 15 sites in southeastern Oregon, north-central Nevada and southwestern Idaho in two different years. We used hydrothermal germination and seedbed microclimatic models to estimate planting date effects on germination and pre-emergence mortality and evaluated these simulations relative to measured germination and seedling emergence in the field. There were clear indications that both germination and emergence were responsive to site-year effects but premature fall germination before winter freezing events was not a factor in emergence rates. In all cases, planting was sufficiently late in the fall to avoid significant post-germination/pre-emergence freezing injury for the sites and years tested. Emergence was weakly correlated to seedbed favorability in the late winter and spring after the principal period of soil freezing. Our data show a relatively small impact of post-germination microclimate on spring emergence but general inferences about planting date effects may have been limited by arid conditions during the 2-year field study relative to long-term climate normals.